Friday January 17 2020

The Winter Weather Advisory issued for Saturday by the National Weather Service just makes the forecast more official. It has been advertised all week and Saturday will be a mess.  The warmer Chesapeake water will limit the impact along the Bay, but west and north of I-95 plan for a thump of snow in the morning, then an icy mix in the afternoon.

Since temperatures will start the day in the 20s across the region, there will be some snow and stickage to consider in the morning between Washington, Annapolis, and parts of Maryland’s Eastern Shore. The shaded counties will get more snow and likely continue to get an icy mix of snow, sleet, and freezing rain through the afternoon.

Winter Weather Advisory

Most areas for 7 AM to 7 PM

 

Compare The Forecasts

First let’s look at the snow potential from the National Weather Service. Then compare to my forecast I already issued and the NAM 3 Km computer model

Maryland, Virginia, and parts of West Virginia

• 1 to 2 inches of snow for the areas in the Winter Weather Advisory.
• 2 to 3 inches The ‘thump’ of snow I’ve been discussing will be an enhanced push of moderate snow for the first 1 to 3 hours. This is highlighted in Carroll, northern Baltimore, and northern Harford Counties.

Pennsylvania

2 to 3 inches in the southern counties that border with Maryland. Heavier snow will fall farther north where it will stay colder for longer.

 

My Original Forecast

My Call For Snowfall (and ice)

Notes:

• The timing is critical! Earlier arrival means more impact for all.
• Plan for the start between 7 AM and 10 AM
• Snow Burst or ‘Thumping’: Arrival of snow can come with a push of moderate intensity.
• The warmer Chesapeake Bay will play a role in stickage, but the initial push should coat the roads and impact travel during the morning.
• The transition from snow to sleet and freezing rain in metro areas will be between 11 AM and 2 PM. Then rain to follow before evening.
• More Snow North! The colder air will last longer (blue shading). This region will also stay frozen with ice into Saturday evening.
• Western Maryland/Wisp: They will get ice Saturday afternoon, then more snow returns Sunday.

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NAM 3 Km High Resolution Forecast

(this is repeated from my prior report)

Saturday Morning

Temperatures – Most of the area will be deep in the 20s

Snow Arrival Simulation –> slider

Morning To Noon

This band to thump of snow is with the mid level warm front. It can drop a quick coating to 1″+ of snow in the two to three hours it takes to pass by.  When it stops, the warmer are at cloud level moves in… That is important with the second batch of ‘stuff’ in the afternoon.

 

Noon Temperatures

 

Afternoon Icy Mix and Freezing Rain —> slider

At this time, the temps at cloud level will be warmer, but the surface temps will remain below freezing inland from the Bay, cities, and I-95

• northern Baltimore County
• Carroll County
• western Howard/Montgomery Counties
• Frederick and Washington County
• Southern Pennsylvania

 

Evening Temperatures 

Notice the freezing line remaining in place in those colder areas, even after the precipitation stops.

 

NAM Model Forecast:

Snowfall (this is lower in some areas that my forecast (see below). A lot depends on the thump of snow in the morning and if there is any snow for part of the afternoon push.

Sleet Forecast

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Freezing Rain Forecast

 

 

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