Heat warnings and watches are in place for nearly 150 million people across 21 states for the holiday period, with dangerous and potentially historic extreme heat due for the West in the coming days and temperatures of 115 degrees possible.
Several daily heat records were broken Tuesday and more than 130 could be set through next Tuesday.
The California cities of San Rafael and Livermore hit all-time highs Wednesday, clocking in at 100 and 110 degrees respectively.
Excessive heat warnings are in place for much of California, southern Nevada, and parts of Arizona, Washington and Oregon. An excessive heat warning means potentially life-threatening conditions, “with a high to very high risk for much of the population due to long duration heat with little to no overnight relief.”
The National Weather Service in the Bay Area warned that “an exceptionally dangerous situation is underway as we enter a potentially historic and deadly heat event.”
It said heat is the number one weather-related cause of death in the U.S. and “it is VERY LIKELY that we add to that statistic if preparations are not taken seriously.”
The extreme heat in the San Francisco area could last 6 to 12 days, the weather service there said, making it the longest stretch of extreme temperatures the Bay Area has seen in at least 18 years.
The city of Los Angeles issued an excessive heat warning Wednesday, noting the stretch of scorching temperatures could last through “at least” Monday, with temperatures that could climb to 106 in parts of L.A. “for many days in a row.”
In Oregon — where temperatures are expected to reach near record-breaking levels this weekend — Gov. Tina Kotek issued a warning Wednesday and said state agencies were working to open cooling centers to combat the heat wave.
And in Seattle, the weather service in the city warned Wednesday that the forecast for a hot holiday weekend remains in tact, with highs in the 90s, peaking on Sunday.
Across the Plains and the Southeast, the heat index — which measures how hot it feels when humidity is taken into account — could reach between 100-115 on Wednesday.
Little Rock, Arkansas, could see a heat index reading of 116 degrees, while Phoenix, Arizona, is set to reach 113 on the same scale.
On Wednesday, Little Rock officially hit 100 degrees for the first time this year, marking 301 days since the last time the mercury climbed that high in the city.
Phoenix hit a high of 113 degrees Wednesday, marking the 16th day in a row that the city has seen temperatures at or above 110.
The Phoenix Police Department said a child died while hiking on South Mountain on Tuesday “as a result of a heat-related medical event.” The department said the victim’s family had been on the trail since early that day.
The Southern Plains and Lower Mississippi Valley will likely see “oppressive heat and humidity” over the holiday, according to the weather service, with temperatures reaching into the upper 90s and low 100s and heat indexes in the 110s. It said the heat wave is expected to spread east into the Mid-Atlantic toward the end of the week.
A number of cities have already canceled or postponed July 4 fireworks ceremonies and parades due to the high temperatures and dry conditions that could cause wildfires.
In California, St. Helena said it was postponing its fireworks show until later in the year when weather conditions are better. And Oroville canceled its Fourth of July fireworks, citing the Thompson Fire, which has been blazing nearby since Tuesday.
Antioch, California, nixed its daytime parade due to the heat, but said it was still planning to put on a fireworks show Thursday evening.
Excessive heat and humidity will stretch from Nashville to New Orleans on Wednesday and Thursday, but slightly cooler temperatures arrive by Friday.
It’s already been a record-breaking year for temperatures. It’s only early July, but Miami has spent more time in or above 105 degrees on the heat index than in the entirety of 2019.
The extreme heat brings with it an increased risk of wildfires. Some 4 million people, mostly in California, are under Red Flag warnings. The warnings urge people to be careful with open flames — an added risk with holiday firework displays taking place.
There is also the chance for stormy weather across the central U.S. to disrupt some holiday gatherings.
Some 13 million people are under risk of severe storms across the western High Plains and the Ohio River Valley. High wind is likely across both areas, along with hail and isolated tornadoes for the region.
For Thursday, 6 million people are under a slight risk of severe storms across much of Missouri and parts of Kansas and Oklahoma.
A secondary area of storms that may light up by afternoon could be Iowa, where a tornadoes are possible. The main threat will be damaging winds for cities like Kansas City, Missouri, and Topeka, Kansas.
A low pressure front over the central High Plains and a frontal boundary stretching from the lower Great Lakes to the central Plains could be “the triggers for some meteorological fireworks,” the NWS said.
Flash flooding as a result of heavy rain is possible between eastern Kansas and the Ohio Valley.