Alaska, 2020Flood in Alaska, August 1, 2020
August 1, 2020 · NWS AJK · 1 event in 1 county or zone
Throughout spring and the first part of the summer Suicide Basin, a side valley that is dammed by the Mendenhall Glacier, filled with water from snowmelt and rainfall. In the afternoon hours of July 30th visual reports showed signs of the basin beginning to drain sub-glacially as the dam was starting to fail.
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- Deaths
- 0
- Injuries
- 0
- Property damage
- None recorded
- Crop damage
- None recorded
- Events
- 1
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
Throughout spring and the first part of the summer Suicide Basin, a side valley that is dammed by the Mendenhall Glacier, filled with water from snowmelt and rainfall. In the afternoon hours of July 30th visual reports showed signs of the basin beginning to drain sub-glacially as the dam was starting to fail. This is after a few days of water overtopping the ice dam. The Mendenhall Lake gage started to show this inflow of water from the basin through the evening hours and by the morning of the 31st the event was well on its way. Over the course of event Mendenhall Lake and River rose about six feet and crested at 11.55ft in early morning of August 1st. This was the 3rd highest crest on record for Mendenhall Lake.
What forecasters said that day
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Juneau, AK wrote its last area forecast discussion before the first event at Jul 31, 8:28 PM AKST, 3 hours 32 minutes earlier.
Area forecast discussion, Jul 31, 8:28 PM AKST, 3 hours 32 minutes before
Southeast Alaska Forecast Discussion...CORRECTED
National Weather Service Juneau AK
928 PM AKDT Fri Jul 31 2020
.SHORT TERM.../Through Saturday night/...A low that has been
nearly stationary south of the Gulf for the past couple days has
begun to move north, bringing with it rain showers. Additionally,
easterly wave showers and some thunderstorms are tracking north
over western British Columbia. On satellite imagery, the
distinction between the easterly wave and the clouds associated
with the low is becoming more and more vague. Cloud cover over
Southeast Alaska will steadily increase this evening as the rain
showers approach. Over the inner channels, gusty winds will
accompany the stronger bands of showers as they move north and
this was depicted very well by the previous shift. Changes were
made to winds over the gulf based on very good model agreement
between the GFS and the Canadian NH, resulting in an area of gales
associated with the low as it moves north.
Very warm temperatures have been observed with at least two
locations reporting temperatures above 90 degrees as of early this
afternoon. A cooler airmass will move in behind the low. This in
addition to the increased cloud cover and precipitation will
result in significantly cooler temperatures tomorrow. Shower
activity will continue through Saturday afternoon. A developing
wave south of the Gulf will move northeast and over the southern
Panhandle by late Sunday night
Overall short term forecast confidence is average.
.LONG TERM...Sunday through Friday...As of 10PM Thu...Long term
pattern looks to provide fairly consistent wet and cool
conditions for the panhandle next week. At the onset of the
forecast, the first of three distinct rainy periods will be in
progress, brought upon by onshore flow ahead of a sfc trough just
off the coast. In terms of rain, this particular event looks to be
on of the least impactful for the week with about a half an inch
of rain or less expected across the panhandle before the trough
dissipates on Monday. A low moving through the northern Gulf
begins to exert its influence on the region on Tuesday and early
appearances indicate that this event should be a bigger rain maker
than it's predecessor. Further, while the current forecast shows
winds of 15 to 20 kt in the Gulf during this event, future
permutations of the forecast could very well see these numbers
trend upward. Yet another front begins to move in on Friday, once
again bringing an increased chance of rain and potentially windy
condition. In between these three separate systems, onshore flow
should keep shower potential alive across the panhandle.
&&
.HYDROLOGY...A flood warning remains in effect for the Mendenhall
River due to a glacial lake outburst from Suicide basin. As of
early this afternoon, the Mendenhall Lake had risen to minor flood
stage of 9 feet. The forecast crest is 10.2 feet, or moderate
flood stage, late Friday night. A glacial lake outburst on the
Salmon River near Hyder is also still in progress. The forecast
crest for that river is between 26 and 28 feet.
&&
.AJK Watches/Warnings/Advisories...
