Area Forecast Discussion
Issued by NWS Sterling, VA

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607 FXUS61 KLWX 230752 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 252 AM EST Tue Jan 23 2018 .SYNOPSIS...
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A cold front will cross the area today. High pressure will build over the area during the second half of the week, then move offshore this weekend as another cold front approaches.
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&& .NEAR TERM /THROUGH TONIGHT/...
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The Mid-Atlantic is solidly in the warm sector of vertically stacked low pressure located over the Great Lakes early on this January morning. Dew points are surging through the 40s and should make it into the 50s ahead of an approaching cold front. A broken line of showers and embedded thunderstorms has been moving eastward across West Virginia overnight. Hi-res guidance has this line weakening as it crosses the mountains, with embedded convective elements re-developing in a larger area of showers that develops east of the mountains. Hints of this are already coming together over central North Carolina. Given the highly unusual warm and humid airmass, moderately strong forcing for ascent and low level wind fields in excess of 50 knots, believe a broken line of heavy showers and thunderstorms should re-invigorate as it crosses the Blue Ridge mountains this morning. This line could be accompanied by isolated surface gusts of over 50 mph with spotty wind damage possible. HRRR guidance has sped up the timing of this line and have trended the forecast in this direction, clearing the I-95 corridor by early afternoon. Dry air racing in aloft should result in a mostly sunny sky by mid to late afternoon for much of the CWA. Winds will shift from south to west and gust to around 30 mph. The cold airmass lags a bit behind the front, so with some sun and downsloping flow, temperatures are expected to once again rise well into the 60s. As the upper trough lifts out to the northeast, upslope snow showers are expected tonight. Flow is blocked, so I don`t think there will be much east of the ridges. But along the western slopes of the Allegheny Front, there will likely be about 1 to 3 inches of snowfall through the night. Elsewhere, dry conditions are expected with more seasonable temperatures (20s and 30s).
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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As the main upper low departs to the northeast Wednesday, a secondary vort max pivots in from the west and reaches the area by nightfall. Believe this will result in a partly sunny day with cumulus floating across ahead of the trough. Another light round of upslope snow showers seems likely (an inch or less) Wednesday evening as the trough axis moves across. 850 mb temperatures of around -8 C and decent mixing should result in high temperatures generally in the 40s (25-30 for the ridges). A secondary pressure surge will probably keep winds up a bit in the evening even in the lowlands, but as high pressure builds overhead toward daybreak Thursday, would expect winds to go light in the valleys allowing for some radiational cooling. Have leaned toward the lower end of guidance for lows in the valleys for this reason. Ridging at the surface and aloft moves overhead Thursday with seasonable temperatures and some high clouds spilling over the ridge expected. Light winds and a mainly clear sky with dew points in the teens should allow temperatures to fall into the 20s Thursday night, possibly lower in a few spots.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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High pressure will remain atop the forecast area Friday. That should translate to nearly clear skies. Temperature-wise though, the thermal trough will start to pull out, but doubt the warm advection aloft will have a tangible effect at the ground so highs will still be in the 40s to near 50. Lows Friday night will be a bit warmer than Thursday night...near freezing. No significant weather Saturday either, as the high moves east and warm advection becomes stronger. The isentropic lift will lead to increasing cloud cover and highs in the 50s. There is a small chance that this lift could lead to some light rain, but those PoPs (30%) will be confined to the mountains. A better chance of precip will come Saturday night into Sunday night...especially during the day Sunday...as a cold front drops across the area. Most of this should be rain. The only question will be whether precip can exit before cold air arrives. Usually it can, but at this time frame there is limited skill in details. Theres not a ton of cold advection behind this front. While temperatures will be cooler once again, anticipating the result to be near climo.
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&& .AVIATION /08Z TUESDAY THROUGH SATURDAY/...
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IFR conditions expected for most if not all terminals for a time this morning mainly before 14-15z. An area of showers with an embedded line of heavier downpours/possible thunder will move from SW to NE during this time. This line may be accompanied by brief gusty surface winds of greater than 35-40 kts. Otherwise, expect LLWS of about 40-45 kts through 2 kft. Winds generally south 10-15 kts gusts 20-25 kts outside of SHRA/TSRA. LLWS decreases and conditions rapidly return to VFR by 15-18z. Winds shift to W 10-20 kts G 25 kts until around midnight. VFR Wed-Thu with NW flow 10-15 kts, gusty at times especially Wed aft/eve. VFR conditions Fri-Sat under high pressure. Flight restrictions could arrive Sat night in rain ahead of a cold front.
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&& .MARINE...
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Sporadic SCA gusts are gradually becoming more widespread as of early this morning. Expect this trend to continue ahead of an approaching cold front. A broken line of showers and thunderstorms is expected to cross the waters late this morning, and could be accompanied by stronger gusts in excess of 30 kts. A few SMWs may be necessary. Held off on a Gale Warning due to relatively cool water and poor mixing on warm S wind. W winds expected behind cold FROPA this afternoon, with SCA gusts expected for all waters until around midnight. As diurnal mixing decreases, wind gusts likely confine themselves to the open waters during the late overnight, before making a cameo during the day Wednesday. Gusts likely persist into Wednesday evening before becoming light late as high pressure moves in. Light winds Friday will increase Saturday ahead of a cold front. However, cool water should keep gusts below Small Craft Advisory thresholds.
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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 midnight EST tonight for ANZ530>532- 535-536-538>542. Small Craft Advisory from 8 AM to 7 PM EST Wednesday for ANZ530>532-535-536-538>542. Small Craft Advisory until 7 PM EST Wednesday for ANZ533-534- 537-543.
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&& $$ SYNOPSIS...DHOF NEAR TERM...DHOF SHORT TERM...DHOF LONG TERM...HTS AVIATION...DHOF/HTS MARINE...DHOF/HTS

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