Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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043 FXUS62 KRAH 270000 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 759 PM EDT Wed Jun 26 2024 .SYNOPSIS... Hot southwesterly flow will persist this afternoon and evening 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 slowly move south into portions of the area early Friday before lifting back north as a warm front. && .NEAR TERM /THROUGH TONIGHT/... As of 315 PM Wednesday... A shortwave trough and cold front currently over the mid-MS Valley will move east to the Appalachians by tomorrow morning. Meanwhile S/SW flow around Atlantic high pressure is bringing a very hot and seasonably humid airmass into the region, with widespread temperatures in the mid-to-upper-90s. Dew points have mixed out into lower-to-mid-60s across the Piedmont but are still in the upper-60s to mid-70s across the Sandhills and Coastal Plain. This is resulting in observed heat indices as high as 105-110, and a Heat Advisory remains in effect from the Triangle south and east until 8 PM this evening. There is also potential for isolated to widely scattered showers and storms for the rest of the afternoon into early evening. Scattered cumulus has developed and a few tiny showers have popped up over the western Piedmont, but deeper convection remains over SC. CAMS vary greatly on coverage, with the ARW and NSSL quite aggressive compared to the HRRR, but the aggressive models appear to be overdoing it based on current radar. Furthermore, unlike yesterday we don`t have a strong moisture boundary/convergence axis across the area to act as a focus for deeper convection. Despite this, SPC mesoanalysis does depict 1000-3000 J/kg of MLCAPE across central NC, highest in the SE. The best chances for any convection are in the Sandhills and central/southern Coastal Plain with the sea breeze, and over the NW Piedmont with the lee surface trough in place. Shear is virtually non-existent so any cells should be short-lived and organized severe weather is not expected. But given the high DCAPE out there (1000- 1600 J/kg), an isolated damaging wind gust can`t be ruled out. As the mid-level trough and cold front approach later tonight, the northern Piedmont and northern Coastal Plain could be grazed by an associated area of showers and storms moving from west to east across VA from about 03z to 12z. However, given the best forcing will be to our north and the unfavorable diurnal timing, it should be fairly weak and only have slight to low chance POPs. Lows tonight will be quite mild once again, in the lower-to-mid-70s (7-10 degrees above normal). && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 315 PM Wednesday... A Heat Advisory has been issued for portions of central NC Thu, with heat indices between 102 and 108 over portions of the Triangle, Sandhills, and Coastal Plain. A frontal boundary will likely be draped northeast to southwest from the Mid-Atlantic into eastern TN to far western NC early Thu. The front will try to move south and east through the day and evening as high pressure settles into the northern Mid-Atlantic in western NY. However, the front will most likely get hung up along the NC/VA border sometime early Fri. Some of the high-res models are indicating a secondary boundary draping southward with convection from Wed night to early Thu morning along US-64. Perhaps this is related to the lingering discontinuity currently over southern VA. However, other guidance indicates less of a defined wind shift. How this evolves may ultimately depend on what happens with convection tonight across northern NC and southern VA. With the uncertainty, we believe that with warm overnight lows tonight in the mid 70s, high dewpoints in the 70s again Thu, and max temperatures over the Triangle, Sandhills, and Coastal Plain in the mid to upper 90s, will lead to another heat risk across the region. Heat indices could be as high as 108 over the far eastern Sandhills and southern Coastal Plain. The only fly in the ointment is whether convection/clouds start earlier in the day to limit daytime heating. For now, though, we hedged toward enough solar heating for the higher heat risk. Highs will be lower in the northwest Piedmont with upper 80s to near 90. As for convection, some CAMs are showing the greatest coverage south and east of the Triangle along their effective boundary, while others extend convection further west to mainly along/east of US-1. We hedged with this further west solution, thinking that any boundary would be draped along US-64. Machine-learning models and guidance suggest the prime storm risk would be between 1 pm and 8 pm, with greatest coverage along/east of US-1, with storms waning by late evening and overnight as a mid-level trough axis slides south of the region. SPC has continued a marginal risk of severe storms mainly over the Sandhills to Coastal Plain. However, we would not be surprised if that expands north and west to include the Triangle in later updates. Point forecast soundings indicate high instability upwards of 2000 J/kg, DCAPE around 1000 J/kg, and decent shear of 20- 30 kts from the WSW supportive of a damaging wind threat with any stronger organized cells. Hail can also not be ruled out. As convection wanes overnight, low stratus or fog may develop by early Fri with lows in the upper 60s to mid 70s. && .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 /00Z THURSDAY THROUGH MONDAY/... As of 759 PM Wednesday... VFR conditions will continue for the most part over the 24 hour TAF period. However, another band of showers (and perhaps a few storms) may glance our northern sites (KINT/KGSO/KRDU/KRWI) late tonight/near sunrise Thursday morning. Associated fleeting MVF/IFR stratus may impact these terminals during this period as well. Conditions should improve to VFR by mid Thursday morning, but some residual stratiform rain may linger across our northern areas. Additional showers and a few storms will be possible Thursday afternoon and early evening. Confidence is too low to include in any TAF except for KFAY where guidance suggests the best chances for an afternoon storm. 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 from 11 AM to 5 PM EDT Thursday for NCZ041-042-077-078- 085-086-088-089. && $$ SYNOPSIS...Kren NEAR TERM...Danco SHORT TERM...Kren LONG TERM...Hartfield AVIATION...Luchetti CLIMATE...RAH