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
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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.
