Boise averages 51.4 days a year above 90°F, with December the wettest month at 1.54 in of normal rain. The hottest day on record was 110°F on Jul 13, 2002; the coldest, −25°F on Dec 22, 1990. The single biggest 24-hour rain event recorded was 1.77 in on May 29, 1990.
Climate and Average Weather Year Round in Boise
Year-round temperature
In Boise, the warmest months are June through September, with average daily highs between 80°F and 93°F. The coldest stretch runs December through February, with highs between 39°F and 46°F and overnight lows reaching 25°F.
Rainfall through the year
Rainfall in Boise averages 1.0 in per month over the long run. December is the wettest at 1.5 in, while August is the driest at 0.2 in.
Days at 90 °F or hotter
Boise averages 51.4 days per year at 90 °F or hotter. The hottest year on record saw 73 such days (2013); the coolest just 2 (2026).
Precipitation this year
As of May 28, Boise has received 6.6 in of precipitation this year — 5% above the long-term normal for this point in the year (6.3 in).