Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 220211 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 911 PM EST Sun Jan 21 2018 .SYNOPSIS... High pressure will remain off the southeast coast through Monday. A cold front will approach the area Monday night and cross the area early Tuesday. This will be followed by another area of high pressure for the second half of the work week. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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High pressure will remain extended from the Atlantic Ocean into the Carolinas tonight. A southwest flow around the high will usher in plenty of warm air for this time of year. Increased moisture will accompany the warmer air and that will result in a bkn to ovc deck of stratocu. Most of the time will be dry due to little in the way of lift...but an isolated shower cannot be ruled out. The best chance for showers will be along/west of the Allegheny Front. Will continue with min temps forecast to be in the lower to middle 40s for most locations...thinking the clouds will keep temps up a bit compared to last night. Patchy fog is also possible...but current thinking is that the stratocu deck will prevent widespread fog from developing. Did allow for fog in the river valleys and rural areas overnight.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/... Southerly flow will increase on Monday with mild conditions expected. Morning strato-cumulus will give way to a cirrus deck by the afternoon. Highs will be able to break into the 60s pretty much area-wide. A cold front will approach the region Monday night, crossing the area Tuesday morning. This will bring rain showers to the region Monday night into Tuesday. As the front moves through, a period of heavier rainfall, gusty winds, and perhaps a convective fine line and a rumble of a thunder will move from west to east. Lows Monday night will be quite mild with southerly flow and increasing moisture, mainly in the 40s to low 50s. Temperatures Tuesday will range from near 50F out in western areas where front will pass first to the mid/upper 60s south/east. Areal- average rainfall should average around a half inch of rain. Cold air advection will begin in earnest behind the front for late Tuesday and Tuesday night, with temperatures falling back into the 20s/30s by Wednesday morning. Gusty west/northwest winds are expected as well, and gusts may reach into the 40-50 mph range across the higher terrain. A Wind Advisory may be necessary for those locations. Elsewhere, gusts in the 25-35 mph range appear more likely. In addition, in the increasing westerly flow, some upslope snow showers are likely along and west of the Allegheny Front with a light accumulation possible. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... The 21/12Z GEFS shows a weak short wave crossing the region on Wednesday. This will cause a chance of snow showers in the favored upslope areas Wednesday through early Thursday, along with the chance of flurries along and west of the Blue Ridge. Daytime highs and nighttime lows will be normal Wednesday and Thursday. GEFS H5 mean height rises begin early Thursday, and continue through Saturday. This will produce an expansive meridional surface high pressure system impacting the entire eastern U.S. seaboard before moving offshore late Friday. Temperatures will be above normal both Friday and Saturday, with increasing chances of precipitation on Saturday. && .AVIATION /00Z MONDAY THROUGH FRIDAY/...
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Predominantly VFR expected through Monday. A stratocu deck around 4-6kt is expected through midday Monday before dissipating from south to north. MVFR cigs cannot be ruled out overnight but confidence is too low to mention in the TAFs at this time. Patchy fog is possible as well...but again confidence is too low for a mention in the forecast since the stratocu deck will prevent some radiational cooling. As a cold front then approaches and crosses Monday night into Tuesday, lower ceilings and a period of rain and possibly a few thunderstorms are likely. This will bring sub-VFR conditions to the region. In addition, low level wind field will be increasing and low level wind shear is expected. Gusty surface winds in a potential rain squall are also possible Tuesday morning. VFR will return Tuesday afternoon with gusty west/northwest winds expected. Low chances of sub-VFR conditions Wednesday through Friday, with the chance of sub-VFR conditions late Saturday.
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&& .MARINE... Sub-SCA winds expected through tonight. Southerly flow will be increasing Monday, but cool waters with warmer air temperatures should limit mixing, so have kept below SCA criteria for now. Low level wind field then increases further Monday night into Tuesday morning, and SCA is in effect Monday night. Gusty showers and gale conditions are also possible as a cold front crosses the region Tuesday morning. SCA conditions are expected to continue Tuesday and Tuesday night with gusty northwest winds developing. Small Craft Advisories may be required post-frontal on Wednesday, and then again on Saturday on strong southwest flow. && .TIDES/COASTAL FLOODING... Increasing southerly flow ahead of an approaching cold front will cause water levels to increase Monday into Tuesday. Minor coastal flooding is possible, especially during the midday high tide cycles Tuesday if the cold front isn`t through by then. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 1 AM to 6 AM EST Tuesday for ANZ530>532-535-536-538>541. Small Craft Advisory from 7 PM Monday to 6 AM EST Tuesday for ANZ533-534-537-542-543. && $$ SYNOPSIS...Lee NEAR TERM...BJL/MM SHORT TERM...MM LONG TERM...Lee AVIATION...BJL/MM/Lee MARINE...BJL/MM/Lee TIDES/COASTAL FLOODING... is the U.S. government's official web portal to all federal, state and local government web resources and services.