Extreme Heat Searing the Southwest This Week;
All-Time Record-High Temperatures
May Threaten Las Vegas and Phoenix

Dangerously hot temperatures are gripping the Southwest this week, potentially threatening the all-time record-high temperature in both Las Vegas and Phoenix.

A large dome of high pressure in the upper atmosphere has developed over the Southwest. Beneath the dome, sinking air is causing temperatures to soar well over 110 degrees in many areas.

This is a classic pre-monsoon heat event for the Southwest region. Some of the highest temperatures of the year can be recorded before the onset of the summer monsoon. Humidity levels are low, so the sun's energy can be used to heat the air rather than being absorbed by water vapor or used for evaporation.

Various heat alerts have been issued by the National Weather Service across Arizona, western New Mexico, southern Utah, southern Nevada and portions of California.

Several daily record highs were set Monday, including Death Valley, California (125 degrees), Phoenix (118 degrees – tied), Tucson, Arizona (115 degrees), Palm Springs, California (119 degrees), Fresno, California (108 degrees) and Reno, Nevada (103 degrees).

The 115-degree high in Tucson, Arizona, on Monday was the third hottest temperature ever recorded in that city and only the sixth time it has been 115 degrees or hotter since the late 1800s.

Dangerous Heat This Week

Here's what can be expected from this excessive heat event.

Arizona

• Phoenix: Highs will reach or exceed 115 degrees through at least midweek. Daily record highs will be within reach (current standing record is shown): 116 degrees for Tuesday and 115 degrees for Wednesday. In fact, Phoenix could approach its all-time record high of 122 degrees (June 26, 1990) on Tuesday. It will also be within reach of tying the record for consecutive days of high temperatures greater than 115 degrees, which is 4 days set in 1990. Not much relief is expected overnight, as temperatures will only "cool off" into the upper 80s to near 90 degrees.
• Tucson: Afternoon readings are forecast to max out near 115 degrees through midweek, which would threaten daily record highs. The high temperature in Tucson has only been 115 degrees or hotter six times since the late 1800s, including June 19, 2017 and June 19, 2016. The all-time record high in Tucson is 117 degrees (June 26, 1990).

California

• Central Valley: Triple-digit heat will engulf Bakersfield, Fresno and Sacramento through this week. Highs will approach 110 degrees in several cities at times this week. Some daily record highs will be within striking distance.
• Southern California: As is typical, the hottest temperatures will be in the deserts with highs 110 to 120 degrees. Areas just inland from the Southern California coast will also be hot, including Anaheim, Ontario and Fullerton.

Nevada

• Las Vegas: Temperatures are forecast to be 110 degrees or hotter through this week, approaching or exceeding daily record highs at times. The all-time record high of 117 degrees could be threatened Tuesday through Thursday.
• Reno: Highs in the upper 90s to near 100 degrees are possible through at least midweek, which would approach daily record highs.

The hot conditions this week will be particularly dangerous for vulnerable groups, such as the sick and the elderly. The NWS offered useful heat safety tips that can be incorporated into a daily routine when extreme heat sets in.

• Job sites: Stay hydrated and take breaks inside as often as possible. Remember that in temperatures above 110, you will not know that you are sweating.
• Indoors: Check up on the elderly, sick and those without air conditioning.
• In vehicles: Never leave children or pets unattended — look before you lock.
• Outdoors: Limit strenuous activities and find shade. Drink plenty of water and avoid alcohol.

Also, remember that flights planes may be delayed or canceled in temperatures of 115 or more due to the lost of lift that planes need to fly.

Summer's Peak Heat Arrives Early in Southwest

The North American monsoon typically begins to take shape in the Southwest as we head through July. This seasonal shift in wind direction brings increased moisture, fueling more frequent showers and thunderstorms.

As a result, parts of the region see their hottest readings, on average, from the latter half of June into early July when the air mass is still very dry. For example, average highs in Phoenix and Tucson reach a maximum of 107 and 102 degrees, respectively, during this time.

The hottest temperatures on record in Phoenix (122 degrees, June 26, 1990) and Tucson (117 degrees, June 26, 1990) also occurred in early summer.

Record-High Temperature Recap

A number of daily record highs were set on Sunday, including Death Valley, California (124 degrees), Fresno, California (107 degrees), San Jose, California (103 degrees), and San Francisco (97 degrees – airport).