Updated Thursday December 24, 2020; 2:30PM EDT
A Tornado Watch has been issued for parts of Pee Dee until 10:00PM EDT, this includes the city of Myrtle Beach.
Strong showers and thunderstorms will have the potential to produce isolated tornadoes Thursday afternoon and evening as well as straight-line wind damage and heavy rainfall.
Tornado Warnings were issued earlier for parts of Columbus County and Horry County as strong thunderstorms marched through. The threat for severe weather will continue through the evening Thursday before conditions gradually improve overnight from west to east.
Updated Thursday December 24, 2020; 11:00am EDT
A line of strong storms ahead of a cold front will continue to move through the Palmetto State this afternoon producing heavy rainfall, powerful winds, and even the chance for isolated tornadoes.
A deepening low pressure system near the Ohio River Valley Thursday morning was continuing to track eastward towards New England dragging a long and formidable cold front behind it which stretches down into the Yucatán Peninsula of Mexico.
Showers and a few thunderstorms will move through the Upstate and western parts of the Midlands through the early afternoon Thursday. Heavy rainfall could trigger localized flash flooding especially around the Appalachians. The severe threat will likely be minimal for most areas west of Columbia, however the line of thunderstorms is expected to gradually strengthen as it moves eastward towards the coast late Thursday afternoon. Fierce winds a few hundred feet above the ground will create an environment of strong wind shear ahead of the approaching cold front. This will help to fuel thunderstorm activity through the afternoon with some storms capable of producing strong, potentially damaging wind gusts, and even a few isolated tornadoes for parts of the eastern Midlands, Pee Dee, and the Lowcountry.
Scattered storms are possible in the Grand Strand area between 1 and 4 PM. These scattered storms pose the greatest risk of isolated tornadoes. The separate line of thunderstorms directly tied to the cold front is forecast to be in the Midlands between 4 and 7 PM, and then arrive in the Lowcountry and Pee Dee between 6 and 8 PM. The line is expected to move offshore in Georgetown and Horry counties between 8 and 10 PM. This line is capable of producing damaging wind gusts and embedded tornadoes.
The Storm Prediction Center issued an Enhanced Risk (risk level 3 out of 5) for southeastern portions of Pee Dee including the city of Myrtle Beach for the chance of strong to severe thunderstorms. A Slight Risk (risk level 2 out of 5) is in place for the remainder of Pee Dee and northern and Central parts of the Lowcountry including the city of Charleston.
Showers and thunderstorms are anticipated to move offshore late Thursday evening with the cold front quickly passing overhead overnight. Upon the passage of the cold front, temperatures will rapidly drop overnight Christmas Eve and into Christmas Day. Some remnant precipitation behind the passage of the front could translate to a wintry mix or even snow showers on Christmas Day.
On the backside of the cold front, the jet stream will dive southward, encompassing most of the Southeast for Christmas Day. Morning low temperatures are expected to sink into the 20s across the Upstate and Midlands with 30s towards the coast. Afternoon temperatures will remain frigid for Christmas Day with highs ranging from the upper 30s in the Upstate to the lower 40s along the coast. Columbia has recorded only 9 days of highs below 40 degrees in its historical record; most recently in 2004. Even colder temperatures will move in overnight Christmas Day and into Saturday with most areas statewide falling into the 20s. Wind chill values could lower into the teens.
Mostly clear skies will dominate the Palmetto State for the weekend with temperatures gradually warming as the arctic air from the jet stream shifts eastward into the Atlantic.