Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 211830 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 230 PM EDT Mon Aug 21 2017 .SYNOPSIS...
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A disturbance will bring showers and thunderstorms to parts of our region this afternoon and evening. High pressure will regain control overnight tonight through Tuesday, before a strong cold front pushes across our region and brings another threat for showers and thunderstorms Tuesday night into Wednesday. The front could stall to our southeast, while a second area of high pressure builds in from the west later this week.
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&& .NEAR TERM /TONIGHT/...
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With temperatures in the upper 80s and dewpoints in the mid 70s the atmosphere east of the mountains has CAPEs of 3-4K j/kg. HRRR has been fairly constant in developing convection east of the mountains during the late afternoon - any storms that develop will be able to feed off that energy and grow rapidly. These will have potential to become severe with damaging winds being the largest threat. Unlike a few weeks ago there is 20-30 knots of steering flow aloft. This makes me think that cells will move - hence lowering the flash flood threat. Thunderstorms possible through midnight east of the mountains.. then some fog possible in the central Shenandoah Valley and in the valleys west of the Blue Ridge. It will be a very warm night - lower to mid 70s east of the mountains...mid to upper 60s west.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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A very warm day on tap Tuesday with highs in the lower to mid 90s. A cold front will move into the Ohio Valley by Tuesday evening...bringing a chance of thunderstorms to the western part of the forecast area late in the afternoon/evening. Given the amount of CAPE that will be available severe weather is a possibility, especially west of the Blue Ridge. SREF has been consistent on weakening the storms after 00Z Wednesday as these attempt to track east of the mountains - we`ll have to see. The front is expected to move through the forecast area Tuesday night into Wednesday morning. This will bring a drop of about ten degrees to the region Wednesday, and the start of some very pleasant weather that will go into the weekend.
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&& .LONG TERM /THURSDAY THROUGH SUNDAY/...
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High pressure passing from the Great Lakes into New England will control the weather pattern over the Mid-Atlantic late this week through the weekend. Temperatures and humidity will be below normal, more reminiscent of late September than late August. Precipitation chances will be minimal during this time.
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&& .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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VFR conditions outside of possible thunderstorms. IAD/DCA/BWI/MTN will be the most likely to experience these. VFR during the day Tuesday. Thunderstorms will again be possible Tuesday night. MRB may be the most at risk. VFR again Wednesday. Mainly VFR expected w/ light N flow as high pressure moves to the north Thu-Fri.
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&& .MARINE...
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A small craft has been issued for the wider part of the Bay and lower Potomac. Thunderstorms will be possible on all the waters for the remainder of the afternoon and this evening. Another SCA is in effect Tuesday afternoon/evening. Generally light flow is expected over the waters late in the week as high pressure moves by to the north.
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&& .TIDES/...
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Anomalies are only around a half foot above normal this afternoon but they are slowly rising with southerly flow. With the new moon, it won`t take much more anomaly for sensitive sites to approach minor flood stage. Current projections indicate Annapolis, Straits Point, and DC SW Waterfront will need to be monitored for flooding during the late night/Tuesday morning high tide cycle.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from noon to 11 PM EDT Tuesday for ANZ530>543. && $$ PRODUCTS...WOODY!/DFH/ADS

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