Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 151939 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 239 PM EST Fri Dec 15 2017 .SYNOPSIS... Low pressure near off the Delmarva coast will move out to sea tonight. High pressure will return for Saturday into Saturday night before weak low pressure passes through later Sunday into Sunday night. Weak high pressure will build overhead for Monday before a cold front passes through Tuesday. && .NEAR TERM /THROUGH TONIGHT/... Low pressure continues to develop off the Delmarva coast this afternoon while an upper-level trough swings through our area. A potent jetmax has caused the low and mid-level flow to back just enough for weak overrunning...and extra lift is occurring since our region is in the left exit region of the jetmax. This has caused light snow to develop overhead this afternoon. There have been a few reports of freezing drizzle as well. Will continue with the Winter Weather Advisory for the Washington and Baltimore Metropolitan areas. However...with the precipitation developing mostly in the 4-7kft layer there has been a lot of riming and accretion of super cooled droplets causing snow pellets and even the few reports of freezing drizzle. Therefore...snow ratios will not be quite as high as previously thought despite the cold temperatures. Have tweaked snow amounts down just a bit for this reason with most locations in the Washington Metropolitan area receiving a coating to an inch. 1 to 2 inches are still most likely near Baltimore. Having that all been said...even the light snow amounts will cause treacherous conditions on untreated surfaces due to the cold temperatures. Temps will remain below freezing through the evening commute...so any snowy and icy conditions will remain in place. Precipitation is most likely to end between 3 and 5 pm near Washington and by 6 pm near Baltimore. Across the rest of the area...a few flurries have occurred today but little or no accumulation has taken place. A few slippery spots cannot be ruled out though due to the cold conditions. High pressure will build to the south tonight while the low moves out to sea and the jetmax moves off to our east. Dry and seasonably chilly conditions are expected with temps in the lower to middle 20s across most areas. Any snow covered or icy surfaces will remain that way through tonight. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... High pressure will remain to our south for Saturday and Saturday night. A southwest flow around the high will usher in somewhat milder conditions Saturday afternoon after a chilly start. Max temps will be in the 40s for most areas. High pressure will move offshore Sunday and a southerly flow will usher in more moisture and somewhat milder conditions. Max temps will be in the 40s for most areas with lower 50s in central Virginia. An upper-level disturbance will pass through late Sunday and Sunday night. A few showers are possible...but forcing from this system will be weak so any precipitation that does fall will be light. && .LONG TERM /MONDAY THROUGH FRIDAY/... Mild conditions expected during the long term period with dry conditions on Monday as we sit between two boundaries and southerly flow settles over our region. Some showers could develop over higher elevations later on Monday and into Tuesday, but still expecting mainly dry conditions over our CWA. A cold front approaches Tuesday night increasing PoPs over our area, but QPFs are not impressive. High pressure settles in behind the front Wednesday into Friday with winds become northwesterly... then becoming southwesterly Thursday into Friday as high pressure moves offshore. Temperatures will be above normal in general with highs reaching the 50s and 60s in most locations, except on Wednesday. Low temperatures will be in the 30s and 40s, but colder on Wednesday night. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... Light snow will end by 23z for the eastern terminals. MVFR to IFR conditions are expected during times of snowfall. VFR conditions are expected tonight through Sunday morning. A few showers are possible later Sunday and Sunday night along with MVFR conditions...but confidence in precipitation is low at this time. VFR conditions expected Monday into Wednesday. Maybe sub-VFR conditions on Tuesday night as showers could move through the terminals. Gusty winds expected on Wednesday, up to 20 kt. && .MARINE... Low pressure will move out to sea tonight. A Small Craft Advisory is in effect for the Maryland Chesapeake Bay south of Drum Point and the lower Tidal Potomac River...closer to the gradient. High pressure will build to the south for tonight through Saturday...but a tightening gradient will result in SCA conditions. The gradient will subside Saturday night and Sunday. A weak disturbance will pass through Sunday night. Winds are expected to stay below small craft advisory threshold Monday into Tuesday. Winds could increase Tuesday night into Wednesday behind a front, requiring a small craft advisory over the waters. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Winter Weather Advisory until 7 PM EST this evening for DCZ001. MD...Winter Weather Advisory until 7 PM EST this evening for MDZ004>006-011-013-014-503>508. VA...Winter Weather Advisory until 7 PM EST this evening for VAZ054. WV...None. MARINE...Small Craft Advisory from 9 PM this evening to 7 PM EST Saturday for ANZ530>533-539>541. Small Craft Advisory from noon to 7 PM EST Saturday for ANZ535- 536-538-542. Small Craft Advisory until 7 PM EST Saturday for ANZ534-537- 543. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...IMR AVIATION...BJL/IMR MARINE...BJL/IMR

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