DEEP DIVE: March heat wave shatters records – and underscores weakness of California water management

The March heat wave (that actually started at the end of February) was truly superlative, causing the steepest March snowpack decline and extraordinary early snowmelt runoff. Both rivers and water users will suffer from the heat wave’s impact on available water – but rivers will fare worse, as allocations to water users have increased despite the extraordinary dry conditions. 

Across most of the Western U.S., March (and in some cases April) high temperature records were broken multiple times, and many new daily records were set. The sweltering dry month caused the meager snowpack to disappear during what is often one of the snowiest months of the year, resulting in dismal April 1st snow survey results and peak snowmelt runoff in late March instead of the more typical April-May. In some watersheds, this turns what was looking in late February to be a near-normal April-September snowmelt runoff season into one of the driest. And the heat wave is not over yet—warmer nearshore ocean temperatures leftover from the heat wave will increase California’s warmth in the coming weeks, and a likely strong El Nino will begin to impact California’s weather later this year. 

Record-breaking Temperatures…

Climate scientist Dr. Daniel Swain, this year’s honoree at Friends of the River’s upcoming  2026 California River Awards, had a lot to say about the heat wave in the March 11 post to his weatherwest.com blog, and in his regular “office hours” on YouTube on March 9 and March 24. According to Swain, “this has probably turned into one of the most extreme heat anomalies in the historical record for the western and central United States… one of the most extreme heat events in an anomalous sense that we’ve observed in North America in modern history” and up there with March 2012 and June 2021.   

It would be “virtually impossible without climate change” according to Swain. Unfortunately, this warm winter won’t be extraordinary much longer—it is just the first of many future years like this, thanks to our species causing the rapid warming of our planet. This winter is a reminder that the warmer future is already here, and while we adapt to the new normal we need to urgently get busy saving our climate from the worst case scenarios. (You can help by signing the petition to measure greenhouse gas emissions from dams reservoirs and supporting FOR’s efforts to set minimum river flows and reduce water export operations that are the biggest energy use in the state(1)). 

So many March weather records were broken that we can’t list them all. Sacramento and Redding tied their all-time record-high March temperatures, and Modesto and Stockton broke theirs. Sacramento tied five daily high temperature records and broke eight. In the Bay Area, the above average March temperatures set new records for the biggest anomalies ever seen in any month at 12 out of 13 official climate monitoring stations. The 13 Bay Area sites all had the hottest March on record, and for 11 of them it was hotter than the hottest April on record. San Jose had its driest March on record. Another 22 sites in the Bay Area all had their hottest March on record, 17 of which were hotter than the hottest April, and 13 had the driest March on record.

In the Sierra Nevada mountains, some sites at nearly 7,000’ in elevation had zero March precipitation and recorded their earliest 80 degree days on record and largest number days in the 80s—as many as five days in some places—in March! 

…and Record-breaking Snowmelt…

The unprecedented rapid loss of snowpack, although reminiscent of recent dry springs, set records as well: the “steepest decline ever observed in California” according to Swain. He cautioned that later in the season, we may actually underestimate streamflow because our models aren’t able to capture the dry conditions (due to “absurdly record-shattering temperatures”). 

Sierran snowpack peaked at 73% of average on February 25th. By April 1st, it had declined to only 18% of average, (second only to 5% in 2015). The snowpack at the 6,900-foot elevation Central Sierra Snow Lab almost doubled in mid-February, where they recorded 9 feet of snowfall in 5 days and which triggered California’s deadliest avalanche. Then it completely melted in March. Dana Meadows, at an elevation of 9,760 feet along the Wild and Scenic Dana Fork of the Tuolumne River near Tioga Pass, where snow survey records go back to 1926, was at 43% of average on April 1st, its fourth lowest snowpack on record after 2015, 1976, and 1977. This extraordinarily low April snowpack followed over 80% of average March 1st snowpack, which was higher than the March snowpack the last two years in a row.