Update Tuesday May 19, 2020: Round after round of showers and thunderstorms will increase the flooding threat across the Upstate and northern Midlands through Thursday.
Showers and thunderstorms have already produced 2 to 4 inches of rain since Monday morning for parts of the Upstate. Rain accumulations are setting the stage for flooding to develop through at least midweek.
A Flash Flood Watch remains in effect through Thursday morning for upstate South Carolina where several waves of showers and thunderstorms will result in additional rainfall totals of 2 to 5 inches by Thursday morning. Locations near the Appalachian Mountains could receive totals up to 6 inches.
Waters may rise rapidly in streams and creeks along with the threat of flooded roadways. River flooding may also occur during the midweek period and could persist through late week or longer.
Drier conditions will return to the region over the weekend as the low pressure system moves south and east away from the state and a high pressure builds back over the region.
Original story published Monday: Moisture has returned to the Palmetto State this week, with the chance of showers and a few strong storms lasting through Friday. Several rounds of heavy rain are also possible, which could produce flooding in some areas.
A Flash Flood Watch has been issued for most of the Upstate region through Thursday morning, where the heaviest rainfall rates are expected over the next few days. Some of the storms may also become strong enough to produce small hail and damaging winds at times. NOAA's Storm Prediction Center issued a “marginal risk" (risk level 1 out of 5) of severe storms for the entire state of South Carolina Monday.
A slow-moving low pressure system developed over the Great Lakes Monday morning, and is expected to drift south into the Tennessee Valley by midweek, where it could linger for many days. The counter-clockwise motion of air around this feature will aid in the transport of copious amounts of moisture into South Carolina, both from the Gulf of Mexico and the Atlantic Ocean.
Excessive rain could produce localized flooding around the state, especially in sections of the Upstate and Midlands regions. Rainfall totals are expected to range from 4 to 6 inches in areas bordering North Carolina, to 2 to 4 inches in central parts of the Upstate and Midlands regions, with lesser amounts of 1 to 2 inches possible in the Lowcountry.
The low pressure system is expected to finally move south and east of the state this weekend, which would be then followed by a drier weather pattern thanks to a high pressure system moving in.