March delivered so much snow to Idaho that conversations among water managers quickly switched from drought to flooding.
Most basins in southern Idaho have more than their median share of water packed in the snow at higher elevations, and cold temperatures have kept that moisture in place. The precipitation has been a boon for skiers and resorts — Bogus Basin will extend its season until May — and it sets farmers up well for irrigation season after more than two years of drought.
But all the snow presents its own risk once temperatures rise and melting begins. Some flooding is expected this year in south-central and eastern Idaho, said Tim Axford, a warning coordination meteorologist with the National Weather Service in Pocatello.
“If we were to melt that really quickly, we would have issues with what we call sheet flooding, or lower-elevation flooding," he said
Streamflow is likely to be above normal in the Boise River, Big and Little Wood Rivers, Big and Little Lost Rivers, the Bear River and the Portneuf River, according to the Natural Resources Conservation Service.
The U.S. Army Corps of Engineers and the Bureau of Reclamation have begun increasing flows from Lucky Peak to the Boise River through Boise to mitigate flood risk later this spring.
The amount of snow sitting on the ground and at higher elevations are important factors for flood severity. But the weather from here on out is key, too. If temperatures rise all at once and are sustained for multiple days, that will lead to more rapid melting. So would rain falling on top of melting snow.
Occasional dips back into cooler weather, though, would prevent all the snow from heading to the rivers at once.
“At night, if we can come back down in the 30s or even in the 20s, that slows that melting significantly," Axford said.
To understand what runoff might look like locally, Axford recommends keeping an eye on the weather forecast a few days to a couple weeks out.
How to prepare for potential flooding
- Move snow away from drains and the foundation of your house
- Sign up for alert systems through the Idaho Office of Emergency Management and counties (Ada County, Canyon County, Magic Valley, Blaine County)
- Check if you are located in a floodplain here or by calling your city or county
- Consider buying flood insurance. There's usually a waiting time of up to 30 days
Find reporter Rachel Cohen on Twitter @racheld_cohen
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