A Forecasting Mess

December 9, 2009

An ice/snow storm fantasy: Monday evening, WRF-GFS, 16 millibars worth of even colder arctic air surging through the Gorge!

This will give you something to gnaw on this afternoon. Actually I went out and bought a new garbage can today. A bear chewed into our current can and garbage was all over the road last week…wife was extremely displeased since I was asleep at the time and she went down to clean it up. But the gnaw & scratch marks (very big!) were cool.

This has nothing to do with the weather except that when I came out of the home improvement store it still seemed really chilly. And it is. At noon PDX and VUO are running 5 degrees below yesterday’s noon temperature. Not much mixing from the easterly wind today AND the actual airmass coming out of the Gorge is slightly cooler (about 2 degrees) from yesterday. We’ll see, but maybe I really screwed up the high temperature today.

Model solutions are a huge mess still for Saturday and Sunday. I see the ECMWF at 12z has some precipitation making it in here on Saturday, as well as the GFS, Canadian (GEM), and WRF-GFS. Our RPM model keeps it south and so does the NAM. Hmmm, odds may be tilting in favor of precipitation showing up Friday night…have to make a decision on the 7 Day forecast about 3 hours from now. I sure don’t expect nearly as much low level warming as models show Friday and Saturday, so I’m very confident it would be snow, maybe freezing rain.

One thing they all agree on…for now: A switch to onshore flow due to the approaching upper low coming down from the north Sunday. This gives pretty good westerly flow across the Cascades, then you get a lee-side trough in eastern Washington and southern British Columbia, or at least kill whats left of the surface high pressure over there. That’s somewhat similar to what we saw that Wednesday last December as low pressure tracked by to the north. Remember the switch to southwest wind?

The Monday-Tuesday setup above is just one run of the GFS. It shows the Hudson’s Bay low rotating down into western Montana during that time…thus the extreme cold shown above. ECMWF has the bitter cold air staying farther north. Roll the dice on that one.

Chief Meteorologist Mark Nelsen