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Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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645 FXUS62 KRAH 180626 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 225 AM 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 /THROUGH TONIGHT/... As of 810 PM Wednesday... Expired the Heat Advisory for the day... As the lee trough moves across the region early this evening showers and storms are possible over the next few hours. The stronger storms along the VA/NC border are expected to continue east along the border, with heavy rain and gusty winds being the main threat. Storms in SC moving into NC is expected to bring another round of isolated showers and storms to the Sandhills and southern Coastal Plain region in the next few hours. The entire area is anticipated to be clear of all precipitation shortly after midnight. Lows in across the area will be in the the mid 70s. As of 242 PM Wednesday...Early afternoon satellite imagery and surface obs depict a weak NE/SW oriented boundary across central NC, located roughly along US-1 as of 18Z. Dewpoints east of the boundary remain in the low to mid 70s whereas they have mixed out into the upper 60s to the west. Along this interface, quite a bit of cu have developed and the first returns of the day are showing up on radar. SPC mesoanalysis suggests nearly 3000 J/KG of MLCAPE on offer eastward into the Coastal Plain and I would expect these storms to continue to develop and expand through mid afternoon. There isn`t much in the way of upper level forcing driving this convection and deep shear remains relatively weak around 20kts, so I wouldn`t expect much in the way of severe weather with this line as it moves east but brief periods of heavy rain and gusty winds are a safe bet with the strongest storms. Meanwhile to the west, longwave troughing across the OH valley and upper level jet dynamics associated with the 120kt 250mb jet over northern Ohio will help support additional showers and storms across the western Piedmont later this afternoon into the evening hours. A few storms have already developed on the mountains and these should expand/move eastward into the CWA by mid/late afternoon. 12Z HREF and several HRRR runs maintain convection along and north of I-85 into the evening hours and I will maintain 40-60 PoPs in those areas through late evening. Meanwhile to the east I`ll keep a few hours of 20-40 PoPs to cover the ongoing convection along the central NC boundary. With storms already starting to develop and an increasing veil of cirrus moving northward, we`re likely at or very close to our maximum heat index for the day which ranges from around 100 upwards of 107-108 depending on location (upper 90s in the western Piedmont). The ongoing Heat Advisory covers things well and may ultimately be able to be cancelled a few hours early but with numerous readings still in the triple digits, we`ll leave it as is for now. It`ll be another mild night tonight with temps falling into the mid 70s. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 242 PM Wednesday... Longwave troughing and the attendant surface cold front will move eastward during the day Thursday, eventually making its way across the mountains and into NC during the afternoon hours. With southwesterly flow aloft, the front will make slow eastward progress as it traverses the state. While the day may start off mostly dry, showers and storms should quickly develop along the front by early afternoon. Exactly where storms initiate tomorrow is still TBD but HREF would suggest somewhere around or just east of the Triad would be the most favored area. From there, anywhere from 1000-1500 J/KG will be on offer but once again deep shear remains meager. By this time upper level support should be displaced well north into New England although we may still feel the effects of the nearby right entrance quadrant of the upper level jet. SPC has placed much of NC within a MRGL risk for severe weather tomorrow, and some of the stronger storms may be capable of producing gusty winds bordering on severe thresholds. PoPs will remain generally less than 20 percent in the morning hours, quickly ramping up to 80-90 percent during the afternoon. Given the slow progression of the surface front through the area, training cells could be a concern. However nearly a week removed from our last heavy rain event, soils should be able to accept at least some rainfall before saturating. Isolated flooding of low lying areas and normally flood-prone locations is a possibility but we aren`t expecting widespread flooding as this line of convection moves through the area. HREF PMM QPF indicates 1-2 inches of rain with the front as it moves through central NC (lesser amounts around 0.50 - 0.75 inches around the Triad, highest amounts across the Coastal Plain). This fits in with NBM QPF and aligns with the WPC ERO SLGT risk for Thursday. As for temperatures, expect highs to range from the upper 80s in the west to the low/mid 90s in the east. For portions of the southern Coastal Plain that will reside in the warm sector for most of the day, heat indices may hit triple digits for a brief time. Elsewhere the arrival of storms and/or debris clouds should keep heat index values below Heat Advisory thresholds. Lows tomorrow bottoming out in the lower 70s. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 225 AM Thursday... As the extended forecast period begins, an unseasonably strong upper low will be over Quebec, with an upper level trough extending south into the Gulf of Mexico. While the upper low will move east over the Atlantic Ocean by Monday, the trough will remain nearly stationary over the Mississippi River valley into next week. Weak southerly flow will allow continued advection of moist air from the Atlantic Ocean and Gulf of Mexico, and with the trough to the west acting as a constant forcing mechanism, showers and thunderstorms can be expected every day. Went with likely pops Saturday through Monday, then capped pops at high chance Tuesday and Wednesday because of the convective nature of the precipitation and uncertainty this many days out. Most of the region will continue to be under a marginal (level 1 of 4) risk for excessive rainfall with any stronger thunderstorms that have high rainfall rates, despite nearly the entire forecast area being in moderate drought. While the weather will remain quite humid, daytime highs limited to the upper 80s and lower 90s with the widespread cloud cover should keep heat indices under 100 degrees, so no heat headlines are expected. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... As of 131 AM Thursday... KRWI and KRDU may experience some residual showers/storms the next few hours, but overall terminals should mainly remain VFR through this afternoon. Scattered to numerous showers and storms are expected to develop this afternoon and evening, peaking near KRDU/KRWI/KFAY later today. As such, expect temporary flight restrictions to develop at these sites at times later today and tonight. The bulk of the heavier rain should move east of central NC late tonight, however MVFR ceilings are expected to fill in over much of the eastern two thirds of central NC starting near 03Z. Beyond 06Z Friday: A cold front will sag into and stall across the region Friday through Sunday which will increase the chances for sub- VFR conditions through this weekend. && .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...Leins NEAR TERM...CA/Leins SHORT TERM...Leins LONG TERM...Green AVIATION...Luchetti CLIMATE...RAH