U.S. states from California to Alabama are bracing for extreme temperatures throughout Sunday, with some southwest regions set to get as hot as 110 degrees Fahrenheit. While the heatwave is expected to hit the hardest down south, some northern areas have also posted heat advisories.

Las Vegas, Phoenix and Tucson, Arizona, are among the cities expected to reach as high as 110 degrees and potentially break their all-time high temperatures records. Elsewhere, Texas cities like Dallas and San Antonio are forecast to hit around 100 degrees.

Through Tuesday, the heatwave is expected to spread across the rest of the country, with 75 locations forecasted to match or break all-time records. Up north, New England cities like Boston and Providence, Rhode Island, are bracing for temperatures as high as 96 temperatures. Elsewhere, the Ohio Valley and Mid-Atlantic regions may reach up to 100 degrees.

“The heat wave will be very long-lived, lasting multiple weeks in some areas with only a few days of near-normal temperatures during that span,” Jeff Masters, founder of Weather Underground, said about the coming heat. “This will increase the odds of heat illness and heat-related deaths.”

The criteria that the National Weather Service (NWS) uses for issuing heat advisories vary depending on the climate of a given region. In San Antonio, for example, an advisory is issued for temperatures 108 degrees or higher. Other cities like Dallas and Atlanta require at least a 105-degree forecast for advisories to be issued.

For desert regions, the issue is more complicated. As these areas are consistently hot for so much of the year, heat advisories are not issued. Instead, the NWS issues excessive heat warnings at varying levels based on a number of factors.

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