Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 230058 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 858 PM EDT Tue Aug 22 2017 .SYNOPSIS...
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A cold front will cross the region tonight into Wednesday morning. Reinforcing upper level energy will help to push the front offshore and allow for high pressure to build in from the northwest Thursday into Friday.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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Much of the convective activity so far today has remained north of the Mason Dixon line or west of the Allegheny Front. However, now with lowering heights and increasing shortwave energy as the upper trough moves into the region, in addition to an approaching cold front, we`re starting to see an uptick in activity. Expecting two "rounds" with the first being the southern end of a developing squall line across Pennsylvania. This has the highest chance to become strong to perhaps locally severe as it traverses across northern Maryland over the next 1-2 hours through an environment with 1000+ J/KG of MLCAPE and 40-50 knots of effective shear. The second will be scattered showers and isolated thunderstorms moving in from West Virginia later this evening and overnight. Instability will be lessening overnight, so not expecting any additional severe threat in these cells. By morning, the front will be draped across the region, continuing to push southeastward. Temperatures will still be quite mild out ahead of the push of cooler/drier air, with lows from 68-75F.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
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Showers/isolated thunderstorms will be possible across the southern 2/3 of the forecast area Wednesday. By Wednesday precipitation should be well offshore. Tonight`s fropa will bring an end to this recent heat wave. Highs Wednesday back into the mid 80s/dewpoints back into 60s. Conditions will continue to become more comfortable Wednesday night and Thursday.
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&& .LONG TERM /FRIDAY THROUGH TUESDAY/... The long term period looks fairly dry with surface high pressure dominating the weather conditions over our area. Some diurnally or terrain driven showers and thunderstorms could develop at times with shortwaves moving through, but at this moment looking at mostly dry weather conditions. Temperatures will be slightly below normal, with highs around 80 degrees, near 70 at higher elevations. && .AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
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Cold front will cross the region tonight into Wednesday morning. This will bring scattered showers and isolated thunderstorms to the region, with the highest chances of thunderstorms at MRB/IAD/BWI/MTN. Brief reductions to ceilings/visibilities are possible, and a stronger storm or two has the potential to bring gusty winds and lightning. Otherwise, VFR conditions expected at all terminals Wednesday through Sunday with high pressure gradually building over our area.
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&& .MARINE...
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Small craft advisories remain in effect through 2 AM for all waters and through 5 AM for much of the Chesapeake and lower Tidal Potomac with gusty southwest winds out ahead of an approaching cold front. In addition, thunderstorms are possible through this evening, and Special Marine Warnings may be necessary, especially across the northern Chesapeake Bay. No marine hazards expected Wednesday through Sunday.
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&& .TIDES/COASTAL FLOODING...
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Anomalies are around 0.5 to 0.7 ft this evening. No flooding is currently forecast with Wednesday morning`s high tide cycle, but may come close at Annapolis, Straits Point, and Washington DC. Then northwest winds will arrive Wednesday, and no additional flooding is forecast past this cycle.
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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 5 AM EDT Wednesday for ANZ531>534- 537>543. Small Craft Advisory until 2 AM EDT Wednesday for ANZ530-535- 536.
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&& $$ SYNOPSIS...MM/ABW NEAR TERM...MM/ABW SHORT TERM...ABW LONG TERM...IMR AVIATION...MM/IMR/ABW MARINE...MM/IMR/ABW TIDES/COASTAL FLOODING...MM/ABW

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