Click the link to read the article on the Alamsosa Citizen website:
May 16, 2025
There’s more snowmelt to come. At least from the eyes of ASO surveys and those measurements across the Upper Rio Grande Basin.
ASO flights – Airborne Snow Observatory – that were conducted in May show a higher level of snow runoff and corresponding water than earlier spring forecasts from the Natural Resources Conservation Service (NRCS) and National Weather Service. The surveys were conducted by Airborne Snow Observatories, Inc., and along with forecasts from NRCS and NWS, are used by the state to forecast a water season for local irrigators and to help Colorado determine the amount of water to deliver downstream for Rio Grande Compact purposes.
“This year it appears that between the pattern of snow accumulation and the early start to the melt season, the runoff forecasts reliant only on the SNOTEL observations have been lower than our snow and runoff estimates that incorporate the full-basin observations of the snowpack,” said Jeffrey Deems, co-founder and chief technology officer of Airborne Snow Observatories, in an email this week to Alamosa Citizen.
“There is of course plenty of runoff season left,” he said, “and always the potential for spring and summer rain (or snow), so how the season unfolds remains to be seen.”
The company was just completing its second flight over the Rio Grande at Del Norte the week of May 12 and had conducted two flights over the Conejos. Its turnaround time on measurements is about 72 hours, and Deems is confident the latest surveys will confirm earlier ones – that there’s more runoff in the high country than the SNOTEL sites could determine.
“In the Rio Grande basin, and especially in the Conejos watershed, the sparse SNOTEL network does not reflect the diversity of terrain and snow environments, and therefore can miss important changes in snowpack volume,” Deems said.
“This year it appears that between the pattern of snow accumulation and the early start to the melt season, the runoff forecasts reliant only on the SNOTEL observations have been lower than our snow and runoff estimates that incorporate the full-basin observations of the snowpack.”
State water division engineer Craig Cotten noted the differences in the ASO measurements compared to the NRCS and NWS when briefing members of the Rio Grande Basin Roundtable at their May meeting. The ASO flights were showing “significantly higher” levels of moisture than the other two sources and the state was “trying to figure out what’s going on with that and why their forecasts are so much higher.”
“We have been discussing our forecasts with the DNR and local water district folks in the Rio Grande and Conejos basins,” Deems said. “In contrast to the NRCS and NWS, our forecast model is informed by our airborne snow surveys which measure the snow water volume over the entire watershed(s), as opposed to only relying on the sparse network of SNOTEL stations that provide an index of snow conditions.”
Water managers through the years have complained of inaccurate readings of snow and there has been a push by the San Luis Valley Conservancy District and Rio Grande Water Conservation District to add more SNOTEL stations to fill in particular areas around Creede and Conejos County.
“Our forecasts start from an accurate snow water volume, and then forecast melt and runoff based on forecasts of future weather, “ Deems said of ASO data. “The NWS forecasts do something similar, but start from a simplified snowpack estimate derived from SNOTEL station measurements of precipitation. The NRCS forecasts use the SNOTEL snow measurements in comparison to a 30-year record as a statistical predictor of dry-season runoff volume.”
In a year when the month of February brought record high temperatures that caused an early melt to a light snow season, and then above-normal precipitation in April and snow in the high country and 1.5 inches of rain in early May, and the early spring predictions of a “dry year” look premature from the air.
“As it stands now, our forecasts are in line with the amount of snow water volume we have measured over our two flights in the Conejos,” Deems said. The next forecast updates from the ASO flight will be available in the coming week, data the state and local manager will be anxious to review.
