Atmospheric Rivers in Southeast Alaska: Meteorological Conditions
Associated with Extreme Precipitation
Abstract
Extreme precipitation events associated with atmospheric rivers (ARs)
trigger floods, landslides, and avalanches that threaten lives and
livelihoods in Southeast Alaska. Six rural and indigenous communities
(Hoonah, Klukwan, Skagway, Yakutat, Craig, and Kasaan) identified
specific needs regarding these hazards and joined the Southeast Alaska
Coastlines and People (CoPe) Kutí Hub to
address the shared challenge of understanding and predicting these
events. This study presents a climatology (1980–2019) of synoptic,
mesoscale, and local meteorological characteristics of ARs and heavy
precipitation across this region. High-amplitude upper-level patterns
across the northeastern Pacific Ocean favor ARs reaching Southeast
Alaska, where moisture is orographically lifted, resulting in heavy
precipitation. In the six communities, ARs occur 8–15 days per month,
yet only 9 AR days per year account for up to 75–90%
of precipitation extremes. Furthermore, 79–95% of days
with extreme precipitation have > 75th percentile
integrated water vapor transport (IVT), demonstrating the strong
relationship between IVT and extreme precipitation. This study also
highlights the relationship between IVT direction and complex coastal
topography in determining precipitation extremes. For example, in
Klukwan and Skagway, 80–90% of extreme ARs have
south-southwesterly or south-southeasterly IVT. Coastal communities like
Yakutat experience higher IVT and precipitation overall, and although
southeasterly IVT is more common, extreme precipitation events are most
common with southwesterly IVT. Collaboration with the National Weather
Service in Juneau, Alaska will lead to improved situational awareness,
forecasts, and Impact Decision Support Services to remote communities,
saving lives and property in a region vulnerable to the impacts of
climate change.