Area Forecast Discussion
Issued by NWS Sterling, VA

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409 FXUS61 KLWX 110903 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 403 AM EST Sun Dec 11 2016 .SYNOPSIS... High pressure will move off the Mid-Atlantic coast today. A warm front will move into and lift north tonight followed by a cold front pushing east Monday. High pressure will briefly move over the area Tuesday into early Wednesday before the next reinforcing cold front arrives mid-week with Arctic air behind it. && .NEAR TERM /THROUGH TONIGHT/... High pressure is over the Mid-Atlantic region this morning. Warm air advection is occuring aloft and clouds have increased across the region. Light radar echoes are apparent across the Ohio Valley and Potomac Highlands however nothing has been reported across the LWX outlook area. Low level dry air is in place and snow showers are having a difficult time reaching the sfc. As activity moves eastward light snow is possible across the northern Potomac Highlands early this morning. Little to no accumulation is expected. The mid-level warm front will move into PA by late morning and dry conditions are expected across the region today. Cool conditions expected today as clouds stick around with temps in the mid to upper 30s and 40s across central VA/southern MD. Warm air advection aloft continues tonight as high pressure moves off the Mid-Atlantic coast. Temperatures will fall into the evening however southerly flow is expected to increase and temperatures will start to rise this evening and continue to rise into Monday morning. A plume of moisture ahead of an advancing cold front will enter the Appalachian region late tonight. Sub-freezing temperatures are expected across portions of the Potomac Highlands as precipitation moves into the region and freezing rain is expected. A brief period of sleet is possible at onset. A freezing rain advisory has been issued for these locations tonight through Monday morning. Across the rest of the Highlands and Shenandoah Valley...less confidence in sub-freezing temperatures and if precipitation will be rain or freezing rain. Stronger southerly flow is expected to increase east of the blue Ridge once precipitation arrives and therefore rain is expected. A 50kt LLJ will be located across the Mid-Atlantic by early Monday morning. Gusty winds are expected on the ridges with some gusts approaching 45-50mph. Precipitation will move across the region by 12z Monday and 0.25-0.5 of liquid is expected. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... Rain will come to an end from west to east Monday. Temperatures will continue to climb Monday and reach the 40s across much of the region and 50s across Central VA. Temperatures will be slow to rise across the Potomac Highlands especially the valleys. The freezing rain advisory goes through 15z Monday for these locations. High pressure will build into the region Monday night into Tuesday and continue through Tuesday night. Temps will rise into the 40s on Tuesday. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... The polar vortex over northern Ontario at the beginning of the period slides across central Quebec then quickly into the Canadian Maritimes on Friday. This feature gives us a brief, glancing blow of arctic air Wednesday night through early Saturday morning, with the coldest period of the week appears to be late Thursday into Friday morning, when temperatures are expected to reach the lower teens as far east as the Chesapake Bay. After the cold dome of high pressure moves offshore on Friday, then a low pressure system over the midwest will approach, tapping Gulf of Mexico moisture into the region. The models have a lot of variability at this moment, but with the frigid air mass in place on Friday, the possibility of freezing or frozen precipitation on Saturday looms. && .AVIATION /09Z SUNDAY THROUGH THURSDAY/... VFR conditions expected through tonight. Sub-VFR conditions expected tonight and will continue into Monday morning as rain moves across the terminals. There is a slight chance of -FZRA at MRB late tonight. A strong jet at 2k feet is expected across most of the terminals late tonight. LLWS is expected however there is some uncertainity as to how much wind reaches the ground late tonight. SW winds 10-15kts with gusts up to 25kts are possible at IAD/DCA. -RA will end from west to east on Monday. VFR conditions expected Monday night-Tuesday night. VFR expected Wednesday through Friday, with possible impacts at all terminals due to strong NW winds on Thursday. && .MARINE... High pressure will shift offshore this morning. Southerly flow increases this afternoon, and a SCA is in effect for most of the MD Chesapeake Bay and lower Potomac. Mixing is expected on the waters tonight and into Monday morning. SCA is in effect through Monday morning. Winds will diminish Monday afternoon/evening. as high pressure moves overhead Monday night and Tuesday. At a minimum, solid small craft conditions will exist with the onset of the artic air mass Wednesday night through Thursday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Freezing Rain Advisory from 10 PM this evening to 10 AM EST Monday for MDZ003-501-502. VA...Freezing Rain Advisory from 10 PM this evening to 10 AM EST Monday for VAZ028. WV...Freezing Rain Advisory from 10 PM this evening to 10 AM EST Monday for WVZ050>052-503-504. MARINE...Small Craft Advisory from 3 PM this afternoon to 6 AM EST Monday for ANZ531>534-537-539>543. && $$ SYNOPSIS...Lee NEAR TERM...HSK SHORT TERM...HSK LONG TERM...Lee AVIATION...Lee/HSK MARINE...Lee/HSK

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