Record Warmth, Dry Start to 2015Written by Arthur Meunler
By Arthur Meunier, National Weather Service Riverton Office Forecaster
2015 started out very dry across Wyoming. The statewide average precipitation for the first quarter, January through March, was only 2.25 inches which was 69 percent of the 20th century average, making it the seventh driest first quarter in Wyoming over the last 121 years.
Wyoming experienced its warmest first quarter of the year after 121 years of records with a statewide average temperature of 30.6 degrees Fahrenheit (F). This was 7.3 degrees F above the 20th century average and broke the previous first quarter record set in 1934 when the statewide average temperature was 29.9 degrees F.
The below-normal precipitation and record warm temperatures combined to leave much below normal snowpack across the state with peak runoff expected from two weeks to a month earlier than normal this spring.
Wyoming began 2015 drought-free.
However, with dry and record warm conditions, moderate to severe drought pushed north from the Eastern Great Basin into southwest Wyoming in February and March. The latest “Drought Monitor” also showed abnormally dry conditions across most other areas west of the Continental Divide and in the northeast corner of the state.
Statewide average precipitation for April was 1.84 inches which was 104 percent of the 20th century average.
The southeast quarter of the state accounted for most of the excess where precipitation amounts were 150 to over 200 percent of normal. Northern and western Wyoming ended April with generally 40 to 80 percent of normal precipitation. One notable exception was Cody, which received 1.66 inches of precipitation in April, which was 157 percent of normal. Just down the road, Greybull reported only 0.11 inches in April, which was 15 percent of normal.
For the current water year, October 2014 through September 2015, statewide average precipitation through April was 7.56 inches, which is 91 percent of the 20th century average.
The southeast and central portions of the state have received from 100 to 150 percent of normal precipitation so far this water year, while the west and northeast sections of the state were the driest with 40 to 80 percent of normal precipitation.
River and streamflow conditions
During the first week of May, mountain snowpack across the state was 55 percent of average.
The Upper Bear River Basin in the southwest corner was on the low end at 13 percent, and the South Platte River Basin was on the high end at 96 percent. Most of the higher mountain ranges across the state were between 55 and 70 percent of average snowpack.
During the first week of May in 2014, the statewide average snowpack was 136 percent of average with all drainage basins above 90 percent of average.
Below normal – from 50 to 65 percent – snowmelt streamflow volumes are expected across all major basins across Wyoming. Several central and southern basins, including the Upper North Platte, the Wind, the Little Snake and the Upper Bear are forecasted to have well below, or less than 60 percent, normal streamflow volumes during the upcoming snowmelt season. The good news is that Wyoming carryover reservoir storages are 110 to 120 percent of average for May.
Fire weather impacts
Years with warmer than average spring temperatures and below average snowpack tend to have the most active fire seasons, especially the number of large fires over 1,000 acres.
1988 and 2012 were the two extreme examples, with over a dozen large wildfires in each year after very warm spring conditions combined with much below average snowpack.
This year, there is a higher than usual likelihood that wildfires will occur and become significant events in July and August across north and central Wyoming.
Precipitation and temperature outlooks
The three-month outlook for May, June and July shows above normal precipitation is most probable from West Texas through the Rockies, including all of Wyoming.
Above normal precipitation is most probable across Wyoming, Colorado and Utah during the summer and early autumn. Above normal temperatures are expected during May, June and July across most of the Intermountain West including western Wyoming.
This temperature trend is also expected to continue through the summer into early autumn.
For more information, the following websites are available.
Visit weather.gov/riw/drought for drought graphics, monthly and seasonal climate summaries, river and streamflow conditions, temperature and precipitation outlooks, snowpack and reservoir information.
The National Weather Service Advanced Hydrologic Predictive Services (AHPS) is available at nrcs.usda.gov/wps/portal/nrcs/site/wy/home.
Water and climate data for the state of Wyoming is available at wrds.uwyo.edu, and the Natural Resources Conservation Service Snow Survey out of Casper, as well as the Wyoming basin outlook reports, snowpack reports and water supply outlooks, can be found at wrds.uwyo.edu/wrds/nrcs/nrcs.html.
The U.S. Geological Survey’s water resources of Wyoming and Montana are available at wy-mt.water.usgs.gov/projects/drought.