Widespread temperatures in the mid to upper 90s and high humidity will boost heat indices to dangerous levels for some across the Palmetto State this week.
The National Weather Service issued a patchwork of Heat Advisories Monday for portions of the Upstate, Pee Dee, and for the entire coastline. The advisories are issued when the heat index is forecast to reach a certain threshold; in this case, 102 to 106 degrees for the Upstate and as high as 110 degrees for the coastal areas. The mid-summer heat is likely to last for much of the remainder of this week and additional heat advisories may be issued for portions of the state.
A powerful subtropical ridge of high pressure is parked directly over the Carolinas. This heat dome has been responsible for record-breaking heat into the Mid Atlantic and New England states, and also parts of the Midwest at times over the past few weeks. This ridge is forecast to stay intact through Thursday, but there are signs in the computer models that it may break down a little bit on Friday into the weekend. Should that occur, the temperature may ease a few degrees, but temperatures are still forecast to reach or exceed 90 degrees this upcoming weekend.
It is common for a small trough of low pressure to form near the ground when the air gets hot immediately downwind of the Appalachian Mountains. This trough, combined with the heat, humidity, and unstable air mass, will encourage the formation of scattered afternoon thunderstorms this week. The storms could occur anywhere, but are most likely to be focused in the Upstate region closest to the trough. The high amount of moisture contained within a storm’s downdraft may cause a microbursts — or isolated pockets of strong, damaging wind — with the strongest storms. Any microbursts will be isolated in nature and most areas getting underneath a thunderstorm will enjoy brief relief from the mid-summer heat.