Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 050805 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 305 AM EST Mon Dec 5 2016 .SYNOPSIS... High pressure will briefly build over the region today into tonight. Coastal low pressure will impact the area Tuesday into Tuesday night before high pressure briefly returns again for Wednesday. A potent cold front will pass through Thursday and arctic high pressure will build overhead during the weekend. && .NEAR TERM /THROUGH TONIGHT/... The upper-level disturbance that brought the rain overnight will move off to the east today while high pressure builds overhead from the west. A northwest flow and subsidence behind the upper- level disturbance will allow for increasing sunshine today and any rainfall early this morning will quickly taper off. Max temps will range from the 40s in the mountains to the middle 50s near Washington and Baltimore. High pressure will shift north and east toward New England tonight while low pressure tracks through the Gulf Coast States into the Tennessee Valley. Most of tonight will be dry...but clouds will increase well ahead of this system. Precipitation will likely move into the Potomac Highlands and central Virginia toward daybreak. Low-level temps may be cold enough for sleet to mix in with the rain...but surface temps should be above freezing for most valley locations into central Virginia. Surface temps across the Blue Ridge Mountains and the Potomac Highlands may be cold enough for freezing rain. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... Low pressure over the Tennessee Valley will transfer its energy to a coastal low Tuesday along the North Carolina Coast. Warm and moist air will overrun the surface colder air in place...resulting in rain across the entire area. Cold air will remain wedged in place so it will be quite chilly. In fact...evaporative cooling at the onset of precipitation will cause low-level temps to drop below freezing. The layer of cold air may cause sleet to mix in at times...but surface temps across most of the Valleys and east of the Blue Ridge Mountains should remain above freezing. However...freezing rain is a concern for the Blue Ridge Moutains into the Allegheny and Potomac Highlands with most guidance showing a layer of subfreezing air between about 1kft and and 5kft. Ice accumulations are likely across these areas and winter headlines may be needed. For locations near the Mason-Dixon Line into the eastern West Virginia Panhandle...a period of snow and sleet cannot be ruled out Tuesday morning. It appears that any accumulation will be light and confined to grassy areas with surface temps just above freezing. The coastal low will gradually shift off to the east Tuesday night. Precipitation will gradually end from southwest to northeast. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Coastal low will be moving off the NC/VA coast by Wednesday morning...with high pressure beginning to build into the area. This will effectively end precipitation chances across the area...with the possible exception of some early morning showers across NE MD and some light rain/snow showers across the Allegheny Front. Remainder of Wednesday will feature dry weather with seasonable afternoon highs. Strong cold front crosses the area Thursday into Friday. High intra-/inter-model spread remains with regards to timing...precip type...and QPF. And...while most guidance shows only light QPF (if any)...precip type/timing will ultimately determine the level of impact. What is certain is artic high pressure building into the area behind the front...likely bringing the coldest air of the season to the region. Friday`s highs will struggle to reach 40F (even in the metros)...while areas west of the Blue Ridge will remain below freezing the entire day. Very cold Friday into Saturday...with lows in the 20s across much of the area. Another cold day Saturday...as arctic high pressure builds overhead. Highs will again struggle to breach 40F. High begins to move offshore Sunday...with a southerly wind component to develop. This will allow for some slight airmass modification...with temperatures back in the low 40s. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... IFR cigs this morning should give way to VFR conditions as drier air works its way into the area from west to east. Most areas should clear out between 12z and 15z. Northwest winds are expected late this morning through this afternoon wtih gusts around 15 to 20 knots expected. High pressure will cause light winds tonight. Coastal low pressure will impact the terminals Tuesday into Tuesday night. Rain and IFR conditions are expected to develop Tuesday morning. Rain may mix with sleet at times...but little or no accumulation is expected with surface temps above freezing. Drier air may work its way in late Tuesday night as the coastal low moves off to the east. Any flight restrictions remaining early Wednesday will quickly ease by early morning as high pressure builds into the area. Cold front crosses the area Thursday into Friday...and while precipitation amount/type is in question...gusty NW winds are expected behind it through early Saturday in strong cold air advection pattern. && .MARINE... Southerly winds channeling up the Bay has caused gusts around 20 knots. A Small Craft Advisory remains in effect until 6 am for the Maryland Chesapeake Bay south of Pooles Island and the lower Tidal Potomac River. Winds will turn toward the northwest late this morning through this afternoon as high pressure approaches from the west. A Small Craft Advisory is in effect for the waters during this time...but it will be marginal with gusts around 15 to 20 knots. High pressure will build overhead tonight before coastal low pressure impacts the waters Tuesday. A Small Craft Advisory is in effect for portions of the waters Tuesday afternoon. While high pressure briefly builds into the waters Wednesday...winds may gust near SCA criteria during period of best mixing (i.e., daytime). Strong cold front crosses Thursday into Friday. SCA are certain behind the front through early Saturday in the strong cold air advection pattern...with Gale Warnings also possible for portions of the waters. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 6 AM EST early this morning for ANZ531>534-537-539>541-543. Small Craft Advisory from 9 AM this morning to 5 PM EST this afternoon for ANZ530>543. Small Craft Advisory from noon to 6 PM EST Tuesday for ANZ532>534-537-540>543. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...MM AVIATION...BJL/MM MARINE...BJL/MM

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