2021

A dark start to winter...

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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.
 

Nooksack flooding, 2021

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It has been a rainy start to autumn in Seattle in 2021. Figure 1 shows a plot of the cumulative precipitation at Seattle-Tacoma (SeaTac) International Airport since the beginning of the 2021-22 water year. Water years in Seattle are date-based construct starting on October 1st and running through September 30 of the following year. These are often used when discussing precipitation events since the west coast of North America and specifically the Pacific Northwest of the U.S. can often be divided into a wet season (late fall through early spring) and a dry season (late summer through early autumn).

The plot below highlights the current water year precipitation accumulation but also includes similar traces for all water years at SeaTac since 2002-03. Compared to recent years, this year – just starting – is quite wet.

Click on any figure below to expand it.

Figure 1. Cumulative rainfall, Seattle-Tacoma International Airport, current water-year. Also show are traces from previous water-years, 2002-03 through 2020-21.

Figure 2 highlights on of the past two decades wettest start to winter for comparison purposes. This was the 2006-07 water year. November of that month registered close to 15.6 inches of rain.

It has not been nearly as wet this November with roughly 8 inches of precipitation so far, about two-thirds of the way through the month. But if you compare the two lines on the chart, Seattle has had a much wetter October in 2021, so the total precipitation to date is similar between the 2006-07 and 2021-22 water years.

Figure 2. Comparison of current water-year cumulative precipitation with the 2006-07 water-year trace.

Figure 3 shows an additional year with a very wet start, the water year of 2016-17. This wet year reached approximately the same total precipitation as 2006-07 for the two-month, OCT-NOV period, a value of roughly 17 inches total. Normal precipitation totals for Seattle-Tacoma for that two-month period is typically about 10 inches. In the 2021-22 water year, with November still one week away from completing, we have seen 13.66 inches of rain since October 1.

Figure 3. Current water-year cumulative precipitation at SeaTac Airport with the 2006-07 and 2016-17 precipitation traces highlighted.

Figure 4 is a little bit different than the first three charts. I often track weather out of SeaTac. But I rarely step out to track weather in other areas, even areas not so far from home. Last week, in the northwestern part of Washington State and in southern British Columbia, large volumes of rain, arriving in the form of an atmospheric river, flooded the region. The flooding was quite severe, impacting many homes and farms, and creating great havoc and damage to many roads and highways. Many people were stranded by the flood waters and needed to be rescued. Several people have died in this storm.

I’ve plotted the cumulative rain totals recorded at the Bellingham International Airport since October 1. Bellingham is a mid-sized city approximately 90 miles north of Seattle, and very close to the flood zone. In fact, parts of Bellingham were under water for several days after these recent storms.

In Figure 4 you can see the total amount of rain falling in Bellingham has been very similar to that of SeaTac. Until about November 8, Belingham was tracking about 2 inches less in rain compared to Seattle from the start of the new water year. But from November 9-15, Bellingham received approximately 6.6 inches of rain, about 2.5 inches more than Seattle in that week.

I regularly keep track of these precipitation vs. time charts for Seattle-Tacoma International Airport. Adding Bellingham totals to the chart was only for comparison reasons only. Inthe most recent storm, it’s likely the Seattle area was protected to some extent by the Olympic Range to our west. Bellingham is not as well protected.

Figure 4. For comparison purposes, this figure shows the current year precipitation trace at Bellingham International Airport with the past 20 year traces at Seattle-Tacoma International Airport. Note: Bellingham is approximately 90 miles north of Seattle.

The United States Geological Service (USGS) keeps track of river flows across the country. Some of this data is exposed to the public. Two gaging stations the USGS keeps near the Whatcom County flood zone are the stations on the Nooksack River at Everson and at Ferndale. Everson is about 12 miles ENE of Ferndale as the crow flies. The monitoring station at Ferndale appears to have records published over a much longer time period, so this data will be used for comparison purposes. The Nooksack river flows from the Mount Shuksan and Mount Baker watersheds. On the other hand, the station at Everson, also on the Nooksack, is much closer to the Sumas River which presumedly caused much of the flooding in the Fraser River Valley in British Columbia.

