NRCS: Utah snowpack in 'uncharted territory,' many basins forecast well below average

Jordan Clayton, supervisor of the Utah Snow Survey at the U.S. Department of Agriculture’s Natural Resources Conservation Service, told the Utah Board of Water Resources on March 18 that statewide snow-water-equivalent has fallen to unusually low levels and that many basins face below-average runoff this spring.

"We are in uncharted territory," Clayton said, noting that the statewide curve is "dipping below the previous range of observations." He reported a statewide snow-water-equivalent that he summarized as roughly 57% of normal but emphasized that many individual SNOTEL sites fall in the bottom 15% of their period-of-record observations.

Clayton said the state-wide snowpack likely already hit its seasonal peak at about 8.4 inches of water equivalent, "a little less than 2 inches below the previous record," and described unusually dense, early snow that is already generating runoff in some locations. He recommended that water managers consider more conservative planning this year, focusing on lower-end exceedance-probability forecasts rather than the median forecast.

The NRCS presenter walked board members through basin-by-basin forecasts based on the 50th exceedance probability (the median) and noted that many basins were well below 50% of average April–July streamflow under that scenario. Examples cited in the briefing included about 54% of average for portions of the Weber basin and roughly 42% of average projected for the Dirty Devil basin; Clayton also flagged the Price–San Rafael and Strawberry headwaters as below average in most scenarios.

Clayton reviewed a range of exceedance-probability forecasts (10th, 50th and 70th) and said that, given anomalous October precipitation and very low January accumulation, the historical analog method offers no close analog year this season. He told the board the 70th exceedance-probability forecast may be a better planning target than the median for this unusual year, and that even the 10th (most optimistic) forecasts leave some basins below normal.

For large reservoirs, Clayton noted the new inflow forecasts for Lake Powell (reported in recent days) and said a 70th exceedance-probability inflow of just under 2 million acre-feet would be "not good news." He also cited a 70th-percentile inflow estimate for the Great Salt Lake at roughly 260,000 acre-feet under current assumptions, and said April 1 forecasts will provide refinements.

Why it matters: lower snow-water-equivalent and below-average runoff reduce available surface-water supplies for municipal, agricultural and ecological uses, constrain reservoir refill, and increase pressure on water managers to conserve and prioritize deliveries. Clayton told board members the NRCS webpages host the underlying forecast charts and that staff will update numbers on April 1.

The board asked technical questions about the period of record used for percentiles (Clayton said the full period of record) and about the range of uncertainty in small or high-elevation catchments. The NRCS speaker closed by noting soil moisture was good in some areas but that the overall runoff outlook remains concerning.

Next steps: the NRCS will refine forecasts April 1; the board and local water managers were urged to factor more conservative exceedance probabilities into short-term planning and reservoir operations.