Flash Flood — Boise, Idaho

2025-08-26 · near Garden Vly, Boise, Idaho

Event narrative

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.

Wider weather episode

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.

View location on OpenStreetMap → (44.0819, -115.4946)

Source: NOAA Storm Events Database, event_id 1295088. Narrative written by the NWS forecast office that issued the report.