January 03, 2018

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....


  1. Or just by simply taking vitamin D regularly, ideally mixed with fish oil.

    1. Vitamin D supplements can be helpful for some people. But be sure to read about the potential side effects.

  2. Maybe this is why our chickens are still laying some eggs! Usually there are none during the darkest months unless you provide artificial light for them. So there is always an upside even if the powder skiing isn't exactly meeting our wildest hopes.

  3. Indeed, the hens are laying here on Whidbey Island.

  4. A Revelstoke December is typically very very grey with cloud in the valley, cloud in the mountains, snow in the mountains, wet snow or rain in town.. None of that this December, long stretches of sunshine in the alpine with a major inversion to start the month, even sunshine in town half the month which is very unusually during the very cold, dry and sunny. Dec has been more in line with the Jan over the previous few years. We need some a classic winterstorm jet stream. Seems we get 1-2 massive cold winter storm with light powder valley bottom to mountain tops before a dramatic shift in weather takes us immediately back to high pressure in one for or another.

  5. Hi Cliff, Any idea whats going on with our winter so far in the central cascades in regards to persistent higher snow levels. I have pictures from the local I-90 summits and this past weekend on Mailbox peak @ 4800ft snow cover is thin, rocks exposed more like October than January, Mt Si was almost snow free. Friday snow levels are predicted at 6500ft with a lowering trend but back up to 5000ft on Monday. I know we have had some brief cold spells but as an avid reader of your blog I know you look for long term trends for evidence of warming and climate change. In this case what is the historical analysis of snow levels over the past several years - is this data even available? It doesn't seem too positive for the snow pack this year running @ 81% according to SNOTEL data with no real "top up" in sight. Seems the north cascades both east and west are well positioned so better news for our glaciers.

  6. Dixon Gifford -

    It is Friday and it is currently 31 degrees on Snoqualmie Pass (elevation 3,022 feet), it is snowing, and they are forecasting snow overnight. When was the snow level at or near 6500 feet today?

    The central/north cascade pass forecast after tonight is for snow levels ranging from 2500 feet to 4000 feet - for all of next week. From the NWS: https://forecast.weather.gov/MapClick.php?zoneid=WAZ568 Where are you seeing snow levels predicted at 5000 feet?

    Re: "long term trends for evidence of warming and climate change":

    "an analysis of snow water equivalent (SWE) of over 200 SNOTEL sites around the NW through 2016 by Mark Albright suggests little trend over the past 30 years..."


    "To drive this point home further, here are the mean melt-out dates for recent decades (again, thanks to Mark Albright). It appears that the melt-out dates are getting progressively later, just the OPPOSITE of what we would expect global warming would do."



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