Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 241842 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 242 PM EDT Mon Apr 24 2017 .SYNOPSIS... Low pressure over Georgia will gradually move northeastward, reaching the South Carolina coast this evening, the North Carolina coast Tuesday evening, and finally off the Mid- Atlantic Wednesday. A cold front will approach the region late Thursday or early Friday and remain nearby through the weekend. && .NEAR TERM /THROUGH TONIGHT/...
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A slow moving closed upper level low is over the SE U.S. this afternoon while a coastal low develops off the SC coast. Northeast flow has persisted across the Mid-Atlantic region leading to a cool day. Warm air advection has increased across the region and has been overrunning the low-level cool air. A southeast fetch in the mid- levels will continue to draw in moisture from the Atlantic and rain is expected through the rest of the afternoon and evening. The coastal low will slowly move northward tonight and the pressure gradient across the Mid-Atlantic region will tighten. Expect a steady E-NE wind 10-15mph overnight with slighty higher winds near the Chesapeake Bay. Coverage of rain will weaken overnight and periods of rain are expected as the upper level low and coastal low become stacked. Rainfall amounts will range from 0.25-0.5 from this afternoon through tonight.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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Rain will ramp back up Tuesday morning as the system moves across the Outer Banks. Rain will continue into Tuesday afternoon with low stratus and mist around leading to another cool, dreary day. An additional 0.5 inch of rainfall is expected Tuesday as low pressure spins to the south. Local enhancements on the eastern slopes of the Blue Ridge are possible due to easterly flow in the low-levels. Low pressure will move off the east coast Tuesday night and rain will end from west to east overnight. Moisture will still lag across the region leading to low stratus overnight. Dry air and sunshine will move into the region from west to east Wednesday. It may be slow to reach the I-95 corridor but sunshine may peak out by late afternoon across Washington/Baltimore. Ridging moves overhead Wednesday night and dry conditions are expected. Temps will rebound into the 70s Wednesday.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/...
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Much warmer weather is expected for later this week and through the weekend, along with the chance for some isolated to scattered showers and thunderstorms. Ridging aloft will move overhead on Thursday, while at the same time, a low pressure system will pull into the Great Lakes. This will lead to increasing sunshine and warmer southerly flow, with highs reaching into the 80s. Late Thursday, Thursday night, and into Friday morning will see the approach of a trailing weakening front that will end up washing out and stalling near or north of the region. A few scattered showers are possible with the front. Lows will be mild, likely holding in the upper 50s and 60s. Highs on Friday will remain warm, in the 80s. Moisture/energy will move along the stalled front near or north of the region over the weekend with chances for some isolated to scattered showers/thunderstorms, especially north and west closer to the boundary. Temperatures will be quite summerlike, with widespread 80s, possibly even nearing 90F in a few spots. Overnight lows in the 60s to around 70F. A strong system is then projected to move into the Great Lakes early next week with a cold front approaching the region. This will bring a more widespread chance of showers/thunderstorms.
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&& .AVIATION /19Z MONDAY THROUGH SATURDAY/...
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VFR conditions will become sub-vfr this afternoon and conditions will worsen tonight and through Thursday. Brief periods of LIFR cigs is possible as well late tonight into Tuesday morning. -RA will continue across the region today/tonight and -RA will become VCSH overnight. -RA moves back into the terminals Tuesday and will taper off from west to east Tuesday night. Sub-VFR conditions are expected Tuesday night and will improve from west to east on Wednesday. After the possibility for some lingering reductions Thursday morning in low stratus/fog, mainly VFR is expected Thursday through Saturday with the potential for localized reductions in isolated to scattered showers/thunderstorms.
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&& .MARINE...
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SCA conditions will continue on the waters today and tonight as a pressure gradient from a low to the south and high to the north strengthens. A Gale Warning maybe needed for middle portions of the Maryland Chesapeake Bay and the lower Tidal Potomac River Tuesday. The strongest winds will be Tuesday morning through midday. The low will weaken Tuesday night and slowly move away from the area Wednesday. A Small Craft Advisory may need to be extended into Tuesday night for portions of the waters. Winds will remain below SCA criteria Wednesday through Wednesday night as weak high pressure builds overhead. SCA will be possible late Thursday and into Friday morning with increased southwest flow ahead of a weakening frontal system. Generally sub-SCA winds are then expected Friday and Saturday. Some isolated to scattered showers and thunderstorms will also be possible during this time.
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&& .TIDES/COASTAL FLOODING...
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Easterly flow around low pressure to the south will foster persistent onshore flow over the waters through Tuesday...which will keep tidal anamolies elevated. Onshore flow has strengthen today and will continue to strengthen through Tuesday...with minor flooding possible near times of high tide. Minor tidal flooding is expected at Straits Point/St. Mary`s county and a coastal flood advisory is in effect for the next high tide cycle through late tonight. There is still uncertainity in flood potential at other sensitive sites for the next high tide cycle. Tidal anomalies will increase through Tuesday and there is a better chance for minor tidal flooding this evening into Tuesday...especially at the most sensitive sites (Annapolis, Straits, and DC). The flow should gradually turn north Tuesday night into Wednesday as the low moves away from the area. Water levels should decrease during this time.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Coastal Flood Advisory until 4 AM EDT Tuesday for MDZ017. VA...None. WV...None. MARINE...Small Craft Advisory until 4 AM EDT Wednesday for ANZ530>534- 537>543. Small Craft Advisory until 6 PM EDT Tuesday for ANZ535-536.
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&& $$ SYNOPSIS...HSK NEAR TERM...HSK SHORT TERM...HSK LONG TERM...MM AVIATION...MM/HSK MARINE...MM/HSK TIDES/COASTAL FLOODING...HSK

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