Here comes a ‘heat dome,’ Boise. Will near-record temps be a sign of things to come?
Temperatures in Boise will skyrocket this weekend to near-record levels as a “heat dome” settles over the southwestern United States.
The National Weather Service forecasts a temperature of 101 degrees on Saturday, 107 on Sunday and 100 on Monday for Boise. The first two days will approach historical levels for their respective dates — 105 degrees for July 15, set in 2005, and 109 degrees for July 16, set in 1898.
Jay Breidenbach, a meteorologist with the National Weather Service in Boise, said there is about a 10% chance of Sunday’s high temperature equaling the record set in 1898.
But even if Boise doesn’t break the record, 100-degree-plus heat is nothing to scoff at.
“The impacts can be felt there for a couple of days, and heat can be really dangerous,” Breidenbach said. “We advise people to stay hydrated and check the back seat. You don’t want to leave children in the hot car or your pets. That’s a really dangerous thing.”
What is a heat dome?
Imagine putting a clear glass dome on a flat service and leaving it in the sun. The heat from the sun will enter the dome and get trapped inside, while everything else, such as cooler air and gasses, will be pushed around the dome.
A heat dome works similarly. A strong area of high pressure, which typically extends to about halfway through the atmosphere, captures warm air from the ocean underneath it, according to the National Oceanic and Atmospheric Administration. The jet stream is forced northward because of the dome, helping trap the heat over the continental U.S. and causing sweltering temperatures.
“If you imagine the flow in the middle part of the atmosphere, air generally flows from east to west,” Breidenbach said. “But when you get this big ridge of high pressure, a heat dome, air flows up and over that ridge way up into Canada, and then it comes around the other side.”
The heat dome will primarily be focused over the southwestern U.S., with high temperatures forecast to hit 120 degrees and hotter in areas like Las Vegas and Death Valley.
Fortunately, Boise won’t be hitting those numbers, but hot air being pulled northward by the rotation of the dome will result in extreme temperatures.
Is this the start of another hot summer?
This weekend’s heat dome is a flash in the pan for Boise. Friday’s high temperature is forecast at 94, and it will drop back to 93 by Tuesday. Those temperatures are normal for this time of the year.
If forecasts for the weekend hold up, these will be the second, third and fourth 100-degree days of the summer, after it was 103 last weekend. The City of Trees still has a long way to go to equal the previous summer’s 23 days of triple-digit heat.
A lower-level trough is expected to break up this weekend’s heat dome, Breidenbach said, but he thinks the dome will try to expand again later in the summer.
“I fully expect we’ll see some more 100-degree days,” Breidenbach said. “As we head out towards the end of July and the first part of August, climatologically, that’s the hottest time of year in Boise.”
The average high in Boise for early August is 95 degrees.
The Climate Prediction Center is forecasting a 50%-60% chance that Southwest Idaho will see above-average temperatures between now and the end of September.
This story was originally published July 13, 2023 at 4:00 AM.
