Halloween is likely to turn dark and stormy for parts of the Palmetto State ahead of the strongest front so far this fall season.
Unseasonably high humidity is expected to surge northward from the Gulf of Mexico and be in place for most of Thursday. The moisture content of the air and warm afternoon temperatures into the 80s will make the air unstable enough for thunderstorms as the cold front approaches. NOAA’s Storm Prediction Center has issued a “slight risk” (level 2 out of a possible 5) for severe thunderstorms for most of the Midlands and Upstate. It also issued a “marginal risk” (level 1) for areas as far south and east as I-95.
In their Wednesday morning forecast, the Storm Prediction Center said strong winds high in the atmosphere will extend through the entire region, creating an environment that may cause a few of the thunderstorms to produce damaging wind gusts. An isolated, brief tornado cannot be ruled out.
High-resolution model simulations forecast scattered strong thunderstorms forming during the early afternoon over the Midlands and Upstate, then spreading eastward toward I-95 shortly after sunset. Here is the best estimate of the arrival time for the storms:
Greenville/Spartanburg 2-5 PM
Aiken 2-5 PM
Rock Hill 3-6 PM
North Augusta 3-6 PM
Columbia 3-6 PM
Orangeburg 5-7 PM
Florence 6-8 PM
Myrtle Beach/Charleston 7-10 PM
Additional welcome rain is also expected from the thunderstorms. The highest amounts are anticipated over the Upstate, where 1 to 3 inches of rain is expected Monday, followed by an additional half an inch to an inch of rain on Tuesday. Heavy rain over the rest of the state will depend on exactly where the storms form, but is expected to be less than what falls over the Upstate.
The storms are forecast to move off the coast around midnight Thursday night. Much cooler air will follow the front this weekend and the National Weather Service in Greenville says there may be patches of frost in the Upstate Saturday night into Sunday morning.