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First Call Snowfall Forecast (20 JAN 16)

  POSTED ON: Wednesday, January 20, 2016 12:15 PM by A.R. Davies

The next four days will bring us two chances for accumulating snow.  The first will arrive on Wednesday evening as a fast moving clipper system could produce up to one inch of snow between 1500 EST and 2300 EST on Wednesday.  The National Weather Service Baltimore/Washington Office has issued a Winter Weather Advisory for Anne Arundel County as the timing of this snow may impact the evening rush hour.  Below you will find the National Weather Service Snowfall Forecast for Wednesday evening.

NWS Snowfall Forecast for 20 Jan 15

The next and more impactful event will arrive Friday afternoon/evening.  A potent midlevel disturbance will dig south into the Mississippi River Valley on Thursday. Despite the 500 mb trough axis remaining fairly progressive, the midlevel atmospheric low will cutoff and focus the atmospheric dynamics toward the Mid Atlantic coast.  Meanwhile, a slug of moisture from the Gulf of Mexico will work its way northward.  These two forcing mechanisms will combine to form an intense low pressure system near the mouth of the Chesapeake Bay Friday night/Saturday morning. The coastal low is currently projected to rapidly strengthen and move northeast along the coast during the day on Saturday.

The exact location of coastal storm formation and the details associated with inevitable storm track are still uncertain; any east/west/north/south change in the storm location or track will consequently move the snowfall forecast east/west/north/south by 50 miles (or more); this can mean the difference between all snow or a snow/mix/rain event.  These final storm details may not be refined for a day or more as the dynamics with this system are subtle and incredibly complex.  It looks like the storm will be out of the area by dawn on Sunday, leaving windy conditions. 

At this time, it appears the snow will begin sometime near or after lunch on Friday (earlier to the south and west of Annapolis).  From past experience forecasting similar snow storms in the Mid Atlantic region, I've noticed that the snow often begins to fall a bit earlier than the models project.  Heavy wet snow will develop and continue to fall through Friday night.  As the system intensifies on Saturday morning, strong easterly winds between 850 mb and 500 mb will pump warm and moist from the Atlantic into the mid-levels of the system.  This will help to increase overall precipitation rate, but may also result in a wintry mix of snow, sleet, freezing rain, and rain east of I95. When, where, and if the snow changes to a mix remains uncertain. By Saturday afternoon/evening, Annapolis and all locations north and west of town should turn back to all snow. Snowfall/wintry mix rates will easily top one inch per hour at times Friday night through Saturday.  

 Given the expected wet and heavy nature of the snow (and the chance for a mixed bag of snow/sleet/rain), accumulation is possible on trees and power lines.  Expect sustained northeast winds around 20-30 mph with gusts 40-50 mph around the Baltimore-Washington-Annapolis region on Saturday.  Stronger winds are likely along the Delmarva Peninsula with gust to Hurricane force strength along the Atlantic coastline. This scenario could result in widespread power outages and blowing snow/white out conditions. Hence, at 1013 EST on Wednesday, the National Weather Service Baltimore/DC Office issued a Blizzard Watch through Saturday night.   The hazards include heavy snow/wintry mix, along with strong winds and near whiteout conditions.  A link to the advisory is found below:

http://forecast.weather.gov/wwamap/wwatxtget.php?cwa=lwx&wwa=blizzard%20watch

The figure below shows my "first call" snow total forecast map (here is a link to the full size map).  This represents the most probable snowfall totals across the Mid Atlantic region at this time.  I will update this map on Thursday morning and this discussion on Thursday morning.  Below you will find the probabilistic snowfall totals for Annapolis:

10% chance of <5" of more mix than snow

25% chance 5-10" snow/mix

40% chance of 10-16" snow/mix

25% chance of 16-24"+ of mostly snow

First Call

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Disclaimer: This is not an official U.S. Navy weather forecast and should not be confused with the official Navy weather forecast provided by the Fleet Weather Center in Norfolk, VA.  Furthermore, the official U.S. Government forecast for the greater Annapolis area is issued by the National Weather Service Baltimore/Washington Forecast Office in Sterling, VA.


Category: General Interest

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