Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 121852 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 252 PM EDT Tue Mar 12 2024 .SYNOPSIS...
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High pressure will continue to influence the Mid-Atlantic through mid-week with well above normal temperatures. A low pressure system will approach the region by Friday, bringing increased chances for rain showers. Another low pressure system may affect the area Sunday or Monday.
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&& .NEAR TERM /THROUGH TONIGHT/...
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A large area of high pressure extends along the Gulf Coast states and into the Atlantic this afternoon, with low pressure centers over Maritime Canada and the upper Great Lakes. The resulting pressure gradient will continue to result in gusty winds of 20-30 mph this afternoon. The downsloping wind, very dry airmass, and plenty of sun (even through the scattered thin cirrus) are resulting in temperatures in the mid 60s to lower 70s. Lighter winds are expected tonight with patches of cirrus continuing to cross the sky. Overnight lows will be in the 40s for most, but sheltered valleys could drop into the 30s.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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The center of the high will move offshore Wednesday. With a weaker pressure gradient, winds will be much less pronounced. A shortwave trough aloft will introduce some mid and high level clouds, but there should still be some sun at times. Temperatures should be a degree or two warmer than today with the airmass still being dry. Clouds will clear Wednesday night with lows in the 40s to lower 50s. Locally, little changes for Thursday, although a low pressure system will be moving into the Mid Mississippi Valley, with a warm front lifting through the Ohio Valley. A shower could reach the Alleghenies by afternoon, but most will be dry and clouds will be slow to increase. Expecting to add another few degrees to daytime highs, so most will be in the 70s, and a few spots could even hit 80. The warm front will extend across Pennsylvania Thursday night while the low moves toward Lake Erie. A few showers are possible across the northern half of the area, although the latest model trends suggest most of the rain will stay to our north. Overnight lows will only drop into the mid 50s with increased cloud cover.
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&& .LONG TERM /FRIDAY THROUGH TUESDAY/...
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The local area will reside in the warm sector Friday with high temperatures in the low to mid 70s for most. However, clouds and rain showers will dampen the mild spring day. Cannot rule out a few thunderstorms given progged CAPE values of up to a couple hundred Joules/kg. Overall QPF does appear to be fairly light with the ensemble consensus of a few tenths of an inch (more in western MD). Once the cold front comes through Friday night, the area will quickly dry out. Highs Saturday will still average about ten degrees above Mid-March norms. Sunday likely starts dry, but guidance divergences on the emergence of multiple waves of energy ahead of a potent sub-522 dm trough progged to move through the area Monday into Tuesday. On the backside of the trough, mountain snow showers are evident across most ensemble guidance Monday into Tuesday. A more pronounced cooling trend ensues which comes with increasingly gusty northwesterly winds. The true extent of the cold blast does not really take shape until Tuesday as temperatures fall back into the mid/upper 40s.
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&& .AVIATION /18Z TUESDAY THROUGH SUNDAY/...
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VFR conditions are expected through Thursday. For today, westerly winds gusting 20-25 knots (lighter at CHO) will continue this afternoon before diminishing by the evening hours. Winds will be lighter out of the west Wednesday and south or southwest Thursday. Only a few periods of mid/high level clouds are expected. S/SW winds Friday in the warm sector turn w`ly behind the cold front Friday night. In the warm sector, scattered showers and thunderstorms are possible. Therefore, sub-VFR conditions are expected at times Friday, especially in any heavier showers or thunderstorms. Behind the front Saturday, conditions will dry out with winds out of the WNW gusting to 15-20 kts.
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&& .MARINE...
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Small Craft Advisory remains in effect until 6 PM with westerly winds gusting up to 25 knots. The strongest winds will be closer to shore (due to warm air over cool waters), as well as on the upper Potomac and north of North Beach. The tighter pressure gradient weakens overnight tonight and into Wednesday, allowing winds to lessen heading into the middle part of the week. Winds take on a more southerly component Thursday but will remain light through the day. As a low pressure system moves into the Great Lakes Thursday night, winds will increase further, potentially requiring SCAs. However there is some uncertainty since even overnight, air temperatures will likely be warmer than the water temperatures. Typical Spring situation Friday over the waters with warm air being in the warm sector over the cooler waters. Soundings continue to show low-level inversions. Cannot rule out SCA conditions in the S/SW flow, but SCA conditions become more likely along the front. Any shower or thunderstorm could produce gusty winds as well. SCA winds will continue out of the WNW Saturday before diminishing near sunset Saturday evening.
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&& .FIRE WEATHER...
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RH values of 20-30 percent and west winds gusting 20-30 mph continue this afternoon. Winds will abate quickly this evening except along the ridgelines. Relative humidities recover to 70 to 90 percent. Lighter winds are expected Wednesday with only slight increases in humidity in a continued very warm and dry airmass, and many areas will still fall below 35 percent. There will also be some increase in mid and high level clouds. Thursday will be warmer still but with further increases in RH with winds becoming southerly. A low pressure system will approach the area Friday and bring the next chance of rain.
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&& .TIDES/COASTAL FLOODING...
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Tidal anomalies are on the increase with lighter west winds in place, and that upward trend will continue through the end of the week. Some tidal sites may near minor flood stage Thursday and Friday as winds turn southerly ahead of the next low pressure system.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ530>543. && $$ SYNOPSIS...ADS NEAR TERM...ADS SHORT TERM...ADS LONG TERM...CPB AVIATION...ADS/CPB MARINE...ADS/CPB FIRE WEATHER...ADS TIDES/COASTAL FLOODING...ADS

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