Flood — Juneau Borough, Alaska

2021-06-29 to 2021-06-30 · near Juneau, Juneau Borough, Alaska

Event narrative

The Taku River water levels were at record daily stream flows hovering just below minor flooding stage of 43 feet by the end on July from well above normal snowpack, delayed snowmelt from a cool spring and then rapid snowmelt from impacts of an atmospheric river and then record high temperatures. One the morning of June 29th the public reported that the glacier dammed lake, Lake No Lake, on the Tulsequah Glacier just over the Canadian boarder was starting to release water into Tulsequah River which is a tributary to the Taku River. The Taku River started to rise steadily for the next 36 hours as the Lake No Lake totally drained. There was about 50,000 cubic feet per second of water added to the Taku River from Lake No Lake and combined with record daily stream flows already occurring on the Taku River it produced record flooding going above the previous record of 45.07 feet from 2004. A number of homes were affected from the moderate to major flooding with water in homes and some foundations being compromised.

Wider weather episode

The Southeast Alaska region saw well above normal snowpack through out the 2020-2021 winter, recording between 175 to 200% of normal snow water equivalent. There was a delay in snowmelt in the spring time due to cooler than normal temperatures in April and May to keep larger river's stream flows below normal. Temperatures started to be closer to normal in the second half of the first week of June over Southeast Alaska which began to prime the snowpack in larger rivers basins like the Taku River which originates in British Columbia, Canada. The Taku River started to see rise from the snow melt from the primed snowpack. Then the region was hit by an atmospheric river which produced moderate rainfall along with high freezing level to significantly increase the ripening process of the snowpack not just over Southeast Alaska but also over northern British Columbia. After the atmospheric river moved through Southeast Alaska a very anomalous heat wave hit British Columbia and Southeast Alaska with record temperatures in the 90s to 100 degrees. The very warm day and night time temperatures produced above normal river levels and daily record streams on the Taku River from the snowmelt. This perfect storm produced record flooding along the Taku River after a glacier dammed lake along the Tulseqhuah Glacier, Lake No Lake, drained. Areas around the Taku River were flooded with homes and cabins getting moderately impacted. The Taku River crested at 45.5ft which was above major flood stage of 45ft and bested the old record stage of 45.07ft from 2004.

View location on OpenStreetMap → (58.5959, -133.6801)

Source: NOAA Storm Events Database, event_id 960721. Narrative written by the NWS forecast office that issued the report.