Heavy rains trigger mudslide, flooding in Treasure Valley. How much did Boise get?

Storms that continued overnight dumped more than 2 inches of rainfall on parts of the Treasure Valley, triggering a mudslide and leading to localized flooding.

Nearly half of an inch of rain fell on the Boise Airport on Tuesday night, while parts of the Foothills saw more than 2 inches, a meteorologist from the National Weather Service told the Idaho Statesman.

The downpour also caused a mudslide that closed a portion of Idaho Highway 21 from Grandjean to Banner Summit, according to the Idaho Transportation Department.

“Ongoing rain is making conditions unsafe for cleanup, so crews have not begun clearing yet,” the state roads agency said in a Facebook post on Wednesday, Aug. 27.

The highway will likely be closed through Thursday, the department said.

Here’s which areas in Boise saw the most amount of rain:

How much rain did Boise area get?

As of Wednesday morning, the Boise airport had received 0.46 inches of rain over the past 24 hours, the National Weather Service meteorologist told the Statesman.

Barber Park got a little over an inch of rain, according to weather officials, while the Foothills saw the most precipitation with more than 2 inches of rainfall some areas.

About 1.71 inches of rain fell at the Lucky Peak marina in the span of 45 minutes, the weather service said in a Facebook post on Tuesday night. The agency also reported wind gusts of up to 40 mph..

Before the storm slammed the Boise area on Tuesday, August was tied for the driest August on record in Boise since 1940 since 1940, with just 0.3 inches of rain recorded for most of the month, according to National Weather Service records.

On Tuesday, a weather balloon above Boise recorded 1.57 inches of “precipitable water” with the potential for rainfall, the weather service said in a Facebook post.

“This amount ranks second most all-time in records dating back to 1948,” the weather service said via Facebook. “Only Aug. 21, 2023, with 1.67 inch from remnants of a tropical storm, had more.”

Rain is expected to continue through 1 p.m. Wednesday, The Weather Channel said.

Did Boise area see flooding?

The National Weather Service said there was no major flooding within Boise city limits, although some areas may have seen minor impacts from water in the streets.

The Ada County Highway District reported localized flooding as storm drains clog with an excess of water, leaves and debris.

What’s the risk for flash floods in Treasure Valley?

On Tuesday, the National Weather Service issued a flash flood watch for the Treasure Valley, the Statesman previously reported.

The flood watch, which impacts parts of Idaho and Oregon, will be in effect through midnight Thursday, the weather service said.

“Heavy rainfall could trigger flash flooding or debris flows in and near recent wildfire burn scars,” the weather service said. “In addition, urban street flooding is possible with the stronger storms.”

Burn scars — areas of land scorched by wildfires — are at the greatest risk for flash flooding during the storms, the National Weather Service said.

When will Boise see rain next?

Following rain on Wednesday, Boise will return back to the dry conditions it’s seen for most of August, the National Weather Service said.

Boise will see warm, sunny weather for the rest of the week, including Labor Day weekend, with temperatures climbing into the 90s, AccuWeather predicted.

Sunday will see the highest temperatures in the coming days with a high of 96 degrees and a low of 64 degrees.

This story was originally published August 27, 2025 at 11:37 AM.