Debris Flows and Flooding in Alaska, December 1 to 5, 2020

Alaska Department of Transportation reports an estimated 36 inches of new snow at White Pass.

Sitka ASOS measured a wind gust of 64 mph.

Juneau Airport measured a 62 mph gust. Multiple power outages were reported due to high winds.

Mesonet station at Salmon Landing measured peak gusts of 67 mph between 6:45 am and 10:55 am akst.

Significant snow fell on the days leading up to December 1 and 2 with about 35 inches at sea level with much more at higher elevations. As the temperatures warm through December 2nd heavy rain fell on the snowpack to increase runoff and slope instability. There were multiple debris flows and avalanches that isolated Hyder Alaska with Stewart British Columbia Canada by blocking the only road connecting the communities for 2 days. Hyder was also without power.

The atmospheric river moved over the Glacier Bay area and Gustavus in the early morning hours of December 1st and persisted through the late evening hours of December 2nd. Heavy to moderate rainfall persisted over 36 hours with the highest amounts coming during the overnight hours going into December 2nd. In the first 12 hours of the event, 2.16 of precipitation fell which is a 5 to 10 year event, some of that precipitation did fall as snow at higher elevations. There was a few inches of snow at sea level but that quickly melted. More warm and moist air moved over the region into the evening hours of the 1st and persisted into the early morning of the 2nd. More heavy precipitation fell through this time frame and produces significant runoff as the ground was totally saturated as well as runoff from snowmelt. Precipitation totals were as high as 7.25 for the event from early December 1st through the early morning hours of December 3rd which is a 200 year event. The 24 hour precipitation amount reported at the Gustavus CRN site on December 1st was 3.76 which is a 10 to 25 year event. The 48 hour precipitation amount from Bartlett Cove in Glacier Bay National Park was 6.43 and Gustavus CRN reported 5.69 which is a 50-100 year event for both sites. The magnitude of the precipitation and snowmelt overwhelmed culverts and produced record water level on the Salmon River. Roads located near the Salmon River were flooded with up to 4 feet in places as wind fall in the river directed high water into the gravel pits and into the road systems of Gustavus. The hardest hit areas were Rink Creek Rd, Wilson Rd, Toad Rd along with areas near the Salmon River. The Salmon River began to rise rapidly through the morning hours of December 1st from the first batch of heavy rainfall. The water levels continued on a steep upward trend through the morning hours of December 2nd as it crested at 17.26 feet for a total rise of over 7 feet from the extreme amount of precipitation. This was a record stage for this site which was installed by the USGS in 2014. Flooding persisted for days after the heavy rain relaxed as it took awhile for the water levels to recede from the saturated sandy soils. The city declared a disaster declaration as homes were damaged from flooding along with road infrastructure damage.

Hydaburg Seaplane Base AWOS measured a wind gust of 60 mph at 11:09 am akst.

U.S. Border Patrol at Haines Customs measured 12.8 inches of heavy wet snow. Still snowing lightly at time of report.

As the atmospheric river moved over the the central inner channels near Petersburg in the early morning hours of December 1st through the early morning of December 2nd it produced significant amount of precipitation. Through that time frame 3 to 6 of precipitation fell with the highest rain rates of .5 per hour in the morning hours of December 1st with another burst of heavy rainfall in the evening. Falls Creek along Mitkof highway in Petersburg rose quickly from the heavy precipitation along with added runoff from snowmelt at higher elevations. The creek went above minor flood stage in the late morning of December 1st and continued to climb above moderate flood stage of 24 feet in the afternoon. The creek crested at 24.38 feet for a 5 foot rise and produced some impacts to the highway. AKDOT had to close the road at times the night of December 1st due to about 8 to 10 inches of water running over the road along with debris that had to clear off the road.

As the atmospheric river moved over the Hoonah and Tenakee Springs area in the early morning hours of December 1st through mid morning of December 2nd it produced significant amount of precipitation. In the first 12 hours of the event 2.5 of precipitation fell with some of that falling as snow at higher elevations. More warm and moist air moved over the region into the evening hours of the 1st and persisted into the early morning of the 2nd. More heavy precipitation fell through this time frame and produces significant runoff as the ground was totally saturated as well as runoff from snowmelt. The Hoonah COOP observer reported 4.70 on December 2nd a all time daily precipitation record and a 50 to 100 year event. It was also a 2 day all time precipitation record of 7.18 for December 1st and 2nd which is a 200 to 500 year event. At the Hoonah RAWS weather station, close to Tenakee Springs, it reported 6.9 in 24 hours and 8.74 in 48 hours which are both a 100-200 year event. During the heaviest precipitation of the event, the evening of December 1st, 3.7 in 12hrs was reported at the Hoonah RAWS with is a 10-25 year event. All of this heavy rainfall along with snowmelt overwhelmed the water treatment plant in Hoonah and damaged the system from debris from the runoff. Also there was extensive damage to roads and culverts from large amount of erosion and debris on roadways. From these impacts a disaster declaration was issued.

