Area Forecast Discussion
Issued by NWS Sterling, VA

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508 FXUS61 KLWX 220759 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 359 AM EDT Sat Jul 22 2017 .SYNOPSIS...
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High pressure remains off the southeast coast. Multiple upper level disturbances will be possible through Sunday. An upper level trough of low pressure will move over the northeastern US early in the week.
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&& .NEAR TERM /TODAY/...
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"The hottest time of the year..." is holding true to form. We have issued a heat advisory for the I-95 corridor from Baltimore to Fredericksburg east to the Bay. Question may be how much cloud cover moves into the area. The way I`m playing it is that there will be a decent amount of sunshine/heating during the morning, then increasing clouds in the afternoon given dewpoints in the lower 70s as well as the approaching MCS which may cap the temp rise in the afternoon. Low to mid 90s air temperature will be common east of the mountains. However this is nowhere near daily record values - in 2011 IAD reached 105 (also monthly record) and BWI hit 106. DCA reached 103 in 1926. The next problem to deal with is potential severe weather this afternoon/evening. The main players are a) the heat and humidity leading to large potential temperature values, and b) the system over Indiana/Illinois. Watches are currently in effect in this area, and if the storms remain on their current trajectories these should impact PA through northern VA during prime severe time. Low level shear is fairly weak but with available CAPE storms will have the ability to grow tall. HRRR is showing 22Z west to 02Z east as being the time of greatest potential. Strong gusty winds will be the primary threat with large hail as a secondary threat - upper atmosphere is very warm with the -20 C being at 26.7K feet.
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&& .SHORT TERM /TONIGHT THROUGH MONDAY/...
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Storms could be ongoing during the evening then another overnight with lows in the 70s. Sunday appears to be shaping up to be another severe convective day. Models progged a stronger upper level disturbance with significant height falls for summertime standards. Shear is also on the increase and many ensemble members show moderate CAPE and some even high CAPE values over 3500 J/kg. Expect clusters of storms to move across the area some with damaging winds. A cold front will approach the region Monday before pushing across the region Monday night. Showers and thunderstorms will develop along and ahead of this front. Highs will reach the 90s again.
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&& .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
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Noticeable change in the weather will occur following the cold frontal passage on Monday. High pressure will build into the Great Lakes behind the front Monday night, and translate eastward into the northeastern United States on Tuesday. This will lead to cooler and less humid conditions with developing northerly to easterly flow. The high will then quickly shift offshore by Wednesday, but lingering easterly flow should still keep the temperatures pleasant across much of the area. There could be some scattered showers/thunderstorms south/west nearest to the old frontal boundary and across the higher terrain. By the end of the week, the flow will turn around to the southwest ahead of an approaching frontal system. Temperatures/moisture will likely spike back up ahead of the front, and along with that the chances for showers/thunderstorms. As far as temperatures, highs Tuesday/Wednesday generally in the 80s, and back to near or slightly above 90F for Thursday/Friday.
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&& .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
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VFR conditions expected today. Thunderstorms with strong gusty winds will be possible late this afternoon/early this evening. Storms will again be possible Sunday. Predominantly VFR expected Monday night through Wednesday. There may be some patchy fog/low clouds each morning, but otherwise no significant aviation weather concerns.
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&& .MARINE...
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Winds will be below SCA values today through Sunday. Strong thunderstorms capable of required SMW`s will be possible late this afternoon/this evening and again Sunday. Mainly sub-SCA winds expected Monday night through Wednesday, generally northerly Monday night, turning easterly by Wednesday.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Heat Advisory from noon today to 7 PM EDT this evening for DCZ001. MD...Heat Advisory from noon today to 7 PM EDT this evening for MDZ011-013-014-016>018-504-506. VA...Heat Advisory from noon today to 7 PM EDT this evening for VAZ052>057. WV...None. MARINE...None.
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&& $$ PRODUCTS...WOODY!/MJM

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