Seattle

Seattle's (relatively) cool winter, Part 1...

in , ,

Updated on April 6, 2023



I first published this blog post on March 18. The day before,  it warmed to the 60’s for the first time since October in and around Seattle. This felt very nice to my cold bones. It has been a relatively cool winter this year if you look at the December – February traditional winter period. January was relatively mild, warm, and dry for a winter period in Seattle. But the traditional meteorological winter was bookended by a coolish December and February. Extend the bookends of the period to November and March (to-date), four of the past five months have been cooler than normal.

My charts only contained data through March 15 when I first published the post on March 18. Now, a week into April, I have data through the end of March. The updated figures below reflect this.

I’ve posted several charts below. Figure 1 is an animation. The chart is a series of traces which track the cumulative average daily temperature recorded at Seattle Tacoma International Airport (KSEA) for the seasonal period of November 1 through March 31 for the years 1949 through 2023.

NOTE: The animation is an animated GIF file programmed to loop through twice. Each loop takes roughly 25 seconds. Refresh the browser window (command+R) to restart the animation.

Figure 1. Accumulated daily average temperature traces by seasonal year, 1949-2023, at Seattle Tacoma International Airport.

A few notes about Figure 1 follow:

  1. I’ve chosen a “made-up” metric. I don’t know if this is used by the National Weather Service, meteorologists, or climatologists with any regularity. I call my metric or index the Accumulated Degree-Day (ADD). It simply takes the average daily temperature recorded at KSEA and adds it to the previous days. It is similar to Heating Degree-Days and Cooling Degree-Days which are commonly summed over a period of time but my ADD does not use a threshold temperature of 65˚F to compare against. But it does give one an idea of how cool or warm the seasonal period has been in comparison to similar periods in other years at a common location.  I suppose it’s units would be ˚F-Days.

  2. The gray traces in the background display each year from 1949-2023 for an aggregate comparison.

  3. A blue trace is highlighted for each individual year as the animation is played.

  4. Since each seasonal period plotted crosses two calendar years, I’ve chosen the latter of the two calendar years to identify each individual trace. So, the trace for the November 2022 – March 2023 period is identified as ‘2023.’

  5. The highlighted blue traces extend to March 31 for each year.

  6. An average ADD trace for all years has been added to the chart for comparison. The ADD trace is shown as a black  hairline. For the total November–March season period, the total average ADD value is 6482 ˚F-Days.

  7. Some data went uncollected by the National Weather Service on March 16-17, 2023 at Seattle Tacoma International Airport which made it difficult to calculate a daily Average Daily Temperature for these dates. The missing data is explained in the chart and the days impacted are shown in a red block on the chart.

  8. Finally, I name the animation a dog tail chart because when played back, especially at higher frame rates, these types of charts look a little like a wagging dog tail. 

 

So why an animation? Animations display motion, and motion display movement over time and, possibly, patterns. You may want to ask yourself; year-to-year is there any rhythm, pattern or trending that becomes obvious that might be difficult to discern when comparing a series of still images or charts. This is especially true when comparing 74 still images if each chart was published separately (and they are further below).

 And there does appear to be some patterns at the distal ends of this period we’re investigating. In the late 40’s and through the mid-1950’s there are a series of coldish winter seasons(7 of 9 between 1949-1957). This is well documented in old photographs of heavy snows in Seattle during this period. And one could argue that the 2010’s have a pattern of warmer than normal winters (6 of 8 between 2014 through 2021). But mostly, this animation shows the high level of variance fluctuating between cooler-normal-warmer winter cycles. The late 2010’s may have shown warmer periods, but this season is quite cooler. And there were warmer winter seasons in the 1950s.

*****

The individual annual temperature traces which make up the animation are shown below. The are shown in order of the earliest year (1949) to the most current (2023). Click on any individual image below to see more detail and to compare.

Temperature changes at SeaTac...

in ,

Weather data collected at Seattle Tacoma International Airport (SeaTac) is generally considered the main data of record for the Seattle metropolitan area, though there are several other sites in the region where meteorologist and climatologists gather their information. Data has been collected at SeaTac continuously since 1948, though some data is missing from the records for the period of October 1, 1996 through October 31, 2005. This missing data is generally the snow and sky cover observations. Temperature, the focus of this page, and precipitation data was collected during this period and is available from the National Oceanic and Atmospheric Administration (NOAA) and their publicly accessible National Centers for Environmental Information (NCEI) Climate Data Online (CDO) tool.

So, having temperature data from 1948 through yesterday (Feb 22, 2023), how much has the average daily temperature changed at SeaTac over the past 75 years (inclusive) if at all? And are there any trends? If so, one would assume that the temperatures have slowly warmed over the years based on all the science and reporting published over the past decade or longer.

 

An undulating plot

The National Weather Service generally reports the daily minimum temperature (Tmin) and daily maximum temperature (Tmax) at the weather stations. The average of these two values is calculated and recorded as the average daily temperature (Tavg). Often when looking at or downloading past data from a weather station, the user receives only the Tmin and Tmax values for a given date. This is common on older records. Sometimes the data includes the calculated Tavg. Regardless, knowing that Tavg is the average between the Tmin and Tmax values, the Tavg shown in the following charts has either been calculated by the NWS and reported, or this author has performed the calculation in the spreadsheet I’ve imported data from the NWS into.

If you plot the TAVG value for every date from January 1, 1948 through today as shown in Figure 1 you get an undulating or wavy curve form. Obviously, the average daily temperature of a summer day is much higher than the same on a winter day in Seattle. It is difficult to determine if there has been a fall or rise in the average daily temperature and, if so, by how much by just looking at this wave form.

Figure 1. Average daily temperatures trace from 1948 to 2022, Seattle Tacoma International Airport.

I’ve added a linear trend line in red in Figure 2. This trend line shows a modest rise in daily temperatures over the 75-year period. The average daily temperature recorded at Seattle Tacoma Airport has risen from roughly 50˚F to about 54˚F during this period, a rise of roughly 4-4.5 ˚F, or 2.2-2.5 ˚C.

Figure 2. Average daily temperatures trace from 1948 to 2022 with red trendline, Seattle Tacoma International Airport.

Annual Cumulative Degree-Day Index (ACDD)

Another method of looking at temperature changes over time and comparing these to other years over a long period is to plot the cumulative total of daily average temperatures and plot that accumulation over the course of a year. Then plot a similar curve for each year in the period of study. This is shown in Figure 3.

