Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 230152 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 852 PM EST Sun Jan 22 2017 .SYNOPSIS... Low pressure will impact the area through Monday before moving away Tuesday. A cold front will pass through the area Wednesday into Wednesday night and an upper-level trough may build overhead for the end of the week. && .NEAR TERM /THROUGH MONDAY/...
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Heights will fall during the next 24 hrs as a strong upper air system deepens as it tracks from the Gulf coast states to near Cape Hatteras. An accompanying sfc low over north Georgia will move off of the mid-Atlc coast by midnight Mon night. Increasing large scale ascent for upward vertical motion will result in periods of rain tonight into Monday with the heaviest rains between 12Z-18Z Mon when strongest easterly upslope winds are expected. 1-1.5 inches of rain are expected with possible higher totals over the eastern slopes of the Blue Ridge. Rain will also start to mix with snow at the highest elevations (> 3kft) of the Potomac highlands as air cools down as upper level low passes to the south. In addition to the rain, tightening pressure gradient will result in strong gusty east winds with strongest winds expected in the 12Z-18Z time frame. A wind advisory is in effect for counties adjacent to the Chesapeake Bay and as far west as Frederick county MD.
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&& .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... Marginal temperatures and warmer air aloft will keep snow totals down across the higher elevations of the Allegheny Front. Around an inch of snow accumulation is possible. An upper level low will continue to spin across the region Monday night into Tuesday and rain showers are expected. Winds will become northwest Tuesday and rain showers will taper off. Dry air will move into the region and the sun should come out by Tuesday afternoon. Gusty winds up to 30 mph expected Tuesday afternoon due to the pressure gradient. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Dry conditions expected Wednesday as upper ridge axis to our east continues to move away, before a cold front moves across the region Wednesday night. Looks like moisture will be limited with this front, therefore not much precipitation is anticipated. Extensive upper level trough and westerly/northwesterly flow could bring persistent upslope precipitation in the form of snow showers from Thursday and into Sunday... mainly over the Allegheny Front... with maybe some showers reaching east of the mountains. Warmest day of this period is Wednesday with high temperatures in the 50s and 60s... followed by a drop in the temperatures of 10 to 20 degrees for the second half of the week and into Sunday. && .AVIATION /01Z MONDAY THROUGH FRIDAY/...
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IFR/Sub-IFR conditions will continue through the next 24-36 hours. RA will increase in intensity tonight and Monday. Although cigs may flirt with MVFR due RA and stronger winds in the cloud layer...Vsbys will likely drop to IFR/SUB- IFR during the heavy rain but due to uncertainty with timing did not add to TAF. Winds rapidly increase late tonight through Monday afternoon with the strongest gusts expected Monday morning and at BWI/MTN/DCA. Gusts may reach 45 kts at times. Further south and east gusts up to 30-35 kts expected. Flight restrictions will continue Monday-Monday night. Gusty winds expected Tuesday afternoon. Dry conditions expected Wednesday before a cold front moves across Wednesday night... with limited precipitation associated to it. An upper level disturbance and west/northwest winds will bring cooler conditions for Thursday and Friday with possible isolated showers over our area. Mainly VFR conditions expected Wednesday through Friday, with possible sub-VFR conditions Wednesday night. Breezy conditions expected over higher elevations through this period.
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&& .MARINE...
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Low pressure will approach the waters through this evening. Winds will gradually strengthen overnight. The pressure gradient will rapidly strengthen late tonight into early Monday morning before gradually dissipating from south to north later Monday. A Gale Warning is in effect for the waters from late tonight through Monday. East to northeast winds will gust around 35 to 40 knots during this time. A Small Craft Advisory will likely be needed for portions of the waters Monday night as the low slowly moves away from the area. Gusty NW winds exceeding SCA criteria remain Tuesday behind departing low pressure system. Winds slacken late Tuesday as influence from low wanes. Mostly dry cold front crosses the waters late Wednesday into Thursday...with gusty winds possibly to SCA criteria behind it Thursday afternoon. Dry conditions expected Wednesday before a cold front moves across Wednesday night... with limited precipitation associated to it. An upper level disturbance and west/northwest winds will bring cooler conditions for Thursday and Friday with possible isolated showers over our area. Breezy conditions expected during this period, possibly needing a small craft advisory.
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&& .TIDES/COASTAL FLOODING...
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Persistent easterly flow will increase the risk for minor tidal flooding during high tide cycles beginning Monday afternoon and lasting into early parts of Tuesday morning (especially at Annapolis, Solomons, and Straits). Developing westerly flow should allow for some decrease in anamolies later Tuesday.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Wind Advisory from 5 AM to 4 PM EST Monday for DCZ001. MD...Wind Advisory from 5 AM to 4 PM EST Monday for MDZ004>006-011- 013-014-016>018-503>508. VA...Wind Advisory from 1 AM to 10 AM EST Monday for VAZ507-508. Wind Advisory from 5 AM to 4 PM EST Monday for VAZ053-054. WV...None. MARINE...Small Craft Advisory until 1 AM EST Monday for ANZ530>543. Gale Warning from 1 AM to 6 PM EST Monday for ANZ530>543.
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&& $$ SYNOPSIS...HSK NEAR TERM...LFR SHORT TERM...BJL/HSK LONG TERM...IMR AVIATION...BJL/HSK/IMR MARINE...BJL/HSK/IMR TIDES/COASTAL FLOODING...HSK

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