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Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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241 FXUS62 KRAH 181752 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 152 PM EDT Thu Jul 18 2024 .SYNOPSIS... A cold front will approach the region today, bringing showers and storms to the area. The front will remain stationary through the end of the week resulting in unsettled weather and cooler temperatures. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... As of 1150 AM Thursday... * Flood Watch expanded southwest to include the Triangle area and the Central Coastal Plain. There was little change to the going forecast for this afternoon and tonight. Based on 24-hour QPF amounts, areas from Person to Halifax Counties received some 2-4 inches of rainfall last night. Based on forecast QPF later today and tonight, 1-3 inches of additional rainfall is possible. Current 3-hr FFG values in these counties ranges from 1.5 to 2.5 inches. As a result, localized flash flooding may occur and we went ahead and issued a Flood Watch until midnight tonight, collaborating with neighboring offices. Storms appear to still be relatively fast moving, even with the latest 12Z HRRR, but given prior considerations from the prior discussion, some training may be possible, especially over previously saturated ground. Surface analysis shows the front is draped presently from eastern TN into portions of WV and central PA. A pre-frontal trough was located across western NC and into western VA. It still appears convection will develop along the trough or just ahead of the cold front, with storms initially being isolated to scattered. That activity is still expected to become numerous to widespread as they track ESE into the mid to late evening hours. The main action still looks to be between about 2 to 8 PM, with most storm activity waning after midnight. The front will slowly settle along the NC/VA border by sunrise Fri. Highs this afternoon are expected to be in the upper 80s to lower 90s, as sunshine ahead of storms should allow us to warm up as most guidance suggests. If radar and observational trends become more apparent this afternoon, the Flood Watch may be expanded to include portions of the Triangle. But as it stands, there was limited confidence to include these counties. Lingering convection over the northern Coastal Plain early this morning will continue to diminish over the next few hours. Aloft, water vapor imagery depicts broad swly flow over the southeast associated with an upper trough currently lifting into the northeast. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... As of 312 AM Thursday... The front will become quasi-stationary over central NC on Friday while the anomalously moist airmass lingers. Shear will weaken Friday afternoon as the upper jet streak pulls off into eastern Canada. As such, upper forcing during the daytime will be minimal as weak ridging builds over the southeast. However, given the presence of the front, and the anomalously moist airmass, scattered showers and storms will likely develop during peak heating Friday afternoon. Overall coverage will likely be less compared to Thursday, but given slower expected storm motion, any training cells could lead to instances of localized flash flooding. The greatest threat for flash flooding Friday will be south and east of Raleigh, areas that will likely receive the highest rainfall on Thursday. Convection should generally wane with loss of heating Friday evening. Max temperatures Friday will reach the upper 80s. Overnight lows will remain warm in the 70s. && .LONG TERM /SATURDAY THROUGH THURSDAY/... As of 1254 PM Thursday... The forecast from Saturday onward will feature broad southwesterly flow aloft as a 594dm H5 ridge remains in place off the southeast coast. Longwave troughing will stretch from eastern Canada back through the Ohio valley into eastern Texas next week, with a series of weak embedded shortwave troughs moving through the flow. This will allow for daily shower and thunderstorm chances, primarily during the afternoon and evening hours with a fairly typical climatological distribution of PoPs (highest values across the NW Piedmont, Sandhills/southern Coastal Plain). While grand ensemble model agreement is good for this time period, timing the exact arrival of any of these shortwaves is a challenge although it looks like Saturday and Sunday may be particularly wet, with decreasing chances Monday and/or Tuesday as mid level dry air works in from the east. A further confinement of the highest PoPs to the NW Piedmont looks warranted Wednesday and Thursday as the center of the offshore ridge migrates closer to the coast, but I`ll maintain at least 30-40 PoPs area-wide given the inherent uncertainty in forecasting convection within low shear environments such as this. The primary threats with any storms this week should be locally heavy rainfall as shear and other thermodynamic parameters are largely unsupportive of widespread severe weather. Temperatures this weekend into early next week should be within a few degrees of normal with highs in the upper 80s to lower 90s. Overnight lows will once again remain on the mild side with readings generally in the low to mid 70s. With these types of temperatures, heat indices should generally remain at or just below triple digits this weekend into next week. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... As of 152 PM Thursday... The threat of showers and storms remain the main challenge for the immediate near term of the TAFs, followed by low CIG and possible fog early Fri. Latest satellite and radar imagery reveals that a trough/boundary extends just south of the GSO/INT terminals. This is out ahead of a cold front that will move through later tonight into Friday and settle south of the terminals Fri morning. Given this boundary, the highest forecast confidence for TSRA is currently at RDU/FAY/RWI between 19Z and 01Z, earliest at RDU and latest at FAY. The storm risk may just miss the Triad terminals, but we kept the TEMPO group in place, between 18Z and 22Z, where confidence is highest for storm coverage. Storms are expected to move south of the terminals late tonight as the boundary slides south. As that happens, guidance shows a strong signal for IFR/MVFR stratus, with perhaps LIFR early Fri morning. Confidence was too low to introduce fog but that chance appears highest at the eastern sites along the front, at RDU/FAY/RWI. Ceilings should lift to VFR by mid to late morning Fri. Outlook: Another round of scattered showers and storms are possible Fri aftn/eve, especially at the south/western terminals of GSO, INT, FAY. Storm chances will persist in the forecast each day into Tue as rich moisture and frontal forcing lingers over the area. Morning stratus or fog is also possible each morning. && .CLIMATE... Record High Minimum Temperatures: 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 July 21: KGSO: 76/2011 KRDU: 78/1932 KFAY: 80/2017 July 22: KRDU: 78/2011 July 23: KRDU: 78/2011 July 24: KRDU: 79/2011 KFAY: 79/1945 && .RAH WATCHES/WARNINGS/ADVISORIES... Flood Watch until midnight EDT tonight for NCZ007>011-024>028- 041>043-078. && $$ SYNOPSIS...DL NEAR TERM...Kren SHORT TERM...Luchetti LONG TERM...Leins AVIATION...Kren CLIMATE...RAH