Where excessive heat will continue this week after record high temperatures

More than 135 million people across the Lower 48 are under heat alerts Wednesday, including on both coasts and in some of the country’s largest cities. In many cases, the alerts have been up for days and will continue until the weekend. They come after a punishing opening to July in which hundreds of heat records were set.

In the West, Phoenix, Las Vegas, San Jose, Spokane, Wash., and Boise, Idaho, are all under excessive-heat warnings. In the East, heat advisories and warnings span from South Carolina to Massachusetts and include Washington, Baltimore, Philadelphia and Boston. Heat indexes — taking into account both air temperature and humidity — should reach 105 to 110 along large parts of the Interstate 95 corridor.

Huge swaths of the Lower 48 are forecast to endure “major” to “extreme” HeatRisk 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 posted its highest temperature on record, soaring to 120 degrees.

More excessive heat is predicted — especially in the West

Through the rest of the workweek, the most extreme heat will plague the western United States. On Wednesday, pockets of record heat are predicted for parts of Washington state, Oregon, Idaho, California, Nevada and Arizona.

Las Vegas is forecast to reach 119 both Wednesday and Thursday. If it weren’t for Sunday’s high of 120, these would be all-time highs. If Sin City’s high reaches at least 115 Wednesday, it will mark a record fifth straight day that hot.

The zone from Las Vegas into parts of Southern California and Arizona is expected to see high temperatures top 120 degrees through Friday.

Triple-digit heat will also continue to roast regions as far north as western Canada, including much of eastern Washington state, the Snake River Valley in Idaho and large parts of the Great Basin.

Highs of at least 110 degrees are forecast for much of California’s Central Valley for the rest of the workweek.

By the weekend, it should stay hot but probably below record levels in most areas because of an increase in moisture from the south tied to the onset of monsoon season in the Southwest.

However, the heat dome — an intense zone of high pressure responsible for the excessively high temperatures — is forecast to mostly remain in place.

In the eastern United States, an expected cool front will allow heat to ease somewhat on Thursday and Friday. However, the heat will attempt to rebuild over the weekend and next week.

The heat has set hundreds of records

Since July began, hundreds of heat records have been set in the United States, many in the West. Through July 9, record highs outnumbered records lows by a factor of nearly 20, according to data compiled by the Southeast Regional Climate Center. There were about 300 heat records set daily on July 5, 6 and 7.

Many locations in the West set at least four calendar-day record highs during the first nine days of the month. They include Reno, Nev.; Las Vegas; Bishop and Redding in California; and Portland and Medford in Oregon.

All-time highs have been set almost daily at least somewhere in the West. On Tuesday, the high of 118 in Barstow, Calif. — about midway between Los Angeles and Las Vegas — tied its all-time high for a third straight day.

Several other locations have set all-time highs, including Palm Springs, Calif. (124 on Friday), Redding (119 on Saturday) and Las Vegas.

Death Valley hit 129 degrees on Sunday — one of its highest temperatures on record — and has observed a seven-day average high temperature of 126.3.

In the East, Raleigh, N.C., hit 106 degrees on Friday, also an all-time high.

The persistence of the heat has been particularly remarkable. Many locations have reported one of their hottest weeks (seven consecutive days) on record, including:

  • Las Vegas: hottest week with an average high of 115.4, topping 115.1 in 2005.
  • Bishop, Calif.: hottest week with an average high of 108.4, topping 107.4 in 2021.
  • Medford: second-hottest week with an average high at 106.4, behind 108.4 in 1981.
  • Palm Springs: fourth-hottest week with an average high of 117.7.

D.C. has posted its fourth-hottest five-day stretch on record, with an average temperature of 88.7 degrees.

The climate connection

Scientific studies have shown that human-caused climate change is increasing the intensity, frequency and sweep of heat waves.

According to the Climate Shift Index from Climate Central, a science communications firm, human-caused climate change has made recent high temperatures four or five times as likely in much of the West and two to three times as probable in the Mid-Atlantic and Northeast.

The planet has an ongoing streak of 13 straight record warm months, while the United States is having its second-warmest year on record to date.

Jason Samenow contributed to this report.

Reference

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