Idaho’s Coolest August Days Arrive Friday Before Weekend Heat and Mountain Storm Threat

Boise, ID – Idaho residents are experiencing the coolest stretch of summer so far, with temperatures running 10 to 15 degrees below average through Friday. The unusual chill is affecting much of the state, particularly Baker City, Brundage Mountain, and Stanley, where early mornings could dip into the upper 30s by midweek.

Cooler Weather Across Cities and Mountains

According to the National Weather Service in Boise, highs will remain mild in major cities like Boise, Meridian, and Twin Falls, where temperatures will hover in the low to mid-80s through Friday. Nampa and Caldwell will stay just shy of 90 degrees, marking the coolest run since late spring.

In the mountains, especially near Mores Creek Summit and Sun Valley, cooler mornings will greet hikers and travelers, with a slight chance for isolated showers and thunderstorms Thursday afternoon over Baker County and the West Central Mountains.

Travel and Outdoor Precautions

Road conditions are expected to remain clear across most regions. However, drivers and outdoor enthusiasts should remain cautious in high-country areas where storm activity could develop. Forecasters recommend layered clothing for early commuters and those planning mountain hikes, as mornings will feel more like early fall than August.

Heat Returns This Weekend

The cooling trend will reverse quickly by Saturday, when hot air surges back into the valleys, pushing highs into the 90s. By Sunday and early next week, monsoonal moisture could fuel more thunderstorms, particularly in the mountains, bringing renewed risks for lightning and sudden downpours.