A strong area of high pressure has positioned itself in the southwest part of the country, bringing extreme heat to not only the desert southwest but also to parts of Texas. This high will intensify over the next few days and block out any relief from Pacific arriving weather systems.

What You Need To Know

  • A heat dome is set up over the soutwestern part of the country

  • Temperatures Wednesday through Friday are expected to be 20 degrees above normal

  • Excessive Heat Warnings and Advisories have been issued for millions of people

Cities that will see potential records in the next few days include Las Vegas, San Antonio, Phoenix and Palm Springs.

Heat dome

High pressure is associated with sunny skies and calm weather, thanks to sinking air. When the high remains in the same location and strengthens, it becomes a heat dome, where hot air is trapped underneath the high, how your car heats if the windows are closed.

This is happening in the southwest. The high also acts to block any incoming storm system and diverts them northward around it. With sinking air, clouds don’t form, and rain can’t fall, so you are left with hot air that transports from the air to the ground.

Tuesday's highs

As the high was positioning itself south of California and Arizona on Tuesday, it transported heat into interior sections of those states, as well as Nevada, Utah and even eastward into New Mexico and Texas. With the high expected to drift further north, the heat will expand with it.

Desert locations don’t have to worry about the heat index, but other areas will feel even hotter thanks to the humidity. San Antonio, Texas, reached a record high temperature of 103 degrees on Tuesday, but considering the humidity, the “feels like” temperature or heat index soared to 117 degrees, breaking the all-time highest heat index for that city.

High temperatures for the rest of the week

The National Weather Service has issued Excessive Heat Warnings and Heat Advisories for the rest of the week for regions expected to see extreme conditions. In locations with higher humidity levels, it will feel even hotter.

Highs are expected in the triple digits with some locations not seeing the mercury go below 80 degrees, even at night. 

Heat arriving early

It may seem like the heat is arriving earlier than in years past, but for some, this is just a typical June. Phoenix and Palm Springs see daily average highs already in the low 100s this time of the year. But for Las Vegas, temperatures will be 15 degrees above average this week, peaking in the 110s.

As for San Antonio, their average high during peak summer is only in the upper 90s, so temperatures surging into the low 100s any time of the year is abnormal.

The heat dome looks to collapse by the weekend, bringing a reprieve from the extreme heat.

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