Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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038 FXUS62 KRAH 261908 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 310 PM EDT Wed Jun 26 2024 .SYNOPSIS... Hot southwesterly flow will result today between high pressure over the Atlantic and a cold front that will approach from the northwest and reach the western Carolinas by Thursday morning. The front will then move slowly east across the central and eastern Carolinas later Thursday through Thursday night. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... As of 1055 AM Wednesday... For the near term update this morning, the previous morning stratocu coverage across a decent portion of the south and east has mixed/cleared out quickly. This doesn`t appear to have limited much of the daytime heating in the last few hours so the previous temp/dewpt trend appears to be on track. The current Heat Advisory therefore remains in effect today with near 105 deg heat indices expected within the advisory area. As far as afternoon chances for any convection... only the Nam nest looks to be the outlier from some other CAMs with triggering and there doesn`t seem to be much of a forcing mechanism today so am not biting on that solution and will keep it mainly a dry forecast through the daytime period. The greater chances remain for later this evening into overnight with the progression of an upper shortwave/disturbance and possible outflow from upstream development. Previous discussion follows... As of 410 AM Wednesday... A Heat Advisory has been issued for today for the Sandhills and a portion of the Coastal Plain and Piedmont in central NC. A 320 dam 700 mb anticyclone centered over the TN Valley in 00Z/26th upr air data will weaken several decameters as it builds across and offshore NC through tonight. 850 mb standardized temperature anomalies beneath and downstream of the high are still forecast to be around 3 sigma above average over the Carolinas, with daily record 850 mb temperatures possible at GSO. Meanwhile, a couple of shortwave perturbations now over MN and NE will modestly amplify and phase as they pivot across the Great Lakes and OH Valley, respectively. The trailing/equatorward portion of an associated positive tilt, synoptic trough will be comprised of convectively- amplified mid-level disturbances/MCVs (including some from a large area of ongoing convection centered over MO) that will extend from srn New England swwd to the Delmarva and TN and lwr MS Valleys by 12Z Thu. At the surface, sprawling high pressure anchored over the cntl Atlantic will extend wwd and across the South Atlantic states, where hot, sly/swly flow will exist today. On the wrn periphery of the ridge, an Appalachian-lee trough will develop over the srn Middle Atlantic Foothills/wrn Piedmont. An effective cold front, the combination of a synoptic front and composite convective outflow, will meanwhile approach from the northwest and settle into the pre- frontal/lee trough position and extend from the Delmarva swwd to the w-cntl Carolinas by 12Z Thu. The pattern described above will favor what will probably be the hottest day yet during the ongoing stretch of hot conditions that began over cntl NC this past weekend, with forecast high temperatures 8-14 F above average and mostly in the mid 90s to around 100, including near the daily record of 102 F at RDU. Seasonable, mixed/afternoon surface dewpoints mostly in the mid 60s west to upr 60s to around 70 F east will yield Heat Index values several degrees on average higher than air temperatures and in the upr 90s over the nw Piedmont to 100-105 F elsewhere. While the most likely locations to reach and marginally exceed traditional Heat Advisory criteria (105 F) will be over the urban Triangle (Raleigh/Durham) and Fayetteville, a combination of near 105 F heat indices and a forecast of major HeatRisk warrant a lager Heat Advisory area for much of the southeastern half of cntl NC. Isolated convection will be possible both along/in the vicinity of the sea breeze (Sandhills and srn Coastal Plain) and lee trough (far nw Piedmont) during the afternoon-early evening, followed by a slightly higher chance (20-30%) of showers/storms accompanying the approach/arrival of the aforementioned convectively-amplified mid- level trough and convective outflow, mainly over the Piedmont and nrn Coastal Plain, tonight. Trailing that possible convection, areas of light stratiform rain/sprinkles, remnant to that or other upstream convection and within a broader mid-level cloud band related to the aforementioned convectively-amplified, mid-level trough, may linger over the Piedmont overnight-Thu morning. It will otherwise be muggy and quite mild, with low temperatures 5-10 F above average and mostly in the mid 70s. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... As of 300 AM Wednesday... A cold front should extend from northeast to southwest across the forecast area Thursday morning, and it will continue to slide southeast through the day. It still appears that the bulk of the showers and thunderstorms will occur behind the front, with greatest coverage during the mid afternoon decreasing through the late afternoon into the evening. Vertical wind shear still remains very low, meaning it should be hard for an organized cluster of storms to develop. However, instability values between 1000-2000 J/kg should be enough to allow isolated strong to severe thunderstorms to develop, with the primary hazard coming from damaging wind gusts. The chance of thunderstorms should linger everywhere into the evening, then remain confined east of I-95 after midnight. While dewpoints may be slightly increased from today, high temperatures should come down between 3-7 degrees. This should result in a day with heat index values in the 90s north of US-64 and in the low triple digits south of US-64. