Millions of Summer Travelers Could Get Caught in a Dangerous Heat Dome This Week. Here are the States Where It Hits Hardest

Summer travel is ramping up nationwide ahead of the July 4 holiday, with airports, highways and tourist hubs expecting heavy traffic across the first week of July. This week, the National Weather Service said a heat dome is building over the southern half of the U.S., putting millions of travelers in states including Texas, Florida, Arizona and Louisiana under dangerous heat.

The heat dome and how big it is

The National Weather Service said on July 3 that a strong upper-level ridge is expanding across the South and parts of the West, a pattern commonly called a heat dome. Forecast maps from the Weather Prediction Center show widespread highs in the 90s and 100s across more than 20 states, with some desert locations topping 110 degrees.

The scale matters because this heat is arriving during one of the busiest travel periods of the summer. AAA said in its 2025 Independence Day forecast that more than 70 million Americans were expected to travel at least 50 miles from home over the holiday period, and a large share of those trips were set to move through the hottest parts of the country.

Forecasters also warned that humidity will make conditions more dangerous in the South and Gulf Coast. In cities such as Houston, New Orleans and Orlando, heat index values were forecast to rise above 105 degrees, according to National Weather Service local offices.

The states where heat is expected to hit hardest

Texas, Louisiana, Mississippi, Alabama and Florida are among the states facing the most widespread combination of high temperatures and oppressive humidity this week, according to National Weather Service forecasts issued July 3. In those states, afternoon highs in the mid to upper 90s can feel much hotter once moisture levels are factored in.

Arizona, Nevada and inland California are also expected to see extreme heat, but with a different profile. The National Weather Service forecast temperatures above 110 degrees in parts of the lower deserts, including areas near Phoenix and Las Vegas, where heat warnings are common in early July but still dangerous for visitors.

Not every local impact is fully pinned down yet. The National Weather Service has issued advisories and warnings for specific counties and metro areas, but a single coast-to-coast list of all affected travel destinations has not been released, and forecast details can still shift by region over the next several days.

Why this is happening and what travelers should expect

Meteorologists say a heat dome forms when strong high pressure in the upper atmosphere traps hot air beneath it for several days. The National Oceanic and Atmospheric Administration has said these setups often lead to prolonged heat, limited cloud cover and warmer overnight lows, which reduce the amount of recovery people get after sunset.

That overnight piece is especially important for travelers staying in cars, campgrounds or older rentals without strong cooling. In parts of Texas and Florida, some overnight lows were forecast to remain near 80 degrees on July 3 and July 4, according to local National Weather Service offices, keeping heat stress elevated even outside peak afternoon hours.

For travelers, the practical impact is straightforward: longer waits on pavement, hotter cars and tougher outdoor conditions at beaches, theme parks and rest stops. Airlines and airports have not announced broad national schedule changes tied to the heat, but local weather offices said dangerous heat can affect anyone spending extended time outside, especially during the afternoon and early evening.