A wave of extreme heat is about to make southern Utah’s hot July even hotter.
Temperatures in St. George are expected to reach 110 degrees for five consecutive days. The city will likely see a peak near 115 degrees between July 15 and 17.
Jon Wilson, a meteorologist with the National Weather Service in Salt Lake City, said that could break records dating back roughly a century.
“Pretty much all of southern Utah is right within a degree or two of those record high temperatures,” he said, “So, definitely the kind of heat that you want to be careful if you’re planning any outdoor activities.”
Even for a region used to blazing summer temperatures, the heat that will blanket the Southwest in the coming days will be extraordinary.
Extremely dangerous heat is on track this weekend in the Southwest. Temperatures at these levels will pose a significant health risk to anyone without effective cooling. Next week, heat will build in the Gulf Coast and Southeast again, before refocusing in the West late in July. pic.twitter.com/hj7NXYPeuv
— NWS Weather Prediction Center (@NWSWPC) July 14, 2023
The hottest July 15 on record in St. George came in 1922 when temperatures reached 112 degrees. The record high for July 16 — 115 degrees — goes back to 1925. Both records, Wilson said, are in danger of falling.
If St. George hits 110 degrees for five days in a row — as the forecast predicts — that would rank as the sixth-longest such streak in the city’s history. If the extreme heat continues further into the next week, it could come close to breaking the longest streak on record of eight consecutive 110-degree days set in both 1994 and 1985.
“It’s definitely common to have these kind of streaks,” Wilson said. “What’s a little less common is just the impressive warmth … the 115-degree territory for several days in a row.”
What’s also unusual, Wilson said, is that there’s no monsoonal rain following the heatwave.
The monsoons that typically show up around this time of year to cool things off aren’t anywhere on the forecast — delayed by the El Niño weather pattern and the cool ground temperatures from the wet spring. That means the region will have to wait longer for rainy relief.
The heat won’t be confined to St. George. In the middle of Lake Powell’s summer tourism season, temperatures there are expected to reach 110 degrees. Even Cedar City — normally shielded from extreme heat by its 5,846-foot elevation — could see triple-digit highs.
With such extremes, Wilson said, it doesn’t take much time for people — especially those who work outdoors or don’t have access to air conditioning — to feel the effects.
The National Weather Service issued an excessive heat warning for the St. George area, Zion National Park and Lake Powell for Saturday through Monday, saying the temperatures will significantly increase the potential for heat-related illness. The NWS also put out an excessive heat watch for the coming days in parts of northern Utah, including Salt Lake City and Provo.
With the very hot temperatures, Excessive Heat Warnings and Heat Advisories are in effect today for the lower elevations of southern Utah. As the dangerous heat spreads northward for Sunday and Monday, these warnings and advisories will expand to include most Utah valleys. #utwx pic.twitter.com/w7LZh4CSoV
— NWS Salt Lake City (@NWSSaltLakeCity) July 15, 2023
The peak hours of 10:00 a.m. to 5:00 p.m. will be the most dangerous time for health impacts, Wilson said. So if you have to be outdoors then, stay hydrated and have a place to go for relief.
“It's just one of those things where you want to know your limits,” he said, “And if you start feeling any kind of different … it's time to stop doing what you're doing and get yourself into a cooler area.”
This type of heat can also take a toll on Utah’s infrastructure.
Utah Department of Transportation spokesperson Kevin Kitchen said roadways, curbs and sidewalks can all buckle as the concrete swells.
“It just doesn't have enough room in those expansion joints,” Kitchen said, “so it may start to crack or pop up all of a sudden.”
Road construction plans can also be disrupted, both because conditions become unsafe for workers and because some of the materials — such as the asphalt and aggregate used on many rural roads — physically can’t take the heat.
“In extreme temperatures, it makes it very difficult for us to be able to put that type of a surface application on,” Kitchen said. “It's like melting ice cream.”
On top of the heat, relative humidity in southern Utah is expected to drop to the single digits. That could ramp up dangerous wildfire conditions, as grasses and shrubs dry out and become fuel.
That lack of humidity also creates a cycle that keeps temperatures elevated, Wilson said, and overnight lows in southern Utah could creep close to the warmest on record.
“The drier you are, the easier it is to become warmer,” Wilson said. “And that's what we're seeing here later this week, especially through the weekend.”
The good news, Wilson said, is that the high pressure system fueling this heatwave should soon weaken and return temperatures to seasonal averages. But for southwest Utah, even those normal temps remain in the triple digits.
The average July high temperature for St. George according to historical records is 101.8 degrees. The record for the hottest average high temp across the month of July is 107.3 degrees, which was set in 2005.
So far, this July’s average sits around 104 degrees. Wilson expects the coming days to push this month’s average past the 107.3-degree record, at least temporarily. The only question will be whether or not late-July temperatures will be cool enough to bring the average back down.
