March 09, 2011

Heavy Rain

Some amazing rain is the radar image at 9:56 PM of yellows--that is all heavy rain. It is pounding on my roof right now.

And today with the front there was a very intense rainfall band crossing the Sound around is the radar image. If you look closely, there were some reds in there....a downpour, probably with some small hail mixed in.

You might be interested in the quantity you are looking at in these images...they are reflectivity--a measure of the scattering of the microwave radiation emitted from the radar. The units are dbZ. You know about dbs on your sound system (db stands for decibel)..a logarithmic system for noting sound volume. This is a logarithmic scale for radar reflectivity.

5-10 greys-light mist or drizzle
15-25 light reds or pinks--light rain
30-35-moderate rain...greens
40-45 -heavy rain...yellows
Above 50--either absolute pouring or hail (reds)

Here is the rain over the past 24-hours from Seattle Rainwatch...some locations have gotten 1.5-2.5 inches today. Nice rainshadow.


  1. Even with less favorable oragraphics we are even receiving heavy rain just east of the mts. tonight. .25 in half an hour at 10:30.

    That new radar would have been soo valuable in watching tonights rain move in. Soon...

  2. The Rainwatch system showed this nice plot at 1210 PDT with "red" (50 to 55dBz) rain over downtown Seattle that then drifted over Capitol Hill. Very spectacular rain for perhaps 10 minutes resulting in some local flooding and runoff down the roads on the hills.

    For me this rain intensity is second only the the December 2008(?) event.

  3. Impressive rain tonight. In Bothell at 8.30p we had .49" of rain. By 11.50P it was up to .94".

  4. 1.64 inches in past 24 hours here in north end of Tacoma, as of 615am.

  5. That was some heavy rain! Lots of ponding and impromptu rivers around town.
    A question: The storm total map on the WSR-88D shows 2.5-3" of rain for Seattle, the rainwatch 24-hr total shows 1.5-2", and the UW Atmos Science rooftop data shows 0.8". I get that the rainwatch product is calibrated and more accurate than the radar output (also the storm total is probably longer than 24 hrs)... but why the big differenve between rainwatch and the UW rooftop? Given how heavy the rain is I'm inclined to believe rainwatch's estimate more... is the UW rain gauge broken?

  6. Why didn`t the NWS issue any urban flood advisory or statement at any time during Wednesday afternoon? It seems to me that the rainfall event was fairly widespread,and that someone at the NWS dropped the ball. I had torrential rains at my place in central Seattle--about .25" in ten minutes,about .50" in one hour-- during the early afternon,then another inch in about 4-5 hours in the evening and early night.(About 2.1" in a little over 24 hours.)My storm drains were overwhelmed,and I had some water get in my basement.

  7. Awesome visable satellite loop today.

    This is a classic PNW storm. A little bit of everything. No huge WOW factor but these are my favorites.


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