Okay! Sorry this has taken so long, but a busy family day today! Ive looked at all the data over the past 24 hours, and I think Ive got a good handle. This is another tricky forecast, in fact, maybe the toughest one this season since it involves so many different aspects and will reflect many different characteristics depending upon where you are in the region. I have to first break this storm down into 2 parts, since what Id described previously, and as early as last Friday, is exactly what will occur (surface low dissipates as it moves into the Appalachians, lee-side cyclogenesis re-occurs farther out into the Atlantic where a 2nd surface low goes into intense strengthening but moves fairly quickly off the New England Coast). Snow/sleet is already being reported in our northern zones, Frederick and Hagerstown. I think well gradually move in the 1st band of precip throughout the overnight hours, but most of it should continue to draw lighter up until daybreak as the initial low loses its characteristics, and upper-level winds and associated upper-level storm draw farther south of our region. Therefore, I think totals under the warned areas encompassing Frederick, Hagerstown, Martinsburg, Charles Town, and Winchester are over forecast for morning snow totals. Right now, for that zone Id go with a 2-4 total with spots within the zone closer to D.C. on the lower end and spots like Hagerstown on the higher end. This first snow will be a heavier/wetter snow too. For an area from Columbia, MD, to Montgomery Village, and SW down to Dulles, Id say youll be hard pressed to land some sleet/snow by daybreak. A slush/coating is possible on the grass, but even for this zone air temps and associated road temps will be above 32º so no slush should be expected on the roads after a day spent around 50º. Note I talk about a mix of precip, thats because atmospheric data has shown me a melting layer showing up right around daybreak closer to the immediate metro, where even higher temps will mean there will be no wintry totals forecast in my outlooks to just south of Baltimore, through Wheaton, over to Bethesda, and down just east of Dulles to Manassas. This is going way under the NWS forecast that calls for at least 1-2 of sleet/snow within the beltway. That covers round 1. For the second part, Im a bit more uncertain because a very strong coastal storm can easily develop a large precip shield quickly, along with even colder arctic air invading the region from the northeast that will change over the snow type to a drier, finer, and/or fluffier snow. Again, all the data Ive seen suggests most of the precip forecast as the storm turns coastal occurs east and northeast of the region, however all forecasts seem to keep a constant light precip shield together right over the region even during the main transition stage (daybreak through midday Monday). One forecast (the ECMWF, European Center for Medium Range Forecasting) does show a considerable lapse in precip, within a north to south tongue formation, but just west of the immediate D.C. metro, around just south of Hagerstown, down through Northern Virginia, and down to east of Richmond. I very much like the idea of a discernible dry slot due to a lack of upper-level dynamics (jet stream winds, upper-level storm system) and surface forcing (cold front, warm front, low pressure). If I were to go bold, Id say points from the Pan Handle of West Virginia, south to Winchester along the I-81 corridor/Shenandoah Valley and farther west, Id say you dont receive ANY snow from the coastal Monday into Monday evening. And if I were to continue out on my own gut feeling, Id also call for some light snow at the equivalent of drizzle falling through the day up until evening through the Washington Metro, only accumulating to around an inch on the grass. Heres where I will put a bit of faith into the modeling, and put another 2-3 in the northwest zone (FGK-HGR-MRB-OKV) and give a 1-3 dry snow possibility all the way from Monday afternoon through Tuesday morning. That means I dont see a very problematic snow would be accumulated over the course of 18 hours! I think road crews would be able to keep up with that rate :) Now, just a bit farther east, we run into some big issues. Will Annapolis fall into the back edge of the coastal heavy snow? Will Baltimore also get clipped? Will it make its way south into Southern Maryland to St. Marys County too? I think Annapolis and Baltimore have the likelier chances to receive possibly several inches of drier snow up through late Monday night before the storm hammers the New England states by that time. Summary: Again, I dont see ANY problems in the metro by Monday morning, and for that matter, I dont see the potential for ANY accumulating snow until after 3 PM - 5 PM Monday afternoon/evening. If I were to be making school/work decisions, deal with the morning mix and lets get to work and school. Now for the afternoon, Id possibly side with a noon dismissal for schools and letting work out by 3 PM if the light snow shield does begin to come into fashion. All together, this storm is taking a MUCH different course than just the above average clipper everyone thought this was going to be last week, unless you caught my forecast Friday afternoon/evening noting Id seen this set-up before ;) Overall, I again feel pretty confident with respect to this forecast. I guess well all know by Tuesday morning! - Devon
Posted on: Mon, 26 Jan 2015 01:43:23 +0000
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