As the atmospheric river moved over the north central inner channels of Southeast Alaska it produced significant amount of precipitation from December 1-2. Heavy to moderate rainfall persisted over 36 hours with the highest amounts coming during the overnight hours going into December 2nd. By mid morning on December 1st, 2 to 3 inches of precipitation fell which is a 5 to 10 year event at the Juneau forecast office and the downtown Juneau LARC. Some of that precipitation did fall as snow, from 9 to 20 inches at elevations above 1000 feet. The snow level rose rapidly through the afternoon of December 1st to be above the mountain tops by the evening hours. This warming at elevation melted the fresh snow that fell with most gains lost by the morning of December 2nd. By the end of December 1st the Juneau airport reported a 24 hour precipitation amount of 4.93 which was a 100 year event and broke the all time daily precipitation record from 1946. Precipitation amounts for December 1st ranged from 3 to 5 inches with a number of daily precipitation records broken. Over the 2 days precipitation amounts were from 5 to 7. The Juneau airport 48hr total of 6.39 remained around the 100 year event. Other areas that did report heavy precipitation did not seem to get the intensity the airport reported. The Juneau forecast office 48hr total of 5.10 was near a 5 year event with the 24hr amount of 4.09 on December 1st was 5 to 10 year event. There was significant runoff from the intense precipitation and from the snowmelt in the mountains. Most of the small streams in the Juneau area began to rise rapidly through the morning hours of December 1st with Jordan Creek going over minor flood stage by the afternoon. As the heavy rain persisted into the evening and overnight hours going into December 2nd the soils continued to be super saturated to produce extreme runoff across the area. This produced record flooding along Jordan Creek in the early morning of December 2nd before it crested around 8am AKST at 11.20 feet for a total rise of 4.5 feet over 36 hours. Multiple homes around Jordan Creek and business in Jordan Square were flooded. Roads near the creek from Jordan Ave, Cascade St, Trout St and the main road of Glacier Highway all were significantly flooded with 1 to 3 feet of water. Due to the intense long duration heavy precipitation, additional snowmelt runoff, and high soil saturation there were multiple debris flows reported across the Juneau area near steep terrain which damaged homes, blocked a number of roads and overwhelmed culverts that damaged roads from erosion. Renninger Street, at the base of Heintzleman Ridge, accesses a city water reservoir along with a middle schools was washed out from erosion on both sides of the road. Residences along Mary Ellen Way on Vanderbilt Hill had multiple debris flows that damaged homes and deposited debris into yard that blocked drainages to divert water into homes. Multiple large debris flows occurred along the lower and upper Salmon Creek Rd and damaged the penstock that brings water from the reservoir to the ALE&P power plant and CBJ water treatment facility. This is the only water supply for DIPAC hatchery that supplies fish stock to all of Southeast Alaska. Without the water DIPAC 2021 stock will die impacting sport and commercial fisheries. A big debris flow was reported along Wire St which damages homes and blocked the Glacier Hwy. Another big debris flow was reported near the AWARE shelter along Glacier Hwy which deposited lots of mud around the shelter and surrounding homes. A home was damaged by a debris flow on Cohen Dr near Tee Harbor as the debris smashed into the side of the home removing a significant portion of the structural support. This was one of the most impactful flooding and debris flow events in recent memory and the data backups extreme impacts. The city of Juneau declared a disaster for this event.

Over 12 inches of wet heavy snow in Skagway reported by Alaska Department of Transportation.

Multiple power outages due to downed trees in the Juneau area.

Sitka ASOS reported a wind gust of 64 mph.

