A broad dome of heat is set to expand across the central and eastern United States beginning Wednesday, with the National Weather Service issuing Heat Advisories from the Southern Plains through the Mid-Atlantic and Northeast. Forecasters expect heat-index readings to top 100°F in Oklahoma and Texas as soon as Wednesday, and to approach the same level in the New York City region on both Wednesday and Thursday. The steamy conditions will be accompanied by a risk of strong thunderstorms. In south-central Pennsylvania’s Susquehanna Valley, scattered storms are likely between 3 p.m. and 10 p.m. Wednesday, with the Weather Service warning of flash flooding where saturated ground meets high rainfall rates. Chicago faces a Level 2 severe-weather outlook during the afternoon and early evening, with meteorologists cautioning that high winds, heavy rain and an isolated tornado are possible as temperatures climb into the low 90s. Farther west, a cold front sliding through Colorado is expected to trigger storms along the mountains and the I-25 corridor late Wednesday. The Boulder and Pueblo forecast offices cite large hail and damaging winds as the primary hazards, though locally heavy rain and an isolated tornado cannot be ruled out. Heat is projected to peak on Thursday, when portions of the Mid-Atlantic and Southeast could feel heat-index values near 105°F. The advancing front should bring slightly cooler, drier air to parts of the Plains and Mid-Atlantic by the weekend, but forecasters warn that the pattern of intermittent storms may persist into next week.