A simple way to check this value is described here. Say the average annual daily temperature at SeaTac is 50˚F. This is the average daily temperature over the course of a year. Some days will be cooler and some warmer. If you multiply (50F DEGREES) X (365 DAYS) you’ll get a value of  18,250 DEGREE-DAYS, or 18,250 DD. I’ll use the term Annual Cumulative Degree Day (ACDD) to indicate the degree-days accumulated over an annual period at a specific weather station.

Looking at the y-scales on Figure 3 shows that summing the average daily temperatures for each day of the year will get you to approximately 18,250 ACDD.

…

Note: My use of an index I call degree-day is not the equivalent of Heating Degree Days (HDD) or Cooling Degree Day (CDD), both indexes used in the building systems world to calculate required heating or cooling loads for designing heating and air-conditioning equipment and systems and both reported on in daily summary statistics from NOAA/NWS data repositories. But it is similar in the sense of understanding the total amount of heat received over the course of a year (as defined by the sum of the daily average temperatures) in any given year at SeaTac airport. Each gray line or trace shown in Figure 3 represents one year in the 1948-2023 period.

Figure 3. Annual Cumulative Degree Days (ACDD) plots for each year, 1948-2022, Seattle Tacoma International Airport (KSEA).

 

Comparing individual years

Figure 4 shows ACDD traces of four individual years (highlighted in red) plotted against similar ACDD traces all years. Of the four selected, 1948 and 1985 started off relatively cool through the end of June and then each had a cool autumn and early winter. The plot for 1966 shows it too started cool through spring and into early summer before a late summer surge gave it a relatively average ACDD Index value for the entire year. The plot for 2015 shows the year had an average winter and spring temperature-wise for this region, followed by a warm period extending through the remainder of the year. For the 74 full years between 1948-2022, this year (2015) was the warmest on record in Seattle.

Figure 4. Individual ACDD trace samples for four select years, Seattle Tacoma International Airport.

 

Small Multiples

Figure 5 is a series of plots grouped as a whole. Each individual plot can be clicked on to expand it. This form of data graphic is collectively called small multiple. It allows one to compare one year to other years easily. It also allows for a deeper dive into any individual year.

Detecting trends requires a little more study, but you can see that, in generally, the ten years from 1948-57 were cooler than average at SeaTac. One can also see that the 10-year period from 2013 through recently completed 2022 have been warmer than average. There was another five-year period running from 2003-07 which were warmer than average. Most of the other years hovered near average, though it is common over any ten year stretch to see back-to-back years running much cooler or warmer than average.

Figure 5. A small-multiples data graphic comparing the Annual Cumulative Degree Days (ACDD) tracing for each of 74 consecutive years at Seattle Tacoma International Airport.

Another interesting thing that shows up when plotting the Degree-Day number for each year is best seen going back to Figure 3. Notice how in the winter and early spring months, Seattle tends toward either warmer or cooler springs. Very few annual periods are “average”. Notice the “gap” that exists between early February through May. This period in the calendar tends towards two groups or strands of tracings which braid together in midsummer. By the end of each calendar period, the tracings have advanced towards split ends.

I don’t know why. I wonder if La Nina years tend towards one strand and El Nino years towards the other. Mathematicians, meteorologists, or atmospheric scientists might understand this “strand” phenomenon or “strand theory” better than I.

An Animated Chart

Finally, Figure 6 is an animated chart. It is an alternative to the small multiples chart shown in Figure 5. It displays each year’s trace above the gray traces of all years sequentially. You can imagine it looking like a dog’s tail wagging. This means of presenting data highlights the year-to-year variability. It also can show trends if over a course of periods of years, the “tail” wags high or lower. You can witness by watching the video the early years of recorded temperatures tend towards cooler days and as time marches forward, the wagging tail inches up the chart. Year-to-year the tail wags randomly (annual variability), but over time a pattern emerges of the tail drifting upwards into warmer cumulative temperatures (periodic trending).

Figure 6. ACDD traces for Seattle Tacoma International Airport, 1948-2023. The animated GIF should loop through once, probably upon initial loading of the web page. Notice that the wagging red line slowly drifts higher as the years progress. Drifting high indicates the total daily temperature load is increasing (e.g. days are getting warmer on average).

HINT: Refresh (Command+R) the web page to cycle the GIF in sequence. And remember to scroll back down to the bottom of the page after refreshing.

That’s all for this post, just some interesting new ways at looking at annual temperature profiles for data from selected NOAA / NWS collection sites. I used SeaTac Airport as an example as I live in Seattle.

An update on this winter's rain and (lack of) sunshine...

in

Originally posted on or around January 22, 2022.

Charts 1 - 3a have been updated on June 19, 11 AM PDT.

Solar Radiation: How much sun are we getting…

A little background first: the Union Bay WSU Solar Radiation Station has been recording solar radiation data since late 2011. Here I’m comparing water-year (WY) cumulative solar radiation totals in Figure 1 thru Figure 3. Water-years begin on October 1 and run through September 30 of the following year. Water-year 2011-12 is incomplete for the Union Bay station – WSU only began publishing data sometime after October 1 that year. Therefore, I’ll compare cumulative traces for the 2012-13 through 2021-22 water-years, a total of ten water-year cycles

***

Weatherwise, it was a dim and grim start to winter, and this extraordinary low level of light has continued through most of winter and through spring 2022 as well. Figure 1 shows since October, we’ve received the least amount of sun over this 10-year period. The total solar radiation received so far this water year equates to roughly 93% of the mean for the previous nine years. Previously, the winter half of 2012-13 had the lowest cumulative amount of solar radiation in this limited dataset.

Figure 1. Cumulative solar radiation since October 1 at the Union Bay Solar Radiation Station. Last updated on June 19 with data thru June 18.

Click to enlarge.

Figure 2 is a Cleveland-style dot plot sorted by cumulative daily solar radiation to-date at the WSU Seattle Solar Radiation Station. This shows the 2021-22 water year cumulative solar radiation total is quite a bit less than the other years in this data set. This past February was abnormally dry (see Figure 4). On February 24, 2022, the solar radiation totals at the WSU station in Seattle for 2021-22 rose above totals for the same period in 2012-13. This elevation in ranking persisted for about three weeks. However, this cloudy spring has dropped 2021-22 back to the lowest total solar radiation levels for the past ten years.

Note too that the X-axis values start above 2000 MJ/sq. meter. Starting the x-axis at zero would show that the totals between years are not as disparate as it might seem in Figure 2. 

Figure 2. Dot plot of solar radiation accumulation since October 1 for the past 10 years.

 

Figure 3 shows the same data as Figure 2, except here in a traditional column chart ordered by year. The recent winter-spring seasons of 2017-18 through 2019-20 were quite a bit lighter (sunnier) than this past year. Perhaps this is the reason the darkness has been so noticeable the past 7-8 months.

