Update: Wednesday, January 11:
Portions of the Upstate, including Greenville-Spartanburg, are now under a Slight Risk, or level 2 out of 5, risk for severe thunderstorms on Thursday. Portions of the Midlands, including Columbia, are under a Marginal Risk, or level 1 out of 5 risk Thursday.
Regarding timing, the leading edge of the line should approach the Upstate during the afternoon on Thursday, before entering the Midlands late in the afternoon/during the evening. During the evening and overnight, the line should weaken as it pushes southeastward toward the I-95 corridor and the Atlantic Coast. Storms are expected to be strongest during the afternoon and early evening hours while the line is over the western half of the state. The primary hazards from the strongest cells embedded within the squall will be damaging straight-line winds and a few tornadoes.
A substantial temperature drop is still forecasted for the entire state Friday and through the weekend. The coldest temperatures are expected to occur on Sunday morning: Lows will likely drop into the 20s, except for along the immediate coast, where temperatures should fall to near freezing on Sunday morning.
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Original story, published on Tuesday, January 10, appears below:
Another cold front will approach and pass through the Southeast later this week, and it will pose a multitude of threats for parts of the Palmetto State. Thunderstorms capable of producing damaging straight-line winds are expected to track across the width of our state on Thursday, and by Friday, northerly winds will cause temperatures to drop.
On Tuesday afternoon, high pressure was building over the Mid-Atlantic and Central Gulf Coast, and conditions over these regions were calm and seasonably cool. However, over the eastern Pacific, yet another strong storm system was approaching the California coast. Through the remainder of the week surface low pressure, aided by a strong disturbance in the mid-levels of the atmosphere, should intensify and propagate eastward into the Southeastward. A broken squall line of potentially strong thunderstorms should herald its arrival to our area.
By Thursday, a cold front extending from the center of this system should track from west to east across the Lower Mississippi and Tennessee valleys. Although exact details regarding timing are not certain, models are generally in consensus that a broken squall line of thunderstorms should approach the Upstate during the late morning or early afternoon on Thursday. The system should track eastward into the Midlands by the mid to late afternoon, before approaching the I-95 corridor in the Pee Dee and Low Country during the evening and overnight hours Thursday into Friday morning.
The primary hazard from the strongest storm cells on Thursday will be damaging straight-line winds. In addition, conditions will be in place to support scattered, weak tornadoes.
Behind the system, winds will turn northerly, ushering in a colder airmass from the higher latitudes. Temperatures across the entire state should fall well below average, and by Saturday afternoon highs will range from the low 50s in the higher elevations to the mid/upper 50s along the Atlantic Coast. Overnight lows will likely drop to the 30s across the state on Saturday morning, and on Sunday, lows in the Midlands could plummet to the mid-20s.
Interests across these regions are encouraged to continue monitoring weather forecasts over the coming days. Residents and visitors alike should know where they will shelter should a severe thunderstorm or tornado threaten their immediate location. In addition, precautions should be taken when temperatures drop: Bring pets inside and cover sensitive plants. Prevent housefires by using space heaters in well-ventilated areas, away from other objects.