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Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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209 FXUS62 KRAH 171740 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 142 PM EDT Wed Jul 17 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 1048 AM Wednesday... * One more day of hot temperatures * Showers and storms possible this afternoon Mid morning water vapor imagery and surface analysis depicts longwave troughing across the lower Great Lakes, with a cold front stretching from western NY through OH and into IL. Across NC, high pressure remains off the coast with broad southwesterly flow aloft. A series of weak perturbations are noted in WV imagery across GA and SC, and there is some ongoing convection off the southeast NC coast, but conditions remain mostly dry across central NC. Despite some early morning cloud cover, temperatures have quickly risen into the lower 80s in the Triad and in the mid/upper 80s in the east. One more day of dangerously hot temperatures and high heat indices are in store for the region as dewpoints remain in the low to mid 70s with air temps in the mid to upper 90s. Heat Advisories were expanded overnight and look good based on obs as of 10am. As for storm chances, 12Z HREF continues to depict an active afternoon not only across the western Piedmont but also across the Coastal Plain. Curiously enough, several consecutive runs of the NAM nest and HRRR aren`t terribly enthused about storm chances in the east, and debris cloud cover from morning convection off the coast could limit heating and storm potential across the those areas. I`ll maintain at least a 30-40 percent chance of storms across the southeast as it is mostly clear across the Sandhills and the entire CWA should rapidly destabilize by early afternoon. However the best forcing for ascent and synoptic scale forcing will be closer to the longwave trough as it migrates into New England this afternoon, and storm chances will remain highest in the NW Piedmont, decreasing as one travels eastward. Forecast remains in good shape overall. Hot today, with overnight lows in the mid to upper 70s. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 345 AM Wednesday... Broad mid-level troughing will dig from New England into the lower MS Valley on Thursday, as a cold front approaches central NC from the NW before moving through on Thursday night. The front will be slow moving given the front-parallel (southwesterly) flow aloft, which could result in training convection. There will be plenty of moisture for this front to tap with PW values of 2 to 2.25 inches, along with marginal to moderate instability of around 1000-2500 J/kg, highest SE. There will also be upper support as we will be in the right entrance region of a jet streak over New England and the northern Mid-Atlantic. Thus widespread showers and storms are expected, and the vast majority (80-90%) of GEFS/EPS/CMC ensemble members depict precipitation. Categorical POPs continue, maximized with daytime heating in the afternoon/evening, though some chance POPs still linger overnight. Total rainfall amounts on Thursday and Thursday night are expected to range from 0.5 inches NW to as much as 2 inches in the east, but locally higher amounts will be possible especially where slow-moving storms occur. WPC continues a slight (level 2 of 4) risk for excessive rain across roughly the eastern half of central NC, with a marginal (level 1 of 4) risk elsewhere. While the strongest mid-level flow will be north of the region, the flow will still be perturbed enough that 20-30 kts of deep layer shear is possible. So SPC has a marginal (level 1 of 5) risk for severe storms, with damaging winds the main hazard. The dangerous heat will finally come to an end on Thursday despite still being ahead of the front, thanks to all the clouds and precipitation. Forecast highs are in the upper-80s to lower-90s (near normal), with lows Thursday night in the upper-60s to lower-70s. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... As of 142 PM Wednesday... The extended will continue to feature high rain chances, particularly in the beginning part of the period into the weekend. Somewhat lower chances, but still above climo, will exist for the early to middle part of next week. On Friday, the cold front approaching from Thu is forecast in most of the guidance to settle along the NC/SC border, then slowly lift back north as a warm front Fri night to Saturday evening. During this time, a trough/shortwave will be present over the TN valley, fueling energy streaming in from the SSW and PWAT values roughly 120- percent of normal. Storm chances will remain elevated at this time with the boundary in place. WPC has retained a slight risk of excessive rainfall across our SE zones Fri along the stalled front. A marginal risk remains in place Sat as the front lifts back northward in the moist southerly flow. Temperatures Fri/Sat look to top out in the mid to upper 80s, warmest in the south to near 90. This will be lower than the past several days with added rain chances and cloud cover. As we head from Sunday into the middle of next week, the front looks to become more diffuse and washed out. A Bermuda high will exert more influence, with continued warm and humid flow persisting. Aloft, the trough over the TN valleys weakens and a ridge over the western Atlantic will gradually shift west, resulting in a slight rise in heights. This should favor a trend toward less rain chances each day. However, PoPs will remain above climatological normals as we remain in that moist and unstable environment, as well as with slight troughing to our west over the Mid-Mississippi Valley advecting in energy from mid-levels. WPC has another marginal risk of excessive rainfall over the entire area Sunday. While there may not be any main surface features, a Piedmont trough and sea-breeze may enhance storm chances, focused mainly in the afternoon and evening hours. Highs will largely hover in the mid/upper 80s to lower 90s, trending warmer by midweek. Heat indices currently look to stay below advisory criteria given the daily rain chances above seasonal normals. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... As of 631 AM Wednesday... VFR conditions will prevail for much of the 24 hour TAF period. However, scattered showers and storms will develop and spread west to east this afternoon through tonight. Associated brief sub-VFR restrictions could develop at any terminal during this period. Any lingering showers/storms should diminish overnight. Early morning stratus looks possible across the I-95 corridor Thursday. However, confidence was too low to include in the KRWI or kFAY TAFs with this package. Outlook: A cold front will sag into and stall across the region Thursday through Saturday which will increase the chances for sub-VFR conditions through this weekend. && .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 this morning to 8 PM EDT this evening for NCZ008>011-024>028-040>043-075>078-084>086-088-089. && $$ SYNOPSIS...MWS NEAR TERM...Leins SHORT TERM...Danco LONG TERM...Kren AVIATION...Luchetti CLIMATE...RAH