Friday, December 31, 2010
You may not believe it, but we are now starting a mini-drought here in Seattle. After a wetter than normal year, there is now no precipitation in sight until the middle of next week. And even better than that, there will also be considerable sunshine each day, which really helps lessen the midwinter blues.
This is all caused by a strong ridge of high pressure over us (see image) and an associated split in the jet stream with
disturbances and rain hitting central and southern CA (see the precipitation forecast over the next 72 h shown below).
Those poor devils in southern CA are getting hit hard, with many locations in southern CA "enjoying" their wettest or second wettest December on record. Downtown Los Angeles has received 10.23 inches this month, 8.4 inches above normal. Snowpack in the Sierras is over 200% of normal....well they wanted more precipitation!
Returning to our situation, Seattle has had 46.99 inches this year, 10.09 inches above normal. Last year Seattle had 38.17 inches...pretty close to normal. Olympia has had 55.44 inches this year, ONLY 4.89 inches above normal (yes, Olympia is much wetter than Seattle, because Seattle is rain shadowed by the Olympics). And Spokane has had 19.03 inches, 2.36 inches above normal. So this has been a relatively wet year over the state. Cascade snowpack is near normal at this point.
Finally, there is one negative with a ridge of high pressure above us this time of year--cold temperatures at the surface with lots of frost. Clear skies allows the earth to radiate energy to space through the long winter night, resulting in cooling at the surface and the development of nocturnal inversions (temperature increasing with height). The roofs are white outside my window right now. And one can also get freezing fog, so be carefully while driving if you see any fog around.
Posted by Cliff Mass at 8:49 AM