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.


  1. It's all good for me in Pete Townsend. We just planted a bunch o' stuff. Let it rain!

  2. So... does this a greater chance of a wet & gray commencement?

  3. Where is *Pete* Townsend? Is it that little Victorian town that I love so much out on the point? :-)

    I need to get my garden in, so I'd be glad for a little break on Wednesday or Thursday...

  4. Pete Townsend? "I Won't be Fooled Again!"

    The Japanese Garden in the Arboretum is a wonderland of Color. So if the sun breaks out, head over with your camera for some inspiration to do your gardening.

  5. Wow! Not five minutes ago there was a clap of thunder, and now we've got a rain/hail storm just beating down on us here in W. Seattle. Glad I don't have to be outside right now!

  6. (...Pete Townsend... isn't he a musician? ;-)

  7. Boy, the convergence zone tonight is really going good for having no sunlight to feed it! Amazing!

  8. Just in from sailing on Lake Union for a Tuesday night race. The Convergence Zone meant wind from Zero to 15 plus knots out of the South, South East, North East, North West, and East, with some clear sky and lots of really hard rain. All of that between 7pm and 8:30. And lightning strikes (Space Needle first) all around. Looks like it cleared up for the sunset.

  9. So I have a question about how weather works here. Last evening, I watched with great interest as the radar showed a mass of orange and yellow heading from seattle toward bellevue and eventually to where I live in Sammamish. Friends from Seattle were recounting the tales of thunder and lightening.

    But as the yellow and orange approached, it turned to green as soon as it got to Bellevue and thus we never got anything but rain up here in Sammamish.

    What is it about the area that causes that complete change?


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