An Unusually Sunny Midwinter

One of the minor negatives of living in the Pacific Northwest is the lack of sun during midwinter, the result of our northern latitude and considerable cloudiness.

Some folks get depressed from the darkness, developing  Seasonal Affective Disorder (SAD).   A problem that can be addressed by securing a light box, getting out during midday, or heading to a southern clime during the holiday season.

But this winter has been much better than most, with more sun than usual.

Noon Today

Let me show you the proof.    Aaron Donohoe of my department has examined the solar radiation data collected on our roof since the year 2000.   Here is his plot of cumulative solar radiation during the month of December.  The black-red line is this year.  For much of the month, this year was the sunniest since 2000, but fell into second place at the end.  No complaints.

And the first few days of January have been plenty bright, as illustrated by Space Needle PanoCam above and the solar radiation measured on the Atmospheric Sciences Dept roof (see below).

The sunny December is a huge boon to Seattle's psyche, since this month is generally the most depressing, with the shortest days and weakest sun.   By the end of January, things are starting to brighten and by the end of February, Northwest spring is upon us.

Why such sunny skies?  Because we have had persistent high pressure over the West Coast, and high pressure is the enemy of clouds.  To demonstrate this, here is the anomaly (difference from normal) of sea level pressure during December.  A big positive (high pressure) anomaly over our region.

And the high pressure also brought extensive dry periods.  Take a look at the cumulative precipitation at Sea Tac during the past 4 weeks.   We had less than normal, and nearly all the rain occurred over a few days when weather systems broke through the ridge.  Most of the month was dry, particularly the first two weeks.

The unexpected sunshine has attracted some Northwest residents out of hibernation.  Here is someone you might know....

from Cliff Mass Weather and Climate Blog http://ift.tt/2EOKqB3