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NRCS May 1 forecast shows Southern Utah runoff in bottom percentiles; state officials warned of dry soils
Summary
At a Utah Board of Water Resources meeting, the NRCS Utah Snow Survey reported May 1 streamflow forecasts that put much of Southern Utah in the lowest percentiles for runoff, citing low April precipitation and dry soils as key sources of forecast error.
Jordan Clayton, supervisor of the Utah Snow Survey for the U.S. Department of Agriculture’s Natural Resources Conservation Service, told the Utah Board of Water Resources that May 1 streamflow forecasts show much of Southern Utah in the bottom 15% of historical runoff.
Clayton said the May 1 April–July streamflow forecast “shows nearly all the Southern Utah predictions are expected to be in that bottom 15% of our observations,” and highlighted specific forecast points in the region: South Creek near Monticello at about 7% of average, the Virgin River near Hurricane at roughly 24% of average, and several smaller creeks and streams near 20–25% of average.
The forecasts for April–July flow dropped compared with a month earlier, Clayton said, primarily because April precipitation was “poor” across much of the state. He described multiple sources of forecast uncertainty, including unexpected post-forecast precipitation, errors in diversion or regulation data, nonstationarity at some sites and unusually dry soils or groundwater that reduced runoff from a given snowpack.
Clayton cautioned about the limits of weather forecasting beyond two weeks and described the NRCS forecast framework: a probabilistic set of exceedance forecasts (10th, 30th, 50th, 70th, 90th percentiles) rather than a single number. He showed that, even on optimistic (30th-exceedance) forecasts, parts of Southwestern Utah still project near-record minimums.
On reservoir and basin indicators, Clayton reported the Great Salt Lake level on May 1 at 4,193.4 feet and said the current forecast peak is about 4,193.7 feet, a downward revision of roughly one-third of a foot from the prior month’s forecast. He also noted statewide statewide reservoir storage at about 83% of capacity, which remains high relative to other western states, and stressed that streamflows statewide are trending low.
Board members asked about longer-term forecasts. Clayton said the NRCS focuses on 6–10 or 8–14 day outlooks for precipitation and does not rely on skillful forecasts beyond about two weeks.
The NRCS presentation was informational and no board action was required. The board later heard separate agenda items on project funding and planning that officials said are being considered in the context of the drier-than-normal conditions in Southern Utah.
Ending: Board members thanked the presenter and moved to the next agenda item; the discussion set the factual context for later items and for the director’s report on drought response.
