Sunday, January 30, 2011
Dry, Sun, and Modified Arctic Air
Well folks, the threat of snow around here is over for a while. Cool, dry, modified arctic air is pushing over the region, showers are rapidly dissipating, and the sun is breaking out. If the models are even half correct, the next 3-5 days will be generally dry here without any significant weather activity other than a cool down (mainly east of the Cascades) and strong easterly flow in the gaps, such as the Columbia Gorge and the Fraser.
In sharp contrast, the East Coast is going to get hit AGAIN Tuesday by a major snowstorm.
Is there a connection between our opposite weather regimes? You bet there is. As shown in this upper level map for Tuesday, when we have a big ridge, a major trough tends to build downstream (east) of us--bringing stormy weather to the central and eastern U.S. Think of the atmospheric flow aloft as analogous to a rope that you are swinging up and down. There are a series of undulating waves in the rope. The wavelength of the waves (the distance between ridge to ridge or trough to trough) in the atmosphere has a typical scale of thousands of kilometers, for reasons I won't get into now, but which is based on basic physics. So the persistent ridging over us, bringing dry, cool weather this week over the NW, brings the opposite to those poor folks east of the Rockies. Want dry weather with lots of sun...forget Florida...head to Seattle.
Locally, the cold, dry air started pushing through the Fraser Valley into Bellingham and NW Washington yesterday. Here is the latest surface weather plot for NW Washington:You can see the northeasterly flow passing over the San Juans and then moving south and west. Winds have been gusting to 40 mph and more in some locations around Bellingham from this Fraser outflow. It is interesting that the first sign of this continental air from the BC interior is often not temperature, but humidity, or rather dew point. Look at the lower, right red numbers (dewpoint) on these plots and you will see what I mean. And here is the high resolution forecast for 10 AM this morning of the winds..the Fraser outflow is quite clear.
Taking a look at the latest visible satellite image, you will see a residual band of clouds over the middle of the state (with lots of holes) and completely clear skies to the north. This full clearing will move south during the day. With cooler, drier air over us and clearing skies tonight, expect cold overnight temps--20s everyhere and some lower values in valleys and cold spots. Protect your plants!
Even colder air is surging southward into eastern Washington (see plot of current observations)
--and that will help strengthen an east-west pressure difference (higher to the east), which will accelerate the winds in the Cascade passes and the Columbia Gorge. Here is a forecast plot of the pressure pattern today...you can see the packing of the isobars...lines of constant pressure..near the Cascade crest. The colors provide lower-atmosphere temperatures and you can see the colder air (blue colors) east of the Cascade crest.
I wanted to mention that I will be speaking next Saturday (Feb 5) at Port Townsend HS at 3:30 PM about regional implications of global warming...more information is found in the link to the right.
Finally, thanks to all of you that have contributed so far....you have provided funds that are sufficient for two uninterruptable power supplies for our main modeling cluster ($900 each).
Posted by Cliff Mass at 9:16 AM