Final Bout of Rain Arriving Before Drier Weekend

Feb 12, 2020

Update as of 8:30 AM Thursday

A line of strong thunderstorms, which prompted The National Weather Service to issue Severe Thunderstorm Warnings for Anderson, Pickens, and Oconee counties early Thursday morning, is moving eastward through the Upstate. Strong winds in the lower part of the atmosphere may transfer to the ground as the line of heavy showers and a few thunderstorms move through the state today. For this reason, the Storm Prediction Center has issued a “marginal risk” (a level 1 out of 5) for severe storms over the state today.

Here are the updated expected arrival times for the line of gusty showers and thunderstorms:

Greenville/Spartanburg: Through 9 AM
Rock Hill: 11 AM - Noon
Aiken: 11 AM - 2 PM
Columbia: Noon - 2 PM
Orangeburg: 1-3 PM
Sumter: 1-3 PM
Florence: 2-4 PM
Myrtle Beach: 4-7 PM
Charleston: 4-7 PM

Areas of light to moderate showers may follow this line into the evening hours, but additional heavy rain behind the line is not anticipated. The last of the rain is on track to depart the Grand Strand and Lowcountry by around dawn Friday morning. Drier weather is forecast for the upcoming weekend, but runoff from recent heavy rains will keep some rivers in the Midlands, Pee Dee, and Lowcountry above flood stage.

Original Story from 1:30 PM Wednesday:

Showers and gusty thunderstorms late Wednesday night into Thursday appears to be the last of the rain over the Palmetto State until next week.

Over the past week, 5 to 11 inches of rain has fallen over most of the Upstate, while between 1 and 4 inches has fallen over the rest of the state. So far, the heaviest rain since Monday has been confined to Spartanburg, Greenville, Oconee, Pickens, and Anderson counties, where an analysis of rain gauge and radar data indicate up to 3 inches has fallen.

A break in the rain developed Tuesday morning and continues into Wednesday, but that is about to change. A strong cold front forming over the western Gulf coast states is forecast to arrive in the South Carolina Upstate near dawn Thursday. It will move steadily through the state during the day and push into the Atlantic around dusk. A band of showers and thunderstorms is likely to arrive near the following times on Thursday:

Greenville/Spartanburg: 6-9 AM
Rock Hill: 9 AM - Noon
Aiken: 10 AM - 1 PM
Columbia: 10 AM - 1 PM
Orangeburg: 11 AM - 2 PM
Sumter: 11 AM - 2 PM
Florence: 1-3 PM
Myrtle Beach: 3-7 PM
Charleston: 3-7 PM

The line may not last more than an hour or two at one location. For this reason, the flood threat is likely to be more limited in area and intensity. As of Wednesday morning’s forecast, NOAA has placed a small portion of the South Carolina Upstate in a “marginal risk”, or level 1 out of 5, for the potential of isolated pockets of flash flooding early Thursday morning. Areawide rainfall totals of about a half inch or less are currently forecast, but locally heavier showers may cause a few neighborhoods to receive more than that, which could still trigger isolated flash flooding.

There is a small risk that a few thunderstorms in line will produce damaging wind gusts. The Storm Prediction Center issued a “marginal risk”, level 1 out of 5, for severe thunderstorms on Thursday. Very strong winds through a deep layer of the atmosphere may transfer to the ground with the strongest thunderstorms. However, the air mass is not expected to be very unstable, and therefore the number of wind damage reports is likely to be limited.

Much of the concern for flooding has been over the Upstate this week, but data from NOAA’s Advanced Hydrologic Prediction Service (AHPS) indicate the greatest river flooding is occurring over parts of the Midlands. The gauge on the Congaree River at Carolina Eastman (south of Columbia) is in moderate flood stage and is expected to stay there through the weekend. The gauges on the Pee Dee River at Pee Dee and the Santee River near Jamestown are in major flood stage as of Wednesday morning or are projected to be in major flood stage by Friday. These areas are expected to remain at or above flood stage during the weekend thanks, in part, from heavier rain over the Upstate earlier this week.

Drier conditions are forecast to settle in over the state this weekend. Showers are in the forecast at times from Monday night into Wednesday, but there are no obvious signs in the global model data of flooding concerns at this time.