Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 170754 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 354 AM EDT Tue Jul 17 2018 .SYNOPSIS...
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A cold front will approach the area today before passing through tonight. High pressure will return for Wednesday and Thursday before moving offshore Friday. Low pressure may impact the area during the weekend.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Skies are mainly clear overnight. A light south to southwest wind exists in a couple spots. Lows will range in the 70s across the region. Dewpoint temperatures are in the middle to upper 60s to around 70 in some places. This translates to high humidity and a sticky airmass in place overnight. A surface cold front, currently elongated with Lake Erie, will approach the mountains this morning, and cross the area later today. Most guidance solutions suggest that the front will be near the I-95 corridor between 22z and 00Z, suggesting that the afternoon hours will be the most active. Sufficient instability will be able to stream north ahead of the front. However, the slightly earlier timing and better forcing north of the area should preclude numerous/damaging wind gusts. Nonetheless, enough low level convergence/lift present for likely PoPs beginning late morning. Most convection will be pushing east of the Chesapeake Bay this evening. We should encounter widespread drier air late this evening and mainly after midnight into the predawn hours Wednesday.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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Lower dewpoint temperatures, thus dry air, will continue to advect southward Wednesday as high pressure builds from the Great Lakes. Wednesday`s highs will be upper 70s-mid 80s, with dewpoints around 60F. High pressure will move overhead on Thursday. Dry weather and well below normal humidity levels expected Thursday and Thursday night. Dewpoint temperatures will be in the 50s Thursday.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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High pressure over New England will shift off the coast during the day on Friday, resulting in a southeasterly flow over the area and dry conditions. The southeasterly winds will help pump in a bit more moisture off the Atlantic, with dewpoints rising in to the middle 60s by the end of the day. Some showers/thunderstorms will be possible late Friday and Friday evening along our far western zones as the eastern periphery of an upper level low over the Great Lakes approaches from the west. Do think much of the CWA stays dry during the day on Friday, with any activity waning overnight Friday. Highs on Friday will top out near or slightly below normal in the mid to upper 80s, while lows Friday night will range from the middle 60s to near 70 degrees as clouds will be on the increase. The upper level low and associated trough will swing further eastward on Saturday, bringing increased shower and thunderstorm chances. Current model guidance favors the latter half of Saturday and into Sunday to carry the highest precipitation chances as moist warm air advection and veering winds aloft increases, as well as vorticity maxima passing overhead. Low pressure over the Great Lakes will stretch a trailing cold front just to our west Saturday night into Sunday, as a warm front lifts into our area. The ECMWF depicts a coastal low garnering support from the upper level jet and traversing the Delmarva during this time period. Details will need to be ironed out the next few days, but at this time, above normal rain chances looking more likely this weekend. The upper level low/trough will park is self overhead on Monday, keeping unsettled weather across the region. Slightly below normal temperatures expected during this time period as a result of the increased rain chances and ample cloud cover.
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&& .AVIATION /08Z TUESDAY THROUGH SATURDAY/...
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Showers/thunderstorms will become more numerous today, possibly beginning as soon as late morning...especially for MRB, and then gradually cross the terminals. The back edge should push east late afternoon...perhaps early evening for DCA/BWI/MTN. While it won`t be raining the whole time (probably less than 50% for the time), flight restrictions as well as gusty winds possible within any storm. Have opted not to include many restrictive details in the TAF at this time due to confidence uncertainties in specifics. VFR flying conditions will be favored on Friday at all terminals with high pressure over the New England coastline delivering a light southeasterly flow and mainly dry conditions. Showers and thunderstorms are a possibility at MRB late in the day on Friday, but confidence in this occurrence is low at this time. A better chance of showers and thunderstorms, and ultimately sub VFR conditions, will be realized the latter half of Saturday into Sunday as a trough of low pressure approaches from the west. South southeasterly winds at 10 knots or less will prevail this weekend.
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&& .MARINE...
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Southerly flow is expected to continue overnight. A Small Craft Advisory is in effect through early this morning for the mid Bay/lower Potomac. Additionally, a longer period Small Craft Advisory is in effect around mid-afternoon today through late morning Wednesday for the advancement of a cold front across all waters. Showers and thunderstorms are expected to impact the waters. Some storms could be strong, producing gusty winds and the need for Special Marine Warnings. High pressure over the New England coastline Thursday and Friday will promote a light to gentle southeasterly breezes across the waters, with sub SCA conditions forecast. Gradient increases on Saturday and Sunday as a warm front lifts northward through the waters and a trough of low pressure approaches from the west. As a result, SCA wind gusts will be possible for the duration of the weekend, as well as increasing chances for showers and thunderstorms.
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&& .TIDES/COASTAL FLOODING...
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Water levels continue to run between one-half and three-quarters of a foot above astronomical normals. Do not anticipate any minor flooding concerns over the next several tidal cycles, but Caution Stage will be plausible at Annapolis and the Baltimore Harbor during high tide this morning and again this evening.
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&& .CLIMATE...
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The high temperature at Ronald Reagan Washington National Airport (DCA) on Monday was 98 degrees. This now stands as the warmest temperature observed in 2018 at DCA, besting the high temperature of 97 degrees observed on July 3rd. The last time temperatures reached 98 degrees or warmer at DCA was on July 20th 2017 when a high temperature of 98 degrees was also registered. Weather records for the Washington DC area have been recorded at what is now Ronald Reagan Washington National Airport since 1941. The official weather record consists of that data back to 1945, and observations taken in downtown Washington from 1871 through 1944.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 2 PM this afternoon to 11 AM EDT Wednesday for ANZ530>543. Small Craft Advisory until 9 AM EDT this morning for ANZ532>534-537-540-541-543.
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&& $$ SYNOPSIS...KLW NEAR TERM...KLW SHORT TERM...KLW LONG TERM...BKF AVIATION...BKF/KLW MARINE...BKF/KLW TIDES/COASTAL FLOODING...BKF CLIMATE...BKF

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