High Wind — Dixon Entrance To Cape Decision Coastal Area, Alaska

2020-12-01 · Dixon Entrance To Cape Decision Coastal Area, Alaska

Event narrative

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

Wider weather episode

A large plume of concentrated moisture or Atmospheric River (AR) with an associated low-pressure system moved across the Pacific Ocean and transported tropical moisture from the southwest which impacted Southeast Alaska (SEAK) from December 1st through December 2nd. This event brought widespread significant, and sometimes historic record setting rainfall to locations across Southeast Alaska. There were multiple waves along the main front to produce a quasi-stationary front and allowed heavy precipitation to persist over the panhandle for a long duration. Rainfall amounts were as high as over 15 at Little Port Walter with most other locations reporting 5 to 12 over the 2 days. Juneau, Skagway and Haines airports broke their all time daily precipitation record on December 1st along with the all time 2 day total when both days are combined. Rainfall intensity recurrence intervals ranged from a 50 to 200 year event when looking at 6,12,24,48 hour time periods. In some locations the precipitation started out as snow, minor accumulations but then changed quickly over to moderate/heavy rain. Significant snowfall did occur mainly at high elevations and along the Haines and Klondike highways before transition to rain as temperatures rose above freezing all the way up to 6000 feet with the impacting warm front. Snow accumulations were very impressive from December 1st into the 2nd with 18 at 800 feet near the Haines US customs border station and a staggering 59 at 2560 feet on Mount Ripinski above Haines. There was persistent precipitation that occured the previous weeks to keep the soils on the wet side. The heavy precipitation and warm temperatures melted snow that had already accumulated on the ground at sea level then as the snow level climbed above the mountain top this increased the amount of runoff significantly from the mountains. All the excess runoff resulted in significant and in places record flooding of roads and homes, erosion that damaged roads and infrastructure, and widespread mass wasting events such as landslides and debris flows. Most of these impacts were reported to have started in the early morning hours of December 2nd and persist into December 3rd or longer. The northern half of Southeast Alaska saw most if not all of these impacts with a few specific rivers, Salmon River in Gustavus and Jordan Creek in Juneau, seeing record river stage values. Widespread damaging debris flows impacted Juneau, Skagway and Haines that took out roads, destroyed homes and caused 2 fatalities in Haines. To go along with the heavy precipitation there was also very strong damaging winds as the waves moved along the front over the panhandle. These strong winds damaged power lines from falling trees.In total there were about 7 communities (Haines, Juneau, Skagway, Gustavus, Hoonah, Tenakee Springs, and Hyder) that declared a disaster from this event.

Source: NOAA Storm Events Database, event_id 934475. Narrative written by the NWS forecast office that issued the report.