Thunderstorms are likely to become more widespread across the Palmetto State over the next three days, thanks to an approaching front. The storms will provide some relief from the heat, but a few of them may become strong enough to produce damaging wind gusts and flash flooding.
A Severe Thunderstorm Watch was issued by the National Weather Service for the Upstate region until 7 pm Tuesday evening. The first round of thunderstorms were developing over the higher terrain of Tennessee Tuesday afternoon, then likely to spread into areas near Greenville, Spartanburg, and perhaps Rock Hill between 5 and 8 PM.
Thunderstorms are likely to ignite again on Wednesday over a larger portion of the state as the front gets closer, particularly after 2 PM. Unusually high amounts of moisture in the atmosphere will boost the threat of flash flooding, particularly along and east of a Rock Hill to Columbia to North Augusta line. The Weather Prediction Center has issued a “slight risk” (one level greater than a “marginal risk”) for flash flooding for the central and eastern portions of the state. Widespread rainfall amounts of 1 to 2 inches, with localized amounts up to 5 inches, may cause flash flooding of urban areas, small streams, and roadways. Some of the thunderstorm downdrafts will become so loaded with water that they could produce a couple reports of damaging wind.
The front is forecast to stall along coastal South Carolina on Thursday, creating a favorable setup for more thunderstorms from Hilton Head to Charleston, Florence, and Myrtle Beach. The primary risk from Thursday’s storms will again be locally heavy rainfall and isolated pockets of flash flooding.
One side effect from the storms is that they will cool many locations off. Heat Advisories were issued by the National Weather Service Tuesday near Anderson and Greenwood, where the heat index (or “feels like” temperature) was expected to reach 105. High heat indices are likely again on Wednesday afternoon before the thunderstorms develop.