Maps show forecast for extreme heat wave scorching the West

A long-duration heat wave is taking shape over the western half of the U.S. and forecast to stick around in the days ahead.

A high pressure system in place over the West is keeping precipitation out, which is also allowing for record heat across a large region. Triple-digit temperatures are forecast in the Desert Southwest but cities even closer to the Pacific Ocean could see unseasonably high temperatures.

More than 600 record-breaking temperatures are expected through the first half of next week for daily highs and overnight lows. Some daily temperatures are forecast to break century-old records in some major cities like in Phoenix.  

For Wednesday, Phoenix is forecast to see its earliest 100-degree day on record. The current such record was set on March 26, 1988. 

Record keeping in the “Valley of the Sun” has been reported since 1896.

What is a heat wave, technically?

A heat wave is defined as a period of unusually hot weather that typically lasts two or more days. The temperatures also must be outside the historical average for a given area. For instance, a 100-degree temperature is pretty typical in Phoenix during the summer but before the official start to spring would be classified as a heat wave.

Extreme heat warnings and heat advisories are in effect through at least Sunday across the Southwest and could possibly be extended. These alerts are in effect for major cities such as San Francisco, Los Angeles, San Diego, Palm Springs, Las Vegas, Phoenix and Tucson. 

Heat is the number one weather-related killer compared to all of other weather phenomena combined (tornadoes, flooding, lightning, etc). If you have to be outside for extended periods of time, drink plenty of water, take breaks in shade or inside an air-conditioned building, and limit any strenuous activities.

Child hot car deaths also rise during heat waves and this could be a cause for concern well before the summer months when it is more common.