Flash Flood in Boise County, Idaho

Flash Flood August 26, 2025 · Boise County, Idaho

Where the report was made, with tornadoes recorded within 15 miles over the years.

What the National Weather Service wrote

A small amount of water in a recently burned area with steep slopes allowed standing water to accumulate to 3 feet next to Hwy 21 near MP 80. This occurred around the same time as mudslides and rockslides on the same highway. While radar captured very little precipitation, this area was known to be susceptible to runoff, especially with the recent wild fires.

The wider storm

Monsoonal moisture surged into the region over a three day period, the most intense of which was the 26th. High atmospheric moisture content combined with weak flow in a monsoonal pattern to produce very moist storms moving very slowly. Additionally, as terrain served as the main trigger for convection, storms would train over the same spots for much longer than normal. Precipitable water was at near record levels around 1.2 inches.

Began near Garden Vly (44.0819, -115.4946).

Source: NOAA Storm Events Database, event 1295088. Narratives are written by the National Weather Service forecast office that issued the report.

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