Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 220115 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 915 PM EDT Mon Aug 21 2017 .SYNOPSIS...
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High pressure will remain offshore tonight and a strong cold front will approach our area Tuesday before passing through Tuesday night into Wednesday. Showers and thunderstorms are possible ahead of this cold front. 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 /UNTIL 6 AM TUESDAY MORNING/...
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Most of the convection from this afternoon and early evening has dissipated. However...very humid conditions persist and a weak surface trough remains near the Blue Ridge Mountains. Therefore...a popup shower or thunderstorm cannot be ruled out through late this evening. High pressure will remain offshore overnight. A southerly flow will continue to usher in warm and quite humid conditions. Min temperatures will range from the 60s in the Potomac Highlands to the mid and upper 70s in downtown Washington and Baltimore. Most places should turn out dry overnight as the nocturnal inversion strengthens. Patchy low clouds and fog are possible...especially in sheltered valleys and areas that have received rainfall from thunderstorms earlier.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/...
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A very warm day on tap Tuesday with highs in the lower to mid 90s. Will have to keep an eye on dewpoints Tuesday...because a Heat Advisory may be needed for portions of the area...particularly along and east of the Interstate 95 corridor. As of now...it appears that the low-level flow may go slightly west of south and this will cause winds to be better aligned with height...increasing mixing. Therefore...dewpoints may drop into the upper 60s and lower 70s. If this occurs...then heat indices will be closer to 100 degrees. However...if not then dewpoints would hold in the middle 70s causing heat indices closer to 105 degrees. Will mention the possibility of heat in the Hazardous Weather Outlook for now. 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 MONDAY/... 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. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/...
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VFR conditions are expected for most of the time through Tuesday. Patchy fog is possible early Tuesday morning. Do have a period of MVFR vsbys for the western terminals...but current thinking is that alight gradient wind will prevent dense fog from developing. 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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Southerly winds will channel up the Bay and lower Tidal Potomac River tonight. A Small Craft Advisory is in effect. There has been a lull in the gusty winds this evening...but wind gusts around 20 knots are expected overnight as the gradient strengthens. Another SCA is in effect Tuesday afternoon/evening ahead of an approaching cold front. 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/COASTAL FLOODING...
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Tidal anomalies are around one half to three quarters of a foot above normal this evening. These anomalies should hold nearly steady through tonight with a southerly flow in place. The next high tide overnight into early Tuesday will be the higher of the two astronomical norms...and water levels will be close to minor flooding thresholds. A Coastal Flood Advisory is in effect for Anne Arundel County where confidence is highest near Annapolis. Elsewhere...will have to watch Straits Point in St Marys County...Baltimore and Washington DC. Did not issue an advisory at this time since the surface flow may go just west of south. A south to southwest flow will persist through Tuesday and into Tuesday night. More minor flooding is possible near times of high tide Tuesday night. An offshore flow will develop behind a cold front Wednesday.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Coastal Flood Advisory from 4 AM to 9 AM EDT Tuesday for MDZ014. VA...None. WV...None. MARINE...Small Craft Advisory until 6 AM EDT Tuesday for ANZ531>534-537- 539>541-543. Small Craft Advisory from noon to 11 PM EDT Tuesday for ANZ530>543.
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&& $$ SYNOPSIS...BJL NEAR TERM...ABW SHORT TERM...ABW LONG TERM...DFH AVIATION...ABW/DFH MARINE...ABW/DFH TIDES/COASTAL FLOODING...BJL

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