A heat wave will roll into the Treasure Valley this weekend, bringing potentially record-high temperatures and a streak of triple-digit temperatures far above normal for the region.
Korri Anderson, a meteorologist with the National Weather Service in Boise, said temperatures will break the triple-digit mark on Sunday, with forecasts predicting 102- to 105-degree temperatures in the Treasure Valley.
And it will only heat up from there. Temperatures for Monday are projected to be 104 to 108 degrees. By Tuesday, they could rise as high as 110.
While Tuesday will likely be the peak of the heat wave, temperatures will stay above 100 degrees until Friday, Anderson said in a phone interview.
Anderson said the heat is caused by a high pressure system that’s building northwest of Idaho.
“It’s basically a large dome of warm air, so that gets centered right over us next Monday and Tuesday and it pulls some of that desert Southwest air into it,” he said.
The predicted six-day streak of triple-digit temperatures would put the Boise area above its average number of 100-plus degree days early in the summer. Typically, Anderson said, the region reports about five triple-digit temperature days per year. Last year, Boise had 10 days at or above 100 degrees. In 2019, there were just three days of 100-plus temperatures.
Mid-week, the toasty temperatures will rival record highs. The June 29 record of 105 was set in 2008. This year, it’s set to be up to 110 degrees that day. The following day, the record high is 104, set in 2014. Anderson said it could get as high as 105 degrees this year.
At the start of the month, Boise set a record when temperatures climbed to 103 on June 3.
Anderson said Boiseans should limit time in the sun, avoid exercising outdoors in the heat and be sure to stay hydrated.
Record temperatures, drought converge as fire danger increases
Overall, it’s been an unusually hot June for the Treasure Valley. The average high temperature for the month as of Tuesday was 87.7 degrees, Anderson said — 6.3 degrees above normal.
The average overall temperature this June is 72.8, which is five degrees above normal. Anderson said the sustained triple-digit temperatures next week will make it a close call with the record overall June temperature of 75.9. That record was set in 2015.
And despite a few days of decent rain this month — Boise has seen 0.71 inches, just 0.04 below normal for June — the area is below the average precipitation for the year by about three-quarters of an inch.
Nearly all of Idaho is in some level of drought, according to the U.S. Drought Monitor. Most of Southwest Idaho is considered abnormally dry or in moderate drought, with some areas in severe drought.
The dry conditions combined with high temperatures prompted the Boise-based National Interagency Fire Center to elevate its National Preparedness Level — an evaluation of fire activity, resources and forecasts — to Level 4, the second-highest level.
NIFC spokesperson Jessica Gardetto said in a phone interview it’s unusually early in the year to be at Level 4.
“We’re just seeing drought throughout the West,” she said. “They’re expecting hot, dry weather for the foreseeable future, no weather relief in sight.”
In a news release, the agency said it’s the second-earliest in 20 years that the Preparedness Level has reached Level 4. The last time NIFC reached Preparedness Level 4 in June was in 2012.
Gardetto said the high fire danger has officials tense as the Fourth of July holiday approaches.
“We are fearful of more human-caused fire,” she said. “The lightning-ignited fires we cannot prevent. But human-caused fires are preventable, and they also comprise about 80% of all wildfires.”
Gardetto reminded Idaho residents that fireworks are illegal on public lands, including in the Boise Foothills.