Sugar Mountain

Summary

SYNOPSIS

... A summerlike weather pattern lingers through mid-week with mainly afternoon and evening showers and thunderstorms expected. Temperatures will trend well above normal through Thursday. Showers and thunderstorms will become more numerous ahead of a strong cold front on Thursday. Activity may linger through early Friday as the cold front pushes east of the western Carolinas. Drier conditions and below normal temperatures return for the weekend as high pressure builds in from the west.

NEAR TERM /THROUGH WEDNESDAY/... As of 1044 PM EDT Tuesday: The showers moving into the nrn mountains have long since dissipated, but now we are watching a thunderstorm over northwest GA with some interest. The environment farther to the east is not as conducive to its survival, with CAPE steadily trailing off to only 500 J/kg east of the Savannah R. The threat appears to diminish as the storm would move east, and it is possible there might not be much left of it before it would get to our northeast GA zones. Generally speaking, the rest of the overnight should be fairly quiet with only a small collection of showers over the mtns, maybe a brief thunderstorm or two. Temp trends still look good.

Otherwise...an active period of weather will continue through Wednesday with multiple rounds of thunderstorms, some of which could be severe, expected. As of this writing, water vapor imagery depicts a large negatively tilted trough draped across the Great Plains into the Midwest with a closed upper low spinning over the Northern Plains. Farther east, upper ridging over the Appalachians will breakdown and shift offshore with a highly perturbed southwest flow regime setting up shop from the Lower Mississippi Valley into the Southern Appalachians. This will send multiple rounds of storms into the area through the near term forecast period.

By the predawn hours, a batch of showers and perhaps a couple thunderstorms will be possible across the mountains and portions of the Upstate. Thereafter, a residual elevated mixed layer will advect into the area and help to keep the atmosphere capped through the early afternoon hours. However, with time, increasing forcing for ascent and surface heating should erode the cap and allow for thunderstorm development. Considerable spread was noted in the high- resolution CAM guidance as to when/where storms will develop. The greatest coverage is expected across the mountains initially with scattered storms into the foothills. As the afternoon progresses, activity will likely spread across much of the area along and north of I-85. The atmosphere will be primed for severe weather with 3000- 4000 J/kg of surface-based CAPE, 6.5-7 C/km mid-level lapse rates, and 30-40kts of deep-layer vertical wind shear. This would be supportive of large hail and damaging winds with the wind threat becoming dominant/more widespread should convection organize into linear segments. As such, the expansion of the slight risk from SPC would appear warranted.

SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... As of 215 PM EDT Tuesday: CAMs show the potential for a couple of rounds of convection crossing the area Wednesday night. Moderate shear and decent elevated instability could allow some of the storms to become strong to severe. The severe threat could continue into Thursday as another round of convection moves through. Moderate shear is likely, with moderate instability possible, especially if the cap can erode and LFCs become low enough. Any convection that does develop should quickly move east early Thursday evening.

The GFS continues to be more aggressive with the next short wave dropping into the area Friday, and the resulting cyclogenesis. It is the wettest guidance, but there is some response from the other guidance. Have gone with the model blend for PoP which favors the mountains and CLT Metro. This is still in the chance range across the entire area. QPF that does fall will be light. Temps will be well above normal Thursday, dropping to around normal Friday.

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 155 PM EDT Tuesday: Not much change in the forecast this period with short waves rotating through a low amplitude long wave trough over the eastern CONUS. Weak surface features move over or near the area in association with the short waves through Monday. There may be enough moisture for isolated to low end scattered showers across the mountains, but any QPF will be light with a dry forecast elsewhere. Model differences develop Tuesday with a stronger wave rotating through the upper trough producing cyclogenesis along the Gulf Coast with the resulting low moving south of the area. How far south is the question with a drier, farther south track and wetter, farther north track. Have gone with the guidance blend which has low end chance PoP developing. Temps below normal Saturday slowly rise to slightly above normal by Tuesday.