Friday January 17 2020

Afternoon Update at 1:20 PM

 

Saturday is going to be a mess!

A Winter Weather Advisory was issued after I published this post. Click here to see the updated information. 

 

Snow will arrive in the morning with temperatures in the 20s. When it arrives, it will stick, and possibly thump a moderate to heavy clip for a few hours. The may be a lull for a few hours, then the next batch will have more of a wintry mix an icing. Typically colder areas inland from the Bay and cities will remain icy through the afternoon.

We are less than a day away from our next weather event. As we get closer, the high resolution models get more attention. The NAM 3 Km in particular is one I often use to show the arrival and change over from snow to ice to rain.  This model highlights the morning arrival time and thump of moderate snow, then a lull for a few hours.

Here is a look at that model, including temperatures at key times, plus the model forecast for snow, sleet, and freeing rain.  The afternoon ice may not be as exciting as measuring snow, but is important to consider for adjusting travel plans. Compare the maps to my forecast map and notes at the bottom of this post.

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.

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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

 

Freezing Rain 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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