The latest Water Supply Outlook Report is now available.
From the Summary:
“Automated Snow Telemetry [SNOTEL] and manual measurements throughout the state showed the snowpack benefiting from a series of late winter storms concentrated in the latter half of March. Snow Water Equivalent [SWE] totals surpassed New Mexico’s reference period median on March 16th, remaining above normal through the date of report publication. March saw well above normal precipitation across the statewide forecast region, primarily in the form of snowfall and concentrated toward the end of the month. This fed a generally increasing snowpack across the major New Mexico forecast basins, despite periods of melt occurring between storm cycles. With these net snowpack gains throughout March, all major forecast basins within the state held normal or above normal SWE totals by April 1. The southerly latitude of New Mexico’s major watersheds contributes to median late season snow persistence being lower and melt generally beginning earlier than may be seen in other mountain states throughout the region. This year’s robust April 1 snowpack represents an encouraging departure from normal statewide spring melt timing, painting a more optimistic picture for surface water supplies across the forecast area than was previously projected at the beginning of March.
Early April marks the midpoint of the 2024 water year, and cumulative statewide precipitation since October 1 has now reached 100% of the reference period median, representing NRCS “normal” conditions for this time of year. March saw characteristic variability in spatial distribution of precipitation across the state, with well above normal precipitation measured for all forecast basins. Despite recent gains in both rain and snow, water year 2023 was still considerably wetter statewide than the current water year as of April 1. Cumulative precipitation can be a particularly useful supplement to snowpack variables for understanding overall surface water inputs into a stream system throughout the water year. This is especially valuable when interpreting fluctuations in daily SWE at a given location as active melt is occurring between spring storms. Strong winter precipitation accumulation has helped alleviate the dry initial conditions observed at the start of the water year across the state. Still, some New Mexico forecast basins have not reached the normal precipitation conditions for this time of year. Slightly below normal precipitation totals remain in place throughout the more northerly basins along the state boundary between Colorado and New Mexico.
Reservoirs with NRCS reporting are again showing below to well below reference period normal storage volumes this month, except for those in the Rio Grande Headwaters basin in southern Colorado. As was the case on March 1, four of the six New Mexico basins which store significant water volumes in reservoirs show improved storage when compared to April 1 values for 2023: the Rio Grande Headwaters, Rio Chama-Upper Rio Grande, Lower Rio Grande in New Mexico, and San Juan. In contrast, the Pecos and Canadian basins show decreased reservoir storage volumes compared to April 1 of last year, indicating considerable surface water inflow will still be needed for these systems to reach prior year water supply totals. Statewide, this amounted to New Mexico reservoir systems holding an additional 16% of the reference period median storage volume above last year’s April 1 totals. With the primary melt and closely related runoff period lying just ahead, New Mexico’s water storage and irrigation availability outlook represents an overall improvement over last April 1 as the state enters the primary water usage season.
Increased hydrologic inputs throughout March have bolstered probabilistic streamflow predictions for the vast majority of forecast points in New Mexico in the official April 1 NRCS volumetric streamflow forecast. These projections currently show the eight aggregated forecast basins within the state centering volumetric forecast probabilities around improved to much improved flows when compared to March 1 model outcomes. Reference period median “normal” flow volumes are now the most statistically likely outcomes for the Rio Grande Headwaters, Canadian, and Pecos systems. Well above normal flow volumes are still the most probable outcomes in both the Gila- San Francisco and Zuni basins. The degree of increase over the last month varied widely across the forecast points within each basin, so a close analysis of specific points of interest and consideration of the full suite of exceedance probabilities for each point will provide the most robust interpretation of a given volumetric forecast. Of particular note to New Mexico water users, forecasts for April 1 have seen significant gains over March 1 predictions in the Lower Rio Grande basin. These Lower Rio Grande forecast points provide flow predictions for mainstem Rio Grande locations which feed into many significant reservoir storage and irrigation systems within the state. Despite the normal peak of snowpack accumulation having passed, it remains important to keep an eye on changing weather and hydrologic conditions to help anticipate the observed streamflow most likely to occur within the range of forecasted exceedance probabilities.”
- Jaz Ammon, Water Supply Specialist (Hydrologic Technician)