Key MESSAGE 1, Very warm and muggy airmass continues to plague much of the Carolinas and southeastern CONUS this afternoon as a frontal boundary remains stalled from the Piedmont into southeastern VA. 1000-850 MB thicknesses between 1430-1435 m point to highs well into the 90s today, and are expected to be a few meters higher tomorrow. Lingering cloud cover from upstream convection could temper full potential insolation, but combined with oppressive Tds expected to jump into the mid to potentially upper 70s, this will result in conditions feeling like 105-110 degrees across almost all of eastern NC. Nbm shows a modest signal for WBGT values of 90 (considered very high) across our southwestern counties south of Highway 70, and it is here where a potential overnight upgrade to Extreme Heat Warning may be considered. For now, however, after collaboration with neighboring offices and considering uncertainty of convective debris cloud cover, have settled for an area-wide Heat Advisory. We continue to encourage anyone planning on spending time outdoors to stay hydrated and to limit exposure to the heat, if able.
KEY MESSAGE 2, Outside of a spotty shower or thunderstorm focused along sea and sound breeze, today will be dry for the region. Latest 12z guidance still depicts a small cluster of showers and storms nearing the northern zones tonight, but with waning instability and poor upper-level support odds do not favor this holding together into our FA. Therefore, dropped PoP mentions overnight.
Attention turns to tomorrow as aforementioned frontal boundary sags southward and mid-level shortwave, currently associated with remarkably persistent MCS over the Great Lakes, quickly pushes towards the mid-Atlantic by mid-day tomorrow on the periphery of a persistent sub-tropical ridge centered over the southeastern CONUS. This should provide more support for scattered shower and thunderstorms, although some questions remain on available lifting mechanisms. Most hi-res guidance points to at least sea and sound breezes doing their usual work, but there is more disagreement on activity approaching from north to south likely stemming from potential MCV progression from expected convective activity across the Midwest this afternoon and tonight. Temperance of instability owing to debris from overnight convection is also a factor. For now, high-end chance PoPs are warranted.
Pre-storm environment tomorrow is marginally conducive for stronger to severe storms as well as isolated flooding potential, supported by both NWP and AI guidance. More favorable environments are displaced farther north and west with effective shear of around 20 kt and MLCAPEs of around 2000 J/kg, along with PWATs around 2 inches. Activity should be mainly diurnal, although there is a risk of some overnight convection as upstream activity migrates along the sub-tropical ridge.
KEY MESSAGE 3, A second frontal boundary looks to approach early next week after a brief lull over the weekend. Still plenty of details to hammer out over 5 days out, but medium- range AI NWP guidance points once again to at least a marginal risk of stronger storms for portions of the Carolinas, along with a heavy rainfall risk as humid airmass remains unyielding. Return of heat early next week also points to another period of potential heat headlines.
18z Thursday through Tuesday Mainly VFR conditions expected through the period with eastern NC under mostly to partly cloudy skies. Progressing sea breeze is kicking up spotty shower and thunderstorm activity southwest of OAJ-ISO, but this threat will quickly fall off overnight. Some debris clouds from decaying convection may push across northern terminals overnight although do not expect these showers/storms to hold together to make direct impacts. Spotty low stratus possible overnight given very humid boundary layer and light, but not fully decoupled winds.
More widely scattered convection expected tomorrow as frontal boundary sags southward and better upper level support moves into the area. Stronger storms could be capable of gusty winds in excess of 40 kt along with torrential downpours that could briefly but severely limit visibility.
Outlook (Friday through Monday): VFR conditions return Sat evening/Sun as high pressure briefly builds into the area. However, yet another potential round of sub-VFR conditions are possible Mon/Tue with the passage of yet another front.
Benign boating conditions expected through most of the period. Closest we will get to SCA will be tomorrow as SW winds increase ahead of an approaching but slow-moving front, boosting winds to 10-20 kt when coupled with typical thermal gradient. An infrequent gust to 25 kt is not entirely out of the question, mainly for soundside waters and coastal zones north of Hatteras, but probabilities are too low to warrant SCA headlines this package. Front will also bring an increased risk of showers and thunderstorms Fri afternoon into the late evening hours, a few which could be strong and produce gusts over 35-40 kt.
A return to more benign boating conditions are then forecast Sat night into Sun as high pressure ridging builds into the area. Yet another front nears the area Sun night into Mon bringing yet another low-end chance at SCA conditions.
Nc, heat advisory from 11 am to 8 pm EDT Friday for ncz029-044>047- 079>081-090>092-094-193>196-198-199-203>205. Heat advisory until 8 pm EDT this evening for ncz044-079>081- 090>092-094-193>196-198-199. Marine, none.
