Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 231841 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 241 PM EDT Mon Oct 23 2017 .SYNOPSIS...
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A cold front will move across the area late tonight and push east of the Chesapeake Bay Tuesday morning. High pressure will gradually build across the region during the second half of the week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Deepening sfc and upper level low pressure area over the OH valley will force a narrow squall line across the area tonight with the line of shallow convection entering Highland county around 9PM and exiting the Chesapeake Bay by 6AM Tue. Despite the lack of instability, the magnitude of the low-levels winds is so strong (40kt at 500 meters) that the line should be able to produce 40-50 mph gusts as it moves through. The strongest part of the line should remain farther south across central VA and may affect Albemarle and Nelson counties. Wouldn`t be surprised if a severe t-storm watch is issued for that part of VA later this evening.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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Cdfnt will push east of the bay by 12Z with showers ending. Still mild under westerly flow. Upper trough axis crosses the area Wed (GFS) or Wed night (ECMWF) with temps staying in the 60s during the day and 40s at night. Any precip would be confined to the upslope areas.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/...
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Troughing will remain entrenched over the eastern CONUS through the period as ridging persists out west and over the North Atlantic. This will lead to near normal temperatures late this week into the weekend. A spoke of energy will rotate around an upper low stationed just southwest of James Bay likely bringing another period of unsettled weather at some point next weekend, but timing/placement details remain fuzzy this far out.
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&& .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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Shallow line of convection will move across terminals tonight first at KCHO between 01Z-03Z and then across the rest of the terminals between 03Z-09Z. MVFR cigs and wind gusts to 45 kt can be expected with this line of showers. No t-storms anticipated due to shallow equilibrium levels. Mainly VFR expected late in the week with light flow.
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&& .MARINE...
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Winds are expected to strengthen rapidly tonight in response to strengthening low-level jet. Main channel of the bay and lower Potomac should experience gale force winds easily while the upper bay and upper Potomac the winds will depend more on strength/intensity of convection. Think there could be a 3-hr period where they also experience brief gales, so raised the gale warning everywhere. Convective line moves east of the bay by 15Z Tue at the latest with winds diminishing and showers ending. SMWs may also be required later tonight. Light flow with high pressure over the waters Thu-Fri.
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&& .TIDES/COASTAL FLOODING...
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Water levels are expected to rise quickly this evening as srly flow strengthens. ESTOFS performing much better than ETSS as it typically does in srly flow, but magnitude of surge is almost always overestimated especially in the upper parts of the bay. Don`t have enough confidence to raise an advzy for Baltimore and Havre de Grace, but have enough confidence that Annapolis will experience minor coastal flooding for the next two high tide cycles, so raised the advzy for them.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Coastal Flood Advisory from 7 PM this evening to 1 PM EDT Tuesday for MDZ014. VA...None. WV...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ530>543. Small Craft Advisory from 8 AM to 6 PM EDT Tuesday for ANZ530>533-537>542. Gale Warning from 6 PM this evening to 8 AM EDT Tuesday for ANZ530>533-535>542. Gale Warning from 6 PM this evening to 3 PM EDT Tuesday for ANZ534-543.
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&& $$ SYNOPSIS...LFR NEAR TERM...LFR SHORT TERM...LFR LONG TERM...DFH AVIATION...LFR/DFH MARINE...LFR/DFH TIDES/COASTAL FLOODING...lfr

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