Figure 3. Cumulative solar radiation beginning each water year on October 1.

 

Figure 3a is new to this post as of May 30. While Figures 1-3 show the total solar radiation measured on site in Seattle’s Union Bay station, Figure 3a shows the cumulative daily cloud cover or sky ratings beginning on October 1 of each trace and extending through May 29 of the following year. This data was gathered at SeaTac airport by the National Weather Service.

A sky cover rating is assigned a value of 0-10 for each day. A sky cover rating of zero indicates no clouds. A sky rating of 10 indicates 100% total cloudiness the entire day. Partially cloudy days are given a rating in whole number values in between this two extremes.

Each trace was plotted by adding up the daily rating values from October 1 of the previous year through the end of May. Steeper line traces indicate cloudier years.

Figure 3A shows that the current October 1 through mid-June period has been the cloudiest over the past 15 years.

Figure 3a. Cumulative daily sky ratings beginning each water year on October 1.

Precipitation: How wet have we been…

Figure 4 displays the cumulative precipitation for all water years at Seattle-Tacoma International Airport (KSEA) from the water years 1948-49 through 2021-22. This represents 74 years of data. SeaTac Airport is approximately 16 miles south of the Union Bay solar radiation site and is the official site of record for Seattle area weather. 

Figure 4 shows a rainy start to our winter season. Seattle had a total of 26.7 inches of rain in the period between October 1, 2021, and January 14, 2022. This placed this year’s early winter rainy season as third rainiest since the late 1940s, following the 1955-56 and 2006-07 early winters. Most of this rain fell after October 19, about 25.5 inches. The October 19 through January 14 period represented 86 days. Therefore, the precipitation rate for this period was 0.30 inches per day. The often sunny, pleasant days we usually see in October seemed elusive this past year and this chart shows why. 

It was relatively dry most days from January 13 through February 26, a period of 43 days. A total of 1.24 inches of precipitation fell during this period, a rate of approximately 0.029 inches per day, or 1/10 of the rate for the previous three months.

Record rains hit starting on February 27 and continued through the next day. A total of 7.9 inches of rain fell from February 27 through March 31. This represented a daily precipitation rate of 0.23 inches per day – a high rate, but not quite the rate of the first three months of the wet season. 

It has been a relatively wet spring as well including through May, especially in late May and early June. This water year’s ranking has moved from the 12th most rainy at SeaTac Airport to the 6th most in just the past few weeks.

Figure 4. Cumulative rain totals at Seattle-Tacoma International Airport for yearly periods beginning on October 1.
Click to enlarge.

This wet spring has moved the SeaTac total precipitation level to the #9 position in the rankings since the late 1940s as shown in supplemental Figure 4a. However, two recent winters have been wetter than this year, 2015-16 (#3) and 2016-17 (#1).

Precipitation traces for past water-years by decade at SeaTac can be found here.

Figure 4a. Rankings of winter precipitation for water years beginning on October 1 at Seattle-Tacoma International Airport (KSEA).

 

Winter / Spring Temperatures: How cold have we been…

It was a chilly winter in 2022, chillier than normal. March ended with a spate of warmer days which took some of the chill off the winter temperature pattern. But April and May have seen a return to the chilly weather. On average it’s been roughly 5-10 F cooler than normal most days since the end of March.

Figure 5 shows the daily average temperature departures from 30Y climate norms at SeaTac Airport. I’ve included data for December 2021 since December is the meteorological start to winter.

Figure 5. Daily average temperature departures from normal, SeaTac Airport. Click to enlarge.

 

Figure 6 takes the same data shown in the previous figure and extends it back to October 1, the start of the 2021-22 water year. It has been cooler than normal for most of the start of the rainy season this year. However, the whole of November may have been slightly milder than most Novembers. You can see the warm period quite clearly in late November when a series of atmospheric rivers blew in across the Pacific and dumper huge amounts of rainfall in Washington and southern British Columbia flooding large parts of the areas around the Fraser and Nooksack rivers.

Figure 6. Daily average temperature departures from normal at SeaTac Airport starting October 1, 2021.
Click to expand.

 

Stepping back further in time, Figure 7 shows the average daily temperature departures from climatic norms from October 1, 2000, to the present. This chart also highlights days where the average daily temperature exceeded or fell short of the daily normal for a given date by 20˚F or more. A particular warmish period when warmer-than-normal days outnumbered cooler-than-normal days began sometime around 2012-13 and continued for about five years before moderating somewhat. With the most recent coolish last few months, that trend appears to have moderated even more. It remains to be seen if this will continue.

Figure 7. Average daily temperature departures from 30Y climatic normals, SeaTac Airport, 2000-2022.
Click to expand.

Sources:

[1] Precipitation and temperature data: NOAA / NWS Climate, Observed Weather: https://www.weather.gov/wrh/climate?wfo=sew
[2] Solar radiation data: Washington State University AgWeatherNet Current Conditions Map: http://weather.wsu.edu

Data Graphics:

All dataworks created using DataGraph 5.0, Visual Data Tools, Inc. for macOS.

A dark start to winter...

in , ,

Updated: December 29, 2021, 6:30 AM PDT

Figure 1 updated with most recent data.
Figure 2 has been updated. Note that the minimal value on the x-axis begins at 320 MJ/sq.meter. Figure 3 has been updated. Note that the minimal value on the y-axis begins at 300 MJ/sq.meter. Figure 4 has been added to show the daily temperature departure for 2021 to date.
Figure 5 has been added to show the daily temperature departures since 2000 at SeaTac airport.

If it seems like it has been pretty dark and rainy this autumn and early winter in Seattle you would be right. I’ve already posted about the high level of precipitation we’ve seen in Seattle and the extended Western Washington area since the start of the 2021-22 water year on October 1. The areas surrounding Bellingham and Vancouver B.C. have been especially hit hard with rain.

But it has seemed very dark in recent months as well, and by dark, I mean low levels of light. Of course all this rain comes in leaden skies. And looking at solar radiation data collected near Husky Stadium and Union Bay (47.66, 122.29) in Seattle confirms this has been the darkest start to winter in the past ten. Washington State University operates a solar collection station in this area and exposes the processed data to the public on their web site. A link to this data is listed at the bottom of this page.

Figure 1 shows the cumulative daily totals of solar radiation (MJ/sq.meter) from October 1 through December 31 for 2013 through the present year. At this writing we are only partly through December this year. But it is clear that this year has been quite dark compared to the other years. Lower traces indicate lower levels of solar energy measured. This year’s trend line is the heavy line. The Seattle area began with a normal October, but around mid-month the rate of cumulative solar energy slowed considerably.

