Debris Flow — Sitka Coastal, Alaska

2015-08-18 · near Sitka, Sitka Coastal, Alaska

Event narrative

A strong cold front with sub-tropical moisture moved into the eastern gulf and moved over the coastal areas of Southeast Alaska. As the front approached the coastal area of Sitka very high rain rates were being reported across the area in the early morning hours which lasted less than 6 hours. In three hours the Sitka airport reported one point seven inches which was a 25 year rainfall intensity return period. The Sitka Magnetic Observatory Climate Reference Station (CRN), which is closer to steep terrain, reported two point zero one inches was a 45 year rainfall intensity return period. Along with the very high rain rates there was also very strong winds of thirty-three mile per hour with much high wind gusts at higher elevations. The combination of the heavy rain and strong winds caused catastrophic debris flows across the Sitka area on the morning of August 18th. Multiple roads were blocked along with homes damaged or destroyed and there was 3 fatalities in Cramer Ave slide. A state of emergency was declared and as one point seven million dollars worth of damage was done.

Wider weather episode

A strong front moved through the Panhandle on the morning of Tuesday August 18th. This system had abundant amount of moisture associated with the cold front as the system originated from the North Pacific and was able to tap into tropical moisture. The front produced very heavy precipitation along coastal locations and prolonged moderate rain further inland. The heavy rain produced flooding over the Sitka area and in the Taiya River basin along the Chilkoot trail near Skagway. The strong winds that accompanied the front along with the very high rain fall rates caused several landslides along the central outer coast with three fatalities in Sitka. As the front moved through the inner channels there was a brief strong wind that occurred near Skagway.

View location on OpenStreetMap → (57.0990, -135.3852)

Source: NOAA Storm Events Database, event_id 611642. Narrative written by the NWS forecast office that issued the report.