As the atmospheric river moved over the far north central inner channels of Southeast Alaska it produced significant amount of precipitation from December 1st-2nd. Heavy to moderate rainfall persisted over 48 hours with the highest amounts coming during the afternoon hours of December 1 through late morning of December 2nd. By mid morning on December 1st, near 2 of precipitation already fell. The snow levels were low at the start of the event with a few inches at sea level in Haines but as much as 12 was reported at 800 feet by the Haines40NW COOP and 20 at the 2500 foot Flower Mt SNOTEL site by the morning of December 1st. Closer to Haines, the Ripinski ridge weather station at 2560 feet reported an estimated snow accumulation of near 59 from before the warm air moved into the area. The snow level rose rapidly through the evening of December 1st to be above the mountain tops by the early morning hours of December 2nd. This warming at elevation melted the fresh snow that fell with Ripinkis Ridge losing close to 30 and Flower Mt losing near 20 by the afternoon of December 2nd. By the end of December 1st the Haines airport reported a 24 hour precipitation amount of 5.49 which was a 25 to 50 year event and broke the all time daily precipitation record from 1946. The Haines COOP reported at 7am AKST on December 2nd a 24 hour amount of 6.62 which also broke the all time daily precipitation record from 2005. Haines40NW COOP along the Haines Hwy reported at 7am AKST on December 2nd a 24 hour precipitation amount of 5.23 a new all time daily precipitation record beating out 1999 and a 25 year event. From December 1st to the 2nd precipitation amounts from the downtown Haines COOP were 8.54 , Haines Airport 10.26 a 200-500 year event, and the Haines40NW COOP 8.12 a 50-100 year event, were all time 48 hours precipitation records. From December 1st to 3rd 10 to 10.50 of precipitation fell from downtown Haines to the Haines border with a 100 to 200 year event. All of this heavy rainfall and snow melt produced significant impacts in the Haines area. In the early hours of December 2 after all-time record rainfall, saturated soils, and a deep snowpack, a second impulse of heavy precipitation moved over the area, and the snow level rose above 2500ft. The rising snow level began to melt the fresh snowfall at high elevation to produce significant amount of runoff that overwhelmed drainage ditches and culverts. The intense runoff began to erode the roads at the base of Ripinski Ridge and by day break there was significant infrastructure damage to all roads near Ripinski ridge which left Piedad Rd, Cathedral View Dr, Allen Rd, Comstock Rd, 4th ave,Young Rd to name a few that were impassable as the roads were washed away from erosion. There was also significant flooding away from the steep terrain from poor drainage not keeping up with the amount of runoff. Up to 4 feet of water flooded the Haines Hitch-Up RV park along with flooding across places at the Haines airport essentially closing it down to flights. To go along with the major road infrastructure damage there were a number significant major debris flows from the intense precipitation, super saturated soils and strong winds to help trigger the slides that blocked roads and damaged homes near steep terrain. Haines was cut off from the Canadian Border and the airport due to debris flows blocking the Haines Hwy. There were also multiple debris flows along Lutak Rd that damaged the Lutak fuel Dock, blocked the road in multiple locations and isolated residence in a subdivision at the end of the road. A few homes at the end of Lutak Rd we significantly damaged from debris flows coming down behind their homes with one getting pushed off its foundation, another with debris in the house and another with minor damage. Mud Bay Rd was blocked by a debris flow which isolated another part of town. A large avalanche came down into Chilkat Lake out the Haines Hwy that damaged a few homes. Residence in the affected areas and other locations near steep terrain were evacuated to emergency shelters throughout the morning of December 2. Heavy rain continued into the afternoon hours and around 130pm AKST a massive landslide occurred along Beach Rd that took out a 200 yard section of the road, destroyed 2 homes while causing major damage to another. One of the destroyed homes was not occupied but the other had to 2 people inside. The 2 people perished from the landslide or what the geologist are calling a geologic mass wasting event. There were about a half dozen homes on the south side of the slide that were evacuated due to the threat of another very large landside. It continued to be very wet with freezing levels going up and down to keep increase runoff not just from the precipitation but also from snow melt for the next week with a 7 day total of 14.85 which is a near 150 year event. The continue precipitation on the super saturated soils kept the threat of more debris flows high through December 7th. There was some minor movements of a home near an old landslide from 2012 called the slump area. This was one of the most impactful flooding and debris flow event since 2005 or ever and the data backups extreme impacts. The city of Haines declared a disaster for this event from the widespread and extensive infrastructure damage, 2 homes destroyed, 7 homes with major damage, 16 homes with minor damage with another 12 home adversely affected from the area damage and the 2 deaths. The governor of Alaska also declared a disaster emergency for Southeast Alaska from the impacts of this event.

As the atmospheric river moved over the northern inner channels of Southeast Alaska it produced significant amount of precipitation from December 1-2. The snow level was near sea level at the on December 1 with accumulations of 5 to 7 inches with as much as 40 inches at high elevations over 2 days. The snow level rose above the mountain tops through the early morning hours of December 2 and started to melt the fresh snow to increase the amount of runoff. Through December 2 there was about 15 inches of snowpack loss at high elevation and almost all the snow melted off at sea level which led to significant amount of runoff into local rivers and overwhelmed culverts that damaged roads from erosion. In Dyea very heavy precipitation of 4 inches fell in 10 hours through the early morning hours of December 2 with a total of 7.5 in 2 days fell. In Skagway, December 1 broke the all time daily precipitation record with 3.67 and it also broke the 2 day all time precipitation record with 6.09. The COOP in Skagway reported 9.92 in 3 days which was close to a 1000 year event. The Taiya River near Dyea rose 4.5 feet in 12 hours and cresting in the afternoon of December 2nd just over bankfull from all the precipitation and snowmelt runoff. That is very high river levels for this time of year along with how fast the river rose. The soils were very saturated from the heavy precipitation and snowmelt to help destabilize the steep slopes at the same time there was some windy conditions to increase the risk of debris flows. Multiple debris flows blocked the Dyea road cutting them off from Skagway in the early morning hours of December 2 when the highest rain rates were occuring.

Large tree fell on a trailer home in the Switzer Creek Neighborhood. One person was trapped and had to be rescued by Fire Department/Rescue.