Wednesday, December 19, 2012

December 19, 2012: Winter Storm Draco Coming!

The Weather Channel has named a new storm, Draco, which is presently creating heavy snow and blizzard conditions across the Upper Midwest.   This is an especially powerful midlatitude cyclone, forecast to track across the Great Lakes and intensify tomorrow and tomorrow night.   The center of Draco will track well to our north, keeping us on the warm side of this winter system.   Draco's circulation will drag a powerful cold front through the region tomorrow night.  This will usher in periods of moderate to heavy rain overnight.  Following passage of the cold front, an intense pressure gradient with northwest winds will build across the Mid Atlantic on Friday.   While skies will become partly to mostly sunny, temperatures will plummet to near the 40 F mark on Friday and into Saturday, and winds will gust to 40-45 mph across the region.  The NWS may very well issue a Wind Advisory for this event.   High elevations to our west (summit of the Appalachians) may experience gusts higher than 60 mph, necessitating a High Wind Warning (this is because winds increase with altitude in mid-latitude cyclones).    A Winter Storm Watch is now posted for the windward side of the Appalachians, for possible heavy snows, during the period of intense W-NW winds (upslope flow) Friday night into Saturday.  Additionally, heavy Lake Effect Snows are likely along the lee shores of the Great Lakes this weekend.  So Draco will bring the first taste of December Winter across a broad region, from the Upper Midwest, Great Lakes, Ohio Valley, Mid Atlantic and into the Northeast.

The diagram below shows the forecast weather map for Saturday morning.  Note the intense low pressure system (the core of Draco) over upstate New York.  Black lines indicate isobars, showing a packed pressure field (tight pressure gradient) over Baltimore.   The colors show wind speeds at 5,000 feet.  Yes, the forecast is for 60 mph winds not far above the surface on Saturday morning!   Some of this momentum is expected to mix down to the surface on the day Saturday, causing very gusty conditions.  Note the 70 mph winds close to mountain top height along the Appalachians.

To summarize, Draco's main impacts for Baltimore will start with bands of rain, followed by onset of strong winds, with wind chills down into the low 30's on Friday and Saturday. 

Courtesy of
We will be watching the possible formation of another, potentially potent midlatitude cyclone, which could impact our region after Christmas Day.  The atmosphere appears to be switching gears into what could prove to be a colder than average, stormy period to close out December.  Winter is finally coming!

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