... Bermuda high pressure over the area will slowly weaken today as a cold front approaches from the northwest. The front will move into the area on Thursday and settle south of the region by Friday, with an additional reinforcing cold front moving through from the north by Friday night. Cooler and drier high pressure will arrive for most of the weekend, but with moisture returning early next week.
NEAR TERM /THROUGH TONIGHT/... As of 935 AM EDT Wednesday: Low stratus continues to hang over a good chunk of the Upstate and western NC mtns late this morning. A few Upstate sites are also still reporting reduced visby, but any lingering fog should burn off over the next hour or so. We're also seeing a fairly broad area of sct convection already firing off to our west. This activity is still expected to gradually spread eastward over the next few hours with new cells likely to fire off over the higher terrain as well.
Throughout the near term forecast period, the subtropical ridge will remain out in the western Atlantic while a quasi-stationary frontal boundary remains to our NW, stretching from the Virginias into north Texas. This pattern allow SW'ly flow to continue, priming the western Carolinas and NE Georgia with PWATs near 1.50 inches. Expect thunderstorms to develop early this afternoon across the mountains, spreading east through the mid to late afternoon and early evening hours. Coverage looks best across western NC, with lower coverage across western SC and NE GA. Went with categorical PoPs across the mountains and NC Foothills, with likely PoPs up to I85 and chance PoPs south of I-85. WPC has the mountains in a slight risk for excessive rainfall today, with a marginal risk east of the mountains for the majority of the fcst area. This makes sense as 0-6 km bulk shear values will be around 5 knots or less leading to slow storm motion. Heavy downpours that sit or train over an area for an extended period of time have the potential to produce a localized flooding risk. Not planning on issuing a Flood Watch at this time as Flash Flood Guidance is around 2 to 4 inches across the fcst area. The overall severe threat today looks similar to what we have seen the last few days, low with isolated severe storms possible. With SBCAPE values ranging from 1000-1200 J/kg, damaging wind gusts will be the main potential threat with any severe storm that develops. Expect another humid day with high temperatures about 2-4 degrees above climo. Tonight another round of convection looks to make a run for the mtns ahead of the FROPA. Activity looks to impact the NC mtns mainly after midnight, lasting into daybreak Thursday. So, maintained chance PoPs into tonight across the mtns. Expect another round of fog and low stratus across the NC mtns and foothills. Lows tonight will remain around 3-6 degrees above climo.
SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 300 am EDT Wednesday: A weak 500 mb trough will move east of the forecast area on Thursday but the passage will help to push a cold front approaching from the northwest through the region. The main band of deeper moisture and forcing ahead of the fropa will likely cross the area Thursday afternoon and evening during peak heating, but precipitation could linger across the southern tier well into the nighttime hours given the anticipated slow progress of the boundary and moisture before deeper-layer drying arrives 09Z to 12Z Friday. Some measure of westerly downsloping is indicated, but this may not provide much inhibition given the overall synoptic scale forcing. Very warm and moist profiles, along with unimpressive mid-level lapse rates, should limit instability and the severe thunderstorm potential for Thursday afternoon and evening. Isolated flooding issues may arise with any training cells, however.
More prominent height falls will carve out from the Ohio River Valley to the Southern Appalachians Thursday night through Friday, with an H5 trough stretching from the Mid-Atlantic region to the central Carolinas Friday night. The amplifying trough will drive a stronger, reinforcing cold front southward across the area Friday, but with more limited moisture in the northerly flow and very limited instability in the drying profiles. PoPs should be mostly isolated to low-end scattered. Max temps will continue to drop about a category each day, with downright chilly min temperatures in the high mountains by daybreak Saturday (some upper 40s.)
LONG TERM /SATURDAY THROUGH TUESDAY/... As of 305 am EDT Wednesday: Deep-layer northwesterly flow will set up over the western Carolinas and northeast Georgia over the weekend as an amplified trough migrates off the East Coast and a strong ridge sets up east of the Rockies. 1022 mb surface high pressure will extend southward from the Great Lakes to the southern Appalachians and low-level northeasterly to easterly winds around the high may generate some upslope cloudiness in and near the mountains - but with moisture too limited to wring out any showers. Maximum temperatures will run 3 to 5 degrees below climatology in most places.
Clipper-type energy may run southeast from the northern Plains on Saturday to reach the southern Appalachians on Sunday, but accompanying moisture remains a huge question. Low-level flow should toggle back southwesterly ahead of this feature to slightly aid moisture recovery. Will feature isolated showers, mainly in and near the mountains. Temperatures will rebound slightly toward climo.
A broader eastern trough will redevelop Monday through Tuesday, with additional packets of upper vorticity arriving in the northwesterly flow. Scattered showers will be possible just about anytime in the period, with another front slowly approaching from the northwest by Tuesday.