Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 120902 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 402 AM EST Thu Jan 12 2017 .SYNOPSIS... A cold front will approach from the northwest today. The front will cross the region early Friday. The front will stall to the south and a few waves of low pressure will ride eastward along the front over the weekend into early next week. && .NEAR TERM /THROUGH FRIDAY/... As of early this morning, the warm front, or whatever was left of it, has cleared the region and almost the entire area is already into the upper 40s and 50s. The few exceptions include Cumberland, where a pocket of cold air trapped in the valley has kept them stuck in the upper 30s with some fog. High pressure is located off the coast and the approaching cold front to the northwest currently extends from near Toronto southwest to St. Louis to Oklahoma City. With strong southwest flow, but forcing staying to the northwest, it should be mostly dry with some breaks of sun, and temperatures should reach the 60s easily. Some question about just how warm it can get given persistent clouds but wouldn`t be surprised if there was a 70 somewhere. The front will start sliding across the northwestern portion of the CWA late this evening and will clear all but the southernmost portions of the CWA by dawn Friday. Forcing weakens as the front moves in so expect just a few showers and most of them should stay near or west of the Allegheny Front. Thus only a low chance or slight chance east of the mountains into the cities. Lows will remain in the mild 40s where the front crosses late, but drop into the 30s in the NW where the front will cross early. All readings will be above normal, however. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... Friday should be dry overall as the colder air pushes south from the very strong high to the northwest. A few showers may linger in western Virginia as the front gets a bit hung up there. While temperatures will be much lower, they still will be above normal with 40s to low 50s common. This is the last mild day for a few, however. Friday night the cold air continues to drain south as strong high to the north pushes eastward. A wave of low pressure will also approach from the west, riding along the stalled front just to the south. As this occurs, warm advection will develop and we will start to see warming temps at mid levels even as low levels continue to cool. Thus, think snow will be limited with this system, with an initial start of snow possible from DC on northeast, but a quick change to sleet and freezing rain likely on Saturday. Precipitation amounts do not look very high, and there remains a great deal of uncertainty in both when precipitation starts and how quickly it changes to ice, but right now thinking is that most places will end up with less than an inch of snow before going over to ice, with little or no snow in central and western VA into WV where the cold air aloft just won`t make it before warm advection precip begins. Ice amounts should mostly be advisory level, though a stray warning level ice total is not impossible. Since we are coming out of warm period, this icing event doesn`t look quite as bad as the one back in mid December, but icy roads and trees will still be likely. The main precipition should diminish late in the day Saturday, with a break possible at night as the low slips east. Temps will remain steady, with low 30s to upper 20s north and mid 30s further south in central VA where rain is more likely. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... A long wave ridge looks to persist over FL through Monday before ejecting slowly east. Low pressure tracks look to be sequestered to the central CONUS/tracking to the Midwest/Great Lakes. Precip rounding the high along a stationary front Sunday warrants chance PoPs for the southern half of the CWA. A rain/wintry mix line looks to set up over the CWA, north of the stationary front. Cold air wins out with the front sagging south of the CWA as a cold front before returning as a warm front ahead of the next low. With low tracks to the west, a warming trend is expected to begin MLK Jr. Day and continue until the next cold frontal passage. The 00Z GFS/ECMWF prog the cold frontal passage to be in the Thursday/Thursday night timeframe. The timing of this Midwest low and associated cold front is the key question to Mid-Atlantic weather late next week leading up to the Friday Inauguration. As of now, went for likely PoPs for the western half of the CWA for Wednesday night with chances east. && .AVIATION /09Z THURSDAY THROUGH MONDAY/... VFR thru Friday, with low level wind shear this morning. Gusty SW winds lighten tonight, then become NW Friday. Icing and low cigs/vis possible Saturday. Slow moving cold front sags south over the area Sunday before returning north as a warm front Monday. Chances for precip with a wintry mix on the north side and IFR conds. Warm front Monday with a mild pattern then at least through the middle of next week. && .MARINE... SCA today and again Friday ahead of and behind passing cold front. Winds diminish Friday night and Saturday as icy system moves in. Weak cold front sags south of the area Sunday, returning as a warm front Monday. Winds expected to be tranquil near this boundary Sunday and Monday. Return flow may begin to channel up the main stem of the Bay Tuesday into Wednesday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 3 AM EST Friday for ANZ530>534- 536>541-543. Small Craft Advisory from 8 AM to 6 PM EST Friday for ANZ530>543. Small Craft Advisory until 10 PM EST this evening for ANZ535- 542. && $$ SYNOPSIS...RCM NEAR TERM...RCM SHORT TERM...RCM LONG TERM...BAJ AVIATION...BAJ/RCM MARINE...BAJ/RCM is the U.S. government's official web portal to all federal, state and local government web resources and services.