Monday, November 26, 2012

Nov 26, 2012: Weak Depression To Bring A Touch of Wintry Mix

10:30 AM

A weak low pressure system is expected to develop along the Delmarva Peninsula tonight.   Enough cold air will be in place at the surface and in the lowest 10,000 feet to bring wintry precipitation to parts of the Baltimore region.  However, there are several mitigating factors against significant accumulation:  (1)  the storm is weak (it is NOT a Nor'easter);  (2) the storm has limited moisture to work with;  (3) the storm will pass quickly to our south and east, exiting into the Atlantic on Tuesday.

The forecast map for tomorrow is shown below.  A stationary frontal boundary separates mild air to the south and east, and sub-freezing air to the north and west.   Thus, the further north and west from the front, the greater the probability of accumulating snow.   The highest amounts are expected across the Maryland mountains and along the Mason-Dixon Line (up to 3").   Within Baltimore, some surfaces may become slushy (< 1").  In Annapolis and along the Bay, just rain will fall.   So the temperature gradient is important in determining precipitation type, and this gradient straddles Washington-Baltimore, as is so often the case.


The NWS in Sterling, VA has issued their snow accumulation map.  It reflects the thinking that you must travel north and west of the D.C.-Baltimore metro to experience air cold enough for accumulating snow:

Timing of the event is critical.  The precipitation will develop overnight and continue through Tuesday morning.   In the cities, look mainly for a cold, light-moderate rain, with snowflakes mixing in at times.  However, the heaviest precip should be falling during the Tuesday AM rush.  This means slushy surfaces could create some delays.  The system clears out Tuesday afternoon.

Again, this is not a Nor'easter, and the storm is not intense enough to warrant a name given by The Weather Channel.

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