Area Forecast Discussion
Issued by NWS Sterling, VA

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635 FXUS61 KLWX 151906 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 306 PM EDT Sat Jul 15 2017 .SYNOPSIS...
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Weak high pressure over the midwest will control the weather through Sunday. An upper level trough will affect the weather Monday. Another cold front may approach the region by the end of the week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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High pressure still west of the mountains. A cumulus field has developed in response to a rather weak 500 mb trough axis. Any instability is capped though, aside from perhaps the Chesapeake Bay. Earlier showers well east over the Delmarva though. The rest of the afternoon will be dry, as will the evening hours. Cold advection will continue for several more hours, although the maximum effect has already been realized, with dewpoints in the lower-mid 60s. Low temperatures overnight will be in that range, although a bit higher downtown DC/Baltimore.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
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Flow will slowly become southerly again Sunday, which will permit a pinch of moisture/instability return. Given terrain circulations and isentropic lift, there is an outside chance that a shower or thunderstorm could develop by the end of the day Sunday. Elevated instability (decent mid level lapse rates) will continue into Sunday night as warm advection ensues, and have kept a slight chance of showers/thunderstorms through the night. Monday`s forecast guidance reflects a considerable amount of spread. However, heights will be dropping as another trough axis shifts across the Mid-Atlantic. That much is consistent. Therefore believe it reasonable that there will be at least a chance of showers/thunderstorms in a marginally unstable atmosphere. However, activity may be scattered in nature as shear weak and insolation questionable, and thus have backed off on the upper end of PoPs slightly. Temperatures near climo through the period.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/...
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Main feature across the United States for the upcoming week will be a large upper level ridge that will shift from the inter-mountain west and into the central US. A lingering upper level trough will still be overhead on Tuesday with chances for some scattered showers and thunderstorms. This will gradually diminish into Wednesday as the western upper ridge builds into the plains states and a second ridge builds westward over the Atlantic. There may still be a few showers/thunderstorms into Wednesday. By the end of the week, a more westerly flow will develop as the ridge builds to our south/west with large scale troughing over Canada. This will likely keep the area in an active pattern along the gradient. Temperatures during the week will trend back up above normal, but nothing unusual for mid Summer, with highs back up into the 90s.
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&& .AVIATION /19Z SATURDAY THROUGH THURSDAY/...
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VFR through the valid TAF period, with diurnal clouds and northwest winds. Any fog would be valley based. Do not anticipate impact at any terminal. If there were, CHO would be the first candidate. Southwest flow will gradually develop during Sunday. There may be a stray shower or thunderstorm late Sunday-Sunday night, but confidence low and coverage would be slim anyways. A better chance at thunderstorms will arrive on Monday as an upper level disturbance crosses the area. Flight restrictions possible in vicinity of any thunderstorms. Predominantly VFR expected Tuesday and Wednesday,, although there will be chances for scattered showers/thunderstorms.
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&& .MARINE...
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Winds beginning to relax across the waters. Have cancelled a portion of the Small Craft. Obs in the remainder suggesting 15-20 kt gusts, which should end before the 5pm expiration. Light winds tonight and Sunday with high pressure, then return southerly flow will begin Sunday night into Monday. Will have to keep an eye on channeling potential, but otherwise confidence is low on SCA conditions being reached. Sub-SCA conditions expected Tuesday and Wednesday. A few showers/thunderstorms are possible.
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&& .TIDES/COASTAL FLOODING...
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Southerly flow developing across the region as high pressure shifts offshore will start to build anomalies Sunday, with minor flooding at high tide possible at our most vulnerable sites (most likely Straits Point) by Sunday PM. This would likely continue into Monday. This could become a bit more widespread by Monday night-Tuesday morning.
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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 5 PM EDT this afternoon for ANZ534- 536-537-543.
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&& $$ SYNOPSIS...HTS NEAR TERM...HTS SHORT TERM...HTS LONG TERM...MJM AVIATION...HTS/MJM MARINE...HTS/MJM TIDES/COASTAL FLOODING...RCM/HTS

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