... An approaching cold front will trigger widespread showers and thunderstorms through Friday morning, prompting a threat for isolated severe weather and localized flooding concerns. After the passage of the cold front by midday Friday, high pressure builds in for the weekend, and looks to dominate through the first half of next week.
NEAR TERM /THROUGH FRIDAY/... As of 550 PM EDT Thursday: We're currently seeing widespread showers and thunderstorms tracking northward across our fcst area. Some of the stronger storms have produced strong straight-line winds and possibly a few tornados. In addition, numerous flood warnings have been issued across the Upstate and southern NC mtns. A cold front will track across the western Carolinas and northeast GA early Friday morning into early Friday evening. This system will continue to lead to widespread shower and thunderstorm development the rest of today into early Friday morning.
Ahead of the low pressure system, SW'ly flow will be in place near the sfc across the Southeast allowing Gulf moisture to stream into the region. This will lead to dewpoints in the 60s across the majority of the CWA through Friday morning. With PWAT values near or just above 1.75 inches, which is above 90th percentile, ahead of the FROPA, plentiful moisture will be in place leading to moderate to heavy downpours at times. With wet soils already in place from prior rainfall the last few days, this could allow for enough runoff for a flash flooding threat across mainly the mountains and NC Foothills. For this reason, a Flood Watch remains in effect through Friday morning for with the potential for excessive rainfall leading to the potential for flash flooding in these areas. A few Flood Advisories and two Flash Flood Warnings are currently in effect for portions of the SW NC mtns as well as a portions of the SC mtns in Oconee County. Rainfall amounts of 2-4 inches have already fallen across portions of extreme NE GA and the SW NC mtns this morning and early afternoon. Isolated rainfall amounts of 6-7 inches are possible along the SW upslope flow zones by the end of this event. The rest of the mountains could see rainfall amounts ranging from 1.5 to 3 inches with isolated areas of 4 inches possible. Areas east of the mtns will likely see totals ranging from 1 to 2 inches, with isolated amounts near 3 inches are possible. So, the rainfall threat will continued to be monitored closely and with heavier precip anticipated this evening into tonight.
There is also the potential for strong to severe storms this afternoon and evening as bulk shear values ranging from 30-40 knots are in place along with SBCAPE values ranging from 500 to 1,000 J/kg. Instability will continue increase as CAD erodes allowing SBCAPE values to creep northward this afternoon. SPC currently has most of our area in a marginal to slight risk. The main potential impacts are damaging winds gusts, isolated tornadoes and large hail. Currently seeing showers and thunderstorms, a few strong, across the western CWA this afternoon. Currently the majority of the eastern CWA, including CLT is mostly dry. Shower and thunderstorm chances will increase later this afternoon and early evening over the eastern CWA. Instability should decrease overnight with the loss of daytime heating, however cannot rule out isolated strong to severe thunderstorms overnight into daybreak Friday. Showers and thunderstorms should mostly taper off from west to east overnight into early Friday morning. However, wrap around moisture behind the FROPA could lead to isolated to scattered showers continuing across the NC/TN border on Friday. A few of these may last past the mountains leading to isolated to scattered showers possible with the potential for isolated thunderstorms late Friday afternoon. High temperatures will remain around 3-7 degrees below climo today and Friday, but will be about 5-8 degrees above climo overnight tonight thanks to precip and cloud cover.
SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... As of 210 pm EDT Thursday: Upper low is forecast to open up as it wobbles across the central Appalachians and vicinity early in the period. As the associated trough axis crosses the area Fri night and interacts with lingering low level moisture, a few light showers may develop across the mtns/northern zones,warranting 20-30 PoPs in those areas through around midnight. Drier air filtering in behind the front will bring an end to any precip chances by daybreak Saturday, with dry conditions persisting through the period. Otherwise, temperatures will be around normal until Sunday, when temps will warm to around 5 degrees above normal in response to rising upper heights/a building ridge to our west.
LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... As of 220 pm EDT Thursday: Global models are in good agreement in developing an expansive anticyclone centered over the central/southern Appalachians Monday morning, which then gradually retreats toward the Ohio Valley/mid-Miss Valley by mid-week. For our forecast area, this will mean a return to very warm conditions, with temps expected to be around 10 degrees above normal by Tue. Conditions will also be generally suppressed in terms of the convective potential, but some isolated diurnal showers and storms could develop Tue afternoon/evening, esp over the high terrain. With the anticyclone retrograding, and global guidance pushing an upper cyclone toward the southeast coast, chances for diurnal convection will steadily increase during the latter half of the period, with 20-30 PoPs advertised Thu afternoon/evening.