May 11, 2017 (UT, WY, CO)
- A wetter-than-normal April and early May led to a bumpy snowpack trajectory through the peak(s) and into the main melt season, and as of May 11, SWE is above normal in all areas except northwestern Colorado, southeastern Wyoming, and southern Utah. The highest, wettest Snotel sites in the region appear to have just peaked, among them Grand Targhee (WY) and Snowbird (UT), both at about 60" of SWE, well above normal.
- With very large snowpacks and the melt well underway, daily streamflows in northern Utah and western Wyoming rivers are at high (>90th percentile) or record-high values, with yet higher flows and flooding potential on tap with upcoming warm, sunny weather. An elevated risk of flooding in these basins, as well as in the Arkansas basin in Colorado, will persist for several weeks.
- The May 1 NRCS spring-summer runoff forecasts changed only slightly from the April 1 forecasts at most points. The regional picture is still tipped towards above-average runoff, though with a clear gradient between the much-above-average (>130%) volumes expected in northern and central Utah and most of Wyoming, and the more variable but closer-to-average volumes elsewhere. Forecasted Lake Powell April-July inflows have slipped again, to 123% of average per NRCS, and 120% of average per NOAA CBRFC.
- April saw mostly above-normal precipitation for the region, with central and western Wyoming, far northern Utah, and southeastern Colorado coming out very wet, while central and southern Utah and western Colorado were on the dry side. Statewide, Wyoming yet again was the winner, in the 93rd percentile for precipitation, with Colorado in the 72nd percentile, and Utah in the 53rd percentile.
- Drought conditions have markedly improved since early April, so that the region now has less drought coverage than at any time since August 2009. There was reduction of drought in southeastern Colorado and northeastern Wyoming, though some degradation to D0 in southeastern Utah. D1 or D2 conditions now cover only 2% of Colorado (down from 22%), 0.1% of Wyoming (down from 9%), and 0% of Utah.
- The tropical Pacific remains on the warm side of ENSO-neutral conditions, though with some cooling in the last few weeks. The ENSO forecast models call for neutral conditions to continue, but with the chances of transition to El Niño conditions rising to ~50% by late summer and fall.