January 1st Water Supply Outlook Report for Utah
While it may not feel like it, Utah’s snowpack season is upon us. This winter has gotten off to a very strange start with record-breaking warm conditions and poor snow cover. We have had very high snow levels in the winter storms that have hit our state, resulting in an unusual amount of liquid precipitation being received at mid and high elevations in Utah’s mountains. While our mountain soil moisture has benefited—a condition that may promote snowmelt runoff efficiency this spring—our snowpack is shallow and dense at most locations around the state, and absent in others. As of January 1st, there were 20 SNOTEL (snowpack measurement) weather stations in Utah that were at record low snow water equivalent (SWE), with 8 more experiencing their second-worst conditions.
While this report mainly relates to conditions in Utah as of January 1st, it should be noted that snowpack conditions have marginally improved since the beginning of the month- particularly for the Bear basin headwaters and portions of the High Uintas. However, the rest of the state’s snowpack has continued to lag way behind schedule, with the Tooele Valley-Vernon Creek and Lower Sevier basins faring worst at close to 30% of normal SWE. As of this writing, there were still 14 SNOTEL sites with record-low SWE in our mountains and 5 sites with second-worst conditions. While our statewide SWE increased from 56% of normal to 75% after the early January storms, we are still way well below where we want to be!
From a statewide level, a few reasonable analogs for this winter’s SWE (as of this writing on January 9th) would be 1990, 2010, 2014, and 2024. It should be noted that three of those four winters finished the snowpack season above normal, so we’ll keep our fingers crossed that this winter similarly starts to ramp up soon.
December precipitation in Utah was close to normal at 107%, bringing the water-year-to-date (WYTD) precipitation to 105% of median by the beginning of the month. Since then, the wet but warm storms that hit our state in early January have driven our WYTD precipitation up to 119% of normal. The Bear basin and mountains of Southwestern Utah have fared the best relative to normal; both areas are close to 150% of normal precipitation as of this writing.
Soil moisture conditions measured at 2”, 8”, and 20” depths at Utah’s SNOTEL sites are well above normal at around the 95th percentile. Soils are at 58% of saturation (19% higher than last year at this time) which is encouraging. However, Utah’s reservoir storage is down 13% from last year and currently at 62% of capacity. The Upper Sevier watershed has seen the largest drop in reservoir storage since last year: from 59% last year to 26% of capacity as of January 1.
January 1 forecasts have significant uncertainty compared with those issued during spring months (closer to peak snowpack conditions) and are meant to be advisory only. NRCS streamflow forecasts for snowmelt runoff volume are included at the end of this report for reference purposes. Note that the atypical snowpack conditions so far this winter have been particularly challenging for modeling snowmelt runoff. Surface Water Supply Indices (SWSI) for Utah basins combine our current reservoir levels with the additional volume of water anticipated for each watershed based on our streamflow forecasts. Because the January 1 forecasts are meant to be advisory-only, we did not include SWSI values for Utah basins in this month’s report but those are forthcoming in our February 1 Water Supply Outlook Report.
Snow water equivalent and water-year-to-date precipitation in the Great Salt Lake (GSL) basin are similar to statewide conditions. As of January 1st, the regional SWE was 57% of normal and WYTD precipitation was at 106% of normal. Since the early January storms, these values have increased to 82% and 125% of normal, respectively. Soil moisture is at 61% of saturation, up 25% from last year at this time. Reservoirs in the GSL basin are at 67% of capacity. Our GSL lake level rise forecast from January 1st until peak lake stage is VERY ROUGH this early in the season and is meant to be advisory-only. Our predictions for lake level rise range from 0.2 to 1.9 feet, with a 50th exceedance probability (most probable) rise of around one ft. As of January 1st, the lake was at 4191.4 ft elevation for context, so this suggests that the lake might peak close to 4192.4, barely rise at all, or exceed 4193 ft elevation. This is obviously a very wide range of possible outcomes. Our ability to predict lake inflow and rise will improve as the snowpack season progresses. We remind our readers that our inclusion of GSL inflow forecasts and predicted lake level rise is meant to provide rough guidance for Utah’s water managers in light of the high level of interest in the lake’s condition and numerous actions to restore lake levels.