El Niño and 45-state drought push July 4 heatwave to 100 million Americans

Wildfire smoke threatens Midwest as heat builds across western US

The National Weather Service expects temperatures over the July 4 holiday weekend to approach all-time highs from Washington, D.C., to New York, with sweltering heat indexes topping 115 degrees Fahrenheit (46 degrees Celsius). The heatwave will affect more than 100 million Americans, the agency said.

The heat is being intensified by a drought affecting 45 states — on par with the severe droughts of 1988 and 2012 — and by the growing influence of El Niño. The first six months of the year were the hottest ever measured for parts of eight western states, according to new data released Tuesday.

In the Colorado River basin, water levels are on pace for new record lows, triggering mandatory water restrictions affecting Nevada and Arizona. Later this summer, water levels could fall below critical thresholds needed to continue operating major hydropower dams along the river, including Hoover Dam.

Across the western U.S., numerous wildfires have broken out, including in the mountains of Colorado, where a record-warm start to the year left a dearth of winter snow. “Our communities are feeling the firsthand impacts of severe drought and imminent fire danger,” Colorado Gov. Jared Polis said at a wildfire briefing Monday.

Local officials have been working for months to strengthen preparations for what is expected to be a brutal fire season, including sourcing additional equipment and seeking federal support from the newly consolidated U.S. Wildland Fire Service. Last week, high temperatures were in the 90s in Seattle and Portland, Oregon — about 20 degrees Fahrenheit warmer than usual for this time of year.

“We have known since April 1st that snowpack is very low across the western US,” said Guillaume Mauger, the state climatologist of Washington. “Knowing what to expect early on gives people time to prepare.” Mauger cautioned that while many factors will influence this summer’s weather, the ongoing drought and a strengthening El Niño will continue to tilt the odds toward unusually warm temperatures. Research has tied low April snowpack to a higher risk of mountain wildfires across the entire intermountain West.

Wildfires in Colorado and other western states have already begun sending persistent smoke plumes toward the Midwest and eastern states, the latest episode in a worsening trend of poor summer air quality for the eastern two-thirds of the country. Minnesota, Wisconsin and Michigan have warned their residents about a heightened potential for unsafe air quality from wildfire smoke this summer. Last year, Madison, Wisconsin, recorded some of the worst air quality in the country for an extended stretch of smoky days in July.

This year’s El Niño is taking place against a backdrop of severe drought that is on par with the droughts of 1988 and 2012, which spawned enormous wildfires and blanketed the continent in smoke. The drought year of 1988 saw weeks-long fires overwhelm Yellowstone National Park, and fires in 2012 plagued California and Texas for months.

The El Niño phenomenon, officially declared underway in June by the National Oceanic and Atmospheric Administration, could be one of the strongest ever observed and is expected to boost global temperatures to new record highs over the next 12 to 18 months. El Niño works to liberate subsurface heat stored in the Pacific Ocean, acting as an accelerant for global temperatures and a powerful influence on weather patterns worldwide.

A similarly intense heatwave in recent days pushed temperatures to their highest-ever recorded levels in France, Germany and Denmark, resulting in hundreds of deaths across Europe. The heat and fires are occurring as evidence grows that human-caused climate change is accelerating, portending increased odds of tail-risk disasters. A rapid study conducted last week found that the European heatwave would have been “virtually impossible” without the influence of climate change.

Extreme heat is the deadliest type of weather in the U.S. in a typical year, but this year is shaping up to boost the risk even further, just as the country is welcoming more than a million international visitors for the World Cup. This weekend’s World Cup matches could rank as the hottest ever played — surpassing even those held in Qatar in 2022. FIFA has instituted cooling breaks during this year’s matches for the first time.

Among vulnerable populations such as children, elderly people, and visitors unaccustomed to hot temperatures, the risk of injury or death during prolonged heat waves is even greater. Regina Toto, a medical director of emergency preparedness at Children’s Hospital of Philadelphia, said her hospital has been planning for months along with local officials to respond to a potential mass casualty event due to a heatwave. “As Philadelphia is one of the host cities for the World Cup, [we have] been part of several planning committees with municipal and healthcare partners to ensure preparedness of the overall healthcare infrastructure,” Toto said.

In areas such as Philadelphia and Phoenix, which rely on air conditioning during intense summer heat, experts and government officials are growing concerned that a surge of electricity use by AI data centers could increase the risk of a simultaneous mass blackout during a heatwave. A 2023 study found that if a widespread blackout occurred during a stretch of record high temperatures in Phoenix, more than half of the city’s population could require hospitalization for heat-related illness or injury — with potentially tens of thousands of deaths.

“The appropriate focus right now is to hedge — prepare for possible impacts in case the worst of the forecasts come true,” said Mauger. “This is why early warnings are so valuable.”