Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 210800 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 400 AM EDT Wed Jun 21 2017 .SYNOPSIS... High pressure will be perched west of the area through Thursday. A cold front will cross the area Friday into Saturday, with tropical moisture streaming into the Mid Atlantic. && .NEAR TERM /THROUGH TONIGHT/...
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Frontal zone hasn`t moved very far this morning. Dew point analysis shows gradient across eastern parts of the area, though better moisture aloft is just to the southeast. This is where the showers reside, which may clip southern MD until mid-morning when moisture axis begins sliding southeast. Elsewhere, the day will start with a veil of cirrus. Attention then turns to a trough axis which will drop southward from the Great Lakes this afternoon. Better forcing will generally be north of the area, but it does appear that some scattered showers and thunderstorms will move southeast from PA. Instability will be weak and shallow, and thus thunder is not given. However, deep layer shear will be plentiful with a deep mixed layer, so any organized clusters/taller storms could pose a gusty wind threat. Think this threat will be confined to far northern areas (aligned with SPC marginal risk). There is some uncertainty with the southern extent of showers, and while I have expanded some low end POPs to the south, am thinking anything near/south of US-50 will be in the form of dissipating showers during the late afternoon/early evening given instability depth is even less with southward extent. Activity should be diurnal, with dry conditions after midnight as weak high pressure builds in from the west. Highs today will reach the mid to upper 80s with overnight lows in the 60s...except staying in the 70s for the metros/bayshore.
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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Whatever is left of the trough axis/front will lift back to the north on Thursday. This should lead to warmer temperatures, perhaps exceeding 90 in some locations. Theta-e advection combined with terrain circulations may be enough to pop a few showers and storms over the mountains. Forecast details are beginning to come into focus with the tropical moisture influx and remnants of Cindy, though some timing and location differences still exist. Leading shortwave will be rounding the ridge to our southeast Thursday night. Good moisture transport should bring some showers to at least the mountains overnight, then potentially overspreading most of the area Friday morning. There may be some subsidence behind this wave, so there are some questions whether destabilization will take place and how much shower/storm activity will occur Friday afternoon and evening. Will maintain high chance to likely POPs though. A cold front will approach from the northwest Friday night. This front will also be steering the remnants of Cindy. Based on current progs, shower chances will increase again toward dawn Saturday. Will have to monitor for heavy rain potential and placement of these features, as precipitable water values will increase near or above 2 inches with high warm cloud depths. Diurnal temperature ranges will be muted Friday with clouds and the moist airmass with highs in the 80s and lows in the upper 60s to 70s.
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&& .LONG TERM /SATURDAY THROUGH TUESDAY/...
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Main concern Saturday is what happens to Tropical Storm Cindy`s remnants. Guidance seems to be sending the circulation to our south, but that doesn`t mean it couldn`t deviate (north or south) or that its moisture would bring minimal effects to our region even if we had just a glancing blow, since there will be an extratropical interaction ongoing. Bottom line is that heavy rain is possible, especially in southern parts of the CWA, but remains highly uncertain. Cooler air moves in behind the cold front Sunday into early next week. Another wave of low pressure may affect the region Monday or Monday night.
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&& .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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Weak trough axis will drop south into the area this afternoon. Better forcing for showers and storms will be to the north, i.e., MRB to Baltimore. However, with weak instability, isolated thunder forecast doesn`t warrant a TAF mention at this time. Less of a chance of precipitation on Thursday, especially at the terminals. Tropical moisture will enter the area early Thursday, and will persist through Friday night when a cold front and remnants of Cindy will approach the area. Will have to monitor for heavy rain and thunderstorm potential and reduced aviation conditions depending on the track of these features. Sub-VFR possible Saturday as remnants of Cindy interact with a passing cold front, with heavy rain possible. VFR likely Sunday with high pressure. Another wave of low pressure may bring showers Monday, but reductions look less probable or severe.
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&& .MARINE...
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Only a few gusts have met SCA criteria overnight, with a further weakening trend after sunrise. Trough axis may bring a few showers and perhaps a thunderstorm to the area late this afternoon into early evening. Winds may increase a bit again tonight over the southern MD waters, but do not appear to warrant a SCA at this time. Weak high pressure will arrive on Thursday. Gradient begins to increase Thursday night and especially Friday as cold front from north and remnants of Cindy approach. SCA is likely based on current guidance. Some periods of moderate to heavy rain and thunderstorms are also possible. Cindy`s remnants interacting with a cold front could result in SCA conditions Saturday, with SCA possible into Sunday as high pressure builds in behind the front.
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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 early this morning for ANZ534-537-543.
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&& $$ SYNOPSIS...RCM NEAR TERM...ADS SHORT TERM...ADS LONG TERM...RCM AVIATION...ADS/RCM MARINE...ADS/RCM

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