Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 310759 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 359 AM EDT Sun Jul 31 2016 .SYNOPSIS...
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An area of weak low pressure will track eastward across the area today. A cold front will move southward on Monday as the low moves offshore. High pressure will build in from the north during the middle of the week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Please see the latest flood statements for the latest information on floodwaters working downstream due to the very heavy rain last evening between DC and Baltimore. The other concern first thing this morning is fog in a humid and stagnant airmass. The CWA is divided, with more fog to the SW and more low clouds to the NE. Several sporadic obs have hit 1/4SM, so will need to continue to monitor for a short fuse Dense Fog Advisory. The pressure pattern is weak across the area, with lower pressure extending from the Mid-Atlantic to the Ohio Valley. Broad upper troughing is located over the Ohio Valley. Both of these features will push eastward today. Other than an isolated shower, most of the morning hours should be dry. Convection should initially fire along the terrain and then push east during the mid to late afternoon. There seems to be consensus that the best coverage of storms will be to the south of the track of the weak low, and with a ridge of higher theta-e air. This is generally SW of the DC metro, although storms could push northward toward the Chesapeake Bay during the evening as the theta-e ridge expands slightly. In terms of parameters, today appears to have less potential to be hazardous. Deep layer shear and PWAT are both lower than Saturday. NCAR Ensemble Max QPF is also lower than yesterday and focused in the above-mentioned area across the southern CWA. With potential for sun for part of the day, highs will again push toward 90. Even though there should be a diurnal downturn to precip, with the baggy low near the area, some showers may linger into the night, especially to the east. Lows generally in the mid 60s to lower 70s.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
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The broad, weak surface low doesn`t make a whole lot of progress eastward on Monday, although NW flow on the back side will begin to advect some slightly drier air into the area. However, the mid-level trough axis will be approaching with an embedded vort max. Therefore, some scattered showers and storms could develop during the afternoon and evening. Shear and instability should be low enough that severe weather isn`t a concern. This activity will diminish during Monday evening. On Tuesday, the drying trend should be more pronounced as the low moves farther offshore and NW flow becomes established. However, mid- level trough will be sharpening over New England, and this could provide enough energy for a shower or storm near the Chesapeake Bay. Cooler air will continue to move into the area Tuesday night.
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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Troughing departs on Wednesday and heights begin to rise. Some guidance is continuing to hint at the potential for some energy/convection to move into the area on NW flow around the periphery of another building central US ridge. However will continue to downplay for now given difficulty of pinpointing these convective systems days in advance, and tendency of them to curl southward into greater instability. Will run with a mainly dry forecast, however an isolated shower/storm possible in the higher terrain as high pressure begins to move offshore and light return flow develops. Highs in the 80s and dew points in the 60s. Ridging continues to build in from the southwest Thursday and Friday, and with that will come warmer temperatures and a return in moisture. Could be some isolated to scattered convection on either day, especially higher terrain. Highs nudge back up towards or above 90F. The next cold front will approach and cross the area next weekend. Thus Saturday looking warm/humid with increased chances for showers/thunderstorms.
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&& .AVIATION /08Z SUNDAY THROUGH THURSDAY/...
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IFR or lower conditions will remain possible through sunrise -- in low clouds around DC/Baltimore, and in fog at MRB/CHO. Much of today should feature VFR conditions with light SW winds. Scattered showers and storms will be possible again today, but less widespread and less intense than Saturday. CHO will have the highest chance. Best time frame will be mid afternoon to evening. Low confidence in any fog tonight, so will not include a mention for now. A few storms will be possible again on Monday as a trough axis swings through, but coverage even less than Sunday. Light west flow on Monday will become northerly on Tuesday as low pressure moves offshore. Tuesday should be dry. Predominantly VFR expected Wednesday and Thursday. Only restrictions would come in some patchy fog at night/early morning and any isolated-scattered showers/thunderstorms Thursday.
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&& .MARINE...
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Variable flow will become S/SW today. Generally expecting winds 10 kt or less, but could increase to 15 kt this evening. Scattered storms will be possible from mid afternoon to the evening, so locally higher gusts will be a concern. Flow becomes W on Monday, then N on Tuesday. Will continue to mention potential for SCA conditions during this period, although current guidance suggests it will be very borderline. Storm threat even lower for Monday and lower still on Tuesday. Sub-SCA winds expected Wednesday. Winds may increase out of the south Thursday and approach SCA criteria. A few showers/thunderstorms possible Thursday as well.
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&& .TIDES/COASTAL FLOODING...
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Tidal anomalies have risen back to around a foot above normal, and this is causing some minor flooding early this morning, most notably at Annapolis. Once this morning`s high tide cycle is complete, no additional flooding is anticipated today, however tonight`s/early Monday morning`s high tide cycle may produce additional minor flooding, mainly at Annapolis.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Coastal Flood Advisory until 8 AM EDT this morning for MDZ014. VA...None. WV...None. MARINE...None.
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&& $$ SYNOPSIS...ADS NEAR TERM...ADS SHORT TERM...ADS LONG TERM...MM AVIATION...ADS/MM MARINE...ADS/MM TIDES/COASTAL FLOODING...MM

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