Wednesday, December 12, 2018

Seattle's Darkest Day in Three Years

Here in Seattle it was extraordinarily dark yesterday.  The darkest day in years.

The total radiation on Tuesday on top of the roof of the atmospheric sciences building was .54 Megajoules (MJ) per meter squared (a joule is a unit of energy).

To give you some perspective, here is a table of the lowest daily radiation amounts since 2004 at the UW, provided by UW Research Meteorologist Mark Albright.  The date of lowest radiation is also noted.  As you can see, yesterday was the darkest since 2015, where the total dropped to .44 MJ per meter squared on December 7th.

  Year           Date        Amount of solar radiation
 2004  1229  0.64 MJ/m**2
 2005  1201  0.61
 2006  1214  0.39
 2007  1202  0.51
 2008  1225  0.79
 2009  1215  0.74
 2010  1223  0.57
 2011  1210  0.68
 2012  1219  0.48
 2013  1220  0.56
 2014  1210  0.55
 2015  1207  0.44
 2016  1219  0.68
 2017  1218  0.69
*2018  1211  0.54

The absolute worst was the obscene value of .39 on December 14, 2006.  On a day like that, you might as well stay in bed.

You will note that the darkest days are all in December, running from December 2 to December 29th.  

So why was yesterday so dark and why are December's the month of most feeble solar radiation reaching the surface?

Two things are happening.  First, a lot of deep clouds, which prevent solar radiation from getting to the surface, and second, this is the period of short days and low sun angle.

The visible satellite image at 2 PM Tuesday indicated a dense frontal cloud band right over western Washington (see below)

And the infrared image at the same time shows that the cloud tops were very high, and thus the clouds were deep.

To make it all worse, the sunrise/sunset table for Seattle shows that we are now experiencing the earliest sunset of the year (4:17 PM).  The day will continue to get shorter until December 21st.

But there is something very positive happening lately:  lots of snow has been falling in the Cascades, with all the ski areas operating this week, although not all the runs are open.    And today (Wednesday) should be a much brighter day, with some intermittent showers.

Monday, December 10, 2018

When Snow Prayers Work Too Well

The boundary between meteorology and religion has always been an amorphous one, with considerable overlap.

In ancient times, Gods were considered the prime movers of weather events, and societies were always looking for the proper supplication to the get rain, snow, or whatever else they hoped for.

But even today, with all our technology and science, folks desperately hoping for a specific weather outcome  frequently turn to praying to the powers up high.

And so it was, last Friday, when a group of snow-hungry skiers, egged on by the management of Snoqualmie Summit ski area, held a prayer vigil in North Bend at Compass Sports (see below).   They prayed, drank libations to certain weather gods, and attempted well-rehearsed weather dances. 

And it worked.  It appears that the gods heard the plaintive cries, and snow has begun to fall in the Cascades.  Before the week is up, there will be feet of white stuff in the mountains and most ski areas will be open for business.

Consider the the forecast total snowfall over the next 72h over Washington. Wow.  2-3 feet over the Washington Cascades and Olympics

Now take a deep breath before you look at the next image.  Here is the total snowfall for the next 72h.   More heavy snow in the mountains.  But there is something even more shocking....snow reaching the lowlands, something not seen since last December.  Our ski friends are going to go powder crazy.

But now the real shocker.  The latest model runs suggest the snow is not going to end.  Now take three deep breaths. 

Here is the ensemble (many model) forecast for total snowfall at Stampede Pass (4000 ft on the eastern side of the central WA Cascades) from the NWS GFS model.   The gray lines are many lower-resolution model forecasts and the blue line is a single higher resolution.  The black lines is the ensemble mean...the average of all the gray lines--normally a very good forecast. 

WOW...just continuous accumulation.
What about the best global model in the world, the European Center model?  Here is the total snowfall during the next 7 days from that vaunted forecast system:

3-4 feet of snow about roughly 3500 ft.  But no lowland snow.

The ski community is going to be ecstatic about what is going to happen.  Great skiing from next weekend through the holiday season.  The snowpack needed for summer water resources will get a huge enhancement.

But might we have too much of a good thing?  Could the prayers move in the opposite direction?  Pleading to the snow gods to turn down onslaught?  Trust me, it has happened before.