Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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043 FXUS62 KRAH 120745 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 337 AM EDT Fri Jul 12 2024 .SYNOPSIS... A frontal boundary over the region will pivot westward and stall out over the western Piedmont tonight. The stalled front will weaken and remain across the area Saturday, before diminishing Sunday. A lee trough will then be in place across the western Piedmont into early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 340 AM Friday... * Flood Watch remains in effect for all but the far western Piedmont counties until midnight tonight * Potential exits for 4+ inches of rainfall over portions of the Piedmont and Coastal Plain All remains on track with the forecast through tonight with little change to the overall synoptic pattern and thermodynamics. Satellite imagery and surface obs reveal a broad area of low pressure offshore of GA/SC. At the same time, a surface frontal boundary was present across the Piedmont of central NC and extending into VA. East of the boundary, dewpoints have risen into the mid to upper 70s, with current PWs upwards of 2.3-2.4 inches. With time, the majority of the guidance shows this area of low pressure to move inland into eastern portions of SC or just along the coast this afternoon, then take a ENE track while weakening into central to eastern portions of NC tonight into Sat morning. The circulation is most evident at 850 mb. With the cyclonic flow continuing to increase through the day, the surface boundary will slowly progress into the far western Piedmont and remain stationary or slowly move back east as the low tracks ENE overnight. There will be multiple waves of showers and storms through the morning, afternoon, and evening with the moist onshore flow, strong moisture transport, and frontogenetical forcing. The most widespread coverage of storms should be focused in the aftn/eve with diurnal heating, as MLCAPE ranges from 1200-1500 J/kg. The coverage of showers and storms should diminish by late this evening as the low pulls to the east and mid-level vorticity/energy shifts east with southwest flow taking over aloft. The 00Z CAMs are indicating the potential for some portions of the Piedmont and Coastal Plain to see 4-5+ inches of rainfall by tonight. The HREF localized probability-matched mean (LPMM), which tries to retain some of the high-res guidance of high rainfall rates, indicates that an early morning (between now and a few hours after sunrise) swath of showers/storms could develop roughly between the Triad and Triangle, roughly from NE to SW from Person/Granville Counties into Chatham to Moore Counties. Where this forms could vary by 50 or so miles on either side due to model spread. But the signal for this is likely due to frontogenetical forcing at the surface and from low-mid levels combined with nearly stationary storm motion. A second area to watch later this afternoon and evening will be along and east of US-1, when peak heating and very low LCLs will generate widespread showers/storms. Combined with slow storm motion, near all- time high PWs of 2.2-2.5 in, and moisture transport maximizing along/east of the Coastal Plain, will favor another swath of potential high rainfall totals. Of course localized totals of 2-3+ inches are possible anywhere in the Flood Watch area, but the two aforementioned locations were most evident in the guidance. Highs should range in the upper 70s N to the mid 80s in the south. Some patchy sun may shine in the Sandhills to southern Coastal Plain, but most of the day will be cloudy overall. After showers diminish in all but our far eastern zones overnight, low clouds are likely to persist, with some fog also possible. Lows should be in the low to mid 70s. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... As of 330 AM Friday... Though weakening, the stalled front will continue to bisect the area. Meanwhile, the axis of anomalously high moisture/PWATS will gradually shift eastward throughout the day. Following a possible early day lull, diurnal destablization should lead to scattered re- development of showers and storms during the afternoon and evening, mainly from the Triangle eastward. Highs ranging from upper 80s NE to lower 90s elsewhere. The moist/humid dewpoint air in the lower to mid 70s east of the front will result in heat indices in the lower 100s from the Triangle eastward. Balmy lows in the lower/mid 70s. .LONG TERM /SUNDAY THROUGH THURSDAY... As of 330 AM Friday... ...Dangerous Heat Returns Sunday Through the Middle Part of Next Week... The main weather story will be the return of Dangerous Heat. Staying under the influence of a ~591dm ridge and low-level W-SWLY flow, 1000-850 thicknesses and h8 temps are forecast to peak during the Monday-Wednesday period, topping out ~1445m and 23-24C respectively. Highs in the mid to upper 90s will be common place for Sunday through Wednesday, with Monday or Tuesday currently forecast to be the hottest day, with some lower 100s possible across central and southern NC. There is a fairly strong and consistent model signal for dewpoints to mix out into the lower 60s(and even quite possibly into the upper 50s)across the western Piedmont each afternoon, which should help to temper the heat risk over the western part of the state. However, four consecutive days of heat indices in the 103 to 108 F degrees is likely from the Triangle eastward. In terms of rain chances, a low-amplitude shortwave trough moving slowly east through the mid-Atlantic region Sunday afternoon through Monday will support isolated to scattered storm development Sunday afternoon and evening, followed by mostly sea-breeze convection Monday and isolated storms Tuesday, owing to the potential for weak disturbances to move through the area. The approach of a front from the NW and associated high rain chances late Wednesday and Thursday will likely break the heat wave and could bring some widespread significant rainfall to the area given the potential for the front to slow down or stall out across the area to end the work week. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... As of 206 AM Friday... A mixture of IFR to VFR conditions are expected to start the TAF period. These mixture of ceilings will trend to greater restrictions of IFR toward sunrise Fri as scattered to numerous showers and embedded storms penetrate westward into central NC with an area of low pressure along eastern SC. The first wave of showers is currently penetrating westward into the Coastal Plain. Most guidance shows this band impacting the eastern terminals (RDU/FAY/RWI) between about 08-13Z. We introduced a TEMPO group for storms during this time for these terminals given a signal of embedded storms in the high-res models. This wave of storms could form along or just west of RDU between 10 and 13Z and near FAY/RWI between 08-12Z. A better chance of widespread showers and storms will be during peak heating, coincident when high-res models show the greatest coverage of storms. It is at this time when restrictions should improve to MVFR to even some VFR. Rather than indicate an entire period of storms at the terminals, we focused the main storm risk when probability was highest, roughly between 18-22Z at GSO/INT, and 18- 02Z at RDU/FAY/RWI. Showers and storms should decrease in coverage between 00z-06z as energy starts to shift east of the terminals, resulting in CIG/VIS lowering back to IFR or lower conditions. Beyond 06Z Saturday: Lingering showers and embedded storms should decrease by early Sat, followed by LIFR/IFR ceilings Sat morning. Scattered storms are again favored Sat, mainly in the eastern sites. Morning low stratus or fog is possible Sun morning. Storm chances Sun-Tue will trend to be more isolated in nature. && .CLIMATE... Record High Temperatures: July 15: KGSO: 97/1974 KRDU: 99/1997 July 16: KGSO: 99/1915 KRDU: 101/1887 KFAY: 103/1937 Record High Minimum Temperatures: July 11: KGSO: 75/1992 KRDU: 77/1981 KFAY: 76/2019 July 12: KGSO: 76/2011 KRDU: 78/2011 KFAY: 80/1935 July 13: KGSO: 75/2017 KRDU: 78/2017 KFAY: 78/2017 July 14: KGSO: 77/1981 KRDU: 77/2017 KFAY: 80/2017 July 15: KGSO: 74/2019 KRDU: 76/1992 KFAY: 78/2015 July 16: KGSO: 75/2010 KRDU: 77/2010 KFAY: 78/1992 && .RAH WATCHES/WARNINGS/ADVISORIES... Flood Watch from midnight EDT tonight through Friday evening for NCZ007>011-022>028-039>043-074>078-083>086-088-089. && $$ SYNOPSIS...Kren NEAR TERM...Kren SHORT TERM...CBL LONG TERM...CBL AVIATION...Kren CLIMATE...RAH