The countdown has begun for Juneau’s annual glacial outburst flood. Suicide Basin reached full capacity and began spilling over the top of the glacier Tuesday morning.
That means flooding could begin any day.
The National Weather Service issued a special weather statement at 8:35 a.m. indicating that it could take between one and six days for the basin to release. From that point, it takes roughly 48 hours for the floodwaters to crest in the Mendenhall River.
The city issued its first emergency alert for the impending flood at 8:39 a.m. Ryan O’Shaughnessy is the city’s emergency manager. He said Mendenhall Valley residents in the flood zone should be in the “set” phase of the “ready, set, go,” emergency framework.
“Now is the time for people to pack a go bag, have that by the door, make sure their phone’s charged, there’s gas in the car, and be ready to evacuate when the basin begins to release,” he said.
Once the flood begins, the Red Cross will set up an emergency shelter at Floyd Dryden Middle School.
O’Shaughnessy said the city will distribute more than 2,000 door hangers in the flood zone with the same information today to ensure residents who haven’t signed up for local emergency alerts are notified.
Aaron Jacobs, the senior service hydrologist at the National Weather Service in Juneau, said the initial forecast is a 16.1 to 16.55 foot flood on the Mendenhall Lake gage, or between 45,000 and 47,500 cubic feet per second of water flowing down the river.
“The event hasn’t started yet,” Jacobs said. “We could see some minor fluctuations throughout the week that could adjust that range by a couple tenths of a foot.”
That initial forecast is a bit lower than the record-breaking 16.65 foot flood last year, which peaked at 48,873 cfs.
Jacobs said to check the Suicide Basin monitoring page for an updated forecast once the release begins and as it progresses. About a day after the flood starts, the National Weather Service might update the forecast.
The city will issue another emergency text alert when the National Weather Service issues a flood warning. That will mean that the basin is releasing and the flood has begun.
KTOO will also share breaking news updates on ktoo.org/flood and on our live blog.
