Saturday, October 10, 2009
Tomatoes Beware! and the Importance of 2 meters
There was more clouds last night then originally predicted and they should hold in much of the area today. With the clouds intercepting and radiating infrared radiation back to the surface, temperatures held up overnight in the 40s over much of the area.
Tonight (Sunday AM) should be different with clearing skies and unusually cool temperatures aloft there will be good radiational cooling. Working against that will be the significant offshore pressure difference, which can keep some wind going in exposed areas. Wind causes mixing which helps stir up cool air near the surface. But sheltered valleys away from water could drop into the 20s tonight...and tomatoes don't like it. Below are two maps showing the low temps tomorrow morning. The first from probcast (www.probcast.com), the UW probabilistic prediction system and the other a straight forecast from our high-resolution WRF numerical forecast model. Cool away from the water, over the SW Washington interior and eastern WA.
Another pulse of cool air hit E. WA tomorrow..and that is when they will get some dust if they get any. This is really a marginal dust event.
Finally, keep in mind that surface air measurements shown on the web and TV are NOT at the surface, but at 2 meters (roughly 6 ft). On cold, calm nights it can be much cooler at the surface than 2 meters...perhaps 2-5F cooler. So keep that in mind while driving. And your car thermometer has the same issue (although it is measuring more like .5-1 meter above the surface).
Posted by Cliff Mass at 7:58 AM