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Monday, November 17, 2008

Snow on Schedule.. Afternoon Update

I just made a brief update on with the 4pm observation. The only thing I wanted to add here was the 18Z (mid afternoon) NAM model update.
I think this is looking a lot like the December 5th event last year. The track, the timing, the strength, and the models not fully seeing it. There is a Winter Storm Warning in the pink on this map... for the mountains of western MD into West Virginia. The forecast is for 6-12 inches of snow. That is giving the terrain credit for uplift, but the track of this low with the strong upper level support trying to catch it may enhance it east of the least as it reaches the coast.

This 500mb (upper level map), shows the vorticity or 'spin' near Indianapolis. I've highlighted that with a white X.
That is still west of the mountains, and just behind the surface low. A smaller piece in the southern Delmarva can be seen in yellow. That will be responsible for our overnight showers, but this shows that there is more to come our way by daybreak.

Jumping ahead to Tuesday afternoon at 3pm, that vort max is now stronger (orange), while rounding the base of the trough in North Carolina. If anything, this might be a little too far south, but the trough axis and support linger into southern MD. This increase in vertical velocity or rising air is a sign of strength. The outlook did have low pressure developing rapidly off of the coast, but I think if might be a little sooner and closer. That will lick our winds up to 30-40mph from the north in the afternoon, and bring the question of how long the snow will last. This may not be a clean solid band of precipitation, but any showers may be able to drop some surprising accumulation. Again, at this point, I don't see an exact repeat of the Dec. 5th, 2007 event when we had almost 5 inches of snow in Baltimore, but some places getting an inch or two looks possible now.

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