255 FXUS62 KRAH 271916 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 315 PM EDT Wed Jul 27 2022 .SYNOPSIS... Strong high pressure will extend across the southeastern United States through Friday. A cold front will approach from the northwest late Friday, then settle across North Carolina over the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 1035 AM Wednesday... The previous forecast and rationale appear on track, with the only notable morning forecast update being an increase in surface winds to 7-12 kts, with occasional gustiness into the mid teens kts. .PREV DISCUSSION... /ISSUED 325 AM EDT Wed Jul 27 2022/ For yet another day, central NC remains on the southern periphery of the main belt of westerlies and mean frontal zone draped from the Mid-MS valley to the Mid-Atlantic States, with a west-to-east oriented upper ridge axis across the southern US. There is plenty of cloud cover on regional satellite imagery this morning, most of which is expected to thin through the morning hours and allow temperatures to climb back into the 90s area wide based on LL thicknesses in the 1430s. There are no explicitly evident upstream disturbances or MCVs at our latitude, so convection is expected to be dependent on differential heating in the mountains or along the north to south vary cloud cover, although some CAMs suggest convection over WV/VA that could eventually drift south into the northern Piedmont areas late this evening. Chance POPs will be heavily favored across the north today, with less Confidence in storms south and east of Raleigh today. Like previous days, there is a marginal risk of damaging wind gusts owing to weak to moderate instability and steep low level lapse rates, albeit well south of the stronger mid-level flow. There is also a marginal risk of isolated flash flood owing to a fair amount of locations receiving over an inch of rain in the past two or three days, though coverage may limit the threat today. With highs in the mid 90s and dewpoints likely remain above 70, and low chances of a showers to offer a reprieve, heat indices may reach 105 across the coastal plain this afternoon. While borderline wrt Heat Advisory criteria, today will be the start of an increase in heat indices through the end of the week, so a Heat Advisory was coordinated with WFOs MHX and ILM based on cumulative impacts in an unchanged weather pattern this week. Expect a rapid reduction in storms with loss of heating this evening and lows in the low to mid 70s. && .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... As of 320 AM Wednesday... Guidance is notably drier on Thursday as the best deep moisture shifts slightly eastward. LL thicknesses increase above 1440m as the frontal zone to our north begins to show some signs of eastward movement. Widely scattered storms are still possible, particularly in the NW Piedmont, but Thursday and Friday are expected to be hotter before the front and more unsettled weather approach this weekend. A heat advisory will likely be needed...and perhaps even more warranted... again on Thursday as highs climb into the mid to upper 90s. Lows Thursday night in the low to mid 70s again. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... As of 315 PM Wednesday... Friday and Friday night: Upper ridging and heat/humidity will continue. Dangerous heat index values of 100-110 degrees with Heat Advisories(+105)likely for areas along and east of the Triangle. While the steep low level lapse rates and resultant strong destabilization will yield a chance for isolated to widely scattered convection anywhere, the highest convective rain chances will remain across the northern portions of the NC Piedmont and coastal plain counties, in closer proximity to the upper trough in place over the Great Lakes and the NE US. Saturday through Sunday night: Anomalously high PWATS between 2.25- 2.5"(2 to 3 S.D. above normal)will pool along a quasi-stationary boundary that is forecast to sag south into the area over the weekend. Shortwave impulses embedded in the low-amplitude, nearly zonal flow aloft, will interact with the front, potentially leading to periods of moderate to heavy rain and an increased threat for localized flooding over the two days. An enhanced belt of shear of 25-30 kts along the Virginia border may also pose a multi-cellular severe threat across the northern counties. Combined 2-day rain totals of 1 to 2 inches are possible with the 2 leading ensemble clusters suggesting the potential for higher qpf amount of 2 to 3 inches. The likely to categorical rain chances and associated cloud cover will curb the heat. Highs ranging from lower/mid 80s north to lower 90s south. Lows 69 to 74. Monday through Wednesday: Low amplitude troughing will build over the region during the early to middle part of next week, temporarily suppressing the ridge before it makes an emphatic return to end the week. This pattern should yield higher than climo/normal PoPs, which should exhibit a diurnal maximum. High temperatures will depend on convective coverage but will generally fall within the seasonable values of mid/upper 80s north to lower/mid 90s south. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... As of 225 PM Wednesday... Scattered showers and storms that may become locally numerous over the Piedmont through this evening will pose the primary threat of sub-VFR conditions through the TAF period. However, a small area of low stratus developed near and just west of INT this morning; and the NAM, although an outlier relative to other model guidance, suggests similar development will be possible there Thu morning. Outlook: Scattered afternoon-evening showers and storms are expected to focus over the Piedmont again Thu, followed by more-numerous ones area-wide, as a front settles into the region this weekend. The chance of stratus and fog will also increase on the immediate cool side of that front and/or any outflow Sun and Mon mornings. && .RAH WATCHES/WARNINGS/ADVISORIES... Heat Advisory from noon today to 8 PM EDT this evening for NCZ027-028-041>043-077-078-085-086-088-089. && $$ SYNOPSIS...BLS NEAR TERM...MWS/BLS SHORT TERM...BLS LONG TERM...CBL AVIATION...MWS