Tuesday March 20 2018

Spring officially begins at 12:15 PM today and that will be just the start of our two day winter storm. We will have a wide variety of weather but most of the impact will be tonight and tomorrow. It now appears that we will get more cold air and snow to affect travel tonight and Wednesday. It is likely there will be many closings tomorrow. I want to keep the words brief and get right to the description. There are lots of maps and an update to my snowfall totals below.

There is a Winter Weather Advisory in effect for the colder metro Baltimore area today. This includes: Harford, northern Baltimore, Carroll, western Howard/Montgomery, and Frederick Counties in Maryland. This is the area on the edge of snow with some stickage today. But most will be on the grass. The Winter Storm Warning is in effect for Southern Pennsylvania to the mountains of western Maryland today. The Eastern Shore kicks in tonight and tomorrow. Central and southern Maryland is under a Winter Storm Watch, but that should be upgraded during the day today. See all of the maps below.

Stats For March 20

Average High: 55ºF

Record High: 85ºF in 1945

Average Low: 35ºF

Record Low: 12ºF in 1885

Snow Record: 4.1″ in 1965

Seasonal Snow To Date (at BWI): 10.5″

Sunrise: 7:09 AM

Sunset 7:18 PM

*Daylight = 2:35 longer than yesterday

*Bay Water Temperature = 42ºF at Thomas Pt. Light House

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Today:

This storm is still in the formation stage. The energy feeding into it produced multiple tornadoes in Alabama and Florida Monday. The initial mix and snow will be in the mountains. Locally our mix with snow and sleet still falls on warmer roads. So wet pavement even as it gradually change to snow. The real issue will be the evening and tonight into Wednesday.

Update at 9 AM

8:56 AM Doppler Radar showed the intensity as heavy sleet on the front edge of this system was enough to overtake the warm ground. I have reports from Frederick to Mt Airy, and Owings Mills. I told my clients it will ease there between 9:10 and 9:20 AM.
This is moving north and should last less than 1 hour if you are in it.
There will be snow or mix most of the day…
But after 10 SM we should get help from the higher sun angle to keep roads wet.

Also See:

Winter Precipitation Types. What is sleet?

Spring Sun Angle and Late March Daily Snow Records

There will be rain and snow building in this morning. It will transit to more snow and sleet in the colder Advisory areas. But roads should remain wet until 6 PM. See the temperatures below the slider. There may be snow travel issues west of Hagerstown

Part 1 Of Storm: Radar Simulation HRRR Model—> slider

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Temperatures

The freezing air will be hard to find. We will be getting snow and sleet from much colder clouds and a sign up the strength of the two part storm.

This Evening Freezing Temps reach northwest suburbs

Full Storm Animation: GFS Model

Part 2 Wednesday: Radar Simulation NAM 3 Km Model —> slider

[metaslider id=60442]

My Call For Snowfall

The map is the same, but totals increased just a little from my initial forecast. There will be more on the grass than the roads.

Our biggest impact time will be Wednesday morning to noon. Icing expected Thursday morning after the storm departs

I labeled this with letters to give each zone a description below. The + is the upside potential. That depends on how much can stick on Wednesday during the day. I went lower out of caution.

A: 12 to 20 inches. Mostly Snow! Elevation will help stickage

B: 6 to 12 inches. (Tuesday part will be 1 to 3 inches) Mostly snow or mix, but melting during the day. Road issues after 6 PM Tuesday into Wednesday. Snow during the day will add up a little. + Upside potential depends on how much can stick during the day. Icing up overnight into Thursday morning.

C: 5 to 10 inches. The ground will be warmer so it will take longer to get stickage. Most accumulation of this amount of snow will be before 10 AM Wednesday. Snow during the day will be tough to accumulate. If it sticks during the day, amounts will be high +. Icing up overnight into Thursday morning.

D: 3 to 6 inches. There will be snow here Wednesday. It will snow most of the day, but battle the sun and warm influence from the Bay. More snow will fall than can stick. There will be icing up by Thursday morning.

E: Slushy 2 to 4 inches. This area will get snow most of Wednesday but most will stick on the grass. Might get Wednesday evening snow and possible freezing of ground into Thursday morning.

Snowfall from NAM 3 Km

This is why there is so much hype. Numbers like this would be more realistic in January. But a lot will be lost to melting and compacting. Especially where temps remain near or above freezing to the south

Snowfall from National Weather Service Regional Offices

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