Area Forecast Discussion
Issued by NWS Sterling, VA

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202 FXUS61 KLWX 240934 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 534 AM EDT Fri Mar 24 2017 .SYNOPSIS... A warm front will cross the region today. A low pressure system will then approach the region on Sunday, and cross the area Sunday night into Monday. Another system will cross the region Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Latest surface analysis shows high pressure sliding east off the Atlantic coast and a warm front approaching from the west. Aloft, a vort lobe is rotating eastward ahead of the warm front, which when combined with warm advection, is supporting a band of light rain which is moving into the region. The forecast for the region remains tricky as temperatures in many spots are either side of freezing. Southeast winds have helped some areas stay above, while other spots which have gone calm have dropped below. With rain now almost on our doorstep and temperatures still below freezing in some areas, have issued freezing rain advisory for northwestern parts of the CWA (W MD, E WV, N VA) through 9 AM. May have to extend or expand based radar and temp trends. Will continue to follow closely. Otherwise, the band of rain should fall apart as it approaches the I-95 corridor this morning, and afterwards, southerly winds should start flooding the region with much milder air. While clouds should remain common today, the gusty south wind should elevate most places into the 50s, with most of Virginia and West Virginia likely to hit 60. Some warm interior valleys of eastern West Virginia may crack 70.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... Southerly winds and milder air flooding the area will be the main theme tonight through Saturday evening. While a ridge will be in place aloft and high pressure will not be far off the East Coast at the surface, it will be rather dirty, with plenty of high and mid clouds. However, with very warm air surging north and some breaks of sun expected, we still expect Saturday to be the first day with widespread 70+ temps since March 9th. IAD`s record is only 76, but DCA and BWI, who`s records include the old downtown offices, have records into the mid 80s. Saturday night into Sunday morning we will continue to watch the potential for a back door cold front to slip back south across the region, particularly Maryland. Uncertainty remains, as guidance has continued to flip back and forth on this somewhat, but right now it looks like most of our forecast region will stay in the warm sector. However, with the next system moving in later Sunday and Sunday night, clouds and showers will keep temperatures down on Sunday. So, Saturday is definitely the better day this weekend. With limited if any instability, we don`t expect much if any thunder through Sunday night, so have kept it out of the forecast for now. && .LONG TERM /MONDAY THROUGH THURSDAY/... Low pressure currently over CO/NM will continue to drift east to the Midwest through Saturday night before dissipating near the Great Lakes under a northern stream ridge Sunday. A second low currently off California will trail the first low, reaching the Midwest Monday night before reaching the eastern Great Lakes Tuesday (and also dissipating) per 00Z ECMWF/GFS. Continued moist southwesterly flow warrants high chance PoPs for the LWX CWA Monday through Tuesday. Possibly a break in action, so Monday night was kept low at this time and Tuesday was raised to likely PoPs across the CWA. Instability possible Tuesday ahead of the cold front, so slight chance thunderstorms were maintained. Continued SWly flow brings max temps well into the 70s Monday/Tuesday assuming no widespread rain. High pressure to the south starting Wednesday maintains above normal temperatures through the rest of the work week. && .AVIATION /10Z FRIDAY THROUGH TUESDAY/... Generally VFR through the TAF period and beyond into Saturday night. Main concern is whether temperatures will be low enough to cause freezing rain as a band of precipitation associated with the passing warm front moves through this morning. Most terminals should warm enough to keep it plain rain, but there remains the chance of some freezing rain at MRB where temps may not have time to warm. Further southeast, rain may dissipate before even reaching BWI/IAD/DCA, but if it does reach there, temps should be warm enough for plain rain. Otherwise, gusty southwest wind develops today with the warm front passing. This evening, as low levels decouple, there could be some low level wind shear as the wind a few thousand feet up will remain quite strong even as surface winds become much lighter. Winds may be a bit lighter on Saturday than today. Sub-VFR cigs and vis become a concern Sunday and especially Sunday night as a low pressure system moves in with some showers. Winds will be uncertain as a back door front tries to drop south into the area, with the greatest uncertainty around MTN/BWI. Southwesterly flow from low pressure to the west/north Monday and Tuesday brings rain showers to the DC metros Monday and Tuesday with a low thunder threat Tuesday. && .MARINE... SCA over the bay this morning will spread to all waters this afternoon as warm front crosses the waters. Winds will gradually diminish tonight. With very warm air over the cool waters on Saturday, right now it looks like winds will stay below SCA, but will need to be watched. SCA again possible Sunday with more southerly channelling as a storm system approaches from the west. Generally sub-SCA SWly flow prevails Monday and Tuesday with thunder chances Tuesday. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Freezing Rain Advisory until 9 AM EDT this morning for MDZ003- 501-502. VA...Freezing Rain Advisory until 9 AM EDT this morning for VAZ028. WV...Freezing Rain Advisory until 9 AM EDT this morning for WVZ050>052-503-504. MARINE...Small Craft Advisory until midnight EDT tonight for ANZ531>533- 539>541. Small Craft Advisory from noon today to midnight EDT tonight for ANZ535>537-542. Small Craft Advisory until 6 AM EDT Saturday for ANZ534-543. Small Craft Advisory from noon today to 6 PM EDT this evening for ANZ538. Small Craft Advisory until midnight EDT tonight for ANZ530. Small Craft Advisory until 6 AM EDT early this morning for ANZ536-537.
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&& $$ SYNOPSIS...RCM NEAR TERM...RCM SHORT TERM...RCM LONG TERM...BAJ AVIATION...BAJ/RCM MARINE...BAJ/RCM

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