Here’s the release from the NRCS (Brian Domonkos):
For the second month in a row all major basins in Colorado experienced below average precipitation during May. To express the degree of the dry conditions, 49 out of 115 Colorado SNOTEL sites received the lowest or second lowest precipitation amounts on record for the combined months of April and May. The combination of low precipitation and warm temperatures have caused accelerated snowmelt rates across the state and particularly in southern Colorado where precipitation has been the least. Recent conditions, combined with a dry late summer and fall last year, have led to an unusual relationship between peak snowpack and snowmelt runoff volumes. NRCS Hydrologist Karl Wetlaufer explains “While most of Colorado reached a near normal peak snowpack, the combination of drought conditions going into winter and recent lack of precipitation have led streamflow forecasts to be much lower than would commonly occur with a similar snowpack. This is particularly notable in southern Colorado”.
In addition to well below normal precipitation, the Colorado mountains have also had warmer than normal temperatures. This combination has led to snowmelt rates that are much faster than normally observed. In Southern Colorado, where snowpack reached near normal peak values, this led to snow melting out of SNOTEL sites several weeks earlier than normal. In northern basins where snowpack was above normal, snowmelt still occurred early but closer to a normal time than in Southern Colorado. This early snowmelt in combination with low precipitation values both have contributed to declines in streamflow forecasts over the last two months.
While the average of current streamflow forecasts in all major basins of Colorado are for well below normal volumes, there are still stark differences between the northern and southern basins. The highest forecast values in the state exist in the North Platte, South Platte, and Colorado basins. The average of forecast values in these basins range from 72 to 79 percent of normal volumes. The Gunnison and combined San Miguel, Dolores, Animas, and San Juan basins both have average forecast values of 55 percent of normal. The lowest streamflow forecasts in the state are in the Rio Grande basin where they average to be a meager 41 percent of normal. The Arkansas basin spans the gap of north to south with much higher forecasts in the headwaters compared to the much drier southern tributaries.
Statewide reservoir storage is currently at 100 percent of average but varies considerably basin to basin. The most plentiful storage in the state is in the combined Yampa and White basins as well as the Colorado basin where there is 115 percent of average storage. On the low end, the Rio Grande basin only has 62 percent of average storage which could pose water resource challenges considering the low streamflow forecasts as well. The water supply will have to be watched closely across Colorado.
For more detailed information about June 1 mountain snowpack refer to the June 1, 2020 Colorado Water Supply Outlook Report. For the most up to date information about Colorado snowpack and water supply related information, refer to the Colorado Snow Survey website.