Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 251904 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 304 PM EDT Fri May 25 2018 .SYNOPSIS...
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High pressure will linger offshore of the North Carolina Coast through the weekend. A trough of low pressure and several weak disturbances will move over the region during the weekend into early next week. A cold front should push across the area Tuesday. A low pressure system may approach from the south during the middle of next week.
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&& .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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With high pressure sitting offshore of the North Carolina Coast, a persistent south to southwesterly wind will continue to bring warm and humid air into the region the remainder of today and tonight. Temperatures are pushing through the middle 80s and could reach close to 90 in a few spots. Dewpoint temperatures, indicating rich moisture, are in the lower to middle 60s in many places. With moisture in place and a cumulus field persisting over the higher terrain in the west, a few showers or a rumble of thunder cannot be ruled out later this afternoon into early this evening. The main threat will be downpours. Around sunset and beyond into tonight, this or any activity should diminish and weaken. Lows tonight will bottom out in the 60s to lower 70s.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
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The weekend will become unsettled with the potential for slow-moving thunderstorms to develop and bring locally heavy rainfall ahead of and then along a slow-moving cold front and associated upper level energy. Not all locations will encounter these thunderstorms as coverage will not be as crucial as intensity, but those locations receiving one of these thunderstorms could encounter very heavy rain in a short period of time, lightning, and a brief wind gust over 40 mph. Precipitable water values approaching 1.8 to 1.9 inches indicates a lot of moisture to work with should one of these thunderstorms feed off of this moisture. Recent antecedent conditions of a wet ground from several inches of rain during the last week or so will leave us on our toes at heavy rainfall with thunderstorms each afternoon. We should remain cognizant of the potential for flooding in any heavier thunderstorms. Wind shear generally 20 to 25 knots indicates that perhaps wind won`t be a huge factor Saturday and Sunday; however, downbursts of rain-cooled air could pose a threat in the stronger thunderstorms. A few showers or a thunderstorm could linger later into the evening hours each day as weak energy pulses push eastward from the Ohio Valley.
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&& .LONG TERM /MONDAY THROUGH FRIDAY/...
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A warm front is forecast to be to our north over eastern PA and Northeastern MD. The 12Z GFS model has backed off on PWAT values over Maryland and Northern Virginia on Monday. PWAT`s are forecast to be in the 1.3 to 1.6 inch range. GFS and NAM have decreased the chances for showers on Monday. Everything suggest that there would likely only be a chance of showers on Monday with thinning cloud cover. Tuesday a cold front will approach from the west and move through the region. Scattered showers and thunderstorms will be possible. Temperatures are expected to be in the upper 70s to mid 80s on Monday and then jump up into the upper 80s to low 90s on Tuesday. A high pressure system will build into the region on Wednesday from the northwest. A southerly 850mb flow will advect in moist tropical air into the region leading to rise dew points and precipitable water values. The increased moisture is being fueled by the flow from the Gulf and a possible tropical storm moving into the Mississippi/Louisiana area. Increasing moisture in the region will lead to the chance for unsettled weather in the form of showers and storms Wednesday through Thursday. The exact path and timing of the tropical storm is unknown and will likely play a major part in what kind of weather we will experience late next week.
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&& .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
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VFR conditions through tonight as high pressure lingers offshore. Although clouds will be increasing during the next 12 to 18 hours, there could be some patches of fog in a few places in the Shenandoah Valley or Virginia Piedmont. A southerly flow of around 10 knots or less expected at all terminals through tonight. VFR conditions again for all terminals during the weekend. A warm and humid airmass combined with weak disturbances and a weak cold front will lead to the potential of showers and thunderstorms Saturday and Sunday, favored during the afternoon and early evening. Impacts will likely be brief, with heavy rain the main threat. Fog could occur overnight in locations that receive rain if skies clear. On Monday, skies will remain mostly cloudy with some thinning cloud layers as we move later in the day. Scattered showers will be possibles with winds of 5 to 15 knots out of the south to southwest. Tuesday, A frontal boundary will move through from the west leading to showers and thunderstorms.
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&& .MARINE...
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A small craft advisory is in effect for the main stem Chesapeake Bay through late tonight and early Saturday morning as we see some southerly channeling taking place in this region. Winds should stay in the 10-15 kt range during the day. Winds may also be marginal on Saturday, but still some uncertainty remains for any advisory. The larger threat may come from thunderstorms during the afternoon and evening. Sub-SCA conditions are expected on Sunday too, though showers and thunderstorms will become likely again during the afternoon and evening. Showers and thunderstorms will be possible both Monday and Tuesday with the best chance being Tuesday. Winds will be mainly out of the south to southwest leading to winds of 5 to 15 knots. A small craft advisory may be needed both Monday and Tuesday.
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&& .TIDES/COASTAL FLOODING... Water levels remain slightly elevated at Washington DC, though trends in the anomalies suggest minor flooding will be a low threat. It will be close for the next several cycles though. No coastal flooding issues are expected elsewhere. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 8 AM EDT Saturday for ANZ533-534- 543.
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&& $$ SYNOPSIS...KLW NEAR TERM...KLW SHORT TERM...KLW LONG TERM...JMG AVIATION...KLW/JMG MARINE...KLW/JMG TIDES/COASTAL FLOODING...KLW

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