A vast and unusually intense heat dome is set to blanket most of the contiguous United States, driving temperatures to dangerous levels in what the National Weather Service (NWS) has described as “significant and dangerous” heat.
Forecasters said the heat wave will begin over the weekend and persist for at least a week, with some regions expected to endure above-normal temperatures through the end of the month. Daytime and overnight temperatures are forecast to run 15 to 25 degrees Fahrenheit (8 to 14 degrees Celsius) above seasonal averages in many areas. Elevated nighttime temperatures are expected to heighten health risks and make it more difficult to contain the country’s already active wildfire season.
Daniel Swain, a climate scientist with University of Agriculture and Natural Resources, “This upcoming heat wave does look pretty remarkable. This is going to be a long duration, widespread and high-intensity heat event that’s going to affect millions of people for over a week.”
A sprawling high-pressure system, often referred to as a dome, is expected to settle over the Northern Plains, trapping hot air much like a lid on a pot while preventing cooling winds and rainfall. However, meteorologists told The Associated Press that the system will be so expansive it could push sweltering temperatures across nearly two-thirds of the continental United States.
Although the East Coast is expected to avoid the worst of the heat initially, forecasters said the heat dome is likely to shift and fluctuate over the coming days, potentially extending from coast to coast for more than 10 days.
Forecasters are expecting record triple-digit highs this weekend in Nevada, Utah, Colorado, Wyoming, Idaho, Montana, North Dakota and South Dakota.
The weather service is predicting more than 90 US local temperature records will be tied or broken through Wednesday, with two-thirds being overnight heat records that can hinder how the human body recovers from broiling days.
“Nights can be just as dangerous as days. If you don’t get heat relief at night, that’s going to spill out into your daytime experience and become extremely dangerous,” said meteorologist Bob Henson with Yale Climate Connections. “Heat is not to be played with. It’s just as dangerous as a tornado or hurricane that can kill you just as easily, just in a quiet and different way.”
Swain said what makes this heat wave so different is how big a warm shadow it will cast and how long it will persist.
In the past couple of weeks, major heat waves have caused extensive suffering in Europe, the US East Coast and most recently the U.S. Southeast. Now any place in the United States that escaped the earlier July heat waves will get this one, Swain said.
Rain is likely to sneak below the southern edge of the heat dome and douse the US Southeast during the daytime, setting up something strange, Climate Central meteorologist Shel Winkley said. Because of the added moisture and humidity, the Southeast could get record-shattering nighttime heat but below-normal daytime warmth, he said.
The weather service is predicting record nighttime heat in a number of locations from Texas to Florida to North Carolina on Saturday. Temperatures won’t drop below 80 degrees (27 degrees Celsius) at night in Fort Lauderdale, Florida; Miami; Tampa, Florida; Galveston, Texas; and Charleston, South Carolina, according to the forecast.
While heat domes are not unusual in the , Winkley said this one stands out because of how strong it is, likely to set records for the amount of high pressure that it will contain. It’s especially unusual for being so far north, he said.
It’s likely to persist so long because drought-stricken areas have less soil and air moisture that would normally slow the warming of the air, Swain said. The drier, hotter air then worsens the drought conditions and stokes more heat in a vicious cycle, he stated.
This will add to wildfire risk, already bad because of the drought, he said.
‘Human caused climate change’
The El Nino that recently formed is too young to have a pronounced impact on this heat wave, but climate change from the burning of coal, oil and natural gas clearly does, the three meteorologists said.
“We know that heat waves are becoming more intense, they’re lasting longer, they’re covering larger areas than they used to because of human-caused climate change,” Swain said. “And so when we see an event like this, we know there is at least a partial contribution by the long-term warming trend.”
Climate Central’s Climate Shift Index uses 20 computer models to compare forecast temperatures with conditions that would likely exist in a world without human-driven greenhouse gas warming. According to the analysis, a 20,000-square-mile (52,000-square-kilometre) stretch of the US, extending from Southern California to northern Minnesota and home to around 24 million people, is expected to experience the highest category of heat on the index this weekend.
That means the extreme are at least five times more likely because of climate change. The organisation reported similar findings during the East Coast heat wave over the July 4 weekend and the recent spell of extreme heat in the southeastern United States.
“Using attribution science we know that those temperatures would be virtually impossible without the influence of climate change,” Winkley said.
