Water Year Review - October 11, 2018 (UT, WY, CO)

Also see the Colorado Climate Center's report on Water Year 2018 for Colorado
 

• Water Year 2018 ended with a whimper, as extremely dry and very warm conditions prevailed over the region in September. Water-year precipitation and streamflows ended up at record- or near-record-low levels across most of Utah and Colorado, accompanied by record- or near-record-high average temperatures and evaporative demand. The cool and wet start to October dampened wildfire danger and raised hopes for the new water year, but deep deficits in soil moisture and water supply persist.
• Dozens of stream gages in the Upper and Lower Green, White, Yampa, Colorado headwaters, Gunnison, Uncompahgre, Dolores, and San Juan basins saw their lowest September monthly flows on record. In late September, the Animas River ran below 100 cfs at Durango for the first time in 107 years of record. Water-year total streamflows were the lowest or 2nd-lowest on record at many gages in southwest Colorado, and at several gages in southern and eastern Utah. Unregulated water-year inflows to Lake Powell were the 3rd-lowest on record, after 1977 and 2002.
• Statewide, Utah is at 54% of average reservoir storage for this time of year, versus 70% one year ago; Colorado is at 46% of average, versus 68% one year ago. As of October 9th, Blue Mesa Reservoir had dropped to its lowest level, 263 KAF, since 1987. Lake Powell held 11.0 MAF as of October 9th, the lowest level since 2014, and per the September 24-Month Study, the most-probable forecast for April 2019 is 9.0 MAF, which would be Powell's lowest level since 2005.
• September was an extremely dry month for the region, capping off a historically dry water year for most of Utah, Colorado, and southern Wyoming. Statewide, Water Year 2018 was the driest on record (since 1896) for Utah, while it was the 2nd-driest on record for Colorado, just ahead of 2002. September was much warmer than average for Utah, Colorado, and southern Wyoming, cinching a historically warm water year. For Colorado statewide, Water Year 2018 tied with 1934 and 2000 as the warmest on record, while for Utah, it was the 2nd-warmest on record, just behind 1934. Both states were 2.8 degrees F above the 1981-2010 normal.

• Drought conditions emerged or worsened in multiple areas in Utah, Wyoming and Colorado during September. D3 and D4 conditions now cover virtually all of eastern Utah and Colorado's Western Slope. As of October 2, 88% of Utah is in D2 or worse, and the remainder in D0 or D1; in Colorado, 64% is in D2 or worse, and 22% in D0-D1; and in Wyoming, 3% is in D2 or D3, and 37% in D0-D1. The 12-month EDDI map shows that relative to previous water years, evaporative demand over Water Year 2018 was the highest (ED4) or 2nd-highest (ED3) on record (since 1980) for much of the region.

• The CPC seasonal precipitation outlooks for the month of October shows very strongly enhanced chances for above-normal precipitation for the region, largely reflecting the wet short-term forecasts as of October 1, i.e., precipitation that now has already fallen as of the 11th. The precipitation outlook for the October-December period shows slightly enhanced chances for above-normal precipitation for Colorado and southern Utah, consistent with the elevated odds of El Nino development by winter. Those odds are still at about 70%, per the IRI/CPC Probabilistic ENSO Forecast.