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Tuesday, November 11, 2008

Chilly Veterans Day. End Of Week Storm Update

This morning, we bottomed out with a low of 29F at BWI. That is the first time we were in the 20s since March 24th when the temperature hit 27F. The next storm, is still complicated, as it looks like it will go through a transition or shift of energy 3 times between now and Friday. This may not be a major storm, but it could spread out into two separate moderate storms overlapping. The importance is whether it sets the stage for the upcoming season. I follow the philosophy that our winter pattern often develops in November, and will repeat itself many times over the winter. So the track and behavior of the cold air with these storm tracks can be crucial in an active season. It may be stormy, but the track will determine whether it's snow or rain for us. But that is speculation, NO SNOW with this storm....

First it surface Low in Kansas this morning. that has already wound itself up, and shifting it's energy southeast (occluding). The new low will develop over Missouri, and head into the Great Lakes. It's the trailing cold front that will be out focus, tapping into the moisture from the Gulf of Mexico. It the upper level energy in the jet stream that will help develop another surface low near New Orleans. So while the rain will look closer on the radar tomorrow, and spread clouds our way, it's south-not west we have to look for our rain.
Thursday will be our wet day, at least how it looks now. The ADONIS model we use on TV shows moderate rain just to our south by Thursday morning, on the way in.
This looks more like and over running event. That is the rain spreading way out ahead of the storm, and bumping into the dry air we have in place. While that would give hours of virga (false rain on radar), we should have an strong easterly wind to add moisture to the air, and I suspect it will be a wet Thursday.

Friday is the day to watch:
The GFS shows rain spreading in from the south, and I have analyzed a developing Low off of the South Carolina Coast. It looks a lot like the last storm. The model shows moderate rain regenerating itself in more of a conveyor belt along a stalled front in the mountains. That set up would keep us wet through Saturday. Notice the strong 988mb Low pressure in Canada. That will be the source of a cold air push behind this storm.. This is not a bad idea, since the low will spin out a day before if builds the cold air and drops south. If it pushes sooner, we could kiss the stalled front goodbye.

The Canadian shows more of a coastal low scenario on the coast. Here is the surface Low in western Maryland on Friday morning, with the larger 'cold core' Low in Minnesota. That is farther south than the GFS, and supports the energy transfer to the coast- ahead of the 'Canadian Cold Air Push'.
The heavy rain is laid out on Friday morning, just off of the coast, but the analysis give me the impression of a coastal low forming near the Georgia/South Carolina border. That would likely push off of the coast, and cut our rain off during the day Friday. A much different expectation giving the same starting point as the GFS.
This looks a lot more like the last two storms, and I have to go with persistence. So given that, let's carry the Canadian a little farther into the weekend. I like this models, because it does perform better in the winter with coastal storms, and it has a better resolution with cold air in Canada.

Here is the Canadian model for Sunday Afternoon. The blue line is the infamous 540 (dm) line of thickness, that translates to a rain/snow line with storms. This also shows the push of cold air surging in by Saturday night. The upper level energy will support heavy Lake Effect Snow, and may bring us the chance of flurries or snow showers by Sunday afternoon. I did not put it on my TV forecast, since I do have a tendency to be bias towards snow. I wanted to wait another day to see if this set up holds over the GFS. One thing for sure, this will push cold air down to the Gulf Coast, and overnight temperatures near freezing could reach northern Florida.
That is a lot to digest, and just two different models. Hopefully there will be more agreement on way or another with today's models. Stay tuned.....

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