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Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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528 FXUS62 KRAH 161323 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 923 AM EDT Fri Aug 16 2024 .SYNOPSIS... High pressure will persist over the Carolinas today then shift offshore late today and tonight. A cold front will approach the region from the west on Saturday. && .NEAR TERM /TODAY THROUGH TONIGHT/... As of 923 AM Friday... Embedded in the W-NW flow aloft between the upper ridge centered over the Southern Rockies and the large troughing over the Great Lakes and Ohio and Tn Valleys, a ribbon on higher moisture, featuring PWATs 2-2.2:, will advect west to east across central NC through night as weak perturbations traverse the area. Steered by the W-NWLY flow, an area of showers and storms, currently across central portions of TN an KY, will progress east across the southern Appalachians later this afternoon, and in weakening fashion move into the western Piedmont between during the late afternoon and evening. Then overnight, some isolated shower activity is possible as the lingering convection continues to move east across central and eastern NC. Shear, instability and forcing are all weak. Thus, no severe storms are expected. The onset of SWLY low-level flow will result in continued warming and a slight uptick in humidity levels. Highs 85-90. Lows 65-70. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... As of 320 AM Friday... The mid and upper level trough will be approaching from the Ohio Valley Saturday and Saturday night. A cold front will remain to our NW, but will approach the mountains Saturday night. There will be a better chance (40-50) of mainly afternoon and evening showers and thunderstorms in the west, with a 30 percent chance east. Highs will be mostly in the mid to upper 80s, with lows in the lower 70s. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 400 AM Friday... A surface low will move east from Lake Huron to Upstate NY on Sunday and Sunday night, as a secondary low develops along the northern Mid- Atlantic coast. This will push a surface trough and cold front through central NC. Looking aloft, shortwave energy diving down from the NW will deepen the mid/upper troughing in place to our west over the Appalachians, increasing height falls across the area. Deep SW flow will help bring dew points into the lower-to-mid-70s, which will contribute to moderate instability (1500-2500 J/kg of MLCAPE) by the afternoon. The upper-level forcing and cold front will combine with the unstable air mass to result in scattered to possibly numerous showers and storms developing during the afternoon and evening along and ahead of the front. One somewhat limiting factor will be the deep-layer moisture which doesn`t look overly impressive, as PW values look to be around 1.5 to 2 inches (close to normal). Widespread heavy rain doesn`t look like a big concern as the latest WPC QPF is only in the quarter to half inch range on average in most places (highest east), but locally higher amounts will be possible. Still have close to 80% of GFS/ECMWF/CMC ensemble members depicting measurable precipitation on Sunday afternoon/evening, so raised POPs to likely (around 60%) in most places. Mid-level flow continues to look as high as 30-40 kts, so some strong to severe storms can`t be ruled out, and SPC has placed all of central NC in a marginal (level 1 of 5) risk for severe storms on Sunday. The main threat will be isolated damaging winds. High temperatures will be in the mid-80s to 90, which is within a few degrees on either side of normal. Rain chances will end from NW to SE on Sunday night as somewhat drier air works in behind the cold frontal passage. Lows will be mid-60s to 70. More showers and storms will be possible on Monday as the mid/upper trough lingers overhead, but moisture and instability will decrease as the low-level flow turns more W/NW. Shear also doesn`t look as impressive. So coverage should be fairly isolated, and POPs are only in the low chance range. Temperatures will start a downward trend as highs range from lower-80s far north to upper-80s far south (slightly below normal) and lows Monday night are in the 60s. A cooling and drying trend will continue from Tuesday through Thursday behind a secondary cold front that looks to move through on Monday night. Surface high pressure will build down from the Great Lakes and Northeast US as the cold front stalls well to our south. The mid/upper trough axis will gradually lift NE, favoring height rises W/NW flow aloft. This will bring below-normal PW values and help dew points mix out well down into the 60s from Tuesday through Thursday. In fact, some guidance even shows some 50s dew points on these days. So largely dry weather and mostly sunny skies are expected. Highs will drop to upper-70s to lower-80s by Wednesday and Thursday, with lows in the upper-50s to lower-60s as there should be decent radiational cooling conditions. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... As of 640 AM Friday... Showers/storms will be possible (15-30% chance) at INT/GSO during the late afternoon into the evening hours as upstream convection leaks across the mountains, although likely in a weakening state. Otherwise, generally After 12Z Saturday: A slow moving cold front will approach this weekend, producing increasing convective rain chances through the weekend with Sunday being the most active/widespread. Showers/storms will potentially linger into Monday as the front finally moves through the area. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...PWB NEAR TERM...CBL SHORT TERM...Badgett LONG TERM...Danco AVIATION...PWB/Swiggett