991 FXUS62 KRAH 040822 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 422 AM EDT Wed May 4 2022 .SYNOPSIS... A lee surface trough will move east and across the southern Mid Atlantic and Carolinas today. A cold front will follow and cross the region tonight. Milder high pressure will then extend across the Mid Atlantic Thursday and Thursday night. && .NEAR TERM /THROUGH TONIGHT/... As of 420 AM Wednesday... A shortwave trough crossing the lwr Great Lakes this morning will continue to deamplify while moving east across the nrn mid Atlantic today and off the srn New England coast this evening. While associated forcing for ascent will remain well north of cntl NC, a trailing, positive-tilt trough axis over srn IN and IL this morning may amplify slightly from the cntl Appalachians to the srn Mid Atlantic coast between 18Z-03Z. Preceding that trough, a couple of MCVs from weakening clusters of convection were evident in radar data over Rutherford Co. NC and over n-cntl GA at 0745Z. RAP model data, which seem to analyze the associated 700-500 mb vorticity field well, forecast the former to move east-northeast across the nrn NC Piedmont through 15Z, and the latter to move northeast across the srn NC Piedmont, Sandhills, and Coastal Plain between 15-20Z. A band of mid level ceilings may accompany those features as they cross cntl NC, but their timing prior to peak diurnal heating suggests their influence on subsequent deep convective development this afternoon would be favored mainly from the Coastal Plain east to the coast. At the surface, a couple of Appalachian-lee surface lows will develop across and offshore the Mid Atlantic today. A preceding lee trough over the Piedmont of VA and the Carolinas will move east across cntl NC through this evening, while a trailing cold front, now west of the Appalachians through ern KY and middle-ern TN, will cross cntl NC tonight. The airmass ahead of the trough and front will become moderately unstable with strong diurnal heating and with near persistence high temperatures into the mid 80s to around 90 F across cntl NC this afternoon, beneath another EML plume that advected across the lwr MS Valley and Southeast during the past 24 hours. With little to no convective inhibition with that strong diurnal heating, generally scattered showers and storms are forecast to develop and focus along the lee trough by early this afternoon, then move east along aggregate outflow and become locally numerous from the Sandhills and Coastal Plain east to the NC coast through the evening. Steep low level lapse rates with heating, beneath generally unidirectional, 25-30 kts of wly mid level flow, will support instances of strong to marginally-severe/tree-damaging wind gusts from a primarily multi-cellular storm mode. The presence of the EML and associated plume of 7-8 C/km mid level lapse rates evident in the BMX and FFC RAOBs last evening, will also favor hail in the most intense cells, including some quarter-sized or greater over the Coastal Plain and Sandhills east to the coast, where MLCAPE is forecast to be maximized between 2000-2500 J/kg. A few weaker cells/showers may accompany the passing synoptic cold front tonight, but any severe should end in cntl NC by around 8 PM. Low temperatures behind the front are likely to range from mid-upr 50s across the nrn Piedmont to mid 60s across srn NC. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 340 AM Wednesday... In the wake of an exiting s/w aloft, the sub-tropical ridge will briefly build through Southeast, shifting eastward Thu night as the next low pressure system moves through the Midwest. At the surface, high pressure will build into the area from the north on Thu. A warm front will begin lifting northward through the area Thu night ahead of the approaching system, but may not progress completely through the area until after daybreak Friday morning. As a result of the CAA from the north and cloudiness across much of the area, high temps should be 5-10 degrees lower than Wed, in the mid 70s NE to mid 80s south. Lows should bottom out in the mid 50s NE to mid 60s south. Still a bit low confidence on the potential for precipitation Thu night, but there is a slight chance/chance rain could move in late Thu night/early Fri morning. && .LONG TERM /THURSDAY THROUGH TUESDAY/... As of 300 PM Tuesday... Thursday should be mostly dry as surface high pressure briefly builds in from the north and relatively flat shortwave ridging moves across the area, in response to an intense closed low over the Central Plains. With E/NE low-level flow on the cooler/drier side of the stalled front to our south, leaned toward the cooler NAM and have forecast highs in the mid-70s to lower-80s (near normal). The front will lift back north through the area as a warm front on Thursday night, with increasing clouds and isolated to scattered showers potentially moving in from the south and west, owing to a weak upper disturbance. The aforementioned closed low will continue to move east, reaching the mid Mississippi Valley on Friday. This will turn the low-level flow southerly once more and increase dew points back into the 60s, with high temperatures ranging from the upper-70s to upper-80s. Thus MLCAPE of 1000-2000 J/kg will be more than sufficient for convective development in the afternoon and evening. Owing to the approach of the low, both the upper forcing and shear look much better than tomorrow, as 500 mb flow will be up to 40-50 kts. Thus POPs are likely across the entire region, and scattered strong to severe storms are possible, with a squall line potentially moving through in the late afternoon and evening. Confidence decreases for this weekend as the 12z GFS and 12z ECMWF continue to diverge on how quickly the closed low and its associated cold front will push east across the Ohio Valley and Mid-Atlantic. The GFS is faster and pushes the low offshore by Saturday night, meaning cooler temperatures and just some scattered showers on Saturday, turning dry by Sunday. The ECMWF (while a bit faster than previous runs) still doesn't move the low offshore until Sunday, allowing for another day of warmth, instability and possible storms (especially east) on Saturday, with showers lingering into Sunday. For now the forecast leans a bit toward the ECMWF. Regardless there should be some precipitation around on Saturday, so have likely POPs and a slight chance of thunder. The best chance of storms would be in the east. The threat of storms will come to an end on Sunday with cool, stable N/NE flow and temperatures dropping below normal (highs in the 60s to lower-70s). However, a few showers may linger in the Coastal Plain, especially if the slower ECMWF verifies. Monday and Tuesday will feature continued N/NE flow as the closed low sits and spins offshore, blocked by a strong mid/upper ridge that will develop over the MS Valley into the Northeast US. Thus it will be dry and cool with highs mainly in the 70s. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... As of 230 AM Wednesday... SSWly winds between 1000-2000 ft AGL have increased to between 40-50 kts across cntl NC this morning per both radar-derived, VAD Wind profile data and also wind observations from instrumentation on a local television tower. Low level wind shear conditions will consequently result throughout cntl NC through 12-14Z. Aside from a chance of IFR-MVFR conditions at FAY between 10-14Z, VFR conditions, with periods of mid and high level ceilings, are expected until scattered showers and storms redevelop along a lee surface trough over cntl NC this afternoon. The probability of occurrence of that convection, and associated sub-VFR conditions, will be greatest from RWI and FAY and points eastward between after 19-20Z today. The passage of a cold front tonight will end the threat of any lingering showers and/or storms and also result in veering low level flow to nnely by Thu morning, at which time that wind trajectory may support the development of patchy IFR-MVFR ceilings at RWI and FAY. Outlook: Stratus and fog will become likely both Fri and Sat mornings, as will showers and storms Fri through Sat. Widespread IFR- MVFR ceilings will then redevelop in cool and moist nnely Sat night into Sun. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...KC LONG TERM...Danco AVIATION...MWS