Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 161913 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 313 PM EDT Wed Aug 16 2017 .SYNOPSIS... High pressure over the region will slowly move east off the coast tonight. A warm front will move northward Thursday into Thursday night followed by a cold front that should pass through the region Friday night. Weak high pressure will build into the area over the weekend. && .NEAR TERM /THROUGH TONIGHT/... Current analysis depicts a slow moving cold front pushing gradually southward across the region. This front will stall just to the south tonight as high pressure slides east off the coast. Low level moisture remains plentiful this afternoon, with plenty of heating, but dry air is very abundant aloft, so any showers or t-storms today should be isolated at best. Expect them to generally diminish by sunset or just after. Overnight, warm advection will develop aloft, resulting in an increase in mid-level clouds. Some lower level clouds may also linger tonight below the capping inversion near 750 mb. Add in the fact that most places will turn out dry all day, and the risk of fog should be much reduced. Have included patchy fog for many areas, mainly in the valleys, but at this point do not expect another widesprA light northerly flow allowed anomalies to drop this morning. However...southerly winds will increase for Thursday through Friday night ahead of a cold front. Minor tidal flooding is possible near high tide Thursday night into Friday morning and again Friday night into Saturday morning for sensitive areas. ead fog event. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... Boundary will slowly move northward back across the area during the day Thursday. PW`s will surge signifiacantly, with values likely to be above 2 inches by late afternoon. A weak shortwave and vort max will also cross the region. However, cloud cover will be abundant, limiting CAPE availability somewhat. The result in soundings is a skinny CAPE profile, more suggestive of a heavy rain/flash flooding threat than a severe threat, but the latter can`t be completely ruled out given around 25 knots of shear. With the clouds, temps should end up a little cooler than yesterday, but still a very warm and sticky day. After the trough/max passes and insolation wanes, expect precipitation to wind down during the evening, but with a very moist environment, a few showers may linger. With the clouds and high humidity, lows will stay very high, with 70s being widespread. Any areas that see a little clearing might see some patchy fog. Friday the next cold front approaches. With more opportunity for sun early in the day and cooling aloft, CAPE should be more plentiful, with shear increasing to around 30 knots. This should result in more of a severe threat versus flash flood threat, though with PW`s still over an inch and a half, any cells that trains could still pose a flood risk. With more sun, highs should approach if not reach 90 in the warmer spots. Front passes across the region at night, with chance of precip rapidly declining. However, warmth and moisture at low levels will be slower to exit, with lows likely in the 70s near I-95, cooler in the mountains. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... A cold front will be stalling to our southeast as a weak high pressure builds over our area on Saturday. Upper level energy could bring some showers Saturday night, with dryness returning on Sunday. High pressure moves offshore as the front slowly pushes away from us and stall over the Carolinas Sunday into Monday. Southerly flow will advect humidity into our area with increasing temperatures into Monday. A pressure trough could enhance afternoon showers and thunderstorms Monday into Tuesday. A cold front will approach from the west on Wednesday with additional showers and thunderstorms possible. High temperatures will be in the mid to upper 80s... some 90s and 70s at higher elevations. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... VFR overall through the TAF period. An isolated shower may affect a TAF site this afternoon and evening, but vast majority of region should be dry. Concern exists for patchy fog overnight, but we don`t expect the kind of widespread IFR cigs and vis that we had this past morning, as incoming mid clouds and a prior dry day should keep fog from being nearly as widespread. Some reductions are still quite possible, however. Main concern Thursday and Friday will be thunderstorms, mostly during the afternoon and early evening hours, which could result in brief intervals of IFR cigs and vis, along with gusty winds. VFR conditions expected Saturday into Monday, with short periods of sub-VFR conditions Saturday night and maybe Monday afternoon due to possible showers and thunderstorms. && .MARINE... Sub-SCA at presnt, but approaching cold front later Thursday into Friday looks likely to bring southerly channeling to the bay and lower Potomac. SCA raised starting late Thursday and likely will need to be extended through Friday. Other marine concern will be thunderstorms each of the next two days (not likely today), with gusty winds a concern. Mainly dry conditions expected Saturday into Monday, with periods of showers and thunderstorms possibly developing Saturday night and Monday afternoon. Wind gusts are expected to stay below the small craft advisory threshold. && .TIDES/COASTAL FLOODING... Anomalies have declined today, but return of southerly winds will bring rising anomalies back to the region on Thursday, with potential minor flooding at sensitive sites by Thursday afternoon/evening and continuing into Friday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 4 PM Thursday to 6 AM EDT Friday for ANZ533-534-537-541-543. && $$ SYNOPSIS...RCM NEAR TERM...RCM SHORT TERM...RCM LONG TERM...IMR AVIATION...IMR/RCM MARINE...IMR/RCM TIDES/COASTAL FLOODING...RCM

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