Weather Blog

Seattle's December proves sometimes it's dark after the dawn too

Seattle's December proves sometimes it's dark after the dawn too
Photo of Seattle taken at noon on Dec. 20, 2012. (Photo courtesy: Puget Sound Clean Air Agency Visibility Camera)

If you've ever wondered needed proof why Seattle tanning salons do a booming business in the winter time, these statistics will help.

According to University of Washington Research Meteorologist Mark Albright, Wednesday's snow and rain came from an overcast so thick that it registered as the darkest December day in Seattle (as in amount of measured sunlight) since 2006.

Without getting into gory details about how they come up with sunlight measurements (it's megaJoules of sunlight radiation energy per meter squared) and instead putting the number in perspective, Seattle typically ranges from low single digits in the winter to a max of about 32-35 MJ/m2 on our sunniest summer days. So to not only be less than 1, but be less than a half is... pretty darn dark.

Wednesday registered a paltry 0.48. It narrowly missed the honor of darkest day of the year which currently belongs to November 19 at 0.46.

But as you've likely noticed, it's not like it's been sunny on the other days. In fact, add up every day in December (which has been on average about 1.8 or so) and it comes to about 35 MJ/m2 -- or about the amount of sunlight energy Seattle receives on one sunny day in June.

(Just not last June, whose peak was about 30 as full sunny days were missing. Clouds sure have been hanging around the past few years!)

So forgive Seattleties if you find there are frequent out of office replies this time of year. They're probably off to Hawaii or some other southern place that gets at least double-digit measurements.