I choose a start date of October 1 since this is the traditional start date of the Northwest water year, the time of year when storms begin to blow off the Pacific with increasing frequency. This date provides a good start or “zero point” for the start of the wet season.

Figure 1. Solar radiation measured at Seattle’s Union Bay data collection site.

 

Figure 2 was added on December 15. This figure is a dot plot showing the total cumulative solar radiation received at WSU’s Solar Station in Seattle. The dot plot is sorted by total solar daily accumulation for the stated period.

This year’s accumulation of sunlight since the start of October is marked by the black dot in the lower left corner. It is substantially lower than the sunnier years at winter’s start. It is substantially lower than the median value for all years shown. The median value is shown by the dash vertical line.

Looking at the years’ positions on the y-axis, there does not appear to be any pattern to the order for the very limited number of years for which data exists.

Figure 2. Dot plot showing cumulative solar radiation sorted by year.

 

Figure 3 essentially shows the same data as Figure 2. In this bar chart, the years are in order along the X-axis (horizontal). It’s a little easier for the mind to see the lack of any pattern by time in this small sample size – we are more often used to seeing date-format data along the horizontal axis, increasing in time from left-to-right. It’s also clear to see how low sun levels have been this Oct-Dec period compared to recent years. All years show data through the date in the title.

Figure 3. Cumulative Solar Radiation, Oct 1 through December, sorted by years, 2012-21.

 

In addition to lower solar radiation levels in Seattle since roughly mid-October, it has been a relatively cool autumn and start to winter. September had mare days that were cooler than normal than days warmer than normal. Same for October. November was pretty mild with a series of atmospheric rivers coming in from the tropics. Those brought warmish, moist air with them. And plenty of flooding in parts of the Pacific Northwest and southern British Columbia. December has been relatively colder than most recent Decembers. This can be seen in the large number of days where average daily temperatures have been below 30Y climatic normals.

Figure 4 shows the daily temperature departures for 2021 up through the most recent date.

Figure 4. Daily Average Temperature: Departure from 30Y normals. Click to enlarge.

Figure 5 shows similar data as Figure 4, daily average temperature departures from 30-year normals going back to January 1, 2000. It appears in recent years, the trend is back towards the climatic normals of the past 30 years after a warming period for several years in the mid-2020s.

The 30Y normal daily average temperature reference values for all years except 2021 are based on the years 1981-2010. In 2021, the comparison is against the normal daily temperature range from 1991-2020. It’s possible that the 1991-2020 30Y normals cycles have increased from the previous 1981-2010 30Y cycle and this year’s lower trend is simply reflecting that change - departures may be comparing against a high reference line..

This data is for the National Weather Services’s Seattle-Tacoma International Airport site.

Figure 5. Daily normal temperature departures for SeaTac airport from 2000 to present. Click to enlarge.

SOURCE DATA
Washington State University AgWeatherNet: http://weather.wsu.edu
NOAA/NWS Climate Data Seattle/Tacoma https://www.weather.gov/wrh/climate?wfo=sew
FULL DISCLOSURE
I am not a meteorologist, climate scientist, data scientist, geologist nor hydrologist. I am simply a (retired) engineer who has some familiarity with numbers, basic statistics and probability statistics who enjoys looking at readily available public data and trying to make sense of things. I enjoy building data visualizations from data I find much like others enjoy working daily crosswords or sudoku puzzles. Local weather, climate and hydrology science are complex subjects. Take what you read and find here with this in context.
 

On Seattle-Tacoma precipitation traces, Part 1...

in ,

This post will display a history of water-year cumulative precipitation traces from Seattle-Tacoma International Airport. A water-year defined here crosses parts of two calendar years and runs from October 1 of year 1 to September 30 of year 2. For instance, the water year 1972-73 runs from October 1, 1972 to September 30, 1973.

The reasons for using water years is simple. The Puget Sound area can be thought of at a higher level of having two basic seasons: a wet season running from October through March when most of our annual precipitation falls, and a dry season which runs from April through September.

Figure 1 is the baseline chart and shows cumulative precipitation traces at Seattle-Tacoma International Airport from 1948-49 through the start of the 2021-22 water years. The data comes from the National Oceanic and Atmospheric Administration (NOAA) and the National Weather Service (NWS). These data extracts normally list daily precipitation totals. I’ve summed these values up for each water year.

Figure 1 also shows some other graphic elements. In the lower left corner, a blue box appears highlighting the first two months of the water year. The reasons for this box is simple. We just completed this two month period for the 2021-22 water year. It was a very wet period in Seattle and the Pacific Northwest in general. I placed this box on the chart to allow for easy comparisons of this year’s heavy rains with other years’. As you will see later, this year’s start to the water year was one of the wettest since the late 1940s, but not the wettest.

Two other key elements added to the baseline chart include a 30Y climatic normal reference line for two climate periods. These periods are the 1981-2010 climate normals for precipitation at SeaTac and the 1991-2020 climate normals. These are standard 30 year daily averages published by NOAA/NWS. As you can see, the more recent 30 year normals show a higher level of daily precipitation than the 1981-2010 period, adding up to a little more than 2 inches additional rain per year at SeaTac.

One final observation is that precipitation rates vary widely within each annual trace and between the final annual totals of all traces. The wettest years had roughly 51-52 inches of rain over the course of 12 months, the driest years had less than 25 inches over a 12 month period.

Figure 1. Precipitation traces for each water year from 1948-49 through 2021-22 (to the current date).

I only have two full water-year traces from the 1940s. These are shown in Figure 2. Interestingly, both years began the first two months with similar trace patterns. After about mid-December, each trace line diverges for the remainder of the year, one towards the high side of annual precipitation totals, the other towards the low end. At a glance, and without performing the statistical calculation, it appears as if the final year-end totals span the first or second standard deviations of all year-end precipitation totals.

Figure 2. Cumulative precipitation traces for available SeaTac data in the 1940s.

The 1950 traces in Figure 3 show that the start of the wet seasons varied widely during that decade and that, in general, it was a decade when annual precipitation totals hewed towards current climate normals or were generally higher in precipitation.

Figure 3. Cumulative precipitation traces for available SeaTac data in the 1950s. Tracks in the 1950s trend towards years with greater precipitation.

Figure 4 shows the 1960s traces were distributed about evenly above and below current climate normals and tend to not have extraordinarily wet or dry annual totals.

Figure 4. Cumulative precipitation traces for available SeaTac data in the 1960s. Precipitation tracks in the 1960s hover more closely to 30Y climate tracks about evenly above and below these normals.

