Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 271738 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 138 PM EDT Tue Sep 27 2016 .SYNOPSIS... A cold front tracks across the region today, stalling along the coast tonight. The front remains along the Mid-Atlantic coast through the end of the work week, resulting in unsettled weather conditions into the weekend. && .NEAR TERM /THROUGH TONIGHT/...
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Updated the grids to reflect the 17Z radar sfc ob trends. Cold front slowly moving east with main band of pcpn pushing east of I95. BINOVC even showing up across NWRN zones. Cut back pops behind fropa and dropped mentioned of thunder. Kept likely/cat shwr/tstrm pops across SERN half of fa as the band continues to move east. Highs in the 70s. PVS DSCN: The upper-level low centers over the Ohio Valley tonight as the frontal boundary remains stalled along the Mid-Atlantic coast. Shortwave energy pushes offshore as low pressure lifts offshore of the Mid-Atlantic coast. Expect a generally downward trend in precip tonight, but based on the air mass in place and the dynamics provided by the deep upper low, will keep chance POP`s through the overnight period. GFS/NAM isentropic surfaces also indicate low level lift behind the front. Lows range from the upper 50`s northwest to mid 60`s southeast.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY/... Anomalous/deep upper-level low settles over the Ohio Valley Wednesday as today`s front aligns along the southeast coast. A brief lull in precipitation is expected Wednesday morning as the associated surface low lifts offshore. However, precipitation returns in earnest Wednesday afternoon as diffluent flow upstream of the upper low results in favorable upper vertical motion along an area of deep moisture convergence over the Piedmont/central Virginia. This represents a westward shift in the highest POP`s compared to the previous forecast. Thermal profiles and cross sections indicate the upper levels will begin to dry, with precipitable waters dropping to around 1-1.25 inches. However, the low levels remain quite moist with 1000-500mb relative humidity values over 75%. Deep lift indicated in the models will be enough to overrule limited moisture, resulting in widespread showers Wednesday afternoon through Wednesday night. Showers may be heavy at times. Went below guidance on temps Wednesday due to a cloudy sky and precip, with highs forecast around 70 northwest to around 80 southeast. Few thunderstorms also possible Wednesday afternoon due to elevated instability (dry air aloft). Lows Wednesday night in the low to mid 60`s. The upper low drops southward over the southern Appalachians Thursday as a prevalent dry slot works into the forecast area. Showers will lift northward through the day, with the best chances confined north of Interstate 64 late Thursday. However, based on the amount of forcing and lingering moisture, will keep chance POPs across the remaining forecast area for light showers. Highs Thursday range from the low to mid 70`s inland to upper 70`s southeast. May begin to see the sun late Thursday afternoon across the south as the sky begins to clear. Per the latest GEFS standardized anomalies, best moisture transport expected to remain north of the region through the short term. However, even with limited moisture over the region, upper level dynamics still expected to result in produce a widespread 1-2 inches inland. Less across the southeast. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Medium range period continues to feature the presence of a deep anomalous upper level low centered over the TN/OH Valley Thu night/Fri, gradually lifting N and slowly weakening/filling across the Great Lakes by late Saturday-Sunday. At the surface, high pressure centered over eastern Canada will also weaken/slide E through the period as a surface low locates close to the upper low, with a secondary area of low pressure over the Carolinas/VA lifting N of the local area by Fri night/Sat. Fairly good agreement exists among the operational GFS/GEFS mean and the ECMWF with this overall scenario. Thus, precipitation chances will initially begin high (especially across the N) Thu night where 50-70% chances have been added to the forecast. Fri will see diminishing POPS (with southern 1/2 of the CWA only having about a 20% POP with at least partly sunny skies developing). Will maintain 30-50% chances N closer to the retreating frontal boundary. Will continue with a mainly dry forecast from fri night through the weekend (except for a 20-30% POP across the NE). Temperatures will be close to seasonal averages with highs generally in the 70s and lows in the 50s W to the 60s along the coast. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/...
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Cold front crossing the region as of 18Z. PCPN to end soon at RIC/SBY but just getting started across SERN TAF sites. Given the sporatic nature to the shower activity, decided to add a TEMPO group for lower CIGS/VSBYS in showers as some mdt to lclly heavy rainfall reported across the region. Kept thunder out attm given no lightning strikes anywhere across the fa, but that could quickly change over the next few hours as the front moves into the warmer air near the coast. Sct showers end this evening with the attention turning to fog potential tonight given a wet ground and high dew point temps. Have indicated MVFR conditions late tonight at all sites except ORF, with some guidance taking progging locally dense fog towards sunrise. Next batch of pcpn advances norhward across the piedmont after 12Z as low pressure along the front moves north. Thus, brought back rain to RIC but kept coastal areas dry for now. OUTLOOK...Unsettled weather conditions expected through the end of the work week as waves of low pressure lift along the cold front. Showers with late day tstms possible each day.
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&& .MARINE... Have dropped SCA headlines across the remaining Bay zones, though a few gusts to 20 KT will persist through daybreak (and an MWS may be issued if showers to the west push over the Bay and enhance the winds briefly). Otherwise, The approaching cold front drops into the area and stalls near SE VA tonight and Wed. Waves of low pressure forming along the front Wed night into Fri should gradually lift the boundary back to the N Thu-Fri (though confidence on exact timing is uncertain). Winds will become mainly ENE across northern areas and S/SE over southern areas Wed-Fri. SCA conditions are most likely over northern coastal waters Thu- Fri as the gradient tightens between the High to the N/NE and the front lifting back to the N. Still a fair amount of uncertainty and if the front is slower to lift to the N, SCA conditions could occur over most of the marine zones. Overall winds will avg 10-15 KT with mainly 1-2 ft waves over the Bay and 3-4 ft seas over coastal waters through this period, with seas to 5-7 ft possible N of Parramore Island. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...None. && $$ SYNOPSIS...SAM NEAR TERM...MPR SHORT TERM...SAM LONG TERM...LKB AVIATION...MPR MARINE...LKB

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