Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 212009 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 409 PM EDT Sun May 21 2017 .SYNOPSIS... A frontal boundary over the Carolinas will lift north as a warm front tonight into Monday Morning as an area of low pressure tracks across the Mid Atlantic. This front will drop back into the Carolinas Monday night, before lifting back north into the region Tuesday and Tuesday night as a potent low pressure system tracks along the boundary. Unsettled conditions continue into the middle of the week as an upper level trough approaches from the west. && .NEAR TERM /THROUGH MONDAY/... The current surface analysis places 1028mb high pressure over the Srn New England coast with a stationary front near the NC/SC border and a broad area of low pressure over NE GA/NW SC. Mostly cloudy to overcast across the area this aftn with a few breaks mainly across interior SE VA/NE NC and along the Atlantic coast of the Ern Shore. Temperatures across the area range from the mid 60s to low 70s. The aforementioned front lifts N into central VA as a warm front later tonight as an area of low pressure tracks along the boundary. Large scale ascent is initially limited late this aftn/early this evening and moisture is largely confined to the 950-850mb layer, with PoPs aob 20% across the E, and increasing to 20-40% over the Piedmont through 03z. Moisture advection and lift increase overnight with PoPs rising to high chc/likely along and NW of an AVC-RIC-XSA line through 06z, with categorical for the extreme wrn Piedmont, and 20-40% farther E. Likely and categorical PoPs overspread areas NW of the aforementioned line after 06-12z late tonight/early Monday morning, before progressing across central and Ern portions through midday Monday. Periods of moderate to briefly heavy rain are possible from the Piedmont through the MD Ern Shore late tonight through midday Monday due to the combination of decent forcing and pw values of +1-2 st dev, with QPF of 0.5-0.75" possible through Monday. The primary forcing pushes offshore by later aftn, with some lingering showers/tstms possible with PoPs diminishing to 20-40%. Instability is limited (500-1000 J/kg of 0-1km MLCAPE) and 0-6km bulk shear is generally less than 25kt, so any threat of severe tstms is very minimal. Lows tonight range from the 50s NE to the 60s elsewhere, followed by highs Monday in the upper 70s to low 80s. Cloudy tonight through midday Monday with a few breaks possible Monday aftn. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/... The front drops back into the Carolinas Monday night 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, with a 20-30% chc of showers. Lows range from the upper 50s to mid 60s. 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. 21/12z NAM/GFS/GEFS/ECMWF 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 120kt jet over the Northeast Conus. Have continued a mention in the HWO for most of the CWA, and nudged into into the NW counties to account for some uncertainty on the NW fringe, with lower QPF expected SE. The current storm total QPF averages 1.5-2.5", but the 21/12z GEFS does show a mean of 2.5-3.5" for much of the area, so higher amounts are possible. The current high temperature forecast now 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 night, with yet another wave approaching from the SW Wednesday as an upper low approaches from the W. Unsettled conditions continue with chc to likely PoPs continuing along with a chc of thunder Wednesday aftn. Mostly cloudy to overcast with lows Tuesday night in the upper 50s to mid 60s, followed by highs Wednesday ranging through the 70s. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... The deep upper trough across the eastern U.S. will continue to affect the Middle Atlantic into Thursday as there are some indications that the trough may slow down and even become negatively tilted as it moves off the east coast Thursday into Friday. This should keep precipitable water values well above normal with an upper jet axis nearby. As such, have raised PoPs to likely across much of the area Wed night and maintained likely PoPs on Thursday across the east before the upper trough axis moves east Thu night. With weak high pressure building across the southeast and Middle Atlantic for Friday and Friday night, will maintain a dry and seasonable forecast with temperatures in the upper 70s/lower 80s. The upper trough finally moves northeast by Saturday, leaving more zonal flow across the region with building heights. The GFS and the Canadian suggest a weak upper disturbance moving through the area in W-NW flow later Saturday into Saturday Night, but the ECMWF keeps this further north as it builds heights across the area faster than the GFS/Canadian. With that being said, will Slight Chance of showers/storms Saturday Afternoon for much of the area with the exception of SE VA and NE NC. Better chances for showers and storms Sunday with better agreement from the models of another upper disturbance moving overhead. In general, temperatures will stay seasonable for this time of year with highs in the upper 70s and lower 80s with lows in the upper 50s to mid 60s. No major warmth is expected through at least next Sunday. && .AVIATION /20Z SUNDAY THROUGH FRIDAY/... MVFR/VFR ceilings across the region early this afternoon. MVFR ceilings are generally between 1500-2500 feet. Satellite imagery showing low pressure system over the Great Lakes with a cold front into Texas and a warm front over the Mid Atlantic region. A good cloud shield accompanies the fronts and guidance indicates increasing clouds through the evening and overnight with rain over the region by early morning. The cold front approaches from the west late tonight and moves through the Mid Atlantic States Monday. Expect deteriorating conditions overnight with IFR conditions possible, especially at RIC after 06Z. Rain becomes likely well inland after 06Z/Mon at RIC and gradually shifts east through the day Mon, with showers and thunderstorms likely by Monday afternoon. MVFR/IFR conditions will continue during heavier precipitation during the rest of Monday into Monday night. Unsettled weather is expected to continue Tuesday and IFR conditions will be possible. By Wed/Thu a series of frontal passages and low pressure systems affecting the Mid Atlantic region. Periods of deteriorating conditions are possible though will tend to become less widespread. && .MARINE... Persistent northeast to east flow have allowed seas across the coastal waters to remain around 5 feet all day. Expect this to continue into this evening and perhaps even into the early morning hours before subsiding as the winds diminish. As such, will maintain the SCA for the coastal waters through 1 am Monday morning. The high shifts off the coast tonight with a weak frontal boundary slowly moving east from the Ohio Valley before stalling out over the area Monday. This will allow the winds to gradually turn SE later tonight. Meanwhile, a weak low pressure system develops along the front over the southern Appalachians and moves toward the area Monday morning. This may allow S-SE winds to increase once again Monday especially on the coastal waters but should stay below small craft advisory criteria. As the low passes NE, expect the winds to become northerly Monday night before another stronger low pressure system moves across the area Tuesday into Tuesday evening. This will bring increased NE winds and potential waves of 4 to 6 ft along the coast. In addition, the bay may see N-NE winds of 15-20 kt as well especially late Tue into Tuesday night. The forecast is tricky as there are some timing differences in the models. However, it is safe to say at some point Tuesday into Tuesday night, winds will become gusty as the low passes by. Quieter marine weather expected for the end of the week as the flow becomes offshore behind the low. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...Small Craft Advisory until midnight EDT tonight for ANZ650-652- 654-656-658. && $$ SYNOPSIS...AJZ NEAR TERM...AJZ SHORT TERM...AJZ/LKB LONG TERM...MRD AVIATION...LKB/JEF MARINE...MRD

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