Update, 2:30 p.m. Monday:
City and tribal officials say they will begin hanging informational door flyers in Mendenhall Valley neighborhoods in the flood zone and launch a flood information hotline Monday afternoon.
The door hangars warn residents that the basin is full and that an emergency shelter will be available at Floyd Dryden Middle School once the flood begins. It also includes advice on how to protect property.
Aaron Jacobs, the senior service hydrologist at the National Weather Service in Juneau, gave an update on Suicide Basin at a press briefing late Monday morning. Suicide Basin reached full capacity and began spilling over the top of the glacier Sunday night.
“At this time there is no signs that the release has taken place,” he said.
He said Monday’s rainfall will likely continue to raise water levels in Mendenhall River and Lake, which could affect the flood height once water does start releasing. But, he expects the precipitation to slowly drop off through Monday evening and into Tuesday.
“I know there’s been some reports of a waterfall being seen at the face of the glacier, and that is what we’re seeing. There is just a general glacial flow in the runoff that we’re seeing from the precipitation and just the regular melt from the Mendenhall Glacier,” he said.
Ryan O’Shaughnessy, Juneau’s emergency manager, said the city continues to advise people to prepare to evacuate. They have not issued a mandatory evacuation order, but officials highly recommend people leave once the flood warning is issued. This year’s flood will be the first test of the flood barrier the city installed this spring.
“We have a lot of confidence in the mitigation measures that have been put in place — that being said, this is not something that we want to gamble with,” he said. “The message to carry across please, is to ‘Yes, evacuate if you do get that notice.’”
The state’s Department of Transportation & Public Facilities is preparing for potential bridge and road closures along the river. Officials say when and where will depend on the height and timing of the flood.
Original story:
The countdown has begun for Juneau’s annual glacial lake outburst flood. Suicide Basin reached full capacity and began spilling over the top of Mendenhall Glacier Sunday night.
That means flooding along the Mendenhall River could begin any day.
The National Weather Service issued a special weather statement indicating that it could take up to six days for the basin to release floodwaters into Mendenhall Lake.
Once the water level in Mendenhall Lake begins to rise, the National Weather Service will issue a flood warning. From that point, it will take about 48 hours for the floodwaters to crest in the Mendenhall River.
The City and Borough of Juneau issued an emergency text alert just after 8 p.m. that notified Juneau residents that the basin was overtopping.
“Now is the time to make last-minute preparations, finalize evacuation plans, and pack a go-bag bag,” the alert stated.
Aaron Jacobs, the senior service hydrologist at the National Weather Service in Juneau, said that the contingency forecast is a 16.5-foot flood — that’s subject to change. Jacobs said to check the Suicide Basin monitoring page for an updated forecast once the release begins and as it progresses.
The contingency forecast is based on estimates that Suicide Basin has expanded compared to prior years and that the ice dam holding back the water is a bit lower.
That forecast is also based on the past few days of increased rainfall, which have raised the water levels in the lake and river. Jacobs said the rain could affect the flood height if it doesn’t flow out to sea before the basin releases.
“So we’re hoping that the basin will not release at this time in the next day or so and then the Mendenhall levels can come back down to more normal levels,” he said.
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.
Copyright 2025 KTOO