Sugar Mountain

Forecast Discussion

Summary

SYNOPSIS

... Seasonal temperatures and humid conditions will persist over the next few days while unsettled weather returns ahead of a front drifting down from the Great Lakes. Drier weather is expected on Friday, but showers and thunderstorms will return over the weekend.

NEAR TERM /THROUGH WEDNESDAY/... As of 2:15pm EDT Tuesday: Thunderstorms are continuing to increase in intensity and coverage this afternoon, as forecast. There is some risk for isolated severe wind reports and isolated flooding issues. A half inch to an inch of rain over the next 24 hours is expected on average, with some locations which fall underneath the heaviest storms receiving more. While more rain is expected in the mountains and foothills, it is likely that all locations will receive some rain.

Synoptically, mid-level wave with a band of PVA is currently crossing the region with sufficient forcing, along with a weak surface trough, to extract a good deal of the nearly 2 inches of precipitable water in the area. Skinny skew-t plots with limited CAPE are suggestive of heavy rain being the main issue, rather than severe winds, though quick movement of the system will limit overall flooding potential to isolated locations. DCAPE has also come down from recent days. CAM models are indicative of thunderstorms persisting until around midnight, followed by something of a lull in activity for Wednesday morning. Despite the progression of the mid- level trough east and out of the area, it is not replaced by ridging, but by a broad, weak trough to the west, with continued low- level moist advection that will keep dewpoints elevated. Bits of vorticity will continue to cross the area on Wednesday, leading to continued showers Wednesday afternoon, though of a reduced intensity compared with today.

Considerable cloudiness may reduce high temperatures a few degrees today and tomorrow, but conditions will remain seasonally warm with humid lows. With weak, broad trough over the area, winds will be light and somewhat variable at times, with a general southwesterly bias.

SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... As of 140 PM EDT Tuesday: Still a concern for severe tstms on Thursday, as a decent mid-lvl shortwave passes by during the peak- heating hours. The strongest forcing will remain north of the area, and the latest NAM shows a decaying MCS entering the mountains from the west during the morning hours. This feature helps delay recovery/destabilization, and as a result triggers the bulk of the convection to our east. So confidence on the threat is still too low to mention in the HWO at this time. But if the MCS fizzles before reaching the FA or is slower in getting here, destabilization of up to 2500 J/kg of sbcape is expected given dewpts in the upper 60s to lower 70s. Bulk shear of 30-35 kts and 0-3 kt helicity of 200 or more may be enough for supercells and/or multicell clusters. Whatever activity does develop should exit to the east by late evening. Temps will be near normal Thursday.

Friday, the wave will exit to our east, and heights will begin to rise with ridging to our west. A dry NW flow should result in a quiet day, with mostly sunny skies and temps slightly above normal (upper 80s to lower 90s across the piedmont).

LONG TERM /FRIDAY NIGHT THROUGH MONDAY/... As of 130 PM EDT Tuesday: Starting at 00Z Saturday with the 500mb pattern showing a ridge building over our region to start the weekend. There are model differences in timing, but the GFS has a MCS feature moving SE from KY after topping the ridge and reaching the NC mountains early Saturday. The EC has a shortwave bringing areas along and north of I-85 convection late Saturday into Saturday night. The GFS has another MCS arriving on Sunday. All medium range models have a strong shortwave arriving from TN late Monday resulting in numerous showers and storms lasting into Monday night then gradually shifting east as they weaken. The strong shortwave will knock down the ridge creating a more zonal west to east movement of systems. Highest CAPEs late Saturday from west of AVL to the Upper Savannah in the range 2000 to around 3000. The rest of the afternoons and early evenings will have pockets of around 2000 CAPE mainly from the Great Smokies to the Upstate.

Temperatures near to 3 degrees above normal with Sunday perhaps the warmest to hottest day.