In the west, extreme heat advisories are in effect for Phoenix, Las Vegas, San Jose, Spokane, Wash., and Boise, Idaho. In the east, heat advisories and warnings are in effect from South Carolina to Massachusetts, including Washington, Baltimore, Philadelphia, and Boston. Heat indexes — which take into account both air temperature and humidity — are expected to reach 105 to 110 along much of the Interstate 95 corridor.
Much of the Lower 48 is forecast to experience “high” to “extreme” heat risk levels, or at least Level 3 on the federal government’s 0-to-4 scale.
The most persistent and widespread Level 4 HeatRisk, considered “extreme,” is concentrated in the Desert Southwest. On Sunday, Las Vegas recorded its highest temperature ever recorded, reaching 120 degrees.
More extreme heat is forecast, especially in the west
The rest of the workweek will see the most extreme heat in the western United States. On Wednesday, record-breaking heat spots are forecast for parts of Washington state, Oregon, Idaho, California, Nevada and Arizona.
Las Vegas is expected to reach 119 degrees on Wednesday and Thursday. If it weren’t for Sunday’s high of 120, those would be record highs. If Sin City’s high reaches at least 115 degrees on Wednesday, it will be a record fifth straight day of highs.
Temperatures of over 120 degrees Fahrenheit are expected through Friday from Las Vegas to parts of Southern California and Arizona.
Temperatures will also remain above triple digits in the far north of Canada, including eastern Washington state, Idaho’s Snake River Valley and much of the Great Basin.
For the remainder of the workweek, highs of at least 43 degrees Celsius are expected in much of California’s Central Valley.
The weekend will remain warm, but most areas are likely to remain below record highs, due to an increase in humidity from the south and the start of the monsoon season in the southwest.
However, the heat dome, an intense high-pressure zone responsible for the extremely high temperatures, is expected to remain largely in place.
In the eastern United States, an expected cool front will cause the heat to ease somewhat on Thursday and Friday, but the heat will try to build back up over the weekend and into next week.
The heat has set hundreds of records
Since July began, hundreds of heat records have been set in the United States, many of them in the West. Through July 9, record highs exceeded record lows by a factor of 20, according to data compiled by the Southeast Regional Climate Center. About 300 heat records were set each day on July 5, 6 and 7.
Many locations in the West set at least four calendar-day records during the first nine days of the month. These included Reno, Nev.; Las Vegas; Bishop and Redding, Calif.; and Portland and Medford, Ore.
Almost daily, records are set somewhere in the West. On Tuesday, the high of 118 in Barstow, California — about halfway between Los Angeles and Las Vegas — tied the all-time high for the third day in a row.
Several other locations reached record highs, including Palm Springs, California (124 on Friday), Redding (119 on Saturday) and Las Vegas.
Death Valley reached 53 degrees Celsius on Sunday, one of the highest temperatures ever recorded, and recorded a seven-day average high of 52 degrees Celsius.
In the east, Raleigh, North Carolina, reached a high of 106 degrees Fahrenheit on Friday, also a record high.
The ongoing heat is particularly notable, with many locations reporting one of their warmest weeks (seven consecutive days) on record, including:
- Las Vegas: Hottest week with an average high of 115.4 degrees, with a high of 115.1 degrees in 2005.
- Bishop, California: Hottest week with an average high of 108.4 degrees, with a high of 107.4 degrees in 2021.
- Medford: Second warmest week with an average high of 106.4 degrees, after 108.4 in 1981.
- Palm Springs: Fourth hottest week with an average high of 117.7 degrees.
DC has recorded its fourth warmest five-day period on record, with an average temperature of 31.5 degrees Celsius.
The Climate Connection
Scientific research shows that human-induced climate change is increasing the intensity, frequency and magnitude of heat waves.
According to the Climate Shift Index from Climate Central, a science communications firm, the likelihood of recent high temperatures due to human-caused climate change is four to five times greater in much of the West and two to three times greater in the mid-Atlantic and Northeast.
The planet is experiencing a sustained streak of 13 consecutive record-warm months, with the United States experiencing its second-warmest year on record.
Jason Samenow contributed to this report.