Snowpack and Streamflow Update
Updated: Apr 26, 2020
The current 2019 Southern San Juan snowpack is not unprecedented, but it's getting harder to find years to compare it to! Winter appears to have lost it' grip and we're finally back to losing rather than gaining snowpack.
Statewide, we're reporting ridiculously high snowpack numbers, but believe it or not, they are actually higher because it's no longer possible to describe the snowpack as the percent of the median.
To calculate the percent of median (the quantity displayed on the above graphic), you divide the current snow water equivalence (SWE) by the median SWE, then multiply by the resulting quantity by 100. But many of the SNOTEL sites are normally out of snow by this date, which means the denominator is zero and you all know what happens when you divide by zero. These stations have been removed from the map.
The Upper San Juan SNOTEL site (10,200 ft) usually runs out of snow on June 1st. Before the math got in the way on June 2nd, the site had 3725% percent of normal! Currently, there are 26.7 inches of SWE barely frozen in the 53-inch snowpack. The Wolf Creek Summit SNOTEL site (11,000 ft) has an incredible 41.6 inches of water stored in the 83-inch snowpack (222% of normal).
Last week, the San Juan River awoke from a nearly 2-week-long snow-induced slumber and nearly doubled the flow from 1200 cfs on 5/31 to almost 2400 cfs on June 2nd. Last night, the flow peaked at 2800 cfs at 1:30 AM, not quite eclipsing the season high of 2900 on May 17th.
So when was the last time we had this much snow in June at the Upper San Juan SNOTEL site? The earliest June 1st SWE measurement that I could find was taken in 1957 and since then, I could only find 5 years with a similar snowpack as 2019. I plotted the SWE vs the peak spring runoff values and included the date when the peak occurred. Based on the graph, 4,000 cfs still seems possible, but of course, it all depends upon the upcoming temperature and precipitation.
Based on the graph below, It seems like we're having a year like 1985 rather than 1980, when the snow melted dramatically in early June, or 1995 where the snow lasted almost till July. The SNOTEL station was established in 1979 so I don't have detailed data for 1965 and 1973. The 1985 snowpack generated 4110 cfs on June 9th.
The weather prediction for Wolf Creek Pass shows mild temperatures with highs in the 50's unlike the warm June of 1980 or cool June of 1995. Notice the low temperatures are not predicted the to dip below freezing, which will keep the snowmelt going all night. However, the afternoon cloud cover should slow the snowmelt.
We'll know soon if my updated spring runoff prediction of 4,000 cfs on June 8th is still on track! At this point, it seems too little high considering the mild high temperatures and cloud cover in the forecast. The Springs Resort might want to start sandbagging just in case!
Go to the USGS website to follow the flow conditions.