Flood — Juneau Borough, Alaska

2018-08-08 to 2018-08-09 · near Douglas, Juneau Borough, Alaska

Event narrative

After a very dry period for the northern inner channels of Southeast Alaska moderate to heavy rains moved over the area on August 7th. The high rain rates continued for the next forty-eight to seventy-two hours. Rainfall totals from this time frame ranged from two to three inches near sea level with four to five inches at higher elevations. The very warm temperatures created very high freezing levels that increase runoff from snow or ice melt. There was also a release of water from the glacier dammed lake in Suicide Basin that added runoff into the Mendenhall River system, but less water than the first release earlier in the summer. The Mendenhall Lake started to rise slowly through August 7th, by the morning of August 8th the rate of rise on the lake and along the river increased as the heavy rain moved over the area. The Mendenhall Lake went above minor flood stage of nine feet in the afternoon and continued on the steady rise through the overnight hours and went over moderate flood stage of nine feet. The Mendenhall Lake crested at ten point forty-two feet by the afternoon on August 9th. As the heavy rain started to diminish the water levels began to recede and the lake and river went below minor flood stage in the early morning hours of August 10th. There was minor to moderate flooding around Mendenhall Lake and the upper portions of the river above Back Loop Road. The Mendenhall campground was evacuated due flooding of up to two feet at the entrance and within the campground, also the Skaters Cabin Road was flooded. View Drive was flooded with one foot of water and the road cut off. There was more flooding along the dredge lakes trail area and a few other trails around the Mendenhall Glacier Visitor Center run by the USDA Forest Service.

Wider weather episode

A deep trough of low pressure with a long fetch from the North Pacific to the Gulf of Alaska produced a very strong and wet weather system. The atmospheric river slammed into northern southeast Alaska panhandle from August 7th and persisted through the 10th. The area received moderate to heavy rainfall with stations reporting two to four inches of precipitation at sea level with five inches at higher elevations. Along with the heavy rainfall there was very high freezing levels which ranged from eight to ten thousand feet. These high freezing level accompanied with the heavy rain increased the runoff from any snow left in the mountains and ice melt from area glaciers. All of the rain and snow/ice melt produce moderate flooding along the Taiya River and flooded the Chilkoot trail, part of the Klondike Gold Rush National Historical Park, near Dyea Alaska. The river crested around seventeen point thirty five feet which is above moderate flood stage of seventeen feet in the evening hours on July 23rd. The Mendenhall Lake also rose above moderate flood stage of ten feet and produced moderate flooding along the Mendenhall Lake area. The Mendenhall Lake gauge crested at ten point forty-two feet in the afternoon of August 10th.

View location on OpenStreetMap → (58.4342, -134.5710)

Source: NOAA Storm Events Database, event_id 774320. Narrative written by the NWS forecast office that issued the report.