National Weather Service forecast high temperatures Sunday. Locations where highs are predicted to be within one degree of a record are circled. (WeatherBell.com)

Interior California and the desert Southwest are bracing for a long and intense heat wave, forecast to start this weekend and continue well into next week.

The worst of the heat is expected Monday or Tuesday, when many locations will witness temperatures 15 to 30 degrees above normal, challenging records.


Forecast temperature difference from normal Tuesday late afternoon from GFS model. (PivotalWeather.com)

The National Weather Service has hoisted an excessive heat warning for Phoenix on Sunday through Wednesday, and excessive heat watches in Las Vegas, San Jose and Sacramento for the weekend and early next week.

In Phoenix, high temperatures are forecast to reach 110 to 120 degrees during this extended stretch.


GFS model 10-day temperature forecast for Phoenix. (WeatherBell.com)

Monday and Tuesday could be historically hot days, near 120 degrees — which would rank among the top five hottest temperatures ever recorded in Phoenix.

Top five hottest temperatures in Phoenix:

1. 122 on June 26, 1990
2. 121 on July 28, 1995
3. 120 on June 25, 1990
4. 119 on June 29, 2013
5. 118 on several days

“Whats crazy about all of this is that the all-time high temperature at Phoenix Sky Harbor is 122 degrees set back in 1990 and there’s a chance we could be near this record and possibly even break it if things continue to trend upward,” the National Weather Service office serving Phoenix wrote in a discussion Wednesday.

The heat wave’s peak is expected to occur about the same time a punishing blast of heat scorched the city a year before. On June 19, 2016, Phoenix soared to 118 degrees, a daily record, and tied for the fifth-hottest day in the city’s history.

Most of Phoenix’s daily record highs in the June 16-20 period have occurred in the previous two years and could be tied or broken yet again:

Date record high
June 16: 115 in 1974
June 17: 114 in 2015
June 18: 115 in 2015
June 19: 118 in 2016
June 20: 116 in 2016

The heat will spread through the desert of southern Nevada and Southern California and then surge northward through California’s interior, into the Sacramento Valley.

The National Weather Service office serving Las Vegas said “near record-high temperatures will be possible” Saturday through Tuesday — about 110 to 112 degrees.

Sacramento and its surrounding valley areas could endure triple-digit heat for at least five days, according to the Weather Service.

“Stay tuned and make necessary preparations,” the Weather Service advised. “Is your AC functioning, do you have neighbors, family or friends that may struggle with extended heat, can you modify outdoor plans to avoid the hottest part of the day?”

The culprit for the heat is an expanding and strengthening area of high pressure aloft, sometimes called a heat dome, forecast this weekend and next week.


GFS forecast for high-altitude weather pattern Monday, showing a heat dome centered over Arizona. (WeatherBell.com)

It is not forecast to be quite as strong as the heat dome which sprawled over this same region a year earlier but still has the potential to produce historically hot temperature readings — especially over Arizona, where it is forecast to reach maximum intensity.