Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 290121 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 921 PM EDT Tue Mar 28 2017 .SYNOPSIS...
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High pressure will build over the region through the midweek. Another disturbance will approach the area late Thursday into early Saturday.
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&& .NEAR TERM /UNTIL 7 AM WEDNESDAY MORNING/...
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The upper low/trough axis has pushed east, and is presently moving off the Delaware coast. Drier air has begun to infiltrate the area, which has all but eliminated the thunderstorm potential. However, there are still a few showers roaming about, including a cell headed toward DC. Overall trend is down, which is already reflected in the database. In spite of the punch of drier air seen on water vapor, the low-levels remain quite moist. It may take a while (as in the pre-dawn hours) for dewpoints to truly drop. That suggests that there may be a low cloud or fog issue to contend with overnight. Mitigating factors tonight include north flow and residual cloudcover. Have included a few hours of patchy fog after midnight, but have it sinking south (into central Virginia) by daybreak.
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&& .SHORT TERM /7 AM WEDNESDAY MORNING THROUGH FRIDAY/... High pressure builds in from the north on Wednesday with a breezy north wind. Temperatures will not be as warm and the humidity will be noticeably lower, but still on the nice side for late March with 60s common. Winds will relax Wednesday night as the pressure ridge pushes directly overhead, and with dry air in place, we may radiate down towards freezing or even a bit below in the colder spots. By Thursday, clouds will start to increase as warm advection begins ahead of the next approaching low pressure. The clouds should limit the insolation and temps will get stuck in the 50s. Some rain may move into western areas late in the day, but think for most areas, it will wait until after dark Thursday night. Low pressure will slide east toward us through the day Friday, with periods of rain looking likely. There is a good southerly fetch with this system overruning the cool wedge at the surface, so potential for some decent rain. Right now, it appears the wedge will mostly hold with this system, so highs Friday look to remain in the 50s. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... The chance for rain showers linger Saturday before drier and cooler air can filter into the region Saturday night when high pressure works its way into the mid-Atlantic. High pressure will settle into the region Sunday through early Monday. Dry and seasonable temperatures expected throughout the period. The next storm system will move into the region midday Monday through Tuesday, bringing the chance for rain showers to the region once again. && .AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
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VFR flight conditions mainly prevail this evening outside of any showers. However, these are on the decline, aside from one passing south of DCA through 02z. There is no additional shower threat included in the TAFs. Drier air will slowly infiltrate from the north overnight. However, there will still be a lot of low level moisture, suggesting there may be a low cloud or fog threat. Mitigating factors tonight include north flow and residual cloud cover. Guidance suggesting that ceilings overnight will be more toward low-end MVFR, and reflected that change in the 00Z TAFs. Have also included a few hours of patchy fog after midnight, with a trend highlighting the northern terminals (MRB/BWI) first, and then sliding south toward CHO. Did not go lower than MVFR in the visibility forecast either. If the forecast goes astray, the most likely culprit will be a delay in the arrival of dry air, which would mean that conditions could hit IFR pre-dawn. Whatever does develop tonight will erode in the morning as north/northwest winds pick up. Some gusts could reach 20 kt. VFR conditions will continue until Thursday night, when the next system will bring more rain and potential for IFR cigs and vis. Mvfr conditions Saturday. Winds northwest 10 knots Saturday. Vfr conditions evolving Saturday night. Winds northwest 5 knots Saturday night.
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&& .MARINE...
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One last shower is passing south of Washington DC at this time. After that, conditions will generally be benign through the night. Guidance does not look that impressive with respect to good mixing/channeling tonight, and have pulled the Small Craft Advisory for the overnight hours. However, winds will pick up with sunrise tomorrow. Northerly winds are expected to gust to 20 kt. Have left the Small Craft Advisory in place for the daytime hours on Wednesday. Winds should diminish Wednesday night and remain sub SCA during the day Thursday with high pressure passing the area. Potential for Small Craft Advisory conditions increases Thursday night and Friday with increasing southeasterly winds ahead of an approaching system. Winds will then turn north/northwesterly on Saturday behind the system, with continued potential for SCA conditions.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 6 AM to 6 PM EDT Wednesday for ANZ530>543.
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&& $$ SYNOPSIS...RCM/HTS NEAR TERM...HTS SHORT TERM...RCM LONG TERM...KLW AVIATION...HTS/RCM/KLW MARINE...HTS/RCM/KLW

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