Figure 5 shows the 1970s traces. It appears most years in the 1970s began relatively dry. From December on, the annual totals varied widely. This might be the decade with the widest and most uniform spread between very wet and very dry years.

Figure 7. Cumulative precipitation traces for available SeaTac data in the 1970s. Half the 1970’s traces hover close to the climate normals. The remaining traces are biased towards both extremes: wet years or dry years.

Most annual traces in the 1980s hewed close to current climatic normals, though biased on the dry side of those normal. Figure 6 shows a few years were substantially drier by year’s end.

Figure 8. Cumulative precipitation traces for available SeaTac data in the 1980s. The 1980’s traces tend to be biased towards drier than climatic normal years. The also tended to start the years tightly around climatic normals.

The precipitation traces for the 1990s, illustrated in Figure 7, appear to be evenly distributed around the current climatic norms much like the 1960s traces. However, the 1990s traces are dispersed more widely, reaching towards the wettest and driest annual limits for all of the traces. Collectively, the 1960s and 1990s traces in the early part of each year exhibit pretty similar patterns, hewing close to current climatic normals except for one particularly dry autumn in each subset.

Figure 7. Most years began with fairly normal precipitation levels except for perhaps two. By years’ end, the traces were evenly, if broadly, distributed around current climatic normals. This decade saw the most varied ditribution of precipitation totals at the end of the year.

Figure 8 shows the traces for the 2000s. The year end precipitation totals tend not to trend towards extremes and are maybe slightly biased towards drier years. But the start of the wet season (October-November) varied widely for this period. Some of the wettest starts to winter began here and even a drier one as well. Many other decade charts showed must tighter distributions around the current climatic normal lines.

Figure 8. Cumulative precipitation traces for available SeaTac data in the 2000s. Traces appear to show wide autumn variations then trending towards an even distribution around climatic norms at years end.

The 2010s year-end precipitation totals trended towards wetter years. These traces are illustrated in Figure 9. This decade, along with four very wet years in the 1990s might explain why climatic normal curves jumped for the 1991-2020 period. The starts of the water-years in the 2010s also trended towards wetter Octobers and Novembers in most years. The 2010s also hosted some very long, dry summer periods.

Figure 9. Cumulative precipitation traces for available SeaTac data in the 2010s. Trends show wide variation in the autumn months and a bias towards wetter year-end totals.

The 2020s are too new to host many precipitation traces. In fact, we’ve only completed one year of this decade and only started a second water-year trace. In Figure 10, the single, complete year hewed very closely towards climatic normals after a wet late winter and early spring. This was followed by a very long and dry late spring and summer period.

The start of its second year has been very wet.

Figure 10. Cumulative precipitation traces for available SeaTac data in the 2020s. The 2020-21 year followed current climatic normals closely. The current year has begun very wet.

Conclusions and Notes

Looking at the traces, I’m not really sure I’m seeing any convincing trending decade-to-decade. The only long-term trending I’m seeing is between the climatic normal lines where wetter late winters and early springs seem to be trending. But these two lines are drawn from only two sets of averaged daily data. I would be more convinced if other 30-year climatic normal periods were plotted here, say for the 1951-80, 1961-90 and 1971-2000 periods. I may do so for Part 2 of this blog entry.

Sure, the 2010s appear to be quite wet. But that decade was preceded by several decades of precipitation traces distributed pretty evenly around the climatic normal curves. And the 1970s and 80s trended towards the drier side of the distributions. They, in turn, were preceded by a pretty normal series of plots in the 1960s and, again, wetter trending in the 1950s. Who knows what’s in store for this decade. It’s way too soon to tell.

And this second point brings up an important third one: the arbitrary definition of a decadal dataset. I used the common calendar dates to group my datasets and plots, begin each set of plots with a year ending in a zero and enclosing the dataset with a trace from a year ending in a nine. But I could have just as easily chosen decadal sets such as 1974-83; 1984-93; 1994-03; etc. Who knows what trends we might detect then?

***

I think I’ll plot a Part 2 post to this topic. It will take some time due to the need to post-process the data. I have data preceding the 1950s going all the way back to the 1890s for the Seattle area. However, this data is typically from other locations, including the Portage Bay area in North Seattle and Boeing Field in South Seattle. These areas are 10-20 miles from Seattle-Tacoma Airport.

I think too, I will plot climatic normal curves for other 30-year periods to see if any trending is detected within those longer-term datasets.

That’s all for now.

Pacific Northwest autumn 2021 rains...

in ,

Updated: December 1, 8:00 AM PDT

This post has been substantially updated on Wednesday morning, December 1.

  • One chart has been replaced by five (5) charts with further explanations and comparisons.

  • Data has been updated to include precipitation totals through November.

  • Vancouver’s annual precipitation totals have been corrected to state the 1981-2010 30Y average for Vancouver International Airport as 46.8 inches. In the original blog post, it listed the 30Y annual average for Vancouver’s Harbour climate station site. This site has a considerably higher average than the airport.

  • On Figures 2 thru 5 a new reference line has been added for the recently released 1991-2020 climate precipitation normals for Seattle-Tacoma International Airport. As you can see, the most recent 30Y normal reference line show it has been wetter in Seattle in recent decades.

All figures subject to correction and, if required, will be noted.

Click on any chart to expand.

The Pacific Northwest almost always experiences rainy Novembers. This year precipitation rates have been high, if not extraordinary. Heavy flooding occurred in northwest Washington and southern British Columbia in mid-month. Since then, rains have levelled off a little but are accumulating nonetheless. This weekend we are expecting more rain in Seattle. Bellingham and Vancouver will likely see even more.

So how does this start to the rainy season compare to others? The charts below shows several comparisons:

Figure 1 sets the table for this data and subsequent charts and shows the cumulative precipitation traces at Seattle-Tacoma International Airport (SeaTac) for the water years 2002-03 through 2021-22 (to-date). Water years are calendar constructs which help visualize the wet season precipitation totals vs. dry season in the Pacific Northwest. Typically a water year begins on October 1 of a given year and runs through September 30 of the following year. Looking at cumulative precipitation traces in this time frame usually show distinct wet / dry season patterns.

Figure 1 also highlights the 2006-07 water year. Seattle experienced an extraordinary level of precipitation in November 2006, the most of any traces for SeaTac in this set of data. The blue box in this and subsequent charts highlights for comparison the level of precipitation versus the first 61 days of the 2006-07 water year and corresponds to the months of October and November.

Figure 1. Record-setting Oct-Nov at Seattle-Tacoma International Airport, 2006.

