Alaska, 2020

Debris Flow in Alaska, October 26, 2020

October 26, 2020 · NWS AJK · 1 event in 1 county or zone

A strong atmospheric river impacted Southeast Alaska on October 26th. This was associated with a southerly jet stream that brought moisture up to Southeast Alaska from the tropics that caused widespread damage across Prince of Wales Island.

Where it happened

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  • Tornadoes
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  • Wind
  • Hail
  • Winter weather
  • Heat and drought
  • Cold
  • Fire, smoke and dust
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The toll

Deaths
0
Injuries
0
Property damage
$4.3 million
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.

What happened

The episode as NWS AJK wrote it up.

A strong atmospheric river impacted Southeast Alaska on October 26th. This was associated with a southerly jet stream that brought moisture up to Southeast Alaska from the tropics that caused widespread damage across Prince of Wales Island. Due to the effective transport of available moisture, rainfall rates with the associated storm were unusually high. This led to multiple landslides across Prince of Wales Island. Rain amounts that triggered the debris ranged from 2-3.5 in 12 hours with a near 100 year return period for a 1 hour rain accumulation. There were about 65 debris flows identified from this one event.

The radar

The national radar mosaic for the moment the first event began.

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Event by event

1 debris flow. Local standard time, as filed.

Debris Flow, Craig Coastal

When
October 26, 5:00 AM AKST to 4:00 PM AKST
Where
Craig Coastal County, 7.29 mi SE of Craig to 12.57 mi ESE of Klawock
Cause
Heavy Rain
Property damage
$4.3 million
Reported by
Emergency Manager
Coordinates
55.400, -133.028

A very strong atmospheric river moved over western Prince of Wales and impacted areas around Craig, Klawock, Hollis, Black Bear Creek, Shaheen Creek and Staney Creek. The Klawock airport reported 3.60 of rain in 24 hours and was the 4th highest daily amount on record. Most of the rainfall fell in a short period of time and it was very exceptional from 600 AKST to 1300 AKST. The 1 hour amount of 0.74 was a 100 year return period. The 6 hour amount of 2.13 was a 25 year return period and the 12 hour amount of 3.42 was a 25 to 50 year return period. All the rainfall produced widespread debris flows that blocked roadways on forest services roads, main highways near Black Bear Creek, between Klawock and Hollis, and Port Saint Nicholas road near Craig. There was so much runoff along with debris in the water that the Klawock water treatment plant was shut down as the reservoir was overflowing and debris clogged the intake pipes. Residence were put on a water boiling notice for a time. The city of Craig declared a disaster declaration after this event.

What these are

Debris Flow
A fast-moving slurry of mud, rock and debris, usually on a slope soaked by heavy rain or stripped by a fire.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

More

Every storm in Alaska in 2020Every state in 2020This day in weather historyWarnings in Alaska, October 2020

Sources

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 2026-10-01. Each event’s entry at NCEI: 925574.