Nearly 1,900 Juneau homes are under an evacuation advisory as a glacial flood nears

Almost 1,900 homes in Juneau's Mendenhall Valley are under an evacuation advisory as Suicide Basin fills toward capacity, with officials warning that a major glacial outburst flood is likely within weeks. That's nearly double the roughly 1,000 homes warned last year.

The zone grew because the city changed how it maps the danger. Planners looked not only at where the floodwater would go, but at where roads could wash out — trapping people who can't get out, or first responders who can't get in. Emergency Programs Manager Ryan O'Shaughnessy said areas were added where "access or travel, including by first responders, may be compromised."

The sandbag-style HESCO barriers protecting the valley are finished, with crews sealing the last gaps by July 20. But officials are blunt that the barriers are no reason to stay home. O'Shaughnessy called the whole system "fragile" and the barriers "essentially sandbags." Chief Engineer John Bohan pointed to last year, when "a tree completely blew up the barriers behind the Field House very quickly, very easily." No one, he said, knows what force might crack one open.

Officials are using a Ready, Set, Go plan. Right now the valley is at Ready: make an evacuation plan and sign up for alerts. The basin is expected to fill between about Aug. 1 and Aug. 9; when it does, a wireless emergency alert will move the area to Set — go bags packed — and a second alert will mean Go, leave now. The city will test the alert system Thursday, July 16, at 3:30 p.m.

Residents can check JuneauFlood.com to see whether their address is in the zone and to sign up for alerts. The Red Cross will run an evacuation shelter at the former Floyd Dryden Middle School, and agencies will demonstrate sandbagging and answer questions at a preparedness event Saturday, July 11, at Diamond Park.