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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 051505 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1100 AM EDT Fri Jul 5 2024 .SYNOPSIS... Surface high pressure across the western Atlantic and Deep South will shift east through tonight as a surface trough extends south across the Piedmont of Virginia and North Carolina. A cold front will approach the region from the northwest this evening and then move into and stall across Virginia and Carolinas this weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 1100 AM Friday... * Dangerously hot today with record high temperatures * Scattered afternoon and evening thunderstorms, especially across the west and north which may produce strong gusty winds The latest surface analysis shows a couple of surface troughs extending north to south across VA and the Carolinas with the eastern trough likely enhanced by convection on Thursday evening. A 1017mb surface high across the western Atlantic extends southwest into the coastal Carolinas and FL. A cold front extends southwest from a weak surface low over northern PA into eastern OH and central KY and central TN. The airmass across central NC is already very warm and humid with surface dew points in the lower 70s with a few mid 70s across the Coastal Plain. Temperatures as of 10am were already in the lower to mid 80s. The morning sounding from KGSO depicted a moist profile with a PW of 1.83 and a generally light westerly flow. The morning low level thickness was observed at 1428m, 10m warmer than Thursday and the KMHX RAOB was 15m warmer as well. These soundings suggest highs will range from 3 to 5 degrees warmer today, than yesterday in many locations. Highs should range in the upper 90s to low 100s in most locations and will threaten daily high records in many locations. The mid shift upgraded the Heat Advisory to an Excessive Heat Warning for the ne Piedmont, nrn Coastal Plain, and the nrn Sandhills, where heat index values around 110 F will be likely this afternoon. The Heat Advisory remains otherwise unchanged in time and location, for peak heat index values generally in the 105 to 109 F range. Visible satellite imagery depicts mainly clear skies across central NC this morning with some patchy stratus across parts of the southern Piedmont and Sandhills. The sunshine will will quickly erode morning convective inhibition and the atmosphere will become moderately unstable with MLCAPE values of 1200 to 2400 J/Kg this afternoon, notably more than on Thursday. Expect cumulus clouds to pop after 11am and they should be more widespread that previous days. Isolated to widely scattered convection may develop in the Piedmont and Sandhills in the vicinity of the lee trough with more numerous thunderstorms apt to develop across western NC and near the VA border area north of the Triad and then push east. Storms today will still have the potential to be efficient wind producers with an inverted-V sounding noted and with DCAPE values in excess of 1000 across the western Piedmont. SPC has introduced a marginal risk of severe storms across the northwest Piedmont area with this in mind. Convection will translate east during the evening and gradually weaken during the mid to late evening but unlike previous nights, it will tend to persist a bit later into the overnight. Outside of cooling from thunderstorms, temperatures will be slow to cool this evening. Expect temperatures to persist in the lower and mid 80s in most locations through midnight or later before eventually dropping into the mid 70s to around 80 by Saturday morning. -Blaes && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... As of 330 AM Friday... * Hot and humid conditions continue Saturday with heat indices climbing to 100 to 105 degrees * Isolated to scattered flash flooding possible as storms will be slow moving and efficient rainfall producers. A compact, but flattening, shortwave embedded within the broad troughing will lift through the Lower Great Lakes into southern Quebec by Sun morning. The related surface pattern will shift a surface low into the Northeast with a trailing cold front extending into the Ohio and Tennessee Valley. Weakening dynamics at the surface will likely prevent the surface cold front from traversing the Appalachian mountains. Ahead of the front and east of the mountains, a continued hot and humid airmass will be in place as early afternoon temperatures quickly rise into the 90s to around 100 degrees with surface dew points in the upper 60s to mid 70s, resulting in heat indices of 100 to 105 degrees. Heat indices over the western Piedmont may be closer to the mid 90s as increasing/thickening cloud