The Nooksack river major flood stage at Ferndale is 23 feet. The Nooksack river crested above this stage on November 16 (Figure 5, lower chart) at 23.7 feet.

Figure 5. Nooksack River stage charts from Ferndale WA from November 15-22, 2021. Chart is courtesy of the USGS.

Figure 6. Nooksack River stage charts from Everson, WA from November 15-22, 2021. Chart is courtesy of USGS.

Table 1 shows the values of historic stage crests on the Nooksack River at Ferndale for crests above 12.25 feet. The values were copied into this table from the source listed below the table. I entered the most recent value (blue entry) for 11/16/2021 since the web site values had not been updated yet.

This November’s flood stage ranked with the top twenty events at this gage site.

Table 1. Record gage levels for the Nooksack River at Ferndale WA. Source: NOAA / NWS.

Source link

Figure 7 is a dot plot of the historic crests on the Nooksack River at Ferndale ordered from great to least. Color coding indicate the decade of the event.

Figure 7. A dot plot showing the historic flood stages on the Nooksack River at Ferndale WA.

Figure 8 is a series of dot plots of the same data as shown in Figure 7. The data has been grouped in decades to see if any trends can be found due to time. Decades are an arbitrary grouping. But often we group data in years, decades and centuries to see patterns time-related data, so I used decade groupings here.

I don’t see any obvious patterns in the decade groupings other than some early decades had fewer but more severe events and more recent decades had more events but events which appeared less severe in terms of gage height. Of course, the 2020s are just beginning. It is possible, I suppose, that less severe events in the early 1910-30 period were not as diligently recorded. And it might also be true that less severe events in more recent decades may do more damage due to greater populations and development in the area. These are just guesses.

Click on any chart to enlarge. You can use left and right arrow keys to navigate between decadal sets of data.

Figure 8. A series of dot plots of ordered historic crests on the Nooksack River at Ferndale WA grouped by decade. Click to enlarge.

 

Figure 9 shows the data in Table 1 in a time-series chart format (which is basically a horizontal dot plot sorted by time rather than rank).

Again, strong patterns are hard to find, other than the first half of the timeline tends to show greater historic crests. I don’t know the reasons for this. Maybe storms were stronger in the past. Perhaps physical river control methods have been installed over the years to help regulate flow. Since 1965, it is difficult to discern any distinct pattern to the historic crests other than every 15 years or so, a moderate-high or major flood event occurs.

Figure 9. Time-series chart of historic crests on the Nooksack River at Ferndale, WA.

 

Finally, it should be noted that parts of northern Whatcom County and much of the Fraser River Valley were flooded and not on the Nooksack River, but rather on the Sumas River. The Nooksack flows west to Puget Sound from the North Cascades. The Sumas River flows north into Canada. The U.S. border town of Sumas was severely flooded the past week as was much of the nearby Fraser River Valley.

There is a point near Everson, WA where the Nooksack river runs very close to the Sumas River. The surrounding land is generally flat. Literature suggests past overflows of the Nooksack have flowed into the Sumas near Everson. The distance appears to be less than two miles at the closest points

I suspect this is what happened this past week. I’m not a hydrologist, so I don’t really know. But with all of the water falling last week and the weeks leading up to this event, it seems likely. River gage data on the Sumas for the public was difficult to find.

Figure 10 shows the proximity of the two rivers. Directionally, north extends into the top background in the image.

Figure 10. Proximity of the Nooksak River to the Sumas River. Image courtesy of Google Earth. Click to enlarge.

The Bellingham Herald is the paper of record in Whatcom County and Northwest Washington. The paper has excellent coverage of the recent floods and photo essays of past historic floods. Flooding in this region is not uncommon. It is a flat landscape at the base of very steep mountains subject to heavy winter rains and runoffs.

 

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.