Western Water Assessment: Intermountain West #Climate Dashboard: Oct Climate Summary & 2021 Water Year Summary

Click here to go to the Western Water Assessment website. Here’s an excerpt:

November 8, 2021 (CO, UT, WY)

  • The 2022 water year started well for much of the region. Large areas of Utah and Wyoming received much-above average precipitation and most areas above 8,000 feet have average to much-above average snowpack. Wet conditions caused a contraction of D3 and D4 drought in Utah and Wyoming, but drought conditions expanded in eastern Colorado and central Wyoming. La Niña conditions currently exist and are likely to continue through at least mid-winter. La Niña conditions typically increase the probability of above average precipitation in the northern part of the region and increase the probability of below average precipitation in the southern part of our region.
  • October precipitation was much-above normal in Utah and Wyoming; large areas of both states received greater than 150 – 400% of normal precipitation.
  • Western Colorado received slightly above average precipitation, but most of eastern Colorado saw less than 50% of normal precipitation.
  • Temperatures were cooler than average in Utah with southern Utah temperatures up to 4 degrees below normal. Most of Colorado and Wyoming saw near-normal temperatures (+/- 2 degrees) except in eastern Colorado and Wyoming where temperatures were up to 4 degrees above normal.
  • Snowfall for most of the region was much-above normal during October. Much of the precipitation that fell in Utah, Wyoming and western Colorado fell as snow at elevations above 8,000 feet. Winter is off to a great start as all regional river basins have above average snow water equivalent (SWE) except for northern Wyoming, South Platte and Rio Grande River basins. While percent of normal figures can be a bit skewed in early and late winter, Utah river basins range from 100 – 800% normal SWE. SWE in Colorado and southern Wyoming ranges from 90 – 200% of normal.
  • Westwide SNOTEL basin-filled map November 3, 2021 via the NRCS.
  • Regional streamflow was higher in October compared to previous months with many rivers flowing at normal levels (25th to 75th percentile). Streamflow in several regional rivers still remains very low (<10th percentile), including the Snake, Yellowstone, White, Dolores, Bear, Logan, and Weber Rivers.
  • Moderate drought emerged in eastern Colorado and central Wyoming during October and now covers nearly 90% of the region. Extreme drought conditions expanded in northern Wyoming, but coverage of extreme and exceptional drought in Utah and western Colorado contracted during October. A small area of extreme drought developed in northeastern Colorado. Surface soil moisture conditions improved dramatically over large areas of Utah, Wyoming and northern Colorado.
  • West Drought Monitor map November 2, 2021.
  • La Niña conditions currently exist in the eastern Pacific Ocean as sea-surface temperatures are -0.8ºC below normal. There is an 80% probability of La Niña conditions persisting through January and a 60% chance of La Niña continuing through March. The NOAA seasonal forecast projects an increased probability for above average precipitation in northern Utah and Wyoming during November and in Wyoming during November – January. The NOAA seasonal forecast for November projects an increased probability of above average temperatures for the entire region and the November – January seasonal forecast projects an increased probability of above average temperature for Utah and Colorado.
  • Significant October weather event. October precipitation was extremely high throughout much of Utah and Wyoming. Cities along the Wasatch Front, including Logan, Ogden, Provo and Salt Lake City observed the 3rd to 5th wettest October. In Wyoming, Lander observed the 3rd wettest October, and it was the 5th wettest October ever in Green River; in Lovell, Pinedale and Worland, October precipitation was in the top ten of all October observations. An important consequence of the wet October was a dramatic wetting of surface soil moisture conditions in Utah, Wyoming and northern Colorado. In northern and western Utah, many locations went from the driest on record to average and above average soil moisture conditions. Except for the Yellowstone Plateau, soil moisture conditions in Wyoming improved from near-record dry to much-above average wetness. Far northern Colorado also saw dramatic improvements to surface soil moisture conditions.
  • Water Year 2021 Summary

