Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 062000 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 300 PM EST Tue Dec 6 2016 .SYNOPSIS... Coastal low pressure impacts the area through tonight before high pressure briefly returns Wednesday. A potent cold front will pass through Thursday. Arctic high pressure builds overhead Friday into the weekend. && .NEAR TERM /THROUGH TONIGHT/... Sfc high pressure is retreating to the northeast while low pressure moves off the Carolina coast this afternoon. Strong moisture advection has resulting in a large area of precipitation across the region. Rain has been reported across the majority of the area however...sub-freezing temperatures at higher elevations has resulted in ice accumulation from sleet and freezing rain. The greatest reports we have received were across the Allegheny Front where one to two tenths of an inch of ice has been measured. This is occuring above 1.5 feet with the greater ice amts above 2k feet. A winter weather advisory continues until 7pm this evening for the Allegheny Front...Blue Ridge Mountains and higher elevations along the Shenandoah Valley and Potomac Highlands. Further extension in time may be necessary especially along the Allegheny Front. A shortwave trough will move across the region this afternoon and rain will end from SW To NE this evening. Low-level moisture will stay in place tonight resulting in fog and potentially drizzle through late tonight. Further ice accretion on surfaces may continue after rain moves out across the Allegheny Front. Drier air will eventually move into the region early Wednesday morning when the coastal low moves out to sea and winds become NW. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... Higher pressure will move into the Mid-Atlantic Wednesday and mostly sunny conditions are expected. Temps will climb into the 40s n/w of the metros and 50s elsewhere. A strong jet stream will be located over the Mid-Atlantic Wed night into Thursday. A disturbance in the SW flow aloft will result in clouds and showers Thursday morning. Rain or snow showers are expected with the activity which will mostly stay south of DC and near the Tidewater region of VA. Although sfc temps will be well above freezing the warm layer may be shallow enough for snow showers. It will likely be light and no accumulation is expected. Mild weather will leave the Mid-Atlantic for awhile Thursday night as an arctic front moves into the region. Temps will drop into the 20s across the region Thursday night. Wind chill values will also drop into the teens/20s. && .LONG TERM /FRIDAY THROUGH TUESDAY/... High pressure is expected to build in from the west Friday through Saturday. This high will reinforce chilly air. An upslope flow could generate snow showers in the Potomac Highlands. The high will move to the East Coast Saturday night, before moving offshore Sunday. Temperatures will remain chilly despite a return flow evolving Sunday. A storm system should move northeast across the Great Lakes toward southeastern Canada Sunday night. A trailing cold front will move across the region Sunday night, bringing a chance of rain or snow showers. The 12z GFS model indicates that the frontal movement to the east will be persistent and move to the East Coast waters sometime on Monday. The 00z European model has a slightly different outcome in which it pushes the front eastward a little slower and stalls the front. Another storm system could develop along this stalled front over the Tennessee Valley Monday. Here is where the discrepancies lie. Throughout the day Tuesday, the newly-formed storm system and associated cold front should move across and east of the region. Strong high pressure should build in behind the front, bringing very chilly air into the region once again.&& .AVIATION /20Z TUESDAY THROUGH SUNDAY/... Cigs/Vsbys will deteriorate this afternoon/evening as rain moves across the terminals. IFR/SubIFR conditions are expected through this evening. Low-level moisture will continue overnight and IFR conditions will likely persist into the early morning hours of Wednesday. NW winds increase overnight and drying will occur. VFR conditions are expected as high pressure builds overhead. VFR conditions will continue Wednesday night. Vfr conditions Friday and Friday night. Winds northwest 10 to 15 knots gusts 20 to 25 knots Friday. Winds west-northwest 5 to 10 knots gusts 15 knots Friday night. && .MARINE... Coastal low pressure will develop along the North Carolina coast today. The gradient will continue to strengthen and a Small Craft Advisory is in effect for middle portions of the Bay and the lower Tidal Potomac River. The Small Craft Advisory continues through this evening. A tight gradient from the coastal low will likely presist across the middle and lower portions of the Bay and lower tidal potomac. SCA conditions will continue into Wednesday afternoon. High pressure will approach for Wednesday and a northwest flow is expected. Wind gusts around 20 knots are possible...but confidence is too low at this time for a headline. Winds will become light for Wednesday night. Light winds across the waters through midday Thursday...before winds increase above SCA criteria Thursday afternoon as cold front crosses the waters. Solid SCA gusts continue Thursday night into Friday morning. Increased mixing during the day Friday could lead to marginal gale force winds...regardless...solid SCA will continue. Winds drop back below SCA Saturday morning as large area of high pressure builds overhead. && .TIDES/COASTAL FLOODING... Persistent and strengthening easterly flow will lead to an increase in tidal anomalies today. Action stage currently forecast at the sensitive sites for this evenings high tide cycle (e.g., Annapolis, Straits Point)...though marginal minor tidal flooding is possible if anamolies are slightly higher than currently forecast. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Winter Weather Advisory until 7 PM EST this evening for MDZ501- 502. VA...Winter Weather Advisory until 7 PM EST this evening for VAZ503- 504-507-508. WV...Winter Weather Advisory until 7 PM EST this evening for WVZ050- 055-501>506. MARINE...Small Craft Advisory until 1 PM EST Wednesday for ANZ532>534- 537-540>543. Small Craft Advisory until midnight EST tonight for ANZ531-538- 539. && $$ SYNOPSIS...HSK NEAR TERM...HSK SHORT TERM...HSK LONG TERM...KLW AVIATION...HSK/KLW MARINE...HSK/KLW TIDES/COASTAL FLOODING...LWX

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