Alaska, 2011Flood in Alaska, July 21, 2011
July 21, 2011 · NWS AJK · 1 event in 1 county or zone
First glacier dam outburst flood on the Mendenhall Lake/River system that produced significant flood took place on July 21 2011. The source of the flood waters was from Suicide Basin and side basin on the Mendenhall Glacier, about a mile up from the glacier terminus.
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- Deaths
- 0
- Injuries
- 0
- Property damage
- $5,000
- 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.
First glacier dam outburst flood on the Mendenhall Lake/River system that produced significant flood took place on July 21 2011. The source of the flood waters was from Suicide Basin and side basin on the Mendenhall Glacier, about a mile up from the glacier terminus. The Mendenhall Glacier was holding back water in Suicide Basin like a dam. The source of the flood waters was unknown for most of the event along with how much water was being impounded.
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 20, 3:00 PM AKST, 11 hours 41 minutes earlier.
Area forecast discussion, Jul 20, 3:00 PM AKST, 11 hours 41 minutes before
4 PM AKDT WED JUL 20 2011
.SYNOPSIS...AT 2300 UTC AN UPPER LOW NEAR DIXON ENTRANCE IS
CONTINUING TO MOVE SOUTHEASTWARD WHILE A UPPER RIDGE BUILDS OVER THE
NORTHEAST GULF OF ALASKA. RAIN AND LOW VISIBILITIES IN SOUTHERN
INTERIOR SECTIONS OF THE PANHANDLE ASSOCIATED WITH THE UPPER LOW WILL
TAPER OFF OVERNIGHT AS THE LOW MOVES AWAY FROM THE AREA. CLOUDS
SHOULD DECREASE BY MORNING.
MIDDLE AND HIGH CLOUDS HAVE MOVED SOUTHWARD INTO THE NORTHERN
PANHANDLE FROM THE YUKON BUT ARE EXPECTED TO DIMINISH AS THE UPPER
RIDGE BUILDS TO THE WEST. ELSWHERE SKIES SHOULD REMAIN CLEAR TO
PARTLY CLOUDY THROUGH THURSDAY.
.LONG RANGE...THE RIDGE ALOFT MOVES EAST OF THE PANHANDLE BY FRIDAY
AS ANOTHER UPPER LOW MOVES ACROSS THE GULF. MODELS PROJECT THE TRACK
OF THIS LOW TO BE FURTHER SOUTH THAN THE PREVIOUS SYSTEM BUT THE
FOLLOWING RIDGE IS ALSO NOT EXPECTED TO BE AS STRONG AS A STRONGER
TROUGH IS ESTABLISHED IN THE GULF BY THE BEGINNING OF THE WEEK.
PRECIPITATION ASSOCIATED WITH THE NEXT TROUGH SHOULD MAINLY AFFECT
THE SOUTHERN PANHANDLE OVER THE WEEKEND BUT THEN INCREASE NORTHWARD
AS THE STRONG TROUGH IS ESTABLISHED IN THE GULF.
.AJK...WATCHES/WARNINGS/ADVISORIES
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ041...042.
Flood, Juneau Borough
- When
- July 21, 2:41 AM AKST to 4:00 PM AKST
- Where
- Juneau Borough County, 13.51 mi NNW of Douglas to 11.93 mi NW of Douglas
- Cause
- Dam / Levee Break
- Property damage
- $5,000
- Reported by
- River/Stream Gage
- Coordinates
- 58.451, -134.523
The two river gauges (Mendenhall Lake, Mendenhall River) on the system both reach the second highest stage in history and went above moderate flood stage. The Mendenhall Lake and River stages continue to rise for a few days when it was clear and dry. The look of the hydrograph indicated a glacier dam release but there no documented large dammed lake. After some investigating it was known that the source was from Suicide Basin 1 mile from the terminus. Near Mendenhall Lake and along the River some homes flooded, campgrounds evacuated, power cut in flooded subdivision with road cut off.
- 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 in Pennsylvania, July 21 to 24, 201125 deaths · 60 injured · 10 events
- Excessive Heat in New York, July 21 to 23, 201120 deaths · 17 events
- Excessive Heat in New Jersey, July 21 to 24, 20112 deaths · 350 injured · 21 events
- Heat in Vermont, July 21, 20111 death · 10 events
- Wildfire in California, July 21 to 23, 201118 injured · $25,000 · 1 event
- Excessive Heat in Indiana, July 21, 20111 death · 1 event
- Hail and Damaging Wind in Nebraska, July 21, 2011$5.3 million · 1 in hail · 3 events
- Damaging Winds in Kansas, July 21, 2011$1.6 million · 70 kt wind · 3 events
- Damaging Winds and Lightning Strikes in Tennessee, July 21, 2011$161,000 · 55 kt wind · 9 events
- Excessive Heat in Virginia, July 21 to 23, 201143 events
- Excessive Heat and Heat in New York, July 21 to 23, 201142 events
- Lightning Strike in Colorado, July 21, 2011$70,000 · 1 event
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: 479306.