Forecast Discussion
Summary
SYNOPSIS
... Cool and dry high pressure will linger across the Carolinas through Saturday, bringing warm and dry conditions. Another cold front will approach late Sunday, and move through the area Monday, before a complex pattern sets up for the rest of next week.
NEAR TERM /THROUGH FRIDAY/... As of 740 PM: A few stray/light showers have developed over southern portions of the Upstate during the past hour or so, but have generally been quite short-lived. Threw in a slight chance PoP for the heck of it in/near Greenwood County for the next hour or two. Otherwise, a weak short wave moves through the cyclonic flow over the area tonight; however, the dry air mass in place means no precip and likely no clouds once the evening dissipates with further loss of heating. With light winds and falling dewpoints, a cool night is expected with lows around 10 degrees below normal, but still several degrees off records.
Heights begin to rise Friday as the upper low over New England finally begins to move east. Very dry high pressure remains over the area with no instability and mostly sunny skies. Deep mixing will help dew points drop well below normal. This means comfortable conditions with highs a few degrees below normal, but RH values dropping to around 25 percent for much of the area. Thankfully, winds are light keeping conditions better than critical fire weather values.
Air Quality Alerts (Code Orange) remain in effect thru midnight tonight for our North Carolina zones although smoke concentrations have diminished over much of the area since yesterday. After coordination with state agencies, a Code Orange will again be in effect for Friday, but only for Meck, Union (NC), and Davie Counties. The AQA will be updated to reflect this later this evening.
SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... As of 129 PM EDT Thursday: Not a lot of wholesale change in the short term this afternoon. The deep upper low that has dominated the synoptic pattern for the last week will begin to lift northeast on Saturday, giving way to quasi-zonal flow / weak ridging across the Southeast. Dry Canadian high pressure will drift out of the Ohio Valley and across the Carolinas...resulting in quiescent conditions persisting through the day Saturday. Temperatures will climb into the mid-80s outside the high terrain, with light and variables winds and sunny skies. Lows Saturday night will fall into the low 60s.
By Sunday, a southern stream upper trough will creep across the Tennessee Valley, and the first ripples of DPVA forcing will arrive around daybreak...amping up cloud cover in advance of rainfall later in the day. It's still questionable whether much afternoon thunder will be able to develop Sunday. The GFS, CMC, and NAM all indicate that a leftover subsidence inversion will need to break up first to permit deep convection; for now, all the operational guidance as well as the majority of CMC-GEPS members depict this breakdown happening by late afternoon for at least the Upstate zones. Lapse rates look fairly anemic, however, so especially for the eastern zones where the mid-levels will still be struggling to moisten, stronger updrafts may have a hard time getting much traction, which paired with PWs approaching 1.8" may result in an outside chance of some isolated heavy rainfall, should any decent cells get going.
LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... As of 212 PM EDT Thursday: Next week will feature an increasingly dynamical pattern over the eastern CONUS, with a compact cutoff low deepening over the Great Lakes...and long-range ensemble guidance in good agreement that this will spur surface cyclogenesis by Sunday night if not earlier. In response, deterministic models show a well- defined cold front sweeping across the Tennessee Valley on Monday...and entering the Carolinas by Monday night. This appears supportive of more widespread thunder chances...with impressive instability developing in the prefrontal trough.
Thereafter, guidance becomes increasingly inconsistent. Most guidance predicts some version of the front stalling across the Southeast, leaving a residual boundary that will lift back north on Tuesday and beyond. It is unclear, however, where this will occur. And this will have important ramifications for the forecast, insomuch as the 500mb low, by this point in time, will be crossing the Mid-Atlantic, providing a good slug of deep shear for any surface-based convection that develops. However, if the boundary makes it too far south, virtually all developing convection could wind up elevated...which would render the shear far less important. The GFS and its ensembles seem to favor a solution more conducive to convection, with the boundary lifting north fairly quickly and permitting a round of surface-based, well-sheared thunderstorms on Tuesday. The remainder of the ENS and GEPS membership point more toward a complete frontal passage, with most convection on Tuesday and beyond remaining elevated.
Otherwise, temperatures are expected to remain in the mid- to upper- 80s through the extended.