The late-June 2021 heatwave brought exceptional temperatures to the Pacific Northwest and western Canada, with rapid mountain snowmelt, wildfires and a severe public-health emergency. Reports from Washington described unusually fast changes in snow and ice around Mount Rainier. The observations raised questions about both immediate runoff and the water that would remain available later in the summer.
Contemporary reporting described cloudy water reaching Puget Sound and discussed glacier runoff as a possible contributor. The milky appearance was an observation to investigate, rather than a measurement of how much glacier ice had been lost. The event was associated with a persistent high-pressure pattern often called a heat dome, which helped sustain unusually hot conditions. In British Columbia, temperatures reached national records and destructive fires affected communities. Around Mount Rainier, the speed of snowmelt drew particular attention because substantial snow had accumulated earlier in the season. A rapid loss of that seasonal covering changes the timing of water delivery even before the longer-term condition of the glaciers is assessed.
Scott Pattee, of the Washington Snow Survey and Water Supply Forecasting, told journalists:
"Now we're melting into glaciers and so probably that is what's causing the milky waters down below. It is a big deal, I mean we've been losing glaciers a lot lately due to climate change or whatever it is - but to have them go this rapidly is really quite scary."
He added:
"In my 30 years here in Washington doing this job, I don't recall ever seeing this rapid of a melt when we have a lot of snow. I've seen this amount of snow when we've had low pack years. But when we have this much snow? No. I think this is definitely unprecedented. We're going to set a lot of records."
Early reports during the emergency discussed almost 500 deaths as investigations were still developing. In June 2022, the provincial government confirmed that the British Columbia Coroners Service had attributed 619 deaths to the 2021 heat event. That later finding is distinct from the preliminary figures reported while the heatwave was unfolding. Communities opened cooling centres as residents sought relief, including people without effective cooling at home. The response showed that an extreme-weather event in the mountains was also an emergency in homes and neighbourhoods.
[h/t: KomoNews]
What later snowpack research found
Scott Pattee’s recollection captures how unusual the melt appeared to an experienced observer. A regional ranking over a century, however, would require comparable measurements covering a defined area and period.
Later research gives the episode a more specific frame. A 2023 study by Luke Reyes and Marc Kramer examined high-elevation snowpack and found that spring heatwaves had already accelerated losses before the late-June heat dome arrived. Washington State University’s account of the work describes snow disappearing roughly three weeks earlier than usual in the study region. The sequence matters: the dramatic late-June event acted on a snowpack that had already experienced earlier warm spells.
Why the distinction between snow and ice matters
Seasonal snowpack and glacier ice are not the same store of water. A mountain can lose its recent snow covering quickly without that photograph alone measuring how much glacier ice disappeared. The National Park Service explains that Rainier’s glaciers store water and release it gradually during summer, connecting mountain conditions with streams below. This makes the timing of melt important as well as the total amount. Snow surveys, glacier measurements and observations of river flow answer related but different questions. A snow survey estimates a seasonal reserve; glacier measurements track a longer-lived body of ice; river monitoring records water moving through a catchment. Bringing those records together helps explain why a mountain can produce abundant runoff during a hot spell and still face reduced water availability later. The early reports and Pattee’s remarks describe the speed of change as it was unfolding, while the later snowpack study adds a wider seasonal perspective. National Park Service’s Mount Rainier climate information.
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