Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 182001 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 301 PM EST Wed Jan 18 2017 .SYNOPSIS...
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High pressure will build toward the region tonight before settling overhead Thursday. A warm front will move into the area Friday and stall out nearby through Saturday. Low pressure will affect the area to start the new week.
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&& .NEAR TERM /THROUGH THURSDAY/...
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Relatively quiet weather expected through Thursday. At present, cold front has cleared the area and the upper low is also heading east away from us. Instability caused by the cold pool of the low passing overhead is waning and clouds are starting to diminish. Pressure gradient and mixing will gradaully wane through tonight allowing winds to also relax. However, it does not completely go away, so we should still have enough of a breeze to keep fog from developing. Upslope flow may keep a few snow showers going along the Allegheny Front, but otherwise dry conditions expected with lows mostly in the 30s. On Thursday, high pressure moves right overhead. Sounds look quite dry so high clouds may be minimal through the day, though some puffy low cumulus or stratocumulus may develop. Temperatures aloft will remain mild for January so surface temps should rise back into the 50s in most of the area thanks to rather plentiful sunshine. Winds will be fairly light under the high.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
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Warm front starts to lift back north towards us on Thursday night and enters southern Virginia before stalling out on Friday. Warm advection surge with the front will result in increasing clouds Thursday night, with a period of rain looking definite starting mid-late morning and lasting into early afternoon Friday. That rain should leave the area late in the afternoon, though lingering low level moisture and light southeast flow may result in patchy fog and/or drizzle which could linger through Friday night. Lows Thursday night will be in the 30s with highs Friday afternoon in the mid to upper 40s generally. Lows Friday night will drop back into the lower 40s with plenty of clouds and the potential for fog/drizzle.
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&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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Weak high pressure will be overhead Saturday into Saturday night. Temperatures will stay mild throughout the period. A separate area of high pressure over New England could aid in some cloud cover with an upslope flow. A few rain showers can`t be ruled out, mainly Saturday night. A storm system will develop over the Mississippi Valley and deepen as it pivots northeastward Sunday and Sunday night. This low could send additional energy into our region Sunday into Sunday night, bringing rain showers to the region. On Monday, the main low will move to the northeast a little further. The threat for showers and perhaps a rumble of thunder exist Monday into early Monday evening. Temperatures will remain mild. Drier air will push in behind the departing storm system Monday overnight. High pressure will usher in cooler and drier air Tuesday and Tuesday night. Clouds will break for sun, except for clouds and upslope rain and/or snow showers in the Potomac Highlands possible. An upper level trough of low pressure will sag from the Great Lakes region toward the mid-Atlantic Wednesday. A return of mild air from the south will evolve ahead of the trough with some sunshine giving way to some clouds.
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&& .AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
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VFR thru the next 36 hours at all TAF sites. High pressure building in from the west is producing a gusty wind of 20-25 knots right now, but this should diminish after sunset. Clouds with 3-5k ft bases should also gradually dissipate overnight. Light winds with limited clouds on Thursday. Cigs redevelop and begin to lower later THursday night with a period of rain and sub-VFR, if not sub- MVFR conditions looking likely on Friday. IFR looking possible with lingering clouds, drizzle and fog behind the system Friday night. Vfr conditions Saturday. Mvfr conditions Saturday night with a chance of a few rain showers, mainly at the CHO terminal. Winds light and variable Saturday. Winds easterly around 5 knots Saturday night.
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&& .MARINE...
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Gusty northwest wind reaching SCA criteria as high pressure builds in this evening should diminish overnight. Not quite sure how quickly gusts die down given the air is not that cool and is blowing over relatively cool water, so mixing may be minimal after sunset. Extends SCA a few hours to cover potential for early evening mixing and will let evening shift re-evaluate if SCA needs to go any further. SHould be sub-SCA for Thursday with high pressure overhead. Warm front approaches from south on Friday with rain and mist, but winds should stay sub-SCA. Drizzle and mist may linger Friday night, but still sub-SCA winds expected. No marine hazards Saturday and Saturday night.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 8 PM EST this evening for ANZ530>543. && $$ SYNOPSIS...RCM NEAR TERM...RCM SHORT TERM...RCM LONG TERM...KLW AVIATION...RCM/KLW MARINE...RCM/KLW

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