Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 210801 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 401 AM EDT Tue Mar 21 2017 .SYNOPSIS...
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A weak high pressure will envelop the region today. A cold front will cross the area tonight. High pressure will return Wednesday through Thursday night. A warm front will cross the region Friday. Low pressure may affect the area Sunday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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A weak upper level disturbance is currently crossing the area. While showers are quite numerous, they are very light and will result in less than a tenth inch of rain. A weak surface low is located in southwest West Virginia. Convective remnants ahead of this low may skirt Highland to Nelson Counties through daybreak. After these showers move out and/or dissipate, only some light upslope rain showers or drizzle will occur through the rest of the morning. Light northwest flow will ensue for the afternoon as the weak low pulls a front into the Carolinas. Clouds will likely be slow to break, but there will be some glimpses of the sun in the afternoon. These breaks should be enough to allow temperatures to rise into the 60s for much of the area.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/...
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While the wave of low pressure developing along the front to our south will be too far away to affect us, there will be a second, stronger cold front dropping into the area late tonight. Moisture will be limited, although some guidance indicates a few light showers may develop, with the best signal in central VA. There may also be a brief period of upslope snow late tonight, but it too should be light. Pressure surge behind the front will likely mean wind gusts pick up noticeably even before the sun rises. Strong cold advection behind the front will result in continued breezy (25-35 mph gusts) conditions into the daytime of Wednesday and temperatures that will be below normal. Highs may fail to reach 40 near the PA border, nudging to 50 in central VA, with 40s in the remainder of the lower elevations. While high pressure will be building in Wednesday night, it won`t be directly overhead, so there will be some variance in decoupling. However, colder spots are likely to dip into the teens with 20s elsewhere. Sunny skies can be expected Thursday as the surface high crosses the area. Temperatures will remain below normal though with most locations in the 40s. Cloud cover increases Thursday night as isentropic lift begins on the back side of the high. Most guidance supports a dry night, although the ECMWF is notably quicker with moving precipitation into the northwestern CWA. A light wintry mix would be possible in this scenario since temperatures will likely drop near or below freezing before clouds arrive.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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Guidance remains in general agreement that a warm front will advance across the region on Friday. The question is just how fast and will there be any rain with it. Since this will be the southeastern, tail end of the front, with forcing increasing further north and west closer to low pressure, odds of any rain will also increase as you go north and west. With warm air advancing into the region, temperatures should turn out milder with near-average readings expected, though with a noticeable northeast to southwest gradient. The high pressure which will bring our cool down Wednesday and Thursday will settle off the Atlantic Seaboard later Friday and Saturday, and with the warm front pushing north, winds will become southwesterly. This same high, acting in conjuction with an approaching low pressure from the west, will then act to bring much milder air northward across the region for the weekend. Widespread highs reaching the 70s for the first time since March 9th are expected Saturday, with mostly dry conditions as the storm continues to slow its approach in guidance. Mild conditions should continue Saturday night, then Sunday the system approaches finally and we see an increasing chance of showers. With temperatures remaining warm, there is a possiblity of some thunder. This will need to be watched. The low pressure slowly pushes across the region Sunday night into Monday with some showers and temperatures dropping. With a colder air mass close by, temperatures are uncertain, and it could try to turn below normal once again.
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&& .AVIATION /08Z TUESDAY THROUGH SATURDAY/...
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Showers associated with a weak disturbance should be pushing away from the terminals by 09Z. Guidance indicates low clouds are unlikely this morning, although lower VFR cigs could occur through midday or so. Otherwise, winds will become northwesterly 5-10 kt as a front slips south of the area. A strong cold front will push south through the area tonight. Precipitation looks unlikely, but NW wind gusts will increase in its wake with 20-30 kt gusts likely. These gusty winds will continue much of Wednesday. Winds decrease Wednesday night into Thursday as high pressure builds across the area. Potential for sub-VFR cigs/vis exists Friday as showers may cross the region, with best chance at MRB. VFR likely to prevail Saturday.
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&& .MARINE...
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Light/variable winds this morning will become northwesterly today around 10 kt as a weak front slips south of the area. A stronger cold front crossing late tonight will bring a surge of northwest winds of 20-30 kt. A brief period of marginal gales late tonight to early Wednesday remains possible, so will continue the mention in the HWO, but current guidance doesn`t exude a solid enough signal to issue a warning at this time. SCA conditions will continue into Wednesday evening at a minimum. Winds will be lighter Thursday into Thursday night as high pressure builds across the area. Wind direction will become southerly by Thursday night.SCA potential with a warm front passing on Friday as a gusty southerly wind develops. Right now, it looks like winds may subside a bit on Saturday.
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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 midnight tonight to 6 PM EDT Wednesday for ANZ530>543.
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&& $$ SYNOPSIS...RCM NEAR TERM...ADS SHORT TERM...ADS LONG TERM...RCM AVIATION...ADS/RCM MARINE...ADS/RCM

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