Update: Winter weather alerts are in effect for most of the Palmetto State. Late Friday morning, a Winter Storm Warning was issued for portions of the Midlands and Pee Dee north of Columbia and west of Florence. An Ice Storm Warning is in effect through Saturday morning for Horry County. For most of the state, a Winter Weather Advisory is in effect through Saturday morning. Radar trends through Friday morning have been generally quiet, however, spotty freezing drizzle has been noted across portions of the Pee Dee and Midlands. High-resolution weather models indicate widespread precipitation will develop Friday afternoon and evening, lasting through the overnight hours. Precipitation will generally be in the form of light freezing rain and some sleet, particularly across the Midlands and Pee Dee. As colder air moves into the state during the predawn hours Saturday, a brief transition to all snow is possible in the Midlands and northwest Pee Dee. Several inches of snow and sleet are possible in the Winter Storm Warning area, with lighter totals on mainly grassy surfaces expected outside of that region. Road conditions will likely be impacted through Saturday morning by wintry precipitation and near-freezing temperatures, especially on bridges and overpasses.
______________________________________________________________________________________
A Winter Storm Watch will go into effect Thursday night across the Midlands and Pee Dee in advance of another storm system. In these areas, heavy mixed precipitation, in the form of freezing rain, sleet, and snow, is forecast to develop overnight Thursday and could last through noon Saturday.
On Wednesday, an area of low pressure was developing over the Ohio River and Mid-Mississippi River Valleys, while at the same time, a strong area of Arctic high pressure was building behind it. The low will is expected to push into the Mid Atlantic early Thursday, and interact with a moderately humid and mild airmass being drawn northeastward from the Gulf of Mexico. This should result in rain showers across most of the state on Thursday. By Thursday night, the Arctic high should have strengthened enough to guide a swath of sub freezing temperatures over the Palmetto state. As this airmass arrives it should cause precipitation to change over to snow, sleet, and freezing rain.
Rain showers will first arrive to Upstate on Thursday morning, slowly progressing eastward throughout the day. By Thursday night, colder air will arrive from the northwest, and it is at this point that precipitation should transition to a wintry mix of sleet and freezing rain for most of the state. A few locations, particularly along I-77 north of Columbia, may experience a few snow showers during the early morning hours of Friday. Wintry mix of freezing rain and sleet should continue throughout the day Friday in the Midlands and Pee Dee, where high temperatures are likely to stay below freezing. As cold air continues to filter in, some models suggest a transition to a wintry mix is possible as far south and east as the Lowcountry, particularly by Friday evening. Precise location of snow, sleet, and freezing rain boundaries remains uncertain. However as of Wednesday night, one to two inches of snow and sleet accumulations are possible in the Midlands and Upstate. In the Pee Dee, one-tenth to a quarter an inch of ice accretion are possible. Regardless of precipitation type or amounts, dangerous travel and power outages are a possibility across the Palmetto State.
Model guidance suggests precipitation should gradually taper off by Saturday afternoon as highs only meagerly rise above 40-degrees. Hazards posed from wintry precipitation should lessen as temperatures inch above freezing, with gradually improving conditions expected for the second half of the weekend.