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Gray returning, but Seattle has passed its peak of the gloomy season

Another rainy day in Seattle on Jan. 26, 2018 (KOMO Image)

SEATTLE -- The sunshine the past couple of days has been a welcome sight for those who crave the light and who feels the weight of stretches of gray, cloudy skies that don’t seem to surrender even when the rainfall takes a break.

But new research indicates even when the rain comes back later this week, it shouldn't be *quite* as gloomy as it was last month.

Aaron Donohoe has gone back and calculated several years of sunshine data recorded at the University of Washington's Atmospheric Sciences building to find which is statistically the gloomiest day of the year -- and conversely, which is the sunniest day.

Turns out if you need to really dodge the gloom, book that Hawaiian vacation for Dec. 11. That is the date that combines the lowest sun angle with the most likely to be cloudy and stormy -- which makes sense. Obviously, the winter solstice would have the least amount of daylight, but mid-late November is typically our stormiest time so average the two together and you get Dec. 11 as the date that has been the stormiest closest to the solstice and thus seen the least amount of sun energy.

The data this season bears it out perfectly. The darkest day so far this winter season was...Dec. 11 at just 0.54 MJ/M^2, according to UW Research Meteorologist Mark Albright. It just eked out the win over Dec. 9 which was 0.55. It was the darkest day since Dec. 8, 2015 when the gauge measured 0.56. The all-time darkest day since the turn of the century was Dec. 14, 2006 at 0.39. That was the "day" before the Hanukkah Eve Windstorm hit later that night.

On the other hand, if soaking up as much Vitamin D is your thing, your date to circle on the calendar is July 5, which coincidentally (or not?) corresponds to Seattle's "unofficial" first day of summer.

Donohoe's research shows Seattle's sunniest day -- as in most likely to have a lack of clouds -- is actually not until Aug. 12 but the odds of sunshine on any summer day is pretty high, and thus July 5th would be a good average of being close to summer solstice and yet getting away from late June which is still inside our "June Gloom" frequent marine layer time frame. To compare, a sunny early July day will usually get about a full 33 MJ/M^2 -- or roughly 60-65 times more sunlight than the dark winter days.

So when the rain returns this week, the gray skies and gloom will return, but sun fans have a few things going for them: 1) It won't be as dark as it was in December and 2) Sunset reaches 5 p.m. on the 25th.

But for those (like me) who like rainy, gray days, still plenty of those in the forecast this season.

By the way: Some other planning dates if you need them -- the statistical driest days of the year are July 30 and Aug. 4 with less than a 10 percent chance it'll rain on those dates in any given year. The wettest date is Nov. 19.

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