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Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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804 FXUS62 KRAH 170100 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 900 PM EDT Tue Jul 16 2024 .SYNOPSIS... A strong subtropical ridge will gradually weaken over the Southeast though mid-week. A cold front will settle into the Carolinas on Thursday, then become quasi-stationary while weakening into the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 900 PM Tuesday... A few showers and storms still developing across the region along the boundary that is stretching from SW to NE. Precipitation is mainly focused over the Sandhills region and then NE along the US1 corridor. As the boundary pushes through the region this evening, energy along with loss of heating is expected to diminish. A few lingering showers are possible late overnight, but any showers are expected to be light. Lows tonight across Central NC will be in the mid/upper 70s. As of 400 PM Tuesday...A positive tilt, convectively-amplified shear axis in the mid-levels will persist from the lwr MS and TN Valleys newd and across the srn Appalachians and Carolinas through 12Z Wed, between a couple of subtropical highs centered over the srn Rockies and the cntl through swrn N. Atlantic. Weak, and weakly perturbed, wswly to swly mid-level flow will result across cntl NC. Within that regime, a couple of small MCVs appear to have developed within clusters of ongoing convection over nwrn NC and sern TN/nrn GA, respectively. The first will move enewd across the NC Piedmont through this evening, while the trailing one over sern TN will move across the Upstate of SC and into the srn/wrn NC Piedmont by 12Z Wed. At the surface, and on the wrn periphery of high pressure centered near and east of Bermuda, a couple of lee troughs have been apparent in observational data from cntl SC/GA newd into the NC Sandhills and over the far wrn Piedmont/Foothills of VA/NC, respectively. These troughs will continue to focus weak convergence and development of isolated-widely scattered convection this afternoon, with some potential for multi-cell clustering and ewd propagation into at least the nw Piedmont through early this evening, then probably in a weakening state as it encounters a nocturnally stabilizing environment from the Triangle sewd through ~01-02Z. While convection should consequently dissipate prior to midnight, some early morning redevelopment cannot be ruled out with the approach of the upstream MCV into the srn/wrn NC Piedmont near, and more likely just after, 12Z Wed. It will otherwise be muggy and very mild and mostly in the mid-upr 70s. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... As of 315 PM Tuesday... ...A heat advisory has been issued for the Coastal Plain on Wednesday from 12 PM to 7 PM... Potentially the final day of the oppressive heat is expected on Wed for central NC. Low-level thicknesses and 850mb temperatures subtly cool with glancing influence from a broad mid/upper trough as it pivots across southern Ontario through the period. The result should be highs not-as-hot as previous days, but still reaching into the mid/upper 90s by early afternoon with forecast heat index values, in the absence of storms, expected to rise above 105 once again in the Coastal Plain. Westward extent of the Heat Advisory remains uncertain as surface dew points mix out in the west and increased deep layer moisture will result in increased cloud cover and earlier storm initiation. The Heat Advisory was issued where greatest confidence in dangerous heat will be possible before storm initiation and may need to be expanded westward to include the Triangle with subsequent updates. Showers/storms are again expected to be in greater coverage compared to previous days as better moisture and slightly perturbed mid-level flow spreads into the area. The airmass by early afternoon will be hot and humid with MLCAPE 1500 to 2500 J/kg and moderate DCAPE around 1000 J/kg. Marginal storm organization will be possible as the upper trough pivots eastward and 15 to 25 kts of perturbed mid- level flow will leak east of the mountains and over the northern portions of the forecast area. Pulse-like airmass storms will be possible south of Raleigh with wet downbursts the most likely hazard. From Raleigh northward, some storm clusters congealing along common cold pool may result in isolated increased wind threat. && .LONG TERM /THURSDAY THROUGH TUESDAY/... As of 216 PM Tuesday... * Widespread rainfall expected Thursday into Friday * Unsettled weather continues this weekend into early next week * Cooler temperatures from Friday through early next week The forecast remains on track for widespread showers on Thursday as a slow moving cold front arrives in central NC, stalls, and remains in the vicinity through the weekend. The surface boundary will be slow to move through the area given front-parallel flow aloft from the southwest and as such, showers and thunderstorms will be slow moving/prone to training over the same areas. PW`s will range from 1.75 to 2 inches immediately ahead of the front and showers will certainly be efficient rain producers. Marginal amounts of instability ranging from 500 J/KG in the NW Piedmont to upwards of 1500 J/KG will be present ahead of the front although deep layer shear will only peak around 15-20kts and the severe weather threat appears to be limited. Taking a look at the grand ensemble of Canadian, GFS, and EC members, anywhere from 80-90 percent of members advertise measurable precip across the area late Thursday morning into the afternoon/evening hours, with a handful of members suggesting more than 2 inches of rain Thursday afternoon through Friday morning. 90th percentile NBM QPF is also in this range as well, and PoPs will be increased a bit during this period. Exact QPF amounts are still a challenge to pin down but the highest amounts should fall across the central/eastern portions of NC. The front will stall across eastern NC on Friday, then slowly retreat northwestward through the afternoon/evening. While the day may start off mostly dry, showers will quickly redevelop across the Coastal Plain and Sandhills by mid morning, then expand northwestward as the front shifts back over the NW Piedmont. Once again, nearly 80-90 percent of ensemble members indicate precip during this period and PoPs will be bumped upward through early Saturday morning. It`s conceivable an additional 1-2 inches of rain could occur during this period although it`s hard to say with certainty where this secondary QPF axis will set up as the front retreats through the area. Regardless, Thursday and Friday should be the wettest days of the forecast with periods of heavy rain and flooding possible. Temps during the day Thursday will remain near or above normal ahead of the front, turning noticeably cooler on Friday given cloud cover and rain with highs generally 5-8 degrees below normal. Looking at Saturday through Tuesday, ridging over Bermuda will gradually strengthen and shift westward, resulting in a return to a fairly typical July distribution of precip chances with the highest chances across the western Piedmont and a secondary focus area from sea breeze convection migrating inland. Temperatures will remain below normal this weekend, gradually moderating closer to normal by early next week. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... As of 745 PM Tuesday... A few thunderstorms are possible around KRDU and KRWI through late evening, otherwise mainly VFR conditions are expected tonight. Outlook: Mainly VFR conditions are expected to continue away from diurnally-driven convection that will gradually increase in coverage through Wed. A cold front will move into NC late Wed-Wed night, then become quasi-stationary over the region Thu-Sat. Higher chances of flight restrictions, both in and away from diurnally-maximized convection, will consequently result. && .CLIMATE... Record High Temperatures: July 17: KRDU: 100/1887 KFAY: 102/1932 Record High Minimum Temperatures: July 17: KGSO: 75/2013 KRDU: 80/1887 KFAY: 77/2019 July 18: KGSO: 76/1986 KRDU: 79/1887 KFAY: 77/2019 July 19: KGSO: 75/2016 KFAY: 77/2023 July 20: KGSO: 75/2019 KRDU: 76/2020 && .RAH WATCHES/WARNINGS/ADVISORIES... Heat Advisory from 11 AM to 8 PM EDT Wednesday for NCZ011-027- 028-042-043-078-089. && $$ SYNOPSIS...MWS NEAR TERM...CA/MWS SHORT TERM...Swiggett LONG TERM...Leins AVIATION...Badgett/MWS CLIMATE...RAH