Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 210134 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 834 PM EST Sat Jan 20 2018 .SYNOPSIS... High pressure will remain near the southeastern US coastline through the rest of the weekend. A cold front will approach the region Monday before passing through Monday night into Tuesday. High pressure will then return for Wednesday through Friday of next week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... High pressure will remain to our south tonight. A warm front, and in reality more of a moisture boundary, will lift northeastward and towards the region overnight. Other than some thin high clouds, skies have started out mainly clear this evening. However...increased moisture around the periphery of the high will move in from west to east...starting late this evening in the Allegheny and Potomac Highlands and overnight across locations farther east. Increasing clouds are expected for most areas. However...an upslope flow to the low-level wind will result in some light rain and drizzle for locations along and west of the Allgheny Front. Other locations should remain dry. Min temps will range from the upper 20s/near 30 in colder valleys and rural areas late this evening to the mid and upper 30s across most other locations. Temperatures may actually rise toward morning as clouds increase. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... As noted by low level theta-e advection, moisture will continue to increase across the region on Sunday. This is expected to lead to a deck of strato-cumulus across the area during the day. Some light upslope rain or drizzle remains possible along and west of the Allegheny Front. Under the clouds, temperatures, while still mild, will likely be 5 to as much as 10 degrees cooler than today, with highs from 50-60 degrees, coolest across northeast MD and warmest in central VA. The warm front/moisture boundary will pull further north Sunday night, leading to continuing warming and moistening low levels. Some patchy light rain, drizzle, or fog cannot be ruled out. Lows should be within a few degrees of 40F. By Monday, with increasing southerly flow and surging warmth in the low and mid levels, the boundary should be well north of the area, placing the region fully in the warm sector by Monday afternoon. Thus, even with potential for morning low clouds and increasing afternoon high clouds as a cold front begins to approach the region, highs are likely to reach well into the 50s and low 60s again. The cold front will push towards the region Monday evening and begin to cross the area Monday night. This will lead to widespread rain, and with the potential for some marginal instability, there is the possibility of a convective fine line with some gusty winds. Rain totals will be generally from a half inch to an inch. && .LONG TERM /TUESDAY THROUGH SATURDAY/... Cold front will finish crossing the area Tue morning with a weak triple point low riding near or over the region. The details of how that low evolves will determine if enough instability can be brought far enough north over us to bring about gusty thunderstorms/showers. Strong winds off the deck will provide the winds if there is any convection robust enough to tap it. At the moment, instability looks very weak. Upslope snow showers will follow in the mountains. A secondary cold front trails and passes through Wed morning, ensuring temps don`t get out of the 40s on Wed...seasonable, and again with upslope mountain snow showers. After that, high pressure gradually passes over and east of the region late week with warming temps again for next weekend. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... VFR conditions expected through this evening. A strato-cumulus deck around 3kft is expected late tonight through Sunday. Winds become light and locally variable tonight and south to southeast around 5 knots Sunday. Strato-cumulus deck likely to persist Sunday night into Monday morning, along with the possibility for some patchy fog, so potential for some flight restrictions exists. Southerly flow will increase by Monday afternoon and Monday night as a cold frontal system approaches, and gusty southerly winds and low level wind shear become concerns. Sub- VFR conditions also likely Monday night in increasing rain chances. Gusty showers and lowered vsbys and cigs may continue into Tue morning with the cold front. LLWS also possible. After that, VFR expected. && .MARINE... Sub-SCA winds will continue tonight and Sunday. As low level winds increase by Monday, SCA probability increases, especially Monday night ahead of a cold frontal system. Gusty showers are possible Tue morning with a cold front. Small craft advisories are possible Tue and Wed as colder air moves back over the waters. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...BJL/MM NEAR TERM...BJL/MM SHORT TERM...MM LONG TERM...CS AVIATION...BJL/MM/CS MARINE...BJL/MM/CS

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