Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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627 FXUS62 KRAH 060617 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 216 AM EDT Sat Jul 6 2024 .SYNOPSIS... A subtropical ridge will continue to extend across the South Atlantic states ahead of a cold front that will move into the southern Middle Atlantic and Carolinas this afternoon, then stall and dissipate over the region through the weekend. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... As of 852 PM Friday... * Very warm and muggy tonight, with storms continuing to slowly wind down... Scattered storms persist at this hour, albeit with gradually decreasing coverage and intensity compared to this afternoon. The latest surface analysis shows a weak trough extending down through the heart of central NC. A steamy air mass remains in place this evening with very light and erratic surface flow being largely driven by the multitude of outflows (generated by earlier and current convection) and sea breeze segments, all noted on radar imagery. Weak to moderate elevated CAPE persists, highest in the east, but decreasing surface temps from scattered storms and the onset of nocturnal cooling have helped CINH to increase over the area, amidst somewhat poor mid level lapse rates. So while PWs remain high over the area 2.1-2.4"), the loss of heating and lack of dynamic mechanisms to support ongoing convection should result in a gradual steady decrease in showers and storms over the next few hours. Storms should be last to dwindle over the N Piedmont, where mid level flow remains the strongest (still modest, though, near 25 kts). Expect partly cloudy to fair skies overnight, more clouds NW than SE. Current temps are still quite warm, in the upper 70s to upper 80s, with dewpoints in the 70s, thus forecast lows in the mid to upper 70s still appears reasonable. -GIH Earlier discussion from 405 PM: The latest surface analysis shows a broad surface troughs extending north to south across VA and the Carolinas. A 1016mb 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 northeast PA into eastern OH and KY. The airmass across central NC is hot and humid with surface dew points in the lower 70s with some upper 60s noted in south central NC and northern SC. It has been an extremely hot day with temperatures at or in excess of 100 at numerous locations including 106 at KRDU; 101 at KFAY, KMEB, KGSB, KVUJ, KPOB, and KFBG; and 100 at KRWI. Widely scattered showers and thunderstorms have developed across the Piedmont and Coastal Plain near and east of the surface trough. With weak shear, the convection has been very pulse-like and limited in breadth. Slightly more organized and more widespread convection developed in the Blue Ridge and across the NC mountains just east of an advancing cold front. This convection will move into the Triad, western Piedmont/Yadkin Valley area and the VA border counties late this afternoon and evening. 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 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 /06Z SATURDAY THROUGH WEDNESDAY/... As of 215 AM Saturday... A weakening convective cluster and now light stratiform rain and mainly VFR visibilities will persist for another hour or two at INT/GSO. It is unclear to what degree upstream redevelopment of showers and storms toward CLT and DCM will hold together as they follow an otherwise similar path toward the nw NC Piedmont, where multiple rounds of convection may have sufficiently stabilized and shielded that area from adverse conditions, through the rest of the morning. To the east, an area of IFR-MVFR stratus now developing over sern VA and nern NC may extend as far west as RWI between 09- 12Z. VFR conditions are forecast otherwise and elsewhere until scattered to numerous, slow-moving showers/storms redevelop with daytime heating along a surface trough/effective cold front this afternoon, then continue into this evening. Outlook: A good chance of fog/stratus will exist late tonight-Sun morning, followed by a somewhat-typical summer time pattern of afternoon-evening showers/storms and morning stratus and fog through mid-week. && .CLIMATE... Record High Temperatures: July 6: KRDU: 102/2022 KFAY: 99/1990 Record High Minimum Temperatures: July 5: KGSO: 74/1999 KRDU: 78/1902 KFAY: 77/2005 July 6: KGSO: 76/1999 KRDU: 79/1900 KFAY: 76/2017 July 7: KGSO: 73/2019 KRDU: 77/1900 KFAY: 78/2017 && .RAH WATCHES/WARNINGS/ADVISORIES... Heat Advisory from 11 AM to 8 PM EDT Saturday for NCZ008>011-023>028- 040>043-075>078-084>086-088-089. && $$ SYNOPSIS...MWS NEAR TERM...Hartfield/Blaes SHORT TERM...DL LONG TERM...np AVIATION...MWS CLIMATE...RAH