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Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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831 FXUS62 KRAH 161837 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 237 PM 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 237 PM 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, showers and storms moving into and/or developing over the higher terrain will progress east, in weakening fashion, into the NW Piedmont during the late afternoon and evening. By midnight, only isolated showers are expected to persist in the relatively stable airmass in place 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. Lows 65-70. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... As of 215 PM Friday... A cold front will loop from Lower Michigan southeast into the Ohio Valley and then southwest into the Tennessee Valleys Saturday morning, slowly moving to the southeast and moving into western North Carolina by Sunday morning. A thunderstorm cannot be ruled out northeast of Raleigh Saturday morning left over from tonight`s precipitation, then it appears coverage could expand a little bit in the afternoon. Different synoptic and high-resolution models are really all over the place with predictions for where convection will occur. There does seem to be some broad agreement that the southern Piedmont will remain dry Saturday afternoon, so with the uncertainty, painted slight chance pops north of I-40 as well as east of I-95. This is a very low confidence forecast considering the lack of agreement from the computer models. There is slightly more agreement in some thunderstorms moving into the region late Saturday night as the cold front approaches, but this will also be occurring at a time when convection is normally at a minimum, and have gone with chance pops to the northwest of I-85. Saturday`s highs will be within a degree or two of today`s values, generally in the mid to upper 80s. Lows will be in the upper 60s and lower 70s. && .LONG TERM /SUNDAY THROUGH FRIDAY/... As of 220 PM Friday... Sun/Sun Night: The leading edge of trailing cold front from a low over the Great Lakes will likely be pinned west of the Appalachian mountains into Sun afternoon with a pre-frontal lee-troughing positioned east of the Appalachians into the VA/NC Piedmont. Surface dew points in the low/mid 70s within and east of this boundary will contribute to 1000-2000 J/kg of MLCAPE by peak heating. The approaching trough should help support deepening convection by early afternoon. Some storm organization is to be expected with 20-30kts of 0-6km shear, but flow parallel to surface boundary will prompt congealing updrafts and linear clusters along common cold pools. Strong winds 30-40 mph will be most common, but isolated severe winds will be possible for well organized clusters that can take advantage of DCAPE around 1000 J/kg, theta-e diff of 25-30K, and low- level lapse rates > 8C/km. A conditional threat for isolated flooding will also exist Sun evening, mainly in urban and poor drainage locations. Storm motions should be quick enough with 20-35kt of mid-level flow, but back- building storms may be possible. Point soundings east of the trough axis show a deep warm-cloud layer > 10,000 feet and strengthening low-level jet after 21z with lingering MUCAPE of 1000-1500 J/kg. Most likely rainfall will range from a couple tenths to around three quarters of an inch, but where any back-building and/or training occurs, locally higher amounts of +2" would be possible. Mon through Fri: An effective front will slowly progress through the area through Mon with another reinforcing front and dropping low- level thicknesses Mon night into Tues. High pressure will continue to build over the Northeast and extend through the Mid-Atlantic into the Southeast through the remainder of the forecast period. Mostly quiet through the work week with only rain chances along the seabreeze. Highs in the upper 70s to mid 80s will become common Tues onward with lows in the upper 50s to mid 60s. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... As of 155 PM Friday... Upstream showers and storms moving into and forming along the higher terrain will apt to move eastward into the western Piedmont later this afternoon and into the evening, potentially bring a brief period of associated sub-VFR restrictions at KINT and KGSO. The convection is expected to weaken significantly and could dissipate all together as the remnant showers continue further east into the central Piedmont and northern/central coastal plain. With the exception of KINT and KGSO, the probability of occurrence is too low to include any mention of shower/storms. Additionally, a brief period of sub-VFR ceilings is possible at KINT and KGSO towards daybreak. Otherwise, VFR conditions are expected through 18z Saturday. After 18Z Saturday: Isolated to scattered shower/storms are expected again Saturday afternoon and evening as a cold front approaches from the west. The front will then move slowly east through the area Sunday through Sunday night/early Monday. Sunday will be the most convectively period with numerous showers and storms expected across all of central NC. Drier conditions return Monday and should remain predominately VFR through mid week. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...PWB NEAR TERM...CBL SHORT TERM...Green LONG TERM...Swiggett AVIATION...CBL