Weather & Air Quality

The Treasure Valley has a high-desert climate that surprises people. Summers run hot and dry — daytime highs in Boise routinely sit in the upper 90s in July, and the valley floor can hit triple digits while the Boise Foothills, just a few hundred feet higher, stay noticeably cooler. Winters are colder and snowier than first-time visitors expect, with overnight lows in the teens and the occasional "inversion" week where cold, polluted air settles in the valley while it's clear and sunny up on Bogus Basin. Spring and fall are short, mild, and the best times to be outside.

Two seasonal hazards dominate local weather. From late July through September, smoke from regional wildfires can push the air quality index from "Good" into "Unhealthy" or worse for days at a time — schools cancel outdoor practice, joggers move to treadmills, and you watch the wind direction. In winter, valley inversions can do the same to particulate levels, prompting voluntary wood-burning bans. Spring brings pollen season, with tree pollen peaking in March–April and grass pollen following in May–June.

Below you'll find the live widgets we trust for a quick read on conditions, plus links to the authoritative sources for forecasts, air quality, river and reservoir levels, and seasonal warnings.

Summer (June–September) is the defining season: hot, dry, and sunny, with Boise highs in the 90s and frequent triple-digit afternoons in July and August. Low humidity makes the heat more bearable than the same temperature back east, and evenings cool off nicely — which is why so much of valley life (river floating, patios, concerts, twilight golf) happens after 6pm. The trade-off is wildfire smoke, which can roll in from regional fires any time from late July through September.

Fall (October–November) and spring (March–May) are short and lovely — mild days, cool nights, peak foothills hiking and biking. Spring is also runoff and pollen season. Winter (December–February) is colder and grayer than visitors expect: periodic snow on the valley floor, lows in the teens, and the valley's signature inversions, when cold stagnant air and haze settle in for days while the mountains stay clear and sunny. A drive up to Bogus Basin on an inversion day is a popular way to escape into the sunshine.

Three air-quality patterns shape outdoor plans here. Wildfire smoke in late summer can push the AQI from Good to Unhealthy for days at a stretch — watch the wind direction, check AirNow, and move workouts indoors when it spikes. Winter inversions trap particulate pollution on the valley floor and can trigger wood-burning restrictions. Pollen runs tree (March–April), grass (May–June), then weeds and sagebrush into fall. The live widgets above give you a quick read, but for warnings always defer to the National Weather Service Boise office, and for air quality to EPA AirNow and Idaho DEQ.