PUBLIC...Areal Flood Warning until 10 AM AKDT Saturday for AKZ025.
MARINE...Gale Warning for PKZ043-051.
Small Craft Advisory for PKZ012-031-035-036-041-042-052.
&&
Fritsch/CDC/JDR
Visit us at http://www.weather.gov/JuneauIn the hours before
Special weather statement, Jul 31, 10:54 PM AKST, 1 hour 6 minutes before
Special Weather Statement
National Weather Service Juneau AK
1154 PM AKDT Fri Jul 31 2020
AKZ020>022-025-012000-
Glacier Bay-Eastern Chichagof Island-
Salisbury Sound to Cape Fairweather Coastal Area-
Juneau Borough and Northern Admiralty Island-
Including the cities of Gustavus, Hoonah, Elfin Cove, Pelican,
and Juneau
1154 PM AKDT Fri Jul 31 2020
...STRONG THUNDERSTORMS THIS EVENING...
As of 1145 PM AKDT, a complex of showers and thunderstorms
extending from Juneau to Sitka to Elfin Cove was moving NW at 30
mph. Frequent lightning and gusts over 40 mph are possible within
stronger storms. Thunderstorm activity is expected to weaken over
the next couple hours; however stronger showers may still be
present through the night across the central and northern
Panhandle.
Flood, Juneau Borough
- When
- August 1, 12:00 AM AKST to 4:00 PM AKST
- Where
- Juneau Borough County, 13.25 mi NW of Douglas to 12.26 mi NW of Douglas
- Cause
- Dam / Levee Break
- Reported by
- River/Stream Gage
- Coordinates
- 58.428, -134.585
This event spanned the months of July and August. In the morning hours of July 30th the Mendenhall Lake and River began to slowly rise, the lake had been on a slow up tick as water from Suicide Basin was over topping the ice dam of the Mendenhall Glacier. Air reconnaissance during the afternoon hours of July 30th over Suicide Basin, which is about 2 miles from the terminus, in the afternoon of July 30th indicated that water had begun to drain from the basin subglacially. Mendenhall Lake and River continue to rise for the next day and a half as the glacier dammed lake emptied. The water levels reach minor flood stage of nine feet by the afternoon of July 31st morning and by 245am AKDT on August 1st Mendenhall Lake crested at eleven point fifty-five, one and half feet above moderate flood stage of ten feet. This was the third highest peak crest on record for this site to date. After the lake and river crested the water level receded slowly which is atypical for these types of events. Water levels went below minor flood stage of nine feet around 445pm AKDT on August 1st. 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 to flooding of up to three feet at the entrance and within the campground with some minor damage done to the road system. The West Glacier Spur Road and the area around Skaters Cabin was flooded with three feet water. View Drive was flooded with two feet of water and the road cut off. There was also more flooding along the Dredge Lakes trail area and and few other trails around the Mendenhall Glacier Visitor Center run by the USDA Forest Service.
- Flood
- Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.
After NWS Directive 10-1605, the rules offices file Storm Data by.
- Excessive Heat and Heat in Arizona, August 1 to 6, 202040 deaths · 34 events
- Drought in Iowa, August 1 to 31, 2020$7.7 million · 7 events
- Wildfire in Washington, August 1 to 5, 2020$450,000 · 3 events
- Drought in South Dakota, August 1 to 31, 2020$270,000 · 1 event
- Damaging Winds in West Virginia, August 1, 2020$113,000 · 55 kt wind · 3 events
- Damaging Winds in Maryland, August 1, 2020$110,000 · 60 kt wind · 2 events
- Drought in New Mexico, August 1 to 31, 202034 events
- Damaging Winds in West Virginia, August 1, 2020$24,000 · 50 kt wind · 12 events
- Flash Flood and Hail in Mississippi, August 1 to 2, 2020$31,000 · 2 in hail · 4 events
- Flash Flooding and Flooding in Texas, August 1 to 8, 2020$25,000 · 52 kt wind · 8 events
- Drought in Colorado, August 1 to 31, 202021 events
- Drought in Iowa, August 1 to 31, 202017 events
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 915695.