Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 240245 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1045 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 /UNTIL 6 AM TUESDAY MORNING/...
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Frontal boundary resides from Ohio through KHTS to western South Carolina at this time. A solid line of showers resides east of there...across the Potomac Highlands through central Virginia and into North Carolina...in a zone of 50+ kt effective shear. Instability, on the other hand, remains quite a challenge. There is almost none (23 j/kg MUCAPE or 1 j/kg MLCAPE) from the 00z IAD RAOB with a capping inversion at 800 mb. Winds have not been mixing down at all. Even where instability, and convective development, is better...mixing has been problematic. Guidance suggesting that there will be another surge in the low level jet between 11 pm and 2 am. This is coincident with the enhanced radar echoes entering Virginia. Therefore, the threat for isolated thunder has not ended. The big question is whether anything will mix to the surface. Would not bank on it, but at the some time cannot completely rule it out either. The shear axis has passed east of Nelson County, so the Tornado Watch has been dropped. In addition, have made adjustments to the Wind Advisory. Still believe that the ridges vulnerable to the low level jet bumping into it. But, given the poor mixing, have removed the I-95 corridor. Further, since the jet will be east of the Blue Ridge, hav cancelled the Advisory for points west.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/... 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. && .LONG TERM /THURSDAY THROUGH MONDAY/... 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. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/...
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Shallow line of convection will move across terminals tonight between 03Z-09Z. Am keeping flight restrictions at MVFR at thsi time. There may be local IFR restrictions, but confidnece low in when/where. Thus far, wind gusts havent made it to the ground either, and will be reducing gust forecasts to 30-35 kt max. Mainly VFR expected late in the week with light flow.
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&& .MARINE... 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. && .TIDES/COASTAL FLOODING... Water levels have increased with the incoming tide up the Chesapeake Bay. Departures have risen to around 1 ft, which would be problematic for Baltimore City/County. Have added them to the Advisory for tonight`s tide cycle. Uncertainty as to how much surge will reach Havre de Grace remains (ESTOFS output overdone) so have kept peak tide under Advisory levels. The margin of error straddles that threshold. An Advisory remains in effect for Annapolis tomorrow. Would not rule out other sites as well. (SNAP-Ex suggests Baltimore should be included.) However, there is copious uncertainty as well. Hopefully we will work some of those issues out once the current tide cycle passes. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Wind Advisory until 6 AM EDT Tuesday for MDZ004>006-503-505- 507-508. Coastal Flood Advisory until 1 PM EDT Tuesday for MDZ014. Coastal Flood Advisory until 2 AM EDT Tuesday for MDZ011. VA...Wind Advisory until 6 AM EDT Tuesday for VAZ037>040-050-051- 501-502-505-507-508. WV...None. MARINE...Gale Warning until 8 AM EDT Tuesday for ANZ530>533-535>542. Small Craft Advisory from 8 AM to 6 PM EDT Tuesday for ANZ530>533-537>542. Gale Warning until 3 PM EDT Tuesday for ANZ534-543.
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&& $$ SYNOPSIS...LFR NEAR TERM...HTS SHORT TERM...LFR LONG TERM...DFH AVIATION...LFR/HTS/DFH MARINE...LFR/HTS/DFH TIDES/COASTAL FLOODING...

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