Monday, May 11, 2009
More showers and a convergence zone.
As promised, the cool, showery pattern is back (see graphic). The same pattern we have been plagued with much of the last five months...northerly flow from Alaska aloft, trough over us. Why? Well, such patterns are more frequent in La Nina years, and we have been in a weak to moderate La Nina since December. So that may be part of it.
The winds really kicked up this afternoon as a trough moved through (graphic). The result was an increased south to north pressure drop in the Sound and an enhanced east-west pressure difference in the Strait. The result...strong southerlies in the Sound (reaching 20-30 mph) and similarly strong westerlies in the Strait. I was outside around 3:30 PM and even heard the crack of a branch failing, with the leaves blowing furiously...it was marvelous.
You can see the pick up of the winds at the UW during the afternoon in the graphic below. There is a very sudden cooling around 5 PM (00 UTC/GMT) as a passing cloud blocked the sun (you can see a drop in solar radiation in the lowest panel). Note that the relative humidity increases as temperature falls.
The next trough is now moving in, with showers moving in tonight and a good chance for a convergence zone tomorrow ( see image). There are some convective-looking showers out there that will be getting here by daybreak.
Wanted to note that I am working on a new lecture I will give at Barnes and Noble, University Village, Seattle, on May 22nd at 7:30 PM-- "A Consumer's Guide to NW Weather". I will describe how to be a good weather consumer...where to get the primo weather information, what web resources are good and bad, how to interpret radar and satellite pictures, and perhaps my views on local weather hype.
Posted by Cliff Mass at 9:01 PM