Don't you just love these National Weather Service graphics? It's hard to find one single graphic that has so many explanations and a model picture, but the NWS issues them when there is some sort of significant weather occurring. Pretty awesome!!!
Over the next few days, we will get a fair amount of rain. The graphic above shows the Seattle metropolitan area getting anywhere from around .75 to 1.25 inches of rain from 5 A.M. PDT Monday to 5 A.M. PDT Wednesday. As is generally the case, higher amounts will be found to the south, as there is less rain shadowing from the Olympics there.
This particular system differs from other weather systems that impact us in the autumn and winter because it will give us several periods of rain instead of one long period of rain before the front passes through. Right now, we have a pretty weak front passing through, with most of the rain heading south toward Cape Mendocino. However, the strong jet stream and unstable air behind the front will support the development of numerous small troughs, which will keep the rain going around our area until early Wednesday morning.
Take a look at the current satellite and radar imagery for our area. They don't look too impressive over Washington. The satellite pic was taken at 7 A.M. PDT, and the radar image was taken 2 hours later. I obtained both of these pictures from the NWS' graphical forecast discussion.
However, the GFS models from this morning show a strong jet stream, currently over southern Oregon, lifting northward into our area. Both of the models below are also from the NWS graphical forecast discussion.
Winds at 250 mb - 11 A.M. PDT, Monday, October 10, 2011
Winds at 250 mb - 5 A.M. PDT, Tuesday, October 11, 2011
With a strong jet stream perpendicular to the mountains and numerous rain bands as the result of unstable air behind us, the mountains will see heavy precipitation, the mountains will see some serious snowfall. The snow level is now expected to be around 1,000 feet higher than forecast earlier this week, so the highest passes should be ok, but places above that line will see a dumping. Take a look at the 24 hour snowfall amounts on the volcanoes! Some places on Mt. Rainier could experience a storm total of over 3 feet!
Valid 05:00 pm PDT Tue, 11 Oct 2011 - 36hr Fcst - UW 4km 12z WRF-GFS 24 hour snowfall
Western Washington could also see some thundershowers tomorrow, as the air is very unstable. Instability leads to convection, and convection can lead to thunderstorms.
Thursday looks like the best day to get outside, and rain returns for the weekend. No major storms in sight... for now.
Thanks for reading.