Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 120136 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 936 PM EDT Fri Aug 11 2017 .SYNOPSIS... A cold front will move through the area Saturday evening and become stationary across the Carolinas early next week. Weak high pressure builds over the area Sunday and holds through the end of next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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A cold front will slowly track through the Ohio Valley overnight while high pressure remains over the Atlantic. A southerly flow between these systems has ushered in plenty of moisture across our area. The deep moisture and forcing from a surface trough has led to showers and thunderstorms this afternoon. The trough will remain in place overnight while an upper-level disturbance passes through in the southwest flow aloft. This is likely to trigger more showers and isolated thunderstorms overnight...especially across northern and central Virginia toward the Washington and Baltimore Metropolitan areas into southern Maryland. This is where moisture will be deepest near and east of the pressure trough. Localized flood/flash flooding is possible due to heavy rainfall. At this point...it appears that flash flooding should be localized so a Flash Flood Watch has been issued with this package...but it will have to be monitored overnight for the urban areas into southern Maryland. Patchy dense fog is possible overnight due to the rainfall and high amounts of moisture.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
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The cold front over the Ohio Valley will approach the area Saturday morning before passing through during the afternoon and evening hours from west to east. Nmrs showers and t-storms are expected along and ahead of the boundary. Greatest risk for flash flooding and severe wx appears over srn MD, the Chesapeake Bay and the Delmarva. Showers should move east and south of the area by Sat evening.
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&& .LONG TERM /MONDAY THROUGH FRIDAY/... Uncertainty remains in place early next week with models diverging on the track of a wave of low pressure progged to move east along the stalled front to our south. The 0Z ECM continued to track it further north, moving across our region, while others such as the latest GFS and 0Z Canadian continue to allow high pressure to the north to build south and generally dominate. However, even with the drier solutions, an easterly flow may result in some clouds and perhaps some upslope showers in the mountains. Overall, however, temperatures will be near to perhaps a bit below normal early in the week. By Wednesday, high pressure dominates on most guidance including the ECM, with temperatures starting to warm a bit. By late Thursday and particularly Friday however, the high shifts off the coast and the next front is approaching, with a gradually increasing risk of showers and t-storms. && .AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
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Showers likely with isolated thunderstorms overnight...especially across the eastern terminals. Low clouds and areas of fog will cause MVFR/IFR conditions overnight. SubIFR conditions are possible due to fog across the western terminals toward morning. Another round of showers/t-storms expected again Sat with fropa. Depending on the strength of easterly flow and the path of a low pressure system moving eastward along the front stalled to the south, a period of sub VFR conditions may occur early next week due either to low clouds or rain. Uncertainty remains high, however.
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&& .MARINE...
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Srly winds will continue overnight with SCA conditions expected. Winds may diminish a bit Saturday...but gusts close to SCA criteria are expected. Have capped gusts around 15 knots for now. T-storms Sat may require SMWs. Uncertainty exists regarding early next week on the strength of an easterly flow as a front remains south of the region and a wave of low pressure pushes east along it. However, at this time SCA conditions are not expected.
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&& .TIDES/COASTAL FLOODING...
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Southerly flow has caused tidal anomalies around one-half to one foot above normal. This will likely cause water levels to reach caution stage for sensitive areas near high tide tonight and again on Saturday. Latest forecasts keeps water levels below minor flooding since the flow will be weakening a bit...but it will be close during the high tide cycle near Straits Point and Annapolis Saturday morning.
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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 AM EDT Saturday for ANZ530>534- 536-537-539>543.
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&& $$ SYNOPSIS...LFR NEAR TERM...BJL/LFR SHORT TERM...BJL/LFR LONG TERM...RCM AVIATION...BJL/RCM/LFR MARINE...BJL/RCM/LFR TIDES/COASTAL FLOODING...BJL

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