Longest day is coming, Boise, and it will be cool. When will it get dark?
AI-generated summary reviewed by our newsroom.
- A June 20 cold front will lower Boise's high to 76°F, with lows dipping to 45°F.
- Despite public belief, peak summer heat in Boise typically arrives in late July.
- On the solstice, Boise will see 15 hours, 26 minutes of daylight, ending around 10:05 p.m.
This year in Boise, the longest day of the summer might also be one of the coolest.
Thanks to an incoming cold front, the June 20 summer solstice Friday will usher in a weekend of temperatures that will give the Treasure Valley a cool start. Temperatures will reach a high of around 76 degrees Friday before dropping to a low of 45 that evening, according to the National Weather Service.
The remainder of the weekend likely won’t exceed a high of 70, with Saturday night dipping to a low of 44.
Jay Breidenbach, warning coordination meteorologist at the NWS, told the Idaho Statesman that the time around the summer solstice is not typically the hottest time of the year, despite some public misconceptions.
“People think, ‘Well, gosh, that doesn’t make sense,’ on first glance, but it’s kind of analogous to how the hottest time of day isn’t at noon,” Breidenbach said.
As the sun remains high in the sky late in the afternoon in Boise, it continues to heat the city up, Breidenbach explained. Similarly, the plethora of daylight throughout the summer continues to heat up the atmosphere, causing peak heat waves to usually hit in late July.
In Boise, the summer solstice will occur at about 8:42 p.m. Friday, marking the moment that the sun will reach the northernmost point in the sky in relation to the equator, Breidenbach said.
Solstices in Boise are unique among U.S. cities because of the city’s geographic position. Daylight on the solstice will last much longer here than many other parts of the country, giving Boise a total of 15 hours and 26 minutes of daylight, according to the U.S. Navy.
According to Breidenbach, daylight will persist much later in the evening here because Boise is so far west in the Mountain time zone and also so far north. In the summer, that positioning means the sun will set more to the northwest rather than the true west.
“Because of that angle, the sun doesn’t dip way below the horizon this time of year, so it it prolongs twilight well into the evening,” Breidenbach said.
Breidenbach said Boise residents will still be able to see signs and view the horizon easily on the solstice until about 10:05 p.m. Then, he said, the sky will be in a phase known as nautical twilight, when it gets difficult to read but light is still apparent, all the way until 10:52 p.m.
“For really keen observers, you still might see a little bit of light,” he said. “You’ll see some of the stars, but not all of them ... until about 11:52 p.m.”
This story was originally published June 18, 2025 at 11:58 AM.
