Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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889 FXUS62 KRAH 041449 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1045 AM EDT Thu Jul 4 2024 .SYNOPSIS... Surface high pressure will extend across the western Atlantic and Deep South through tonight and then weaken and shift east on Friday. A cold front will approach the region from the northwest late Friday and then move into the Carolinas during the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 1045 AM Thursday... * Hot and humid conditions will return this afternoon. * Scattered thunderstorms will drift into north-central NC this afternoon and move into the NC Piedmont this evening as they weaken. * Storms will be efficient in producing strong gusty winds. The morning surface analysis shows high pressure centered across the western Atlantic extending west into the eastern Carolinas and the eastern Gulf of Mexico. A cold front extends from the eastern Great Lakes southwest across the western OH Valley and into the MO Valley. A weak lee trough is noted across central VA and NC. Further aloft an anomalously strong west to east 500mb ridge was centered across the Deep South. The main belt of westerlies extend from a trough across across western KS/NE and into the Great Lakes. The air mass across central NC this morning is warm and relatively moist with PW values of 1.6 to 1.8 inches or around 110% of normal. Morning low level thickness values ranged from about 1410 to 1420m, with the greatest thickness values extending south to north across the western Piedmont of the Carolinas. KGSO observed a thickness values of 1418m this morning, that`s 25m greater than yesterday at 12Z. Regional radar imagery shows a few clusters of showers and storms moving across eastern KY and southern WV early this morning. This convection is supported by a series of disturbances around the periphery of the upper level ridge including a couple of MCVs from overnight convection. The latest visible satellite imagery shows mainly clear skies across central NC with some enhanced cumulus clouds in the NC mountains and cloudiness across KY/WV associated with the convection. The upper level ridge will relax a bit today allowing the train of disturbances across the TN Valley to take a slightly more southern trajectory into southern VA and perhaps northern NC this afternoon and evening. With a slightly weaker ridge, mid-level lapse rates will steepen slightly and strong diurnal heating combined with dewpoints in the upper 60s to lower 70s will result in moderately unstable airmass this afternoon with MLCAPE values ranging around 1500 J/kg. Isolated convection may develop late this afternoon near the lee trough with slightly better convective coverage likely across southern VA in the stream of disturbances aloft that will be aided by differential heating, the lee trough, and outflow from ongoing convection to the north. This area of widely scattered convection will shift south and east into northern NC late this afternoon and into the Piedmont this evening as it weakens. Recent high res guidance suggest a downward trend in coverage from last nights guidance, especially during the evening, focusing rain chances in the Triad and near the VA border counties. With strong heating today and deep boundary layer mixing, inverted-V thermodynamic profiles are expected supporting DCAPE values well in excess of 1000 and likely resulting in efficient production of strong gusty winds with convection. With limited forcing for ascent, expect the convection to wane during the mid evening and would be surprised if much if any rain makes it south of KRDU or KRWI with all of the convection dissipating by midnight. With a hotter airmass and low level thickness values 25m higher than yesterday in many locations, highs today will range between 6 and 9 degrees hotter than on Wednesday and range in the mid 90s to around 100. Expect highs to reach daily records at RDU and FAY. With boundary layer mixing, dewpoints will mix out a bit this afternoon and temper heat index values that will range in the upper 90s to lower 100s in most locations with a few spots including KRDU, KFAY and KGSB flirting with 105F. Skies will be partly cloudy overnight with a mix of some patchy high clouds and perhaps some patchy stratus or low clouds across the south and southeast. It will remain warm and muggy tonight, with lows mainly in the mid 70s. -Blaes && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 410 AM Thursday... ...Hot and humid conditions bring the risk for heat related illnesses Friday and Saturday... A mid-level subtropical ridge centered over the GOM states will extend up through the southern Mid-Atlantic in between broad troughing over the central CONUS and a closed low drifting by Bermuda through Sat. At the surface, an occluded low over the Upper Great Lakes will slide ENE into southern Quebec by Sat evening as a compact shortwave lifts through the eastern edge of the longwave troughing. Within the deep tropospheric southwesterly flow, low- level thickness steadily rise to around 1445m (30m above normal) and 850mb temperatures soar to 21 to 23 C Fri afternoon. In the absence of showers and convective outflow during the afternoon, this pattern will support well above normal temperatures into the upper 90s and low 100s with heat index values ranging from 100 to 107 degrees. Little overnight recovery is expected Fri night as continued humid airmass and lingering cloud cover will keep lows in the mid to potentially upper 70s in spots. This would result in heat illnesses likely for anyone without access to effective cooling and/or adequate hydration. Some afternoon relief will be possible on Sat especially over the western Piedmont mid/upper level clouds spread in from the west ahead of trailing cold front. The cooler and drier air behind the cold front will likely struggle to traverse the mountains with another night of mid 70s expected. As for convective potential, on Fri greatest coverage of showers/storms will likely originate over the NC mountains in the vicinity of the lee trough and slowly shift eastward through the afternoon into the evening hours. The airmass within and ahead of the storms will be characterized by around 2000 J/kg of MLCAPE and 20 kts of 0-6km shear. Little storm organization is expected given the weak deep layer shear, but isolated strong to potentially severe wet downbursts and isolated congealed clusters could certainly be possible with above normal moisture and DCAPE around 1000 J/kg. By Sat, the mid/upper trough will sag farther southeast and direct more perturbed 500mb flow into the western Piedmont and combine with lee trough and/or differential heating boundaries to develop more widespread showers/storms. Deep layer shear will again be weak, but closer to 15-25 kts (highest NW) and may result in some cold pool organized clusters resulting in mostly a wet downburst threat as well. Confidence on Sat is low given it will likely depend on the prior day activity. &&. .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 410 AM Thursday... Overall a stagnant pattern will exist over Southeast and the Mid- Atlantic through the remainder of the forecast period. Central NC will be tucked between broad reinforced troughing through the central CONUS with the stationary sub-tropical high broadly draped across the western Atlantic in the eastern GOM. At the surface a diffuse pressure gradient will feature a lee-trough redeveloping over the region each afternoon with unseasonably moist 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 THURSDAY THROUGH MONDAY/... As of 800 AM Thursday... VFR conditions, influenced by high pressure extending from just offshore the Middle Atlantic coast southwestward into the Carolinas, will continue through early afternoon. An Appalachian-lee surface trough and/or outflow from upstream convection will provide foci for shower/storm development that will probably affect INT/GSO and surrounding vicinity across the nw NC Piedmont this afternoon- evening. Some of that gusty outflow, and focus for additional, isolated to widely scattered showers/storms, may drift to near RDU and RWI through 00-03Z, before dissipating. Outlook: A chance of showers/storms will exist Fri and especially Sat through Mon, as a pre-frontal trough and surface front move into and stall over cntl NC. Late night-early morning stratus and fog will also be possible this weekend. && .CLIMATE... Record High Temperatures: July 4: KGSO: 98/1970 KRDU: 101/2012 KFAY: 98/2019 July 5: KGSO: 98/2012 KRDU: 102/1999 KFAY: 101/2002 July 6: KRDU: 102/2022 KFAY: 99/1990 Record High Minimum Temperatures: July 4: KGSO: 73/2018 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... None. && $$ SYNOPSIS...Blaes NEAR TERM...Blaes SHORT TERM...Swiggett LONG TERM...Swiggett AVIATION...MWS CLIMATE...RAH