 Heat advisory from 10 a.m. to 8 p.m. today for Dorchester, Wicomico, Somerset, Worcester, Acomac and Northampton counties. And what the National Weather Service is saying in both cases is heat index values up to 110. So what's the difference between an excessive heat warning and a heat advisory? I can't really tell by based on what the National Weather Service is telling me. But certainly, though.