The Cold Truth

Several of you have note that it is not the cool temperatures or even the rain that bothered you this last few months, but the lack of sunlight--sort of like a summer version of seasonal affective disorder (SAD).   So what is the truth about clouds this spring and summer?

In such situations there is ONE expert on our local murk that I trust, a local scientists who has spend a great time looking a the climatology and trends of local clouds.   I have mentioned him before---Dr. Jim Johnstone, AKA Dr. Fog, a researcher here at the UW. 

Here are some of his depressing results--the average number of hours a day with clouds at Sea-Tac for April through June.  2010 and 2011 have simply been the worst over the past 60 years. We are talking about 18-19 hrs a day of cloud on average.  And the general trend the last few decades is for more clouds.  Now you will hate me for telling you this... but I have a project with Dr. Eric Salathe to simulate Northwest weather under global warming. 

Guess what.  These high-resolution simulations suggest more low clouds west of the Cascades as the interior heats up.  More interior heat causes the pressure to fall to the east and global warming seems to be associated with a stronger East Pacific High--the result:  more low clouds offshore and more onshore flow.

 And what about his results for temperature?  Here are the April-June temperatures for the entire state.  I bet you know which year was the coolest.  This year.  It is in a class of its own.

 

Or how about a plot of where the daily maximum temperature records (both record high maximum and record low maximum temperature)  have occurred this year during April-June?  The big concentration of record low maxima (blue symbols) is over the Northwest, while record high daily maxima were found over the southeast.

But if you really want to get into the murk, take a look at the amount of radiation measured at the top of the atmospheric science building at the UW.  On July 25th  the UW's sensor's measured  4.51 megajoule (unit of energy) per square meter,  the darkest day in almost 4 months.  On a bright sunny day we would be up in the low 30s.  Not since 4 April 2011 with 3.47 MJ/m2 have we seen a darker day in Seattle as measured at the U of WA.

This weekend....below normal temps but perhaps acceptable.  A disturbance approach from the north will get mighty close on Sunday, so go south and east for better weather.