Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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340 FXUS62 KRAH 051926 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 326 PM EDT Fri Jul 5 2024 .SYNOPSIS... Surface high pressure across the western Atlantic and Deep South will shift east through tonight as a surface trough extends south across the Piedmont of Virginia and North Carolina. A cold front will approach the region from the northwest this evening and then move into and stall across Virginia and Carolinas this weekend. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... As of 1100 AM Friday... * Dangerously hot today with record high temperatures * Scattered afternoon and evening thunderstorms, especially across the west and north which may produce strong gusty winds The latest surface analysis shows a couple of surface troughs extending north to south across VA and the Carolinas with the eastern trough likely enhanced by convection on Thursday evening. A 1017mb surface high across the western Atlantic extends southwest into the coastal Carolinas and FL. A cold front extends southwest from a weak surface low over northern PA into eastern OH and central KY and central TN. The airmass across central NC is already very warm and humid with surface dew points in the lower 70s with a few mid 70s across the Coastal Plain. Temperatures as of 10am were already in the lower to mid 80s. The morning sounding from KGSO depicted a moist profile with a PW of 1.83 and a generally light westerly flow. The morning low level thickness was observed at 1428m, 10m warmer than Thursday and the KMHX RAOB was 15m warmer as well. These soundings suggest highs will range from 3 to 5 degrees warmer today, than yesterday in many locations. Highs should range in the upper 90s to low 100s in most locations and will threaten daily high records in many locations. The mid shift upgraded the Heat Advisory to an Excessive Heat Warning for the ne Piedmont, nrn Coastal Plain, and the nrn Sandhills, where heat index values around 110 F will be likely this afternoon. The Heat Advisory remains otherwise unchanged in time and location, for peak heat index values generally in the 105 to 109 F range. Visible satellite imagery depicts mainly clear skies across central NC this morning with some patchy stratus across parts of the southern Piedmont and Sandhills. The sunshine will will quickly erode morning convective inhibition and the atmosphere will become moderately unstable with MLCAPE values of 1200 to 2400 J/Kg this afternoon, notably more than on Thursday. Expect cumulus clouds to pop after 11am and they should be more widespread that previous days. Isolated to widely scattered convection may develop in the Piedmont and Sandhills in the vicinity of the lee trough with more numerous thunderstorms apt to develop across western NC and near the VA border area north of the Triad and then push east. Storms today will still have the potential to be efficient wind producers with an inverted-V sounding noted and with DCAPE values in excess of 1000 across the western Piedmont. SPC has introduced a marginal risk of severe storms across the northwest Piedmont area with this in mind. Convection will translate east during the evening and gradually weaken during the mid to late evening but unlike previous nights, it will tend to persist a bit later into the overnight. Outside of cooling from thunderstorms, temperatures will be slow to cool this evening. Expect temperatures to persist in the lower and mid 80s in most locations through midnight or later before eventually dropping into the mid 70s to around 80 by Saturday morning. -Blaes && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... As of 300 PM Friday... * Hot and humid once again with Heat Advisories across the east * Storm chances increase by early afternoon, periods of heavy rain could result in flash flooding Upper low over the western Great Lakes will gradually weaken as it moves into Ontario on Saturday. Longwave troughing and the associated attendant surface cold front is likely to get hung up west of the mountains and wash out before it ever arrives across central NC. However, lingering boundaries from today`s (Friday`s) convection will likely lay down a boundary somewhere across central NC this evening, and that will serve as a focal point for shower and thunderstorm development once again on Saturday. Thermodynamic parameters aren`t overly impressive on Saturday with MLCAPEs generally topping out around 1000-1500 J/KG. The combination of modest instability, generally weak steering flow running parallel to the stalled surface boundary, and 99th+ percentile PW`s across the area (2.25 - 2.5 in) would suggest that anything that develops tomorrow will be extremely efficient at producing rainfall. HREF Local Probability Matched Mean QPF suggests the potential for upward of 3-4 inches of rain (if not higher) where storms develop, with the Sandhills suggested as the favored location for heaviest rainfall. While the stalled boundary will likely help concentrate precip across the eastern half of the CWA, it`s hard to pinpoint exactly where the highest rainfall would be. Going to hold off on a Flood Watch at this point given some of the geographic uncertainty of where storms are most likely to occur. Also, the ground should be able to accept at least some amount of rainfall given recent dryness but high rainfall rates, especially across highly urbanized areas, could necessitate a few short-fused flood advisories and/or flash flood warnings tomorrow afternoon/evening. Before any showers develop though, temps should easily rise into the mid/upper 90s once again. Moisture pooling on the eastern side of the stalled boundary and dewpoints once again in the mid to upper 70s will result in another dangerously hot day especially across the Triangle and the Coastal Plain. While Heat Index values and ambient air temperatures may fall a few degrees shy of today`s (Friday`s) observed values, they will still be high enough to warrant a Heat Advisory across eastern portions of our forecast area. Relief in the form of clouds and rainfall will certainly help, although temps and heat indices will likely reach dangerous values for several hours before that relief arrives. Temps will be just a bit cooler in the west (lower 90s) with heat indices hovering right around 100 degrees. Lows tomorrow night will be tricky given lingering cloud cover and rain cooled air but low to mid 70s is the general consensus. && .LONG TERM /SUNDAY THROUGH FRIDAY/... As of 326 PM Friday... A potentially unsettled pattern with daily pops aoa climo is shaping up for much of the long term period, thanks to 1persistent lee trough along with moist s to sw flow in the lower troposphere resulting in abundant antecedent moisture as noted by forecast PWAT values aoa 2 inches. Scattered shower/tstm activity will be primarily diurnal in nature, as typical this time of year. Meanwhile, we`re not expecting any notable change to the hot airmass, so any prolonged dry episodes will result in above, or well- above normal hot temperatures; however, since we`re likely to see an abundance of clouds and scattered shower/tstm activity during this time, high temps should mostly remain closers to climo (lower 90s) each day. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... As of 315 PM Thursday... Scattered showers and thunderstorms will continue to develop across central NC this afternoon and evening. Convection will be most favored a little later this evening perhaps 21 to 01Z in the Triad terminals at KINT and KGSO where a line of convection moving east from the NC mountains approaches. Convection will become widely scattered or isolated late this evening before dissipating after midnight. Some localized patches of stratus and perhaps fog will develop tonight, favored in locations where rainfall occurs and across the Coastal Plain and Sandhills where moisture is greatest. Generally fair weather is expected for Saturday morning before scattered convection begins to develop during the afternoon. Light mainly south to southwest at less than 10 kts are expected during the period. In addition, a brief period of marginal LLWS may occur overnight, most favored near and to the northeast of the KRDU terminal. Outlook: A more typical summer time weather pattern will setup late in the weekend through mid week featuring scattered afternoon and evening showers/storms and a good chance of late night and early morning stratus and fog. -Blaes && .RAH WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 8 PM EDT this evening for NCZ007-021>023- 038-039-073>075-078-083>086-088-089. Excessive Heat Warning until 8 PM EDT this evening for NCZ008>011-024>028-040>043-076-077. Heat Advisory from 11 AM to 8 PM EDT Saturday for NCZ008>011- 023>028-040>043-075>078-084>086-088-089. && $$ SYNOPSIS...Blaes NEAR TERM...Blaes SHORT TERM...DL LONG TERM...np AVIATION...Blaes