Interesting system for Wednesday into Thursday

Although the National Weather Service is not too excited with the system for tomorrow into Thursday, I’m a little concerned. The storm will be strengthening once it hits the Mid-Atlantic coastline, which could promote something called “dynamic cooling”. This occurs as precipitation falls through the column helping to lower surface temperatures, while colder air also moves in from the northwest. If “bands” form, then the snow could fall heavier in certain locations. This is a borderline situation and will require forecasters to “nowcast” the event tomorrow, so don’t be surprised if snowfall amounts change.

Sterling, VA NWS total snow accumulation map for 2/13/13-2/14/13.
Sterling, VA NWS total snow accumulation map for 2/13/13-2/14/13.

When you look at the snowfall map above, the I-95 corridor looks to escape most if not all of the snow. My personal feeling is that we should see more snow in this area, especially if the dynamic cooling is realized tomorrow evening. I do agree with the storm starting as rain though. My forecast numbers for DC area 1″ or less, while the Baltimore area could see 2″-4″. I do think there is a tight gradient with this event. Farther north, the Mt. Holly, NJ NWS office has not issued a snowfall map. I think it’s possible that snow falls in NJ tomorrow night, with higher amounts possible along the coast. If I was to go out on a limb, I would say 2″-4″ as a general early forecast. Remember, this is my current idea and could change tomorrow morning.

18z GFS surface pressure and precipitation forecast for 03z (10 pm EST) on 2/13.
18z GFS surface pressure and precipitation forecast for 03z (10 pm EST) on 2/13/13.
18z NAM surface pressure and precipitation forecast for 03z (10 pm EST) on 2/13/13.
18z NAM surface pressure and precipitation forecast for 03z (10 pm EST) on 2/13/13.

My support for the more snow option is in the two models above. The dashed blue lines represent thicknesses which we relate to temperatures between the surface and 15,000 ft. When those lines move south and east, it indicates cooler air moving over any given location. There should still be precipitation falling when the first blue dashed line (540 dam) thickness moves through the DC/Baltimore area. This would promote a changeover to snow by early to mid-evening. Now, the European model is drier and a bit warmer, which might be why forecasts are moving away from the snow option.

Bottom line: I think forecasts will change tomorrow and there will be more of a snow threat heading into the overnight period tomorrow night into Thursday. This is not a big storm by any means, certainly nothing like the last storm. I am going out on a limb with very little support, especially from the NWS, but I’m going to follow my gut. If things look different by tomorrow morning, I’ll issue an update.

Thank you for reading and sorry for not writing during the blizzard! Even a meteorologist gets a vacation from time to time. 🙂

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