Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 211906 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 306 PM EDT Tue Mar 21 2023 .SYNOPSIS...
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High pressure will move offshore tonight through Thursday. A cold front will drop into the area from the north Thursday night into Friday. The front will stall out nearby through Friday night. Low pressure will pass to our west Saturday into Saturday night before high pressure briefly returns Sunday. Another low may impact the area early next week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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High pressure will move offshore tonight. A light and persistent southerly flow will result in milder temperatures tonight. Lows will be in the 30s to the lower 40s in downtown Washington and Baltimore. A weak piece of mid-level energy will move into the area late tonight. An isolated shower or sprinkle cannot be ruled out over the Allegheny Highlands. Most areas will be dry.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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Another piece of energy will pass through the region on Wednesday. The southerly flow will increase some during the afternoon. Mild temperatures, similar to this afternoon, are anticipated Wednesday afternoon. Highs mainly in the 60s with slightly cooler temperatures in the mountains and along the Bayfront. A long positively tilted trough of low pressure will setup over the Great Lakes into the Rockies Wednesday night. The surface cold front associated with this trough will remain over the same area. Southerly winds will continue to usher in milder conditions for Wednesday night with lows in the 40s for most areas (near 50 in downtown Washington and Baltimore). Stronger warm advection will draw in some more moisture from the Gulf of Mexico. The warm and moist air overrunning cooler air near the surface will increase lift, and this combined with shortwave energy means that there will be a better chance for showers, especially near and north of Interstate 66 and US 50. Low pressure will likely pass by to our north Thursday with a southwest flow across our area. Warmer temperatures expected with highs in the 70s and dry conditions. A cold front, associated with the low pressure system, will drop into our area from the north Thursday night, bringing an increased chance for showers.
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&& .LONG TERM /FRIDAY THROUGH TUESDAY/...
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Temperatures later this week are forecast to be well above normal, but there still remains a good bit of uncertainty regarding the temperature forecast for Friday and Saturday. A stalled frontal boundary will be to our north/northwest creating a large spread in temperatures across the area. Uncertainty remains regarding where the boundary stalls and where the cooler temperatures are each day. The most likely scenario shows temperatures in the upper 60s and 70s for the southern portions of the forecast area with temperatures in 50s along the Pennsylvania and Maryland state border. In addition to the large temperature spread on Friday and Saturday, the stalled frontal boundary will bring increased rain chances. Up to half an inch of rainfall is possible in the northern portions of the forecast area with those along and west of the Alleghenies possibly receiving over an inch of rainfall. Given how dry it has been, rainfall looks to be mostly beneficial at this time. As an UL trough pivots over the region on Saturday, there is a risk of thunderstorms. With CAPE values near 200 J/kg and over 70 knots of bulk shear, convection cannot be ruled out. Dry conditions return on Sunday as high pressure temporarily builds overhead. Rain chances return Sunday night into Monday as another system approaches the area.
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&& .AVIATION /19Z TUESDAY THROUGH SUNDAY/...
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VFR conditions are expected through Thursday. High pressure to the east and offshore will allow for a south to southwest flow to develop, persist, and increase some through the next 36 to 48 hours. A few showers are possible Wednesday night into early Thursday, but most places will be dry. A cold front will likely drop into the area Thursday night, increasing the chances for showers and subVFR conditions. Sub-VFR conditions are possible Friday and Saturday during rain showers as a frontal boundary stalls nearby.
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&& .MARINE...
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A southerly flow will develop and continue through Thursday. This flow should increase enough that small craft advisories have been issued for the Upper Potomac and the northern half of the Bay. The gradient will strengthen for Wednesday through Thursday, and an SCA will likely be needed for portions of the waters. The breeziest conditions will most likely be Thursday afternoon with some gusts around 20 to 30 knots possible (mainly away from the open waters). A cold front may drop into the area from the north Thursday night, but an SCA may still be needed. Northerly winds on Friday will be right at SCA criteria throughout the day. Winds shift to easterly on Saturday and will likely be SCA criteria. Gusty winds are possible during convection.
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&& .FIRE WEATHER...
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A southerly flow is expected to continue with dry conditions. The relative humidity will stay near 15 to 25 percent for most areas. Temperatures will be in the 60s for most areas. Southerly winds of 10 to 15 mph. The next weather system will approach Wednesday and atmospheric moisture will begin to increase. Small chances of light rainfall exist Wednesday and Thursday, but higher chances of areawide rainfall won`t arrive until the end of the week.
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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 2 PM to 10 PM EDT Wednesday for ANZ530>532-535-538>540.
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&& $$ SYNOPSIS...BJL NEAR TERM...KLW SHORT TERM...KLW LONG TERM...AVS AVIATION...AVS/KLW MARINE...AVS/KLW FIRE WEATHER...KLW

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