The National Weather Service in Pocatello has issued a flash flood watch for the Big Rock burn scar near Heise, effective from early Tuesday morning through Wednesday at midnight.
The watch was issued at 12:43 a.m. MDT on August 12 and remains in effect until August 14 at 12:00 a.m. MDT. Forecasters warn that excessive rainfall expected Thursday afternoon into Thursday evening could trigger flash flooding and debris flows across the burn scar area.
Why the Risk Is Elevated
Burn scars from wildfires create terrain highly susceptible to flooding because vegetation that normally absorbs and slows water runoff has been destroyed. When heavy rain falls on these denuded landscapes, water moves rapidly downslope, concentrating into channels and gullies where it can gain tremendous force and carry debris—trees, rocks, and soil—downhill at dangerous speeds.
The Big Rock burn scar, located in the Heise vicinity near the Bonneville County line, presents particular concern given the forecast heavy rainfall. Residents and travelers in the affected area should remain alert to changing weather conditions and be prepared to evacuate if warnings are issued.
What to Know During the Watch Period
A flash flood watch means conditions are favorable for flash flooding, though it does not guarantee flooding will occur. The watch allows residents and emergency managers time to prepare. Flash flood warnings, which indicate flooding is imminent or already occurring, would be issued separately if conditions warrant.
Drivers should avoid flooded roadways, as water depth can be deceptive and even shallow-moving water can sweep vehicles off roads. The National Weather Service emphasizes that most flash flood fatalities occur when people attempt to drive or walk through flooded areas.
Residents near canyon areas, creek beds, and drainage paths should monitor local weather updates closely. Even areas that appear dry can experience sudden flooding when water rushes downslope from burn scars during heavy rain.
Related Hazards in the Region
The flash flood watch comes as Bonneville County continues monitoring the aftermath of recent fire activity in the region. The Heise Fire in Bonneville County has reached 72% containment as road closures persist, with evacuation areas and access restrictions affecting the surrounding terrain. Combined fire danger and flood risk underscore the need for heightened awareness during the remainder of the forecast period.
Residents should check the National Weather Service Pocatello office website for updates, as conditions can change rapidly. Emergency management officials in Bonneville County are monitoring the situation and will issue additional alerts if necessary.
What Comes Next: The watch period extends through Wednesday morning. Residents should prepare now by reviewing evacuation routes, securing important documents, and keeping emergency supplies accessible. Monitor weather forecasts for any upgrades to flash flood warnings or changes to the watch timeline.