Below average summers, by far, not even close. I've greatly paid attention to exactly what were talking about and it's affects on the local glaciers in the sisters range, any cool summer preserves the glaciers well, basically all of the glaciers in the PNW (except northern Washington) are high enough that they get snow, even in an Atmospheric river, what matters is how much precip there is in the winter and how cool the summer is.
2021 was a brutal year, bad spring and a HOTTTT summer.
I agree. Lower elevation glaciers however, are threatened by warm winters. The snowfall they receive is more sensitive to even small changes in temperature. It doesn't take much warming to turn "warm snow" to cold rain.