Figure 2 highlights the amount of precipitation SeaTac has received so far this water year. As mentioned in the updates, the 1991-2020 climate normal reference trace has been added to this and subsequent charts.

Figure 2. Seattle-Tacoma International Airport cumulative precipitation for Oct-Nov, 2021.

Figure 3 shows the accumulated precipitation trace (red) for Bellingham International Airport. Bellingham is approximately 90 miles north of Seattle and was hard hit by the mid-November flood.

Figure 3. Oct-Nov accumulated precipitation for Bellingham International Airport compared to SeaTac totals, 2021.

Figure 4 shows the accumulated precipitation (blue) trace for the Vancouver International Airport weather station. Vancouver is approximately 50 miles north of Bellingham. In the last few days of November, Bellingham has seen more rain than at Vancouver’s airport climate station.

Figure 4. Vancouver International Airport and Bellingham International Airport cumulative precipitation totals for Oct-Nov, 2021.

Figure 5 compares the accumulated precipitation at Vancouver’s airport in it southwest corner to its Harbour climate station located near Stanley Park. This station is near the core of downtown Vancouver. The station at Vancouver’s Harbour has seen far more rain this water year than at the airport.

Figure 5. Vancouver International Airport and Vancouver Harbour precipitation totals for Oct-Nov, 2021.

Preliminary observations:

  • Seattle and Bellingham have had similar precipitation totals through this period though they arrived at this point in slightly different manners. Over the past 48-96 hours Bellingham has received substantially more rain than Seattle.

  • The precipitation totals at Vancouver International Airport for October-November are similar to Bellingham’s.

  • The precipitation totals witnessed at Vancouver’s Harbour climate station far exceed totals in the Washington cities and at Vancouver’s airport. I don’t know if this level of disparity is typical. However, with regards to the comparison with Washington cities, Vancouver typically sees approximately 46.8 inches of rain per year; Seattle sees – with the new 30 year climate normals – about 39.3 inches of precipitation per year.

Sources:

[1] NOAA / NWS Climate\Observed Weather: https://www.weather.gov/wrh/climate?wfo=sew for SeaTac and Bellingham data.

[2] Canadian Government Historical Climate Data: https://climate.weather.gc.ca/historical_data/search_historic_data_e.html

 

ABOUT THIS BLOG / FULL DISCLOSURE

I am not a meteorologist, climate scientist, data scientist, geologist nor hydrologist. I am simply a (retired) engineer who has some familiarity with numbers, basic statistics and probability statistics who enjoys looking at readily available public data and trying to make sense of things. I enjoy building data visualizations from data I find much like others enjoy working daily crosswords or sudoku puzzles. Local weather, climate and hydrology science are complex subjects. Take what you read and find here with this in context.

Seattle-Tacoma's hottest days...

in

Charts updated: August 14, 2021, 8:00 AM PDT

We’re in the midst of a second heat wave this summer. Our first, in late June, was a scorcher, setting an all time high record for Seattle at Seattle-Tacoma International Airport (SeaTac) on June 28 of 108˚F. We had three days of temperatures greater than 100˚F in that period.

This week’s heat wave (and now smoke wave) isn’t quite as hot. But temperatures are back above 90˚F. This is a arbitrary threshold, but it is as good as a threshold for a heat wave as any, so we’ll use it.

****

So, how often does it get to 90˚F or greater in Seattle, The Land of No Air-Conditioning? It is pretty much a summer only phenomena and is not as uncommon as one might think. Figure 1 shows maximum daily temperatures at SeaTac going back to January 1, 1949. Most summers record at least one or more days of 90˚F, but not all. This year is about average. We’re not through with this current heat wave, so one can expect to see another red dot for today and probably tomorrow. I can’t predict beyond tomorrow whether we will see anymore really hot days. But it is becoming late summer. Days are gradually getting shorter and nights longer and we only have about 2-½ more weeks until September begins.

Ironically, in the six or so weeks between this summer’s heat waves, we’ve had one of the most pleasant, if a bit dry, summers in my 38 years here.

Click on Figure 1 to expand it. I’ll update it over the next few days as this heat wave plays itself out.

Figure 1

Figure 2 was added on August 14. It shows a zoom-in of Figure 1 for the last 10 years. Most summers in Seattle experience at least a few days with temperatures reaching 90˚F.

Figure 2 also shows the extraordinary heat wave Seattle experienced in June 2021 where temperatures exceeded 100˚F for three straight days.

Figure 2

© itterrocks.com, 2021.. All rights reserved.
Please contact litterrocks via the Contact link in the lefthand margin for permission to use.

Tags: Tmax, maximum temperatures, weather, Seattle-Tacoma International Airport, KSEA, summer, heat

On summer's maximum daily temperatures...

in

I looked at the extreme departures from 30-year normals of the daily average temperatures in my last blog post in late June, 2021. This was right after Seattle and the Pacific Northwest endured record high temperatures for several days.

Today, on the National Weather Service (NWS) site there is a warning of warm temperatures ahead for the next few days. They don’t expect the temperatures in Seattle to exceed the 100˚F mark as it did in late June. But they expect a couple of the days will reach above 90˚F. Other areas in the West to the south and east of Seattle are expected to have temperatures exceed 100˚F over the next few days.

In my book, anything above about 85˚F is hot. Maybe not uncomfortably hot, but it’s certainly starting to hit the unpleasantly hot range for me. I grew up in the Great Lakes Midwest, so hot summers are nothing new. But my most recent 38 summers have mostly been spent in Seattle, a city with generally cooler and more pleasant summers than those in the Midwest. I enjoy those and have become accustomed to those temperatures. I’ve become a heat wimp.

However, though not common, temperatures at 85˚F or greater are not rare in Seattle summers. Here’s a look at several charts depicting days – over a very limited 21 year time scale – where maximum temperatures match or exceed the following thresholds: 85F, 90F, 95F, 100F, and 105F at Seattle-Tacoma International Airport, Seattle’s official NWS site of record.

Click on any image below to expand it. Hint: once you expand the first chart, you can navigate to the others using your “left” and “right” arrow keys on your keyboard.

A winter to forget...

in ,

The past year (and then some)

This is my final post on this cold snap / winter topic. First, I think the weather is changing and winter really is exiting. Second, as a subject, it has become a little tired. So, here goes. 

I suspect the extended coolish pattern we’ve experienced over the past three months has finally had its run. I’m not a meteorologist nor a climate scientist. Just someone working on my writing and data presentation skills. It just seems that we’re approaching the end of a pattern. The longer term forecasts seem to point towards more normal temperatures.

