This is a developing story. Check back for updates.
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.
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