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... As of 310 PM Wednesday... This above-normal temp stretch will hit yet another crescendo this weekend, with convection chances peaking late in the weekend. A brief temp respite arrives early next week, however this will quickly give way to a return to excessive heat midweek. Fri/Fri night: The weak surface front is likely to settle across our S areas Fri morning, then quickly wash out as the surface high to our N shifts offshore by afternoon, resulting in a trend to light low level flow out of the SE as warm mid level ridging spreads into the Carolinas from the W. PW will be lower across the N but remain close to 2" across the S, where weak low level confluent flow may help organize scattered afternoon convection. Will carry chance pops across the SE, where an inland-moving sea breeze could help focus scattered convection, with a secondary chance over our NW given the potential for terrain convection to drift into the Triad region. Overall, though, coverage will be low as PW will be at or below climo. Expect little or nothing across the NE, within the exiting surface ridge, where LREF probabilities of substantial SBCAPE are low. Highs should be in the upper 80s to the mid 90s. Heat index values are projected to be 100-103 from the Triangle to the SE. Sat-Sun night: Low level thermal ridging builds back into central NC over the weekend from the SW, as a flat mid level ridge extends E from the S Plains into NC through early Sun, our thicknesses rising to 10-15 m above normal with deep mixing and weak lee surface troughing over the Piedmont. Pops Sat will be similar to Fri, low chances focused across the SE and NW. This ridge aloft then retrogrades by late Sun as a potent northern stream trough moves from the Upper Midwest/N Great Lakes through S Que/St Lawrence Valley and into the interior Northeast by Sun/Sun night, digging down the Mid Atlantic coast. Deep layer shear will be marginal Sun, but moderate SBCAPE is expected, and the increasing and deepening moisture (projected PWs nearly 2.5") with the approaching surface front tied to the trough aloft will support higher pops in the good chance to likely range, highest across the NW Sun afternoon through the evening before shifting to the S and E as the front pushes to our SE overnight. Expect highs from the low 90s NW to upper 90s SE with high dewpoints well into the 70s, indicative of increased heat stress as heat index values reach 100-110 over all but the extreme NW both days (but likely a bit higher Sun than Sat), although confidence in reaching extreme heat levels is lower Sun given the potential for clouds and convection. Mon-Wed: As the front settles along our S and E early next week, pops should be on the low side, chance pops mainly S Mon and even lower Tue, as surface high pressure builds in from the N within mid level troughing. Low level thicknesses suggest highs fairly close to normal, with highs in the upper 80s to lower 90s. The heat will begin to return Wed as the surface high pressure exits and strong mid level ridging builds once again, centered over the Mid South and N Gulf states, sending thicknesses soaring back above normal once again. After highs in the upper 80s to lower 90s Mon/Tue, highs should again be in the low-upper 90s Wed. -GIH && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... As of 200 PM Wednesday... While predominantly VFR conditions are expected across central NC through this evening, isolated showers and storms may develop, particularly across the Sandhills/southern Coastal Plain (including FAY) and NW Piedmont (including INT and GSO). Any storm may result in brief sub-VFR visibilities and gusty winds. Another area of showers and storms may graze the northern Piedmont and northern Coastal Plain as it moves east from about 03z to 12z. IFR or MVFR ceilings can`t be ruled out at RDU and RWI as it moves through. Even though FAY should stay dry late tonight and early tomorrow morning, IFR/MVFR ceilings from low stratus are still possible there, as has occurred the last couple mornings. Conditions should improve to VFR everywhere by mid to late morning, but some light stratiform rain/sprinkles may linger across the north. Outlook: IFR-MVFR stratus will again be possible especially at FAY and RWI in the early morning from Fri through the Mon. The chance of mainly afternoon-evening showers/storms will be highest on Thu at FAY and RWI, and again area-wide Sun-Sun night. && .CLIMATE... Record High Temperatures: June 26: KRDU: 102/1952 KFAY: 101/1951 June 27: KFAY: 102/1998 June 30: KFAY: 102/2012 Record High Minimum Temperatures: June 26: KGSO: 74/2010 KRDU: 76/1902 KFAY: 76/1997 June 27: KGSO: 76/1969 KRDU: 76/1952 KFAY: 77/1998 June 28: KGSO: 76/1969 KRDU: 76/1952 KFAY: 78/1914 June 29: KGSO: 74/2010 KRDU: 78/1914 KFAY: 76/1969 June 30: KGSO: 74/1936 KRDU: 80/1936 KFAY: 79/1936 July 1: KGSO: 77/1970 KRDU: 75/2012 KFAY: 76/1990 && .RAH WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 8 PM EDT this evening for NCZ025>027- 040>043-075>078-083>086-088-089. && $$ SYNOPSIS...MWS NEAR TERM...MWS/AB/AS SHORT TERM...Green LONG TERM...Hartfield AVIATION...Danco/MWS CLIMATE...RAH