Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 170130 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 930 PM EDT Mon Apr 16 2018 .SYNOPSIS...
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A large area of low pressure will depart northeastward into the Canadian Maritimes through Tuesday. A weak area of high pressure will slide eastward off the southeast coast Wednesday. Another area of low pressure will move across the Great Lakes dragging a cold front across the area Thursday. Canadian high pressure will return from the Ohio Valley Friday into the weekend.
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&& .NEAR TERM /THROUGH TUESDAY/...
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A large storm system will depart toward the Canadian Maritimes overnight and Tuesday. A piece or two of upper level energy will pivot around the main low and bring occasional rain showers or sprinkles to central portions of our region and a few possible snow showers or flurries at higher elevations of the Potomac Highlands. Much cooler conditions will unfold in the wake of the main low and its spokes of energy. Temperatures will drop to or just below freezing in parts of our region overnight into early Tuesday. The primary areas will be in the Shenandoah Valley. There is currently a freeze warning in effect from the eastern West Virginia Panhandle south through the Shenandoah Valley to Augusta County, as well as the higher elevations of the Blue Ridge Mountains. Sensitive vegetation could be damaged or killed should temperatures drop to or below 32 degrees in these areas. As the storm system continues its track to the northeast, a northwest flow should result in partly to mostly cloudy skies and occasional upslope snow showers. We can`t rule out a few sprinkles or flurries east of the higher terrain Tuesday. High temperatures will be near 50 degrees outside of the higher terrain.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
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High pressure will move by to our south Tuesday night. Diminishing northwest winds will become light southwest winds or light and variable, which could result in near freezing temperatures again in some places. For now, we won`t go for any freeze watches just yet. If there are opportunities for freezing temperatures, it would be mainly in the Shenandoah Valley and central Virginia Piedmont regions. Temperatures rebound rather nicely on Wednesday as transient ridging pushes across the region. Highs should reach well into the 60s. Clouds will increase later Wednesday evening ahead of low pressure approaching the Great Lakes.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/... On Thursday, aforementioned low pressure will move to our north from the Great Lakes region. The low looks to remain in central PA or further northward in New York. Winds will remain out of the west leading to a drier frontal passage, though scattered showers are still likely. The low pressure system moving to the north will result in a fairly tight pressure gradient, translating to gusty winds Thursday. Temperatures will be mild, in the mid to upper 50s to low 60s with overnight lows reaching into the 30s and 40s. A few areas could drop to the freezing mark. A freeze watch may be needed. A Wind Advisory may be needed for the strong winds, especially over higher elevations. Friday through Sunday, a high pressure system will build in from the Midwest leading to clearing conditions. Winds will remain light and precipitation is not expected at this time. Temperatures look to remain below average for this time of the year with highs in the mid to upper 50s to around 60. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/...
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Mainly VFR expected through Wednesday night. Any showers or sprinkles overnight shouldn`t create flight restrictions. Winds will diminish overnight into Tuesday morning. Winds increase diurnally Tuesday before slackening Tuesday night. As high pressure passes to the south Wednesday, winds will become more southerly around 10 kts. A low pressure system moving to the north of our region will bring strong winds to the region Thursday. Winds gusts over 30 knots are possible. Brief sub-VFR conditions are possible on Thursday, but mainly VFR conditions are expected through Saturday.
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&& .MARINE...
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A Small Craft Advisories remain in effect for all waters through Tuesday night. Winds should gradually decrease later Tuesday night into Wednesday morning as high pressure passes to the south. Southerly winds could gust a little over 20 knots Wednesday but warmer air over cooler water brings mixing into question. On Thursday, a low pressure system will move north of our region across the Great Lakes. The low is forecasted to have a tight pressure gradient which will lead to strong winds on Thursday. Gale Warnings may be needed. Friday into Saturday, a high will build over the region leading to lighter winds. Sub Small Craft Advisory conditions are expected during this time.
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&& .HYDROLOGY...
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Small streams will continue to recede overnight since the heaviest rain has ended several hours ago. However, water levels remain high along the Potomac and Shenandoah River Basins. Most areas should crest below flood stage, except for Opequon where minor flooding is occurring and Springfield(affecting Hampshire and Hardy Counties) where minor flooding is expected overnight. These areas should drop below flood stage late tonight into early Tuesday at Opequon and during the day Tuesday at Springfield. High water may cover some low water crossings overnight near the north fork of the Shenandoah River in Shenandoah County.
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&& .TIDES/COASTAL FLOODING...
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Coastal flood advisories remain in effect up and down the Potomac River and Chesapeake Bay through the remainder of the evening. Gradually one by one, the advisories will be lowered to account for a persistent westerly wind and developing northwesterly wind overnight into Tuesday. Tidal anomalies should subside Tuesday as northwest flow continues.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Coastal Flood Advisory until 1 AM EDT Tuesday for DCZ001. MD...Coastal Flood Advisory until 9 AM EDT Tuesday for MDZ014. Coastal Flood Advisory until 5 AM EDT Tuesday for MDZ016. Coastal Flood Advisory until 7 AM EDT Tuesday for MDZ017. Coastal Flood Advisory until 6 AM EDT Tuesday for MDZ018. Coastal Flood Advisory until 2 AM EDT Tuesday for MDZ508. Coastal Flood Advisory until 10 PM EDT this evening for MDZ011. VA...Freeze Warning from 3 AM to 9 AM EDT Tuesday for VAZ025>031- 507-508. Coastal Flood Advisory until 5 AM EDT Tuesday for VAZ057. Coastal Flood Advisory until 1 AM EDT Tuesday for VAZ054. WV...Freeze Warning from 3 AM to 9 AM EDT Tuesday for WVZ051>053. MARINE...Small Craft Advisory until midnight EDT Tuesday night for ANZ530>532-535-536-538>540. Small Craft Advisory until 6 AM EDT Wednesday for ANZ533-534- 537-541>543.
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&& $$ SYNOPSIS...KLW NEAR TERM...KLW SHORT TERM...KLW LONG TERM...CJL AVIATION...KLW/CJL MARINE...KLW/CJL HYDROLOGY...BJL TIDES/COASTAL FLOODING...KLW

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