  • The 2021 water year was the second consecutive year of drought in the Intermountain West. The year began with 100% of the region in drought and over 50% of the region in extreme drought. A below average to near-average winter snowpack yielded a much-below average spring runoff seasons. Seasonal runoff volumes from most regional rivers varied from 8-57% of normal and the inflow to Lake Powell received 28% of normal streamflow. Higher seasonal streamflow volumes were observed for river basins east of the Continental Divide in Colorado and Wyoming. Heavy precipitation in eastern Colorado relieved drought by June 1st east of the Continental Divide. Elsewhere in the region, drought conditions peaked in July as Lake Powell and the Great Salt Lakes reached all-time low elevations. An overall dry and drought-riddled water year finished on a positive note as a very strong North American Monsoon brought above average July-August precipitation to much of the region and regional soil moistures have recovered somewhat from all-time lows during early summer.
  • Precipitation during the 2021 water year was below normal for most of the region, except for the Front Range and southeastern Colorado where precipitation was up to 120% of normal. Northwestern and southern Utah, southwestern and eastern Wyoming and northwestern Colorado received less than 70% of average precipitation. Temperatures were generally above normal in western Colorado, most of Utah, and southwestern and northeastern Wyoming. Temperatures were cooler than average in eastern Colorado and southeastern Wyoming. Summer temperatures were extremely hot in the Intermountain West in 2021; Utah saw the hottest June-August on record while Wyoming and Colorado experienced the 3rd and 4th hottest summers since 1895.
  • Winter was slow to start regionally; January 1st 2021 snow water equivalent (SWE) was 50-80% normal in most locations. By April 1st, SWE was near average in Colorado (93% statewide average) and Wyoming (94%), but below average in Utah (79%). Snowmelt proceeded extremely quickly during April and May, especially in Utah and western Colorado; May 1st SWE was 52% of normal in Utah and 71% of normal in Colorado. One June 1st, SWE was 12% of normal in Utah and snow was completely melted from all but 3 sites compared to 17 sites with snow on a normal June 1st.
  • Much like the 2020 water year, streamflow volumes in the 2021 water year were significantly lower compared to average than snowfall. While April 1st SWE varied from 50-80% of normal in most locations, April-July streamflow volumes varied from just 8-57% at those same locations. The inflow to Lake Powell was 28% of normal in 2021. April-July streamflow volumes were closer to normal east of the Continental Divide where snowfall was near to slightly above normal. The 2021 water year produced an inefficient runoff for all river basins in the Intermountain West similarly to the 2020 water year. Streamflow volume forecasts were very low on April 1st at <60% of normal runoff for most of the region. Warm temperatures, dry soils and below average spring precipitation led to a very fast snowmelt in Utah and western Colorado.
  • By June 1st seasonal streamflow volume forecasts predicted <50% of normal runoff for nearly the entire Upper Colorado and Great Basins. One cause of inefficient runoff during 2021, was extremely low soil moisture to begin the water year. October 1st 2020 soil moisture values were very low in Utah, western Colorado and parts of western Wyoming. Soils in large areas of Utah and western Colorado were at the lowest moisture levels observed (since 1948) to start a water year. Very low October 1st soil moisture meant that melting snow in spring needed to first recharge soil moisture reservoirs before snowmelt could reach regional rivers.
  • The 2021 water year was a year of extreme drought for the entire region. The water year began with 99% of the region in drought and over 50% of the region in extreme drought. The worst drought conditions were found in Utah; during July, when conditions were driest, 100% of the state was in at least extreme drought and 70% of the state was in exceptional drought. Two periods of rainfall outside of winter brought improvements to drought during 2021. Much above average precipitation during March – May 2021 in eastern Colorado led to the complete removal of all drought conditions east of the Continental Divide by June 1st. The wet period began on March 13th with a very large upslope snowstorm that brought 18 – 52” of snow to an area from the north slope of the Uinta Mountains east to Cheyenne, WY and south to Denver, CO. Except for eastern Colorado, drought conditions generally worsened throughout the region until mid-July when monsoonal precipitation began to push northward into southern Utah and southwestern Colorado. Strong monsoonal precipitation continued into August when Utah, western Wyoming and northwestern Colorado received above average precipitation; large areas of Utah and western Wyoming saw greater than 200% of normal August precipitation with some locations breaking monthly rainfall records. The 2021 water year closed with some improvements to the severity of drought compared to the beginning of the water year; regional coverage of D1-D3 drought decreased by 10-20%.
  • Monsoonal rainfall during July and August did improve drought conditions, but the region is far from recovered from drought. One impact of long-term drought is reflected by the amount of water in large reservoirs and terminal lakes. Both Lake Powell and the Great Salt Lake reached all-time low elevations during summer 2021. During August, Lake Powell reached a new record-low elevation of 3,551 feet above sea level; Lake Powell is currently at an elevation of 3,544 feet, 29% full and is expected to fall another 30 feet before spring runoff begins. The Great Salt Lake is a terminal lake in northern Utah that marks the end of the Bear, Weber and Provo/Jordan Rivers. Because it is a terminal lake, its elevation is a function of water inputs and water withdrawals. Drought, climate change and human consumption of water have led to a long-term decline in the Great Salt Lake’s elevation and area. The lake reached an all-time low elevation during of 4,191.3 feet in August, about 20 feet below its all-time high elevation in 1986. Because the Great Salt Lake is such a shallow lake, the area of the lake fluctuates by nearly a factor of 3, ranging from an area of 965 square miles in 2021 to 2,395 square miles in 1986. Above average precipitation during August – October has kept Great Salt Lake elevations hovering around record low levels, but not consistently lower as predicted earlier in the summer.
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