No doubt, we will still get cooler-than-normal days. Just as we’ll get warmer-than-normal days. But I think the persistent patterns are breaking down. Looking at those cooler-than-normal patterns on the right of Figure 1 shows that up until about March 9, we were still seeing strings of continuous cool days. However, the last few days have been mild, and the temperature deficits have been shrinking since about early January.

A couple of things seem clear from Figure 1: 

  • This coldish spell was persistent and long — almost 3-½ months long (with a few brief interruptions);
  • it was preceded by at least 11 months of predominantly warmer-than-normal weather; and
  • the change from one state to the other was quite abrupt in early December. It was as though a switch was flipped.

Figure 1. Temperature departures for the past 15 months. Click to enlarge.

****

Temperature Deviations - A longer comparison (2000-2017)

Figure 2 shows similar temperature deviation data to Figure 1, except it covers a much longer stretch of time backwards. The red zones depict the approximate stretch of winter (Dec-Feb) for each annual period.

I mentioned in the section above that prior to the recent three month cold snap, Seattle experienced 11 months of warmer-than-normal temperatures. Well, looking at a longer timescale backwards, the stretch of warmer weather goes back at least about three years, aside from occasional brief spikes of temperatures in the opposite direction.

For most of this period, specifically the dozen or so years extending from 2000 through 2012, the daily differences from normal temp appear to be more evenly distributed between short warmer and cooler periods. The year 2011 appears to have a long stretch of cooler temperatures — more in the early spring-to-fall time frame rather than winter. And the two year period of 2003-04 appeared warmer than normal in winter as well. I recall during this time thinking to myself that after 20 years, I was finally becoming accustomed to cool, rainy Northwest winters and they weren’t as bad as they previously seemed to me. It turns out, I may had just been experiencing a milder series of back-to-back winters.

Figure 2. Comparison of temperature deviations over time (2000-2017). Click to enlarge.

****

What about the rain

The temperature discussion above focuses on the traditional winter months of December through February. In Seattle, our average winter day temperatures don’t differ much than late fall or early spring temperatures. We have mild winters, mostly and coolish springs. In fact, I’ve always considered the period between mid-October to mid-April as one long winterspring season. This time period nearly coincides with the first half of the west coast meteorological water year which typically runs from October 1 to September 30 each year. Seattle, and much of the northern West Coast has a wet season and a dry season. So I’ll use the Oct-Sep water year as a time period to discuss this winter in terms of precipitation.

Figure 3 shows the accumulated precipitation since the beginning of the water year. This year’s line is the blue dashed line. The orange line represents the climatic averages from the years 1981-2010 from SeaTac International Airport. Clearly, we are experiencing a very wet rainy season. So far — and the rainy season for this year is not over  — we have had about 11 more inches of rain than normal since October 1 of last year.

Figure 3. Cumulative precipitation since October 1, present year and historical. Click to enlarge.

So we're having an extraordinarily wet year. Big deal — some years are wet; some are dry. However, are these wet years becoming more frequent? I don't know if we have enough data to establish this claim for the long run, but recent years seem to be.

Figure 4 shows more recent years in the same chart as Figure 3. Last year, the 2015-16 water year, is the heavy black line. Last year was also an exceptionally moist year, the wettest of the previous 14 years shown. The medium gray lines reflect the water years: 2014-15; 2013-14; 2012-13 and 2011-12, the years precluded from the 1981-2010 average. The light grey lines represent the nine preceding years before 2011-12 since I have the data handy and they give some balance to the discussion.

The chart in Figure 4 illustrates:

  • Though it has been very wet since October and we are approach last year’s surge of rain, it is unlikely we will catch it. We are currently about 5 inches behind and are slowly approaching our drier months. Back-to-back years of this flow of water lends understanding as to why many are griping about this winter;
  • This year’s totals are in a tight race for second place of the wettest years of the past 15 years. Today, we are about even with 2006-07, which produced a notably wet start to winter [1];
  • Of the six (6) years since the 1981-2010 climate reference period, three are near the reference average and three are well above it (assuming the 2016/17 water year keeps accumulating precipitation at even the climatic average rate). Simply put, in an annual accounting of rain, we have been in a pretty wet period since 2010.

Figure 4. Cumulative precipitation based on the water year calendar, multi-years. Click to enlarge

So, what happens if you take the averages of the most recent past six water years, not included in the climatic data range, and compare them to the historical averages. Keep in mind that the 2016/17 water year is not even half way completed. This is shown in Figure 5. There has been a significant bump in the amount of precipitation we've seen recently. From the chart, it appears most of this bump has occurred in the months of October, February and March. September also shows an uptick in precipitation as well, but not as pronounced as those three. One could also make the case that summers are slightly drier (seen by the flattening of the blue curve in comparison to the orange one for these months).

Figure 5. Comparing the past six years to the climatic average. Click to enlarge.

 

Seattle has received over 246 inches of rain since October 1, 2011. Climatically, Seattle would be projected to receives about 214 inches of rain during this period. We've received nearly 34 inches of additional rain in the past six years. Table 1 illustrates this clearly.

This is almost an entire year's worth of additional rain squeezed in those six years. Much of that additional precipitation has occurred in the past two years.

Actually, it is worse than that. I included 2011-12 in Table 1 since it is not included in the 1981-2010 historical averages. I wanted to include all recent years not included in the historical average in an exploration to see where the data took me. 

Since Table 1 shows the 2011-12 water year to match essentially the historical average for the period, you can leave that year out of the discussion. Our near additional year of rain has been squeezed into the past five years. And — again — this water year is not half over yet.

In this context, one may like the rain but should also understand the weariness people are experiencing and the accompanying complaints.

****

Shades of gray

Aside from rain, the most common characteristic of Seattle winters (and wintersprings) is the near constant cloud cover. So, how did we stack up with regards to cloud cover? I’ll use the first half period of the water year for the time scale, since this is traditionally when the clouds roll in.

We began the water year with one of our rainiest Octobers. This was followed by a normal November, typically our rainiest month. So that in itself a sign that it might be shaping up for a pretty dismal winter. However, if you look at Figure 3, the rains softened in December. This can be seen by looking at the slope of the blue curve in December. Further, the last half of January saw little rain. In fact, December and January were cold, but not too rainy. If the skies were not completely clear, we experienced some sun during those months. More than usual, I’m guessing, without looking deep into the data. 

The rains returned in February at an accelerated rate. February 2017 was one of our wettest Februarys. The month of March, to date, has been dismal as well.

The National Weather Service gives a rating for sky cover for each day based on an 11-point scale, going from 0-10. In maybe an oversimplification, a day rated 0 is clear with no clouds. A day rating of 10 has 100% cloud cover. We can sum the scores for each day since October to see how this year compares to other years.

