Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 241903 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 303 PM EDT Wed May 24 2017 .SYNOPSIS...
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Low pressure will approach the area tonight before passing through Thursday. The cold front associated with the low will move through Thursday night and high pressure will return for later Friday into Friday night. The high will move offshore Saturday and a warm front will stall over the region for later Saturday through Sunday. A stronger cold front may pass through the area Monday.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Cutoff low pressure continues to develop over the Ohio Valley this afternoon. High pressure is moving off the New England Coast and an easterly flow has ushered in unusually cool conditions for this time of year. Max temps will hold in the 60s for most locations...with perhaps some areas across northern Maryland reaching the lower 70s where there have been a few breaks of sun. The warm front associated with the low will move into the area tonight. A strengthening low-level jet will cause moisture to overrun the surface cooler air in place causing rain to overspread the area from southwest to northeast this evening. Increased frontogenetical forcing from the strengthening low- level jet and shortwave energy rotating around the upper-level enhance rainfall rates at times. Therefore...a soaking rain is expected this evening into the overnight hours. The dry slot will move in from south to north late tonight diminishing rainfall rates. Since the dry slot is expected to move in quickly late tonight...this will keep rainfall amounts down a bit. However...widespread rainfall amounts around one inch are expected. Localized rainfall amounts around 2 inches are possible...especially along the eastern slopes of the Blue Ridge Mountains and Potomac Highlands. Despite stable air near the surface...there still will be elevated instability so a few rumbles of thunder are also possible. Severe weather is not expected since thunderstorms will not be rooted within the boundary layer. Localized flooding is a concern...especially along the Blue Ridge Mountains into the central Shenandoah Valley where FFG Values are lower due to rainfall from last night. Still leaned against a watch for now thinking that rainfall will be spaced out over 6 to 12 hours and the fast moving dry slot will cause rainfall rates to diminish late tonight. Min temps will be in the 50s for most locations.
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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The dry slot will cause rain to dissipate for a period Thursday morning...but surface low pressure will build overhead Thursday. The cutoff upper-level low will also move overhead Thursday. A southerly flow ahead of the low will allow for moderate amounts of instability. Popup showers and thunderstorms are expected to develop later Thursday morning and afternoon. Thunderstorms may contain gusty winds and hail due to colder air aloft associated with the upper-level low. The low pressure will move away from the area Thursday night and the cold front associated with this system will pass through Thursday evening before moving off to the east and northeast Thursday night. Low pressure will continue to move up the New England Coast Friday. Breezy conditions are expected behind the low. A popup shower cannot be ruled out...but most of the time will be dry seasonable. High pressure will briefly build overhead Friday night.
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&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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Brief dry period expected Saturday morning. An upper level shortwave trough could increases PoPs Saturday afternoon into the evening before a boundary settles near/over our CWA Saturday night into Sunday. A cold front then slowly moves across Sunday night into Monday. Showers and thunderstorms possible during this period. Conditions begins to dry out on Tuesday before another -weaker- front approaches on Wednesday. High temperatures will be in the 70s and low 80s... some 60s at higher elevations.
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&& .AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
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A soaking rain is expected to overspread the terminals this evening. Cigs/vsbys will continue to deteriorate and IFR conditions are expected this evening through late tonight. Steady rain will end toward Thursday morning. Cigs/vsbys will improve later Thursday...but popup showers and thunderstorms are expected later Thursday morning into Thursday night. VFR conditions are expected Friday and Friday night as high pressure builds in from the west. VFR conditions expected early on Saturday. Then sub- VFR conditions return Saturday afternoon and into Monday with rounds of showers and thunderstorms moving through our region with a boundaries stalled/moving through our region.
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&& .MARINE...
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An onshore flow will strengthen ahead of low pressure tonight. A Small Craft Advisory is in effect for the waters. Low pressure will move overhead Thursday and the gradient may weaken a bit. However...low pressure and its associated cold front will move away from the waters Thursday night. A Small Craft Advisory is in effect for portions of the waters Thursday night and it will likely be needed Friday into Friday night. Dry conditions early on Saturday before periods of showers and thunderstorms move through Saturday night into Monday as front stalls and moves across our region. Winds will be below the SCA threshold Saturday into Monday.
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&& .TIDES/COASTAL FLOODING...
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An onshore flow will strengthen tonight and tidal anomalies will increase. The next high tide will be the higher of the two and the lunar phase is at a new moon...so minor flooding is likely during the high tide cycle later tonight into Thursday morning. A Coastal Flood Advisory is in effect for many locations along the western shore of the Chesapeake Bay and the Upper Tidal Potomac River. The flow will weaken and turn to the south Thursday before turning southwest Thursday night and eventually to the west and northwest Friday. Significant blowout should not occur until later Friday...so minor tidal flooding is possible during the high tide cycles Thursday through Thursday night.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Coastal Flood Advisory from 6 PM this evening to 11 AM EDT Thursday for DCZ001. MD...Coastal Flood Advisory from midnight tonight to 8 AM EDT Thursday for MDZ014-018. Coastal Flood Advisory from 11 PM this evening to 6 AM EDT Thursday for MDZ016-017. Coastal Flood Advisory from 4 AM to 10 AM EDT Thursday for MDZ011. VA...Coastal Flood Advisory from 11 PM this evening to 6 AM EDT Thursday for VAZ057. Coastal Flood Advisory from 6 PM this evening to 11 AM EDT Thursday for VAZ054. WV...None. MARINE...Small Craft Advisory from 6 PM this evening to 9 AM EDT Thursday for ANZ530>534-537>543. Small Craft Advisory from 6 PM Thursday to 6 AM EDT Friday for ANZ532>534-537-540>543. Small Craft Advisory from 6 PM this evening to 6 AM EDT Thursday for ANZ535-536.
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&& $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...IMR AVIATION...BJL/IMR MARINE...BJL/IMR TIDES/COASTAL FLOODING...BJL

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