Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 230017 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 817 PM EDT Mon May 22 2017 .SYNOPSIS... Low pressure will track off the Mid Atlantic coast this evening with a frontal boundary dropping into the Carolinas. This front will lift back north into the region late tonight into Tuesday and Tuesday night as a potent low pressure system tracks along the boundary. Unsettled conditions continue Wednesday and Thursday as an upper level trough approaches from the west. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Current surface observations, radar imagery, and satellite imagery depict a compact low tracking newd across the Peninsula. Periods of moderate to heavy rain are possible across the Tidewater and Ern Shore late this aftn through early evening as this system pushes through due to the combination of decent forcing and pw values of +1-2 st dev. QPF of 0.5-1.00" is possible through this evening, with some locally higher amounts. Instability has climbed to 1000-2000 J/kg, but 0-6km bulk shear is generally less than 25kt, so any severe threat has bee localized, and should end by 5 pm along coastal SE VA/NE NC. Temperatures this aftn are mainly in the low/mid 70s, with low/mid 80s across NE NC. The front associated with the low drop back into the Carolinas this evening with some drying aloft as the shortwave aloft and surface low push offshore. PoPs drop below 15% across the N with some partial clearing possible, while mostly cloudy conditions continue S. A chc of rain returns across srn VA/interior NE NC overnight as moisture from the WSW begins to increase along the frontal boundary. Likely to categorical PoPs arrive for the SW corner of the area by daybreak Tuesday. Lows range from the upper 50s to mid 60s. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/... The flow aloft remains SW Tuesday, with another wave lifting newd across the Carolinas during the morning and the Mid- Atlantic during the aftn and evening, with deep layer moisture returning. Categorical PoPs overspread the entire area Tuesday. Categorical PoPs overspread the entire area Tuesday after 12Z for much of the area (and after 15-18Z across the NE). 22/12z NAM/GFS/GEFS/ECMWF/CMC continue to show some differences in timing and location and strength of this wave of low pressure, but the general theme is for a potent system with deep anomalous moisture transport per strong H925-H700 southerly flow and pw values climbing to ~1.75" collocated with the favorable RRQ of a potent 120-130kt jet over the Northeast Conus. The threat for heavy rain and possible flooding will continue to be mentioned in the HWO, and have opted against a flood watch at this time as 6hr FFG is generally 4-6" across much of the area, with some values of 3-4" across the Piedmont and MD Ern Shore. QPF through 00z Wednesday averages 1-3" across the region, and higher amounts are possible. Storm total QPF through Thursday ranges from 1.5-3.5" (tonight through Thursday) The axis of heaviest rain per 12z model consensus is generally in the I- 85/US 360 corridor. The current high temperature forecast shows generally low/mid 70s SE to the upper 60s/around 70 F central and mid 60s far NW. This shortwave/surface low push offshore Tuesday evening. However, 22/12z NAM/ECMWF depict a secondary wave lifting across the srn half of the are 00-06z Wednesday, so have bumped PoPs up to 40-70% S to account for this. Yet another wave approaches from the SW Wednesday aftn as an upper low approaches from the W. This wave tracks across the region Wednesday evening through the early overnight hours bringing another round of likely PoPs along with a chc of embedded thunderstorms. Current 12z guidance suggests the best instability remains offshore. However, the potential for some strong to severe storms will need to be monitored with 500mb height falls and strengthening/veering flow at the 500mb level. Unsettled conditions continue into Thursday with chc to likely PoPs continuing along with a chc of thunder. Mostly cloudy to overcast Tuesday night through Thursday with lows Tuesday night/Wednesday night in the upper 50s to mid 60s, followed by highs Wednesday/Thursday ranging through the 70s. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Trough axis tracks across the region Thursday night as the surface low tracks just north of the region. Will keep mention of chance POPs across the northeast portion of the local area Thursday night. Dry conditions and a clearing sky is forecast Friday as the trough axis and deepest moisture push offshore and westerly flow aloft commences. Temperatures Friday generally around average in the mid to upper 70`s. Upper level flow becomes northwest Friday night and Saturday ahead of an upper level ridge building over the Ohio Valley. A warm front lifts into the region Saturday, providing a focus for showers and thunderstorms, but overall moisture is expected to be limited. Will keep only slight chance POPs for the Piedmont Saturday at this time. Warmer, with highs in the upper 70`s to low 80`s. Better chances for showers and thunderstorms are expected Saturday night as upstream convection develops and tracks along the frontal boundary and into the region. However, spatial and timing differences exist so have capped POPs in the low end chance range. Thereafter, unsettled conditions persist Sunday through Monday as an upper level trough tracks across the Midwest into the eastern CONUS. A great deal of uncertainty exists in the medium range guidance, but it appears moisture return will be limited. Will keep mention of low end chance POPs in the forecast. Highs both days generally in the low to mid 80`s. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... Low pressure and associated precipitation have moved off the coast. Much of the stratus has cleared but some remains including southeast Virginia where ORF continued with an IFR ceiling. A cold front just southeast of the TAF sites will settle a little farther to the south before returning to the north on Tuesday. Low pressure develops along the front and moves northeast across southeast Virginia. The exact track of the low will impact both wind directions and areas of IFR. The lower ceilings will generally occur to the northwest of the track. IFR ceilings are expected to return overnight and especially toward sunrise. Widespread precipitation develops Tuesday morning and continues most of the day. The rain will be heavy at times... reducing visibility. IFR ceilings will be widespread... especially northern and western portions of the area. OUTLOOK...Other low pressure systems will impact the area but not to the extent as the one on Tuesday. Nevertheless...aviation conditions will be reduced at times through Thursday. High pressure builds over the area Thursday night and Friday with drying. Moisture returns with a chance for precipitation developing during the weekend. && .MARINE... Latest surface analysis centers a compact area of low pressure over southeast Virginia/northeast North Carolina with a cold front over the Piedmont. Winds were generally from the east to southeast at or below 15 knots, with a few gusts to around 20-25 knots in convection. Seas average 2-4 feet and waves 1-2 feet. The compact area of low pressure slides offshore this evening, slowly drifting to the northeast. The cold front stalls along the coast. Winds north of the boundary become northerly, and remain west to southwest south of the front with speeds generally at or below 10 knots tonight. Low pressure lifts northeast of the area Tuesday as another area of low pressure develops along the stalled frontal boundary. That area of low pressure lifts across southeast Virginia Tuesday afternoon. Could see an uptick in east to southeast winds Tuesday afternoon ahead of the surface low, but pressure falls are not particularly impressive. Have kept speeds around 15 knots Tuesday afternoon. Have held off on SCA headlines at this time due to low confidence based on differences in guidance and marginal conditions. The low slides offshore Tuesday as the front pushes offshore. Flow becomes north to northwest, but a lack of cold advection results in sub-SCA conditions. Seas could build to 4-5 feet out 20 nm in the northern coastal waters Tuesday night. Again, low confidence so no SCA headlines at this time. Flow becomes onshore Wednesday as another area of low pressure tracks into the Ohio Valley. Seas generally 2-4 feet with speeds of 10-15 knots. The next front pushes offshore Thursday night, with increasing southwest winds Thursday ahead of the front. SCA conditions are possible. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...None. && $$ SYNOPSIS...AJZ/LKB NEAR TERM...AJZ SHORT TERM...AJZ/LKB LONG TERM...SAM AVIATION...LSA MARINE...SAM

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