... Shower and thunderstorm chances will increase Thursday and Friday ahead of an approaching cold front, with the front likely crossing the region on Saturday. The front may stall near the southern part of the area for the latter half of the weekend into early next week, keeping isolated to scattered showers and thunderstorms in the forecast.
NEAR TERM /THROUGH TONIGHT/... As of 11:11 AM...Forecast is in good shape, so no changes will be made.
Upper ridging and stg downward motion will weaken this afternoon as a broad h5 trof advances over TN. Heights will fall and a weak sfc trof will dominate the llvl pattern thru the period. There will a degree of GOM moisture adv arnd the Atl ridge, however, and this shud be enuf to instigate -shra/tstms across the NC mtns during the afternoon and evening. The models still have varying ideas as to the amt of sfc-based instability and overall coverage. So...continued to advertise low-end PoPs. The NAM as usual has abt twice as much sbCAPE as the GFS and believe this is overdone as mlvl LRs don/t steepen until the overnight period. Still, some of these pulse storms could become stg and produce hail and stg outflow winds. Max temps will reach abt 5 degrees abv normal in good insol and continued sw/ly flow. Mins will also be held abv normal levels overnight.
SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 325 am Wednesday: The synoptic pattern will become increasingly favorable for convective activity across the Southeast during the short term, as a weakness develops in the subtropical ridge from the TN Valley into the Deep South. Meanwhile, short term models depict a plume of relatively steep mid-level lapse rates (6.5-7 C/km) lingering across the forecast area Thu afternoon. With low level moisture still on the increase, CAPE of at least 2500-3000 J/kg appears likely during peak heating. The result should be numerous coverage of convection over the mtns, with SW steering flow carrying activity into the NC foothills and western Piedmont later in the afternoon into the evening. Robust instability and moderate downdraft CAPE will allow for at least a few pulse severe storms, although low level shear of ~15 kts may allow for some small scale clustering along cold pools, which would pose a slightly higher threat of downburst winds. Although cell movement will likely be in the 10-15 kts range, locally excessive rainfall will be possible in locations where cells are able to train.
Increasing deep layer moisture Friday will result in weak mid-level lapse rates/slightly weaker afternoon instability, but PWATs increasing above 1.5 should make up for the relative weaker instability. Thus, more of the same is expected for Friday afternoon/evening, with perhaps slightly higher chances for locally excessive rainfall, and slightly lower chances for severe convection. Temps will be a category above climo through the period.
LONG TERM /SATURDAY THROUGH TUESDAY/... As of 335 am Wednesday: With an area of height falls passing over the northeast Conus early in the medium range, a frontal boundary, along with pre-frontal/lee surface trough is expected to impact the forecast area Saturday...likely resulting in another round of at least scattered, mainly diurnal convection. Lower theta-e air looks to filter into the area for early next week in the wake of the boundary, but sufficient moisture/weak instability may linger to warrant inclusion of token small pops for mainly diurnal showers and a few storms Sunday and Monday. The expectation of moisture increasing from the west warrants slightly higher pops for Tuesday. Max temps will be close to normal, and mins about a category above climo through the period.