cover spreads in from the west and proximity to greater chances for showers/storms and convective outflow slowing rise in afternoon temps. Although details will be dependent on convective activity Fri/Fri night, another heat advisory will likely be needed for at least the Coastal Plain and eastern Sandhills for Sat. Showers and thunderstorms are expected to initiate along a lee trough that develops with diurnal heating over the western Piedmont with the a hot and humid airmass in place along and east of the trough. Moderate instability is expected to develop by early afternoon as MLCAPE values rise to 1500-2500 J/kg and MLCIN erodes. Flooding will likely be the primary hazard with these storms with anomalous deep layer moisture (PWAT >2.25), warm cloud layer between 10,000 to 15,000 and weak cloud layer flow and Corfidi vectors. Additionally, deterministic Hi-Res guidance depicts initial storm outflow to congeal creating basically an effective front draped SW to NE across central NC that slowly progresses eastward with time. This orientation would align cloud-layer flow parallel to the front which would bring a risk for training storms. 00z HREF aligns with theses thoughts depicting of 1" to 2"/hr rain rates and the strongest storms capable of over 3"/hr. Current forecast has widespread rain of 0.5 to 1.5 inches, but as finer details become clear expect the range between min/mix to increase with isolated locations capable of seeing over 3 inches. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 330 AM Friday... A rather persistent pattern is expected through the remainder of the extended as central NC will be tucked between broad reinforcing troughing through the central CONUS with the stationary sub-tropical high broadly draped across the western Atlantic in the eastern GOM. NWP guidance has been consistent with a closed low drifting across the western Atlantic and retrograding towards the Carolina coast, but is expected to remain over the Atlantic. At the surface a diffuse pressure gradient will feature a lee-trough redeveloping over the region each afternoon with continued anomalous deep layer moisture in place as PWAT values remain at-or-above 2 inches. This pattern will favor continued above normal temperatures with highs in the mid 90s in the urban areas and overnight lows only reaching into the mid 70s. With continued heat related stresses heat related illnesses will be possible especially among individuals sensitive to heat and do not have access to effective cooling and/or adequate hydration. Diurnally favored showers/storms and storms will also be possible each afternoon into the evening, likely focused along the lee-trough and any subsequent outflow boundaries thereafter. Organized convection appears to be at a minimum with deep layer shear remains weak around 10 to 20 kts, strongest across the NW Piedmont, and result in mostly pulse summer-time showers/storms. Greatest coverage could be Tues into Tues night with proximity of mid/upper troughing swings through the Great Lakes region. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... As of 745 AM Thursday... Patchy MVFR visibility restrictions around GSO will become VFR by ~12Z. VFR conditions are otherwise expected away from scattered showers/storms that are expected to redevelop with afternoon heating. Some clustering and more-prolonged risk of showers/storms will be possible at INT/GSO this evening-early tonight, where lift will be maximized in the vicinity of a lee surface trough, outflow from upstream convection, and glancing influence of a mid-level trough. A slightly better chance (than recent mornings) of stratus and fog will exist late tonight-Sat morning, especially at INT/GSO, as low-level moisture and humidity values gradually increase. Outlook: A good chance of morning stratus and fog and mainly afternoon-evening showers/storms will exist through early-mid next week, as a surface trough/front settle into the region and interact with an unseasonably moist air mass in place. && .CLIMATE... Record High Temperatures: July 5: KGSO: 98/2012 KRDU: 102/1999 KFAY: 101/2002 July 6: KRDU: 102/2022 KFAY: 99/1990 Record High Minimum Temperatures: July 5: KGSO: 74/1999 KRDU: 78/1902 KFAY: 77/2005 July 6: KGSO: 76/1999 KRDU: 79/1900 KFAY: 76/2017 July 7: KGSO: 73/2019 KRDU: 77/1900 KFAY: 78/2017 && .RAH WATCHES/WARNINGS/ADVISORIES... Heat Advisory from 11 AM this morning to 8 PM EDT this evening for NCZ007-021>023-038-039-073>075-078-083>086-088-089. Excessive Heat Warning from 11 AM this morning to 8 PM EDT this evening for NCZ008>011-024>028-040>043-076-077. && $$ SYNOPSIS...Blaes NEAR TERM...Blaes SHORT TERM...Swiggett LONG TERM...Swiggett AVIATION...MWS CLIMATE...RAH