Figure 6 shows this. So far, this water year has been cloudier than all of the previous 10 annual periods except for one. But, with this chart it doesn't appear to be much.

Figure 6. Seattle Cumulative Sky Cover ratings, 2016-17 water year. Click to enlarge.

Figure 7 illustrates this method of comparison with a close-up of the data shown in Figure 4. So far, through March 10, SeaTac Airport has accumulated about 50 more sky cover points than the average for previous 10 years. These additional sky points don't buy you an upgrade; only a slight downgrade, unless you love clouds.

However, spread evenly, 50 sky points divide by 161 days (Oct 1 to Mar 10) account for only about .3 sky points per day. Or, another way of thinking things, the maximum sky cover points any day can have is 10. Divide 50 sky points by 10 points per really cloudy day and we have had roughly 5 extra really cloudy days more than average during this time period.

Figure 7. Cumulative Sky Cover rating points for annual periods running from October 1 through September 30. Click to enlarge.

A simpler way of observing the cloudiness of the past 5-½ months is to look at the total number of cloudy days in a table and compare this year’s numbers to past years. Table 2 shows  this comparison. 

To date, Seattle had about a 68% chance of seeing an all cloudy day this past wet season. Normally, in recent years, this would be a 64% chance. This winter, Seattle also had about an 8% chance of seeing a pretty clear day. In the recent past, we would have a 12.5% chance of seeing a reasonably clear day. The chances of a partly cloudy day are essentially the same for this year and the recent past.

So, yeah. It’s been a bit cloudier than normal; though not that much more. Still, every little bit adds up.

 

****

Final thoughts...

Yeah, this winter in the Pacific Northwest has been pretty dismal. More dismal than normal. More dismal than most. The coldish streak was a bit long — I grew very weary of it. But the low temperatures were not that cold. Consider the Midwest or Northeast in any normal winter. Our coolish winter temperatures this year were still pretty moderate in comparison.

We had snow a couple of times. Deep enough for some fun and some nice photos. Not too much to cause trouble for commuting in the lowlands, though the mountain passes got hit hard at times.

This area doesn’t seem to suffer too often from daily extreme temperatures, humidities, or even heavy rains. We get strong winds blown in off the North Pacific occasionally, but we don’t see hurricanes or tornados often. 

Where we see extremes, it seems to me, is that we settle into long, long patterns, whether long heat streaks; long coldish streaks, long rainy streaks, and — for me the most dreaded — endless cloudy stretches. 

This winter combined most of those long streaks. I’m happy to see it ending and am looking forward to longer days, brighter skies and warmer temperatures. 

****

References:
[1] City That Takes Rain in Stride Puts on Hip Boots; Yardley, Wm.; New York Times; November 27, 2006.
[2] Data Sources NOAA NWS Seattle Local Climate site (click on text for link).

Charts and Graphics Notes:
Data from NOAA/NWS Climate site was post-processed in Microsoft Excel for Mac 2016.

Figures 1-7 were produced using DataGraph 4.2.1 software from Visual Data Tools, Inc. and available on the Apple App Store. A terrific product that keeps improving — support good engineering and design.

Base charts were copied to Adobe Illustrator CS6 for post process refinement and scaling.

Tables 1 and 2 were developed in Adobe InDesign CS6.

 

 

 

 

The cold return...

in ,

In mid-February there was some small hope that we’d break out of this coldish streak we’ve encountered in Seattle since early December. It turns out this was wishful thinking. There were maybe a week’s worth of slightly warmer-than-normal days to enjoy, but these were accompanied with some heavy rains as well. For a week now, we’ve flipped back to a cooler-than-normal situation. The long-term forecast is much of the same continuing through March. It’s not really that cold; it’s above freezing. But I think a lot of us are looking forward to some more springlike temperatures. I’m pretty sure the plants are.

Daily departures from 30-year normals.
Click to enlarge.

As I mentioned, we had some heavy rains the first half of February. These nearly matched the heavy rains of last October, before we hit a relatively normal-to-dry period from November through January. For a brief period, it appeared we might catch up with last year’s very wet winter. But the rains seem to have taken a pause now that the cold weather has returned.

Onto March…

Click to enlarge.

A warm, wet storm arrives. Is this a turn towards spring?

in ,

Early this morning, about 3:30 A.M. a pounding, wet rainstorm woke me up. I sleep beneath a skylight, and though it has yet to leak on me in 17 years, I suspect one day it will. It is in a skylight’s nature to do so. This squall came after an all day rainy Wednesday.

The seasonal water year begins on October 1 in Seattle and runs through the next September 30 for any given period. This year’s water year began exceptionally wet starting about mid-October. Storm after wet storm blew in. But in December — a normally wet month — we seemed to get a reprieve. January was similar except for perhaps a few rainy, individual days.

February seems to have picked up where October left off. We started with snow, but it’s been the strong storms the past few weeks which have really added to the precipitation totals. 

They say more is on the way later this weekend. If true, we may catch up with last year’s very wet winter. But, even with these heavy rains, that would be a tall order.

 

Cumulative Precipitation for Several Seattle Water Years. Seattle is known for rain. But mostly our rains come in the winter half of the year. Therefore, a local meteorological measure of time is the water year, which runs in our region from Oct 1 through Sep 30. The chart above tracks the cumulative amount of this year's water precipitation (blue, dashed line).

The most recent five water year tracks are illustrated in black, with last year's water year track in shown as the heavy black line. The remaining gray tracks are water years for the 2002-03 through 2011-12 seasons.

Click to enlarge.

 

****

The recent rains have been warm. This is shown on the far right end of the chart below. Spring often hits Seattle in late February, with our relatively mild Pacific climate. Maybe the cold snap we recently experienced (highlighted on the chart) is over for good and we’re moving into spring. The daylight sure is stronger and richer.

I hope this is true, but it's too early to tell.

 

Daily Temperature Departures from 30-year (1981-2010) Averages. A significant change occurred in the early part of December where a lengthy, relative warm year switched to a cold period for about two months.

Click to enlarge.

Continued cold...

in ,

Our coldish winter in the Pacific Northwest continues. About halfway through winter, cooler days than normal days are the dominant pattern. Here in Seattle we received about four inches of snow on Monday. It's not a large amount, even for here, but it is the first significant snowfall we've had in five years.

Starting a few days into December, the mean daily temperatures switched abruptly from warmer than normal for most of 2016 to cooler than normal. Aside from a few days, it has remained consistently cool.

Click on to enlarge.

A wintry white scene in Seattle's Volunteer Park on February 6, 2017.