Table 2. Description of model covariates.

Variable	Description	Years Available	URL / Source
CRflow.spr	Seasonal Columbia River flow as measured at The Dalles Dam (USGS site 14105700)	1978-present	http://waterservices.usgs.gov/rest/DV-Service.html
CRflow.sum
CRtemp.spr	Seasonal Columbia River temperatures at The Dalles Dam (USGS site 14105700)	1997-present	http://waterservices.usgs.gov/rest/DV-Service.html
CRtemp.sum
cui.win	Seasonal coastal upwelling index	1946-present	http://www.pfeg.noaa.gov/products/PFELData/upwell/monthly/upanoms.mon
cui.spr
cui.sum
cui.aut
mei.win	Seasonal Multivariate ENSO Index	1950-present	https://www.esrl.noaa.gov/psd/enso/mei/
mei.spr
mei.sum
mei.aut
npgo.win	Seasonal North Pacific Gyre Oscillation	1950-present	http://www.o3d.org/npgo/npgo.php
npgo.spr
npgo.sum
npgo.aut
npi.win	Seasonal North Pacific Index (index of Aleutian Low Pressure)	1899-present	https://climatedataguide.ucar.edu/sites/default/files/npindex_monthly.txt
npi.spr
npi.sum
npi.aut
oni.win	Seasonal Oceanic Niño Index	1950-present	http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml
oni.spr
oni.sum
oni.aut
ersstWACoast.win	Seasonal sea surface temperature for coastal Washington	1900-present	https://www1.ncdc.noaa.gov/pub/data/cmb/ersst/v5/netcdf/
ersstWACoast.spr
ersstWACoast.sum
ersstWACoast.aut
ersstArc.win	Seasonal sea surface temperature from Johnstone and Mantua (2014)	1900-present	https://www1.ncdc.noaa.gov/pub/data/cmb/ersst/v5/netcdf/
ersstArc.spr
ersstArc.sum
ersstArc.aut
transport.win	Seasonal measure of Sverdrup transport along the Washington coast, most correlated with the temperatures in the upper 20 meters.	1967-present
transport.spr
transport.sum
transport.aut

Description of the environmental variable names, the years of available data, and the website location of the data.