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Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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899 FXUS62 KRAH 190519 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 117 AM EDT Fri Jul 19 2024 .SYNOPSIS... A front will remain will settle across central NC through the weekend resulting in unsettled weather and cooler temperatures. && .NEAR TERM /THROUGH TONIGHT/... As of 310 PM Thursday... Latest satellite and radar indicate that the surface cold front likely extends from eastern TN into south-central VA. A surface trough/boundary extends from just SE of the Triad into the northern Triangle region and the far NE Piedmont into the northern Coastal Plain. Over the next several hours into the late afternoon, a line of showers and storms presently over the Triangle and northeast Piedmont should continue to progress south and east into the central Coastal Plain into early evening hours. Damaging winds will remain the primary threat with these storm cells. Mesoanalysis also reveals a weak surface low over the Triangle. In addition to the severe risk, the Flood Watch remains in effect and isolated flash flooding could develop over the next few hours along and east-northeast of the Triangle as training of storm cells becomes increasingly favored along the low pressure system. The flood threat should wane by mid to late evening. A second batch of storms also exists across far western NC out ahead of the cold front. The ARW, which has depicted the current placement of storms reasonably well, shows this activity reach the southern sections of the Triad into the southern Piedmont and Sandills later this afternoon and into the mid to late evening. This seems reasonable given upstream development just west of Charlotte. This batch will also have the threat of damaging winds. Isolated flash flooding cannot be ruled out with these line of storms as well but fast-moving cells should prohibit any flood watch in these areas at the moment. Most storm activity should wane by late evening, exiting the Coastal Plain and Sandhills around midnight or shortly thereafter. Guidance again favors the development of low clouds and possible fog as the cold front settles into the NC/SC border by Fri morning. The best chance of fog would appear to be along/south of the boundary, where moisture-rich air remains. This would be in the Sandhills to Coastal Plain region, but perhaps also the Triangle. Overnight lows will dip into the upper 60s to lower 70s. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... As of 230 PM Thursday... The weak frontal zone (more of a sturdy outflow than a true synoptic cold front) will be pushed to along the E and S edges of the forecast area by Fri morning, propelled in part by large scale mid level troughing from New England and the N Mid Atlantic coast SE across the Ohio Valley and central Miss Valley. The front is likely to stall there and weaken further through Fri night as a wavy mid level southern stream southwesterly flow persists, parallel to the surface frontal zone and on the E side of a mid level trough extending from SW MI through the Miss Valley to NE TX. The deepest moisture, in the form of a stream of 2.2-2.4" PW, will be pushed to across our SE half. While there will not be quite as much upper divergence as today, the upper jetlet snaking from central TN through N PA and off Cape Cod and the Canadian Maritimes in conjunction with passage of a series of minor mid level perturbations may provide added forcing for ascent, on top of the favorable thermodynamics (projected SBCAPE of 1500-2000 J/kg), although deep layer bulk shear will remain rather modest at just around 20 kts. Given the fairly slow storm motion, the potential for multicell clusters, and the deep warm layer nearing 4 km, the threat for locally heavy flood-producing downpours across the SE remains valid, and this threat will be enhanced in areas that get considerable rainfall through tonight. Will have highest pops across the S and SE, but expect above-climo pops areawide. Showers/storms should have plenty of juice in terms of low level moisture and warmth to keep moderate CAPE going well into the night, so expect storms to be maintained through the evening and slow to wind down overnight. After highs in the 80s to around 90 under variably cloudy skies, expect lows of around 70 to 75 Fri night. -GIH && .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 /06Z FRIDAY THROUGH TUESDAY/... As of 117 AM Friday... Aviation conditions are expected to further deteroirate this morning as MVFR/IFR (and possible fleeting LIFR) stratus develop across most of central NC. Confidence in sub-VFR ceilings is highest at KRDU/KFAY/KRWI. KINT/KGSO may see a bit more inconsistent sub-VFR ceilings through sunrise. Otherwise, a few lingering showers/isolated storms should continue to dissipate with time this morning. Any lingering stratus should rise to VFR by mid to late morning. Additional isolated to scattered showers/storms are then likely this afternoon, with the best chances at KRDU/KFAY/KRWI. While these showers/storms will wane this evening, additional showers and storms will be possible late tonight as an upper wave approaches from the south. Beyond 06Z Saturday: Showers and storms will continue into this weekend as a front stalls over the area. Early morning fog and stratus will be possible each day as well. The wet pattern will continue into early next week. && .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... none. && $$ SYNOPSIS...Luchetti NEAR TERM...Kren SHORT TERM...Hartfield LONG TERM...Leins AVIATION...Luchetti CLIMATE...RAH