The large heat dome that has prompted the issuance of heat advisories and warnings over a large swath of the central and eastern United States is making its presence felt here in South Carolina.
Widespread temperatures in the mid to upper 90s, along with high humidity, will result in heat indices around 105 degrees over the Midlands and Low Country. The greatest combination of heat and humidity is forecast over the Pee Dee and Grand Strand regions, where the National Weather Service has issued heat advisories. Heat indices are forecast to reach 108 degrees in the advisory area.
The reason for the toasty temperatures is a large ridge of high pressure that is dominating much of the country, east of the Rocky Mountains. The air underneath this ridge tends to suppress — but not entirely eliminate — afternoon thunderstorms. The extra hours of mid-July sunshine are boosting temperatures and the high moisture content of the air near the ground is elevating the humidity. This pattern isn’t expected to change much over the weekend.
There are signs of possible relief next week as the weather pattern will undergo a transformation. Global model simulations predict a trough of low pressure to form over the Great Lakes and dig southward toward South Carolina. This pattern would erode the heat dome over the state. Troughs tend to result in more cloud cover and greater coverage of showers and thunderstorms. That wouldn’t put an end to the high humidity, but it’ll take an edge off of the hot temperatures the state will experience into this weekend.