Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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791 FXUS62 KRAH 220537 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 138 AM EDT Sun Sep 22 2024 .SYNOPSIS... An upper level disturbance will track southeast through the Mid Atlantic region tonight. A back-door cold front will move south through the area late Sunday followed by surface high pressure extending south into the area through much of the upcoming work week. && .NEAR TERM /TONIGHT/... As of 852 PM tonight... Cluster of thunderstorms approaching northern NC for late evening... The cluster of showers and thunderstorms over central and southern VA continues to move southward toward northern NC. Satellite data suggests the weak short wave diving SE through VA. The latest data analysis indicates a weak low pressure over southern VA, with the best moisture convergence just to the west of the clustering of storms near Roanoke. However, lingering MLCape values were around 1000-1500 J/kg over NW into north-central NC, with some CINH showing up as well as temperatures cool with sunset. The latest RAP and most CAMS indicate the showers/storms entering northern NC between 930 and 1030 PM, then weakening as they move toward/into the eastern portions of the Triad, Triangle, and Rocky Mount areas between 1100 PM and 200 AM. Radar currently depicts some cores of the storms with 60+ dbz up above 20k feet with a Severe Thunderstorm Warning 25 miles north of Granville and Vance Counties. It is possible a warning will be needed, but we expect most if not all storms will weaken into the "garden variety" or below severe limits in the next hour. Previous discussion as of 203 PM Saturday... A line of scattered showers and thunderstorms is progged by all of the HREF members to develop to our north this evening then drift S and SE across our CWA between 04-10Z tonight... all in response to the weak short wave trough that is currently crossing the Ohio Valley, which is forecast to move ESE across the Mid Atlantic region tonight and move off the coast by Sunday morning. In the meantime, we`ll see intervals of sct-bkn shallow cu the remainder of the daytime hours today, esp west of US-1 where currently the best moisture and instability is located... then high clouds moving in this evening out ahead of the upstream shower/tstm activity. Then during the hours right before daybreak, there could be a couple hours of patchy fog, esp locations the see the greatest coverage of showers/tstms overnight. Lows tonight in the low-mid 60s. && .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 115 PM Saturday... Aloft, the sub-tropical ridge will progress eastward through the srn/ctl Appalachians and into the Carolinas through Sun night. Central NC should be under nwly flow on the northeast periphery of the ridge. At the surface, a low will continue sliding sewd through central NC Sun morn/aft. A backdoor cold front should slide south through the area Sun aft/eve, with high pressure ridging in behind it. There could be some lingering showers across the east Sun morning. Additional showers/storms could slide swd through the Coastal Plain/far ern Piedmont Sun eve/night as the backdoor front slides southward through the area. There could be about a 10 degree spread in highs from SW to NE due to the front, around 90 degrees SW to low 80s NE. Lows could drop to around 60 degrees in the northeast Sun night, with generally mid 60s expected elsewhere. && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 230 PM Saturday... * Near to slightly above normal temperatures into midweek, followed by seasonal to slightly below average late week and weekend * Shower and storm chances highest Tue into Thu * Forecast confidence decreases mid to late week as ensemble systems continue to differ on the overall synoptic pattern and possible tropical influences We will start the week with ridging building into the area at mid- levels from the north and northeastern Gulf. High pressure will build into the area from the Eastern Seaboard and Canada. Models still show a lingering backdoor front to our southwest in northern SC, though it appears models have trended further south with its location. As such, rain/storm chances are lessened Mon aftn/eve, but still cannot rule out a 20-30 percent chance over the western and southern Piedmont. Temperatures will be near normal in upper 70s to low 80s. Ridging will continue into midweek, though we should get increasing influence from a trough over the MS/OH valleys and Great Lakes late Tue through early Thu. Model and ensemble solutions start to diverge on how the trough evolves as it moves east, but there does appear to be a general consensus that a cold front will try to move through sometime Thu morning. It`s still unclear whether it will actually move through or stall out and linger NW of us. Ahead of that front, shower and storm chances should increase (30-60 percent), primarily in the late Tue through Wed night period. Temperatures should rise above normal ahead of the front to above average in the low to mid 80s. Probabilistic and ensemble solutions continue to vary widely in the Thu to Sat timeframe with respect to the synoptic pattern. Some ensemble cluster solutions indicate troughing over the MS valley and ridging off the western Atlantic (aka latest GFS/CMC), which would favor warmer highs and help draw northward any disturbance in the Gulf later in the week. Where it tracks though is widely varied. Other solutions show troughing nearby with the aforementioned cold front, keeping rain chances elevated. And still a third solution shows a rex/omega ridge pattern near the OH valley and troughing on either side, which could favor drier conditions to start but also advect any tropical system in the Gulf over the weekend. This is seen in the prior 00z ECMWF. Speaking of the Gulf, NHC now has a 60- percent chance of tropical development late next week over the south- central Gulf. Where the system would move is highly dependent on the pattern discussed above, which is too uncertain, but certainly bears watching, given a wide range of potential impacts. As a result, have kept rain chances low Thu to Sat, with temperatures near to slightly below normal in the upper 70s to near 80. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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As of 138 AM Sunday... A cluster of showers and storms and associated sub-VFR restrictions will impact KRDU and KRWI through 08z, and KFAY through ~10z. In the wake of the convection/rain, some patchy fog and MVFR ceilings may develop around or shortly after daybreak, mainly at KRWI. These sub-VFR ceilings could linger at KRWI into the early afternoon before lifting. Elsewhere, flight conditions should remain VFR. Then during the afternoon and evening, a back-door cold front, denoted by a NELY wind shift, will push southeast through the through the area, bringing widespread LIFR to IFR restrictions in stratus and fog Sunday evening/night. After 06Z Monday: Mainly VFR conditions expected each day, with the exception of sub-VFR fog/stratus each morning. There is a chance for mainly afternoon/evening showers/tstms each day, which could also briefly reduce flt conditions at times.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...np NEAR TERM...Badgett/np SHORT TERM...KC LONG TERM...Kren AVIATION...CBL/np