Area Forecast Discussion
Issued by NWS Sterling, VA

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196 FXUS61 KLWX 161757 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 157 PM EDT Mon Apr 16 2018 .SYNOPSIS...
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A large area of low pressure will depart northeastward across New England 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 TONIGHT/...
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The large storm system that brought flooding and severe weather to much of the country, including parts of the Mid-Atlantic, is finally departing toward the Canadian maritimes. In its wake are breezy and much cooler conditions. The summerlike temperatures will be a thing of the past for the next several days. In fact, temperatures may drop below freezing for parts of the area tonight (particularly in the I-81 corridor/higher elevations). Although it is likely near to below freezing temperatures are observed in parts of the area tonight, exactly where remains uncertain. For this reason, I`m holding off on a Freeze Warning. The Freeze Watch remains in place, with forecast lows in the lowlands (where the growing season has started) generally between 31 and 33 degrees west of the Blue Ridge mountains.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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The backside of low pressure/upper troughing will continue to slowly depart to the northeast on Tuesday. PVA/NW flow should result in partly to mostly cloudy skies and occasional upslope snow showers. A few sprinkles or flurries may jump east of the mountains as well, but no accumulation is expected east of the Allegheny Highlands. Highs a few degrees on either side of 50 are expected outside of the higher terrain, feeling about 5-10 degrees cooler due to 15 to 25 mph northwest winds. Winds become lighter Tuesday night, but with the center of high pressure passing well to the south, where exactly the wind goes calm (and temperatures drop) is a little fuzzy. The usually sheltered sites in the Shenandoah Valley and central Virginia Piedmont would be most susceptible for freezing temperatures, but anywhere west of I-95 may drop close enough to freezing to warrant frost/freeze headlines (lighter winds would also make frost development more likely). Temperatures rebound rather nicely on Wednesday as transient ridging pushes across. 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 SUNDAY/...
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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.
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&& .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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Mainly VFR expected through Wednesday night (MVFR should depart MTN by 20Z). Scattered showers should pivot out of the region by late this afternoon. Any showers likely won`t result in much if any flight restrictions. NW flow around 15 kts with gusts of 25 kts diminish a bit late this afternoon into early evening, with sporadic gusts possible overnight. 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 Advisory is in effect for all waters through midnight Tuesday night. Gusts over more sheltered waters could become a bit sporadic overnight, but the gradient seems strong enough to just keep the headline going through the overnight hours. Winds should gradually decrease 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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&& .TIDES/COASTAL FLOODING...
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Moderate coastal flooding was observed at Annapolis, with near moderate at DC SW Waterfront. Strait`s Point is expected to hit moderate this evening, and Annapolis could come close again as water levels remain elevated (NW flow has kicked in but not strong enough over the waters to get rid of the surge). Minor flooding is expected elsewhere. 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...Freeze Watch from late tonight through Tuesday morning for MDZ003>005. Coastal Flood Advisory until 11 PM EDT this evening for MDZ014. Coastal Flood Advisory until 5 AM EDT Tuesday for MDZ016. Coastal Flood Warning until 6 PM EDT this evening for MDZ017. Coastal Flood Advisory from 6 PM this evening to 7 AM EDT Tuesday for MDZ017. Coastal Flood Advisory until 6 AM EDT Tuesday for MDZ018. Coastal Flood Advisory until 4 PM EDT this afternoon for MDZ508. Coastal Flood Advisory until 10 PM EDT this evening for MDZ011. VA...Freeze Watch from late tonight through Tuesday morning 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 Watch from late tonight through Tuesday morning 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...DHOF NEAR TERM...DHOF SHORT TERM...DHOF LONG TERM...JMG AVIATION...DHOF/JMG MARINE...DHOF/JMG TIDES/COASTAL FLOODING...DHOF

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