Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 121353 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 953 AM EDT Tue Mar 12 2024 .SYNOPSIS... High pressure will continue to influence the Mid-Atlantic through mid-week. Temperatures will steadily warm to well above normal through the end of the work week. A low pressure system will approach the region by Friday, bringing increased chances for rain showers. Another system approaches early next week. && .NEAR TERM /THROUGH TONIGHT/...
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High pressure centered to the south will bring mostly sunny skies today. The pressure gradient remains tight across the area today with the departing low to the northeast and the high to the south. Winds out of the west will gust to 20 to 30 mph at times through the midday and afternoon, especially across the northern half of the area and higher elevations. The main change to the forecast this morning was to bring temperatures up and dew points down. 12Z IAD sounding indicates the eventual mixing layer may extend near or above 6500 ft. Combined with the gusty downsloping wind component and abundance of sunshine, it seems likely we`ll be on the fringes of warm and dry guidance. The only issue may be standing mountain wave clouds. CAMs actually forecasted the patch currently over the DC metro, but eventually move it away. Some additional clouds may form in the lee of the Appalachians as well, but they may be somewhat transient too. Lighter winds are expected tonight. Overnight lows tonight will be in the upper 30s (higher terrain) to mid 40s (near the waters) with some high clouds lingering around.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... The surface high pressure will gradually move offshore during the day on Wednesday. This will allow for a more moist airmass and bring more clouds to the area. There will still be a mix of sun and clouds throughout the day. Highs are expected to be similar to Tuesday with upper 60s to near 70 across much of the area. Winds will be on the lighter side with the pressure gradient weakening as the high moves further offshore. Cannot completely rule out a stray rain shower along the highest elevations out west but overall a dry day and night is expected. Overnight lows Wednesday night will be in the mid to upper 40s for much of the area with mostly clear skies. Warm, moist air will funnel in on Thursday ahead of an approaching low pressure system. Highs will be in the low to mid 70s for the lower elevations while the mountains top out in the mid to upper 60s for the afternoon. Mostly dry conditions early in the day before rain chances move in late in the day and into Thursday night across the northern half of the CWA as a warm front aligns across the MD-PA border during this time. Overnight lows will only fall into the low to mid 50s with increasing cloud coverage ahead of the approaching low pressure system expected to impact the area on Friday. && .LONG TERM /FRIDAY THROUGH MONDAY/... A split flow regime is in place across the country with a rex block over the western U.S. and a subtropical ridge over the southeastern U.S. Within the amplified northern stream, a band of heights pushes through late in the work week which leads to a pattern shift. A cold front accompanying this system brings the next chance for rain, and perhaps some thunderstorms depending on the frontal timing. On Friday morning, a warm front is forecast to sit north of the Mason- Dixon Line and continue pushing northward through the day. This places the Mid-Atlantic region squarely in the warm sector which carries Friday`s highs into the mid 70s. Compared with mid-March climatology, this is easily 15 to 20 degrees above average. This stretch of very mild March weather does come to an end as the mentioned cold front races through late Friday. Shower and thunderstorm chances gradually wane overnight as cooler and drier air works in from the northwest. Saturday should bring a mix of clouds and sun, accompanied by temperatures in the 60s. A more potent upper trough descending from the high latitudes leads to a more substantial pattern change into next week. By Sunday/Monday, a sub-522 dm mid-level low sits near Hudson Bay. The associated cold front pushes through late Sunday which may bring some showers with the frontal passage. 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. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/...
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VFR conditions are expected through Wednesday night and even into most of Thursday. For today, westerly winds gusting 20-25 knots (lighter at CHO) are likely during the late morning and afternoon before diminishing by the evening hours. Continued VFR through Thursday with some high clouds mixing in at time. Squarely within the warm sector, winds across the area on Friday will be out of the south to southwest. As a cold front approaches from the west, there will be increasing chances for showers and perhaps some thunderstorms. Thus, expect some sub-VFR conditions at times before the area dries out late Friday night. This leads to VFR conditions for Saturday. Winds shift over to north-northwesterly on Saturday before becoming more variable in nature Saturday night.
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&& .MARINE...
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Small Craft Advisory remains in effect through most of today with westerly winds gusting up to 25 knots. The strongest winds this afternoon will be closer to shore (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. No marine hazards are expected into Thursday as well. Southerly warm advection continues for much of Friday. Given the mild temperatures on top of cool water, low-level inversions should make any vertical mixing difficult. Small Craft Advisories are more likely Friday evening into the night as the cold front approaches from the west. This may even bring a few thunderstorms to the waterways. West-northwesterly winds become commonplace on Saturday with near-advisory caliber winds through the afternoon. These come down pretty quickly before sundown.
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&& .FIRE WEATHER...
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Have adjusted temperatures up (MaxT from mid 60s to mid 70s) and dew points down for this afternoon, resulting in MinRH values of 20-35 percent (many locations are already at these values, but they shouldn`t go lower since dew points aloft are actually higher than the surface). Wind gusts of 20-30 mph will be most likely on the ridges and north of US Route 50. Patches of mountain wave cirrus may provide some shading, but they likely won`t persist the entire day. Lighter winds are expected Wednesday with only slight increases in humidity in a continued very warm and dry airmass, and many areas may still fall below 35 percent. The next chance of rain will arrive on Friday.
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&& .TIDES/COASTAL FLOODING...
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Tidal anamolies remain low for the time-being. Anamolies likely begin to increase later today through the end of the week with some tidal sites nearing minor flood stage by the end of the week ahead of the next low pressure system on Friday.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ530>543.
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&& $$ SYNOPSIS...ADM NEAR TERM...ADS/ADM SHORT TERM...ADM LONG TERM...BRO AVIATION...ADS/BRO/ADM MARINE...BRO/ADM FIRE WEATHER...ADS TIDES/COASTAL FLOODING...LWX

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