WASHINGTON — More than 100 million people across the US were under heat warnings on June 23, with cities on the East Coast bracing for record-breaking temperatures as the heat dome causing the dangerous conditions expands to the West Coast.

Baltimore and Philadelphia are forecast to touch records near 38 deg C on June 23, while temperatures rise into the 30s deg C in states like Idaho, Montana and Wyoming, as much as 8 deg C above normal for this time of year. The extreme heat will then shift to Nebraska and Kansas on June 24, the National Weather Service (NWS) said.

Officials are warning of dangerous conditions in the Philadelphia region, where high humidity could drive heat indices above 41 deg C, making it feel even hotter than the actual temperature.

"It likely means we'll be seeing periodic periods of excessive heat across a decent part of the country into July," NWS meteorologist Marc Chenard said. "Not continuous at any one spot, but the overall pattern will continue to favour these above normal temperatures."

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