Boise Climate Trends
Idaho · US States · 50 years of climate trend data
This page tracks how Boise's climate has shifted over 50 years of daily measurements, warmer summers, milder winters, and changes in rainfall, rather than current conditions. The two clearest signs of change: extremely hot days have grown by 32.6 a year and warm summer nights have grown from 4.6 to 21 a year. Measurement period: the last 50 years (1976-2025).
Data through September 12, 2026.
Frequently asked questions about Boise's climate
How much warmer have summers in Boise become?
The average daytime high across June, July and August rose by 3.8°C between 1976-1980 and 2021-2025. That is a five-year average at each end rather than two isolated summers, so a single exceptional heatwave or cool summer does not drive the number.
Have winters in Boise become milder?
The average daytime high across December, January and February rose by 0.7°C between 1976-1980 and 2021-2025. In many capitals in this dataset winter is changing faster than summer, which shows up most clearly in the frost-day count below.
How many days above 30°C does Boise get a year?
Boise averaged 79 days a year above 30°C in 2021-2025, up from 47 in 1976-1980. These are the days that set peak cooling demand and the days hospitals see heat complaints rise.
How many frost days does Boise still get?
Boise averaged 107 frost days a year in 2021-2025, down from 113 in 1976-1980. Fewer frost days sounds pleasant, but water pipes, heat pumps and garden planting are all sized for a cold season that increasingly no longer arrives.
Is spring arriving earlier in Boise?
Spring now starts about 0.6 week later than in 1976-1980. The start point is the first day the trailing seven-day average high crosses 12°C, a fixed in-house measure used only to compare Boise against itself rather than against other cities.
Has the growing season in Boise grown longer?
The growing season is about 2 days shorter between 1976-1980 and 2021-2025. That is the stretch between the start of spring and the first autumn night below freezing, which is exactly the window gardens, farming and pollen seasons run inside.
Is rainfall in Boise getting heavier?
Boise averaged 0.6 day a year with more than 20mm of rain in 2021-2025, down from 1.4 in 1976-1980. This capital gets fewer heavy rain days now, which brings its own problems in a drying climate.
