Monday, May 18, 2009
Front and convergence zone
A fairly wet spring front is now moving through--the radar shows it clearly (see image). You every notice that the heavy rain never seems to spread over the Cascades? Why? blockage of the radar beam by the terrain. Most of the time you see the radar image from the lowest elevation angle (.5 degrees above the horizon). Many of us are hopeful that the new coastal radar will go lower (0 elevation angle)..which will more information near the surface close to the radar and give more range. The radar has a wavelength in the microwave part of the spectrum and the national weather service radars have about a megawatt of power. I can imagine what kind of cooking it could do.
The front will pass by tonight and the models indicate a strong Puget Sound convergence zone by daybreak (see image), with showers in the mountains. In fact, here is a 7 AM update (see radar picture)..the convergence zone formed as predicted...although shifted a bit north of predicted position. But we couldn't do this 20 years ago!
Additional showers will roll in tomorrow...but the remainder of the week and memorial day weekend looks good. But June gloom is threatening as the atmosphere over the Pacific become more stable as high pressure builds northward. A stable atmosphere allows the lower atmosphere to moisten and saturate...producing a huge stretch of low clouds that invades western Washington.
Posted by Cliff Mass at 9:29 PM