Hot weather is hitting the Treasure Valley next week, forecasters say. Starting Tuesday, some places could reach 105 degrees or above — the summer’s hottest temperatures yet.
The heat will be caused by a large system of high pressure moving into the Pacific Northwest and Northern Rockies, Jaret Rogers, science and operations officer for the National Weather Service in Boise, told the Idaho Statesman. Air in this region sinks towards the Earth’s surface, trapping heat.
As of Thursday, the Weather Service forecast highs in Boise to be in the low to mid-90s Thursday through Monday. Forecasters said temperatures will surge to 100 degrees on Tuesday, 101 on Wednesday and similarly high temperatures Thursday in Boise and across the Snake River Plain as high pressure over the Desert Southwest moves into the Intermountain West.
Temperatures might return to normal after the coming week or two, but it’s hard to reliably forecast that far out, Rogers said.
This summer heat isn’t a surprise — July and August are the hottest months in the Treasure Valley. But with climate change, scientists expect to see that the window for hot temperatures expands over time, Rogers said. A few decades from now, hot temperatures could start earlier and end later, and overall temperatures could be hotter within that window.
Warming is ubiquitous, meaning that it’s happening in most regions of the world, Mojtaba Sadegh, assistant professor of civil engineering at Boise State University, told the Statesman.
“That means this summer is going to be one of the coldest summers that I will experience for the rest of my life,” Sadegh said.
Boise has seen a gradual upward trend in both high and low temperatures, especially over the last 30 to 40 years, Rogers said.
But that trend doesn’t necessarily mean this summer is going to be warmer than last year — just that it’s going to be warmer than historical averages, Sadegh said. For someone who has lived in Boise for several decades, this summer is going to be warmer than what they’re used to, he added.
Are some spots in the Treasure Valley hotter than others?
Some big cities have “urban heat islands” — areas where urban structures absorb and hold heat. Because Boise has lots of vegetation, it doesn’t have many of these islands, Rogers said.
Temperature doesn’t vary by much more than a couple degrees within the Treasure Valley, Rogers said, and local temperature changes are largely driven by terrain, elevation, and vegetation.
For example, water and vegetation keeps the banks of the Boise River cooler than the Boise Airport, but this effect doesn’t extend far beyond the river bed, Rogers said.
And places with higher elevation, like Bogus Basin, will generally be a few degrees cooler than Boise proper, Rogers said. But different wind patterns and the shape of the land can also have an effect.
Additionally, winds from the southeast can heat the eastern part of the Treasure Valley, increasing temperatures by five degrees, Rogers said.
Idaho susceptible to wildfires, but predicting them is tricky
Heat and wildfires are closely related, Sadegh said.
Idaho is generally susceptible to wildfires, but some parts of the state are at increased risk, Rogers said. Southern Idaho has lots of grassland, and the Treasure Valley has grass and sagebrush in the open desert outside of the urban area, Rogers added.
Idaho had a lot of precipitation this spring, which led to huge grass growth, Sadegh said. Once vegetation dries in the summer, it becomes ignitable fuel, vulnerable to incidents like fireworks or lightning.
But that’s not the only factor at play. This year’s forest fire risk could be below normal because of the wet spring, Sadegh added, as forests will carry much of that moisture into the summer.
Additionally, many fires are driven by wind once formed, so areas susceptible to wind could be at risk too, Rogers said.
All in all, it’s not easy to pinpoint when and where exactly we might see fires this summer.
Fires are stochastic processes, Sadegh said. “You need the triangle: dry, hot, windy.”
As of July 1, 2022, the National Interagency Fire Center predicts normal significant wildland fire potential in July for all of Idaho. For August, it predicts above normal potential in Southwest Idaho and South Central Idaho.