Juneau area again monitoring potential for glacial outburst flooding on Mendenhall River

Hi everyone, today was a travel day home from St. Louis where I was working with my family on tasks related to my mom’s estate. I am planning a full weather update newsletter tomorrow, but in the meantime I wanted to share a quick post about the potential for flooding in Juneau, AK several days from now.

The Juneau area has been impacted the last few summers by serious flooding along the Mendenhall River due to glacial outburst flooding. This is flooding that occurs when the Suicide Basin — a side basin of Mendenhall Glacier — becomes full with meltwater and releases a torrent of water down the river. There have been glacial outburst floods from this basin annually back to 2011, but the floods have grown more serious in recent years with major impacts occurring in the Juneau area.

Last year, the Mendenhall River was already near flood stage due to heavy rainfall in the days prior to the glacial outburst, and as a result record flood levels were reached when the outburst occurred. While mitigation activities helped reduce flood impacts somewhat from what was seen in the previous few years in spite of the record levels, flooding of homes and roadways still occurred.

This year the river is much lower than it was last year — and hopefully when the glacial outburst occurs the lower antecedent levels will keep the crest more manageable than the record seen in 2025. However, forecasting this sort of event is very challenging, and I encourage you to take a look at my article from last year detailing glacial outburst floods and the specifics of what takes place along the Mendenhall River. NWS Juneau has an excellent overview and monitoring page where you can keep track of what is happening with this unique flooding situation.

Programming note: I am posting semi-regularly again — but family commitments and travel after the passing of my mom will mean those posts will not be as frequent or consistently timed as they typically have been.

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