090 FXUS62 KRAH 280738 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 338 AM EDT Tue Sep 28 2021 .SYNOPSIS... Warm high pressure across the Southeast will shift offshore today. A cold front across the mid-Atlantic this morning will move across the Carolinas tonight and early Wednesday. Cool high pressure will build into the area on Wednesday through the end of the work week. && .NEAR TERM /THROUGH TONIGHT/... As of 330 AM Tuesday... Latest surface analysis shows a 1019 mb surface high centered across coastal Georgia. A cold front extended from northern New England southwest to the northern Ohio Valley. The upper level flow across the mid Atlantic was diffuse ahead of an southeastern advancing upper level trough moving across the eastern Great Lakes. The upper level trough will advance southeast today and move offshore this evening and amplify with time with decent height falls noted across the mid Atlantic. A Piedmont trough will develop across VA and the Carolinas this afternoon as the cold front reaches the northern Chesapeake Bay by sunset and then into central NC by daybreak Tuesday. The air mass ahead of the front in central NC will warmer today than Monday with low level thickness values about 12 to 16m higher. Relatively modest and somewhat dry mid level flow atop a light southwesterly flow will limit moisture transport into the area. By late afternoon, PW values will range around 1.0 to 1.25 inches with a rather dry boundary layer highlighted by afternoon surface dew points in the lower 60s. With limited moisture arriving with the front this evening, rain chances will be limited and PoPs will be excluded from the forecast. Further north, there is better moisture and forcing for ascent, so scattered convection is apt to develop across VA during the late afternoon and advance into southeastern and southern VA during the evening. Convection allowing models keep this activity outside of the RAH CWA with the closest approach and time period with the greatest but still quite limited chance of storms brushing the northern Coastal Plain near Roanoke Rapids from 9pm to 1am. Given the low probabilities will keep the forecast dry but we will need to monitor this. Given the dry soundings, higher based convection with high DCAPE values and steep mid level lapse rates to our north, strong to severe storms are possible in VA, if this convection was able to over perform and sustain itself, it could pose a threat for the northern Coastal Plain. For now, this appears to be a limited threat. The air mass across central NC will be warmer than the past several days with morning lo level thickness values in the 1395 to 1400m range, supporting highs ranging in the lower 80s near the VA border and Triad, mid 80s in most locations, including the Triangle and the upper 80s across the Sandhills and southern Coastal Plain. Very little cold advection will arrive by daybreak, so lows tonight will range 3 to 9 degrees above normal, in the upper 50s to the lower 60s. -Blaes && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 320 AM Tuesday... The cold frontal passage early on Wednesday will bring in lower 1000- 850 mb thicknesses under northeasterly surface winds. While the passage of the front is expected to remain dry, forecast model soundings are showing development of afternoon fair weather cumulus with daytime heating. Highs should range from the upper 70s in the northeast to the middle 80s in the south and west. With weak high pressure settling into the northern Great Lakes, along with lower thicknesses, overnight lows Wednesday night should be a few degrees cooler than Tuesday night in the middle to upper 50s. The closed mid-level low pressure system over far southeastern Canada and west of Maine on Wednesday will rotate and move into southeastern Maine by Thursday afternoon. Several weak shortwaves will rotate around this trough, the most impactful one being during the day on Thursday. The GFS/NAM keep most of the shortwave north and east of central NC, while the ECMWF is further west. Regardless of the exact solution, the GFS does show some weak low-level isentropic ascent over the Sandhills and southern Coastal Plain in the morning and early afternoon on Thursday, which is also evident in forecast soundings. Thus, have continued a slight chance of showers during the day in these locations, even though lift is weak. Highs on Thursday a few degrees cooler and closer to average in the upper 70s/low 80s, again lowest over the north. The mid-level trough over the northeast is forecast to lift east of the Carolinas by early Friday, resulting in rising mid-level heights and surface high pressure to settle over central Pennsylvania. Overnight lows Thursday night to be in the mid to upper 50s in the south and lower 50s in the north. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 240 PM Monday... The forecasts from the GFS and European models haven't changed much over the last couple of days for the end of the work week and into the weekend, even if those forecasts are not quite in agreement with each other. Wednesday will feature a cold front with very little moisture, and the frontal passage should still be relatively cloud-free. With the front taking its time to move from north to south, highs will drop several degrees in northern counties, but highs should remain similar to Tuesday's values across southern counties. Between the GFS, NAM, European, and SREF, all models show some precipitation across central and eastern North Carolina Thursday, although there is little consistency as to where this precipitation could develop. As a result, have made no changes to the inherited pop forecast, continuing a slight chance of showers southeast of Raleigh. The GFS and European continue to have different depictions of an upper level low over New England and eastern Canada, the GFS the stronger and more progressive solution and the Euro the weaker, slower, and broader solution. Although not as large as yesterday's differences, the 00Z MOS solutions from the GFS and European remain 7-10 degrees for daytime highs, so have continued to undercut the NBM guidance which shows greater agreement for the GFS solution. Finally, while a surface high is expected to be in control over the southeastern United States over the weekend, the high will be pushed offshore by a developing low near the Great Lakes and a trailing cold front. As is typically the case, the GFS is quicker in bringing precipitation into the state than the European, so for now have just added a slight chance of showers to most locations on Monday. The coolest temperatures are expected Friday and Friday night, near climatology, with a minimal rise in temperatures through the rest of the forecast. && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... As of 220 AM Tuesday... 24 Hour TAF Period: VFR conditions are generally expected across central NC through tonight with just a couple of exceptions. Some patchy fog may develop before daybreak this morning a few, fog prone locations. In addition, an approaching cold front may trigger some scattered showers or storms across southern/southeastern VA late this afternoon that could skirt the northeastern portions of central NC this evening. Probabilities are limited and will not include a mention in the KRWI terminal at this time. Very light, mainly southwesterly winds overnight will become light southwest this morning and will shift to north behind the front late tonight. Outlook: The cold front will move across southern NC early Wednesday morning and then offshore. A rogue shower or storm may still threaten northeast sections late tonight. Fair weather with mainly VFR conditions are expected for Wednesday through Friday as high pressure builds into the area. A limited chance of a shower arrives for Friday night into Saturday. -Blaes && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Blaes NEAR TERM...Blaes SHORT TERM...AK LONG TERM...Green AVIATION...Blaes