Low pressure and scattered rain showers crossed the region on Monday, December 7. Morning low temperatures warmed from the 30s and 40s into the mid-50s to low 60s, which was slightly cooler than normal. As rain moved through the state, there were reports of small pea-sized hail in Aiken, Edgefield, Kershaw, and Richland counties around late afternoon that could have been graupel as cold air undercut the warmer air mass. There were multiple confirmed reports of graupel in and around the Charleston area during the evening. Colder, drier air rushed in behind the main cold front and overnight lows dropped into the mid-20s in the Upstate and into the upper 30s near the coast. Even under clear skies, temperatures only reach the upper 40s to mid-50s across much of the state.
On Wednesday morning, minimum temperatures were in the upper 20s to mid-30s, nearly ten degrees below normal for the second day in a row. With high pressure over the area, the airmass started to moderate with temperatures five to ten degrees higher than Tuesday, as daytime highs reached the upper 50s. The high pressure remained in place through the end of the week, with high and low temperatures continuing to rise above normal by the end of the weekend. On Thursday and Friday, maximum temperatures reached the mid to upper 60s, with a few stations near the coast recording highs close to 70 degrees.
The high pressure shifted offshore, heading into the weekend, allowing for moisture to return across the region. Daytime temperatures were nearly ten degrees warmer than normal, reaching the upper 60s and lower 70s across the state. A weakening cold front approached the area on Saturday, and with the added moisture, some light rain showers fired up during the late evening hours. Another, stronger cold front pushed into the region on Sunday into Sunday night, with better chances for rain showers that would linger into Monday morning. Many stations reported unseasonably warm temperatures for December, with high temperatures in the lower 70s and morning temperatures in the upper 50s. Sunday marked the start of the last King Tide cycle for 2020, and the tidal gauge in the Charleston Harbor reached 7.14 ft MLLW, and there were a few reports of shallow coastal flooding.
(Note: The highest and lowest official temperatures and highest precipitation totals provided below are based on observations from the National Weather Service (NWS) Cooperative Observer network and the National Weather Service's Forecast Offices.)| Weekly* | Since Jan 1 | Departure | |
|---|---|---|---|
| Anderson Airport | 0.02 | 58.56 | 16.6 |
| Greer Airport | 0.01 | 71.34 | 26.4 |
| Charlotte, NC Airport | Trace | 56.43 | 16.7 |
| Columbia Metro Airport | 0.31 | 53.52 | 10.8 |
| Orangeburg Airport | 0.11 | 42.28 | -2.6 |
| Augusta, GA Airport | 0.25 | 53.55 | 12.0 |
| Florence Airport | 0.23 | 59.74 | 18.7 |
| North Myrtle Beach Airport | 0.06 | 52.64 | 2.5 |
| Charleston Air Force Base | 0.10 | 52.18 | 3.1 |
| Savannah, GA Airport | Trace | 48.70 | 2.5 |
| *Weekly precipitation totals ending midnight Sunday. M - denotes total with missing values. |
4-inch depth soil temperature: Clinton: 54 degrees. Columbia: 60 degrees. Barnwell: 55 degrees. Mullins: 61 degrees.
During the period, most of the rainfall was confined to the Upstate. Some locations measured totals just shy of two inches in isolated places at higher elevations of Oconee and Pickens counties. The remainder of the state received less than half an inch of rain. However, higher totals were reported in the localized areas of the Midlands. The year-to-date rainfall totals across the state continue to be above-normal, mainly due to the wet start to 2020. However, portions of the Lowcountry are still experiencing abnormally dry conditions, especially in areas near the Lower Savannah.
Because the rains during the period fell over the mountainous portion of the Upstate, keeping streamflow gauges in the Upper Broad and Yadkin-Pee Dee River at values well above normal. Even though the streamflow values were high, the river heights in the upper portions of these basins remained below flood stage. The lack of substantial rainfall elsewhere across the state led to streamflow values dropping closer to near-normal conditions. River height gauges at the end of the Santee basin showed some minor flood state levels but were slowly dropping.
