Monday January 28 2019

The National Weather Service has issued a bunch of Winter Weather Advisories for Tuesday. I say a bunch because the timing on the map is staggered as the cold air moves across our region. If you saw my earlier report, this fits with my expectation on the timing. It also lines up with my thought on the impact in the morning on the north side. But this can be very confusing, which is why I tried to assist on the map. The snow timelines and my forecast are below. First, let’s explore the advisories by location:

1 AM Tue to 1 AM Wed for Southern Pennsylvania:

Adams, York, and Lancaster… This area will stay below freezing for the entire event.

6 AM Tue to 9 PM Tue for Counties:

Frederick MD-Carroll-Northern Baltimore-Northwest Montgomery-
Northwest Howard-Northwest Harford

This area will have some snow and ice in the morning and more snow total with the afternoon round.

Noon Tue to 10 PM Tue for Counties:

Southern Baltimore-Central and Southeast Montgomery-
Central and Southeast Howard-Southeast Harford-
Prince William/Manassas/Manassas Park-Fairfax-Northern Fauquier-
Southern Fauquier-Western Loudoun-Eastern Loudoun-

This area may have some wintry mix in the morning. But should thaw, then turn back to snow noon to 2 PM. Roads will become icy.

3 PM to Midnight Wed for Counties:

District of Columbia-Prince Georges-Anne Arundel-Charles-
Arlington/Falls Church/Alexandria-Stafford-Spotsylvania-

This area will turn to snow mid afternoon and get stickage on the roads for the afternoon commute. Travel will be icy into the evening.

4 AM to Midnight Wed for Counties:

New Castle-Cecil-Somerset-Mercer-Delaware

This area should stay below freezing for most or all of the event. Some morning snow, then the harder hit will be afternoon and evening.

My Forecast:

There will be some morning snow in the mountains. But the developing situation will be over our central are to the Delmarva.

Zone A:

Most likely to have morning impact, stay near or below freezing all day, and have the most snow.
Snow Totals: 2 to 4 inches. There is potential for some higher amounts.

Zone B:

Marginal risk for morning issue on the roads.
Thaw mid day, then change to snow between noon and 4 PM
Snow Totals: 2 to 3 inches

Zone C:

No morning weather problems
Change to snow after 4 PM
Wet roads will get stickage and turn icy of the evening
Snow Totals: Up to 2 inches

The arctic blast on the way is being led by a little storm system. Each update from the computer modeling shows this speeding up and enhancing Low Pressure forming over our region ahead of the arctic air. There is one model I have been showing you that has been most aggressive with the front end. I can’t ignore it and need to share that information with you. If this verifies, then some snow and ice could be a problem Tuesday morning for northern areas. Metro areas are on the fence for the morning. But if there is and early hit, should thaw mid day. Northern counties should remain below freezing all day.

The arctic front will be responsible for all of our area to change to snow during the afternoon and evening. Then we are set up for flash freeze on the roads. This will be followed by the arctic blast. The coldest air this round will be with us Thursday morning.

Biggest Tuesday Weather Concerns:

Morning: Worth watching for snow or ice near and north of the city. Timing would bring this in 3 AM to 6 AM.
Noon: Some warming late morning in Central Maryland where roads should be wet. The change to snow will occur (noon to 2 PM) before temps drop below freezing. So wet roads will eventually get stickage and turn icy.
Afternoon/Evening: Annapolis to Eastern Shore change to snow after 3 PM. Roads turn icy for the evening.

UPDATE: Winter Weather Advisory for southern PA 1 AM Tue to 1 Am Wed. This is for Adams, York, and Lancaster Counties. Their NWS Office is State College PA.

Central MD is under another office and we should get this expanded from them shortly

Snow and Ice Timeline —> slider

This NAM 3 Km Model is the most aggressive with the morning snow and ice.
I could not ignore the potential for morning snow despite other models not showing a morning impact. This is with watching since this model has performed well in recent events.

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Afternoon Snow Timeline —> slider

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The NWS Baltimore/Washington Forecast Map

This matches my forecast.

(If your area is not on this map, you are under a different NWS Office jurisdiction)

NWS Impact Map: Experimental Graphic

This shows the moderate impact where temps stay below freezing all day in southern PA. However, I think this should include Northern Frederick to Carroll County, and the Hereford Zone.