THEWEATHERMOGIL:: Major snowstorm looms for the Mid-Atlantic
For days, National Weather Service (NWS) computer and manmade forecasts have pointed to a major winter storm for the mid-Atlantic states. Snow and other associated wintry weather was expected as far south as northern Georgia and as far north as southern New England.
Now, closer to the event, the bulls-eye seems to be the greater Washington-Baltimore area where two feet of heavy, wet snow or more can fall between this Friday and early Sunday. Parts of the nearby Appalachians southward into the western Carolinas can expect between one and two feet of snow. To the south and east of the heaviest snow zone, a mixture of snow, sleet and freezing rain can be expected. An array of winter weather watches, warnings and advisories is posted from the middle Mississippi River Valley to the East Coast (Fig. 1).
The culprit behind this event is a developing low-pressure system that will be tracking across the Gulf Coast states and then reforming along the Atlantic Coast (Fig. 2). This redevelopment keeps the cold air in place over most land areas and allows for ample Atlantic moisture to be entrained into the storm system. South of the low, across parts of the Gulf Coast states from Louisiana to Florida, warm and humid air, along with a strong upper level jet stream, will conspire to generate severe thunderstorms and tornadoes (Fig. 3).
As the storm develops, winds will be increasing over both land and water areas. A blizzard watch has been posted for parts of the mid-Atlantic for Friday and Saturday. This means snow and blowing snow, along with high winds can reduce visibility to near zero at times (a.k.a. “whiteout” conditions). Winds will continue, especially along coastal areas from the mid-Atlantic to New England, even after the storm passes.
Offshore waters can expect gale (and possibly storm) force winds by early Saturday. With winds reaching 50 miles per hour or more, seas will build to 15 to 25 feet by Saturday and continue at these levels, even after the storm passes.
With strong onshore winds expected, coastal flooding is a risk from the Carolinas northward.
As is always the case in storms of this magnitude, snowfall gradients and transitions between mixed frozen precipitation and either all rain or all snow can be impressive. That’s why the “50-mile rule” needs to be at play. This means that any point weather forecast can be shifted up to 50 miles in any direction, leading to a significant variance from the forecast weather type and/or forecast snowfall amounts. In Fig. 1, look at the sharp demarcation between the blizzard watch and areas in Pennsylvania that aren’t even under a winter weather advisory. Shift the storm 50 miles to the north and Philadelphia and parts of New Jersey could expect blizzard conditions. Shift the low 50 miles to the southeast and Washington, DC could receive single digit snowfall amounts and miss the highest winds. Keep this “rule” in mind as the storm unfolds.
This is a major winter event and can severely disrupt travel, impact electric service, and pose life-threatening situations across a large part of the mid-Atlantic and nearby locations. There are many safety rules and precautions one should be aware of. I’ll address these later today in another posting. However, common sense should be everyone’s primary safety rule.
Please stay safe!
© 2016 H. Michael Mogil
Originally posted 1/21/16