Spring runoff on the San Juan River started alarmingly fast with an early spike of 1670 cfs on 4/22! Since that spike was higher than last year's peak of 1460 cfs on 5/22/21, I wasn't sure what the river was going to do (and then the USGS stream gauge went down for several days). An April peak seemed possible since the river surprised everyone two years ago by peaking at 1930 cfs on 5/2/20. However, a spring peak on 4/22 would rank as the 2nd earliest snowmelt peak since 1935!
Normally, the San Juan River peaks around 2450 cfs on May 24th. However, on 2 occasions since 1935, the river peaked in April (a mind-boggling 296 cfs on 4/15/2002 and 1430 cfs on 4/27/2012). Notably, two of our area’s recent fires, the Missionary Ridge and Little Sand fires, occurred in 2002 and 2012 respectively. Fortunately, the San Juan River reached a season-high of 1810 cfs last night and it should climb even higher tonight.
Predicting the peak runoff date for the San Juan River has always been difficult, but 2022 has proven even more challenging. Despite our average snowpack, the snowmelt is occurring about 3 weeks early mostly due to the dirty condition of the snowpack. Over the winter, Wolf Creek Pass accumulated sediment from 7 dust events.
The Colorado Dust-on-Snow Program rates the current dust conditions in Colorado’s southwestern mountains as “maximum”, which is their highest category. As a result, the San Juan River nearly set a high flow record for April 22, as the albedo (reflectivity of the snow) plunged when multiple dust layers merged and were exposed on the surface of the snowpack.
Fortunately, night-time air temperatures have continued to drop below freezing so far this year, however, maximum air temperature climbed to the mid-50s from April 17through April 22. The above-average temperature and dust conditions fueled the usually high flow event on 4/22. Fortunately, Wednesday's cold front slowed the melt, but temperatures have rebounded quickly and are predicted to be well above normal through the extended forecast.
The snow-water equivalent (SWE) at the Upper San Juan SNOTEL site (10,140 feet on Wolf Creek Pass) peaked at 28.6 inches on April 5th, which is 99 percent of normal, but 9 days early. However, this morning, we only had 3.7 inches of SWE left, which is 17 percent of normal. Usually, the snowpack doesn’t completely melt until June 1st, but we’re on track to run out of snow in the next few days. In fact, the Weminuche Creek SNOTEL site, which sits at 10,749 feet in the Upper Piedra watershed ran out of snow on 4/30, which is 2 weeks earlier than normal.
Air temperature, albedo, soil moisture, and sublimation are all variables that influence the magnitude and timing of our spring runoff, but my high school students developed a relationship to predict the spring runoff event based solely on the amount of water in the snow at the Upper San Juan SNOTEL site.
Based on the 2022 peak SWE of 28.6 inches, our model predicts that the river should crest at 2400 cfs on 5/21. Clearly, that is not going to happen due to the near-record high flow in April. An alternated model based on 12.4 inches of SWE on May 1st predicts that the river will peak on 5/16 at 1500 cfs. However, the river has already eclipsed that flow value in April. The dust conditions have clearly made our models unreliable.
A less quantitative way of predicting peak runoff involves tracking the snowfields on the surrounding mountain peaks. I’ve photographed Pagosa Peak around 5/1 over the past few years. Despite a near-normal snowpack, the snowfield on Pagosa Peak’s west face is non-existent compared to 2020 and 2021. The current snowfield conditions on Pagosa Peak appear similar to 2018, which unfortunately was the worse water year since 2002.
Two other prominent snow gauges are located on the eastern range. According to local folklore, when the cutthroat jumps out of the snowfield on Blackhead Peak and the snowfield geese emerge and fly north on Quartz Ridge, the spring runoff will recede. The cutthroat has nearly left the snowfield and the geese have emerged. In fact, the snowfields on Blackhead Peak and Quartz ridge are similar to the snow conditions in early June of last year. Although the cutthroat and geese appear similar in size in both pictures, the good news is there seems to be more snow left in the trees than there was in June of last year.
Hopefully, summer rains will materialize and reduce our fire hazard this summer. In the meantime, take advantage of the high flows while they last! See you on the river!