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INTERMOUNTAIN WEST CLIMATE SUMMARY, JANUARY 2008 Spri n9 and Summer Streamflow Forecasts for the 2008 Runoff Season Due to below average snowpack across most of the Intermountain West Region, streamflo\v forecasts are mostly for below average conditions, with some southern basins expecting above average (Figure 14). Colorado has the highest streamflow forecasts, with most of the state near average. The highest forecast is for the Rio Grande River basin at 130% of aver- age, and the lo\vest is for the North and South Platte River basins at 85-90% of average. Utah has a similar north-south pattern, but there is a much greater dif- ference than Colorado: 51 % of average is expected in the Bear River in the north and the 122% of average expected in the San Juan River in the south. Wyo- ming has below average snowpack, with most basins projected to have belo\v average streamflows. The forecasts project average streamflows in the Shoshone and Clarks Fork, Snake, Yellowstone and Madison River basins, but the rest of the state is expected to get between 59% and 89% of average streamflows. Notes Forecasts of natural runoff are based principally on measurements of precipitation, snow water equivalent, and antecedent runoff, influenced by precipitation in the fall before winter snowfall (Figure 14). Forecasts become more accurate as more of the data affecting runoff are measured (i.e. accuracy increases from January to May). In addition, these forecasts assume that climatic factors during the remainder of the snow accumulation and melt season will have an average affect on runoff. Early season forecasts are, therefore, subject to a greater change than those made on later dates. The graphic shown here is from the NRCS, but the forecast is a collaborative effort between the NRCS and the NOAA River Basin Forecast Centers. You can see the official NOAA streamflow forecasts on the individual river basin forecast centers' websites. (See On the Web box below for links to the official NOAA forecasts.) -- - ^ Ul .....;J \0 ~ ~ V Ul ~ ~ ~ ~ w ~ 0 ~ ~ Ul .....;J \0 ~ ~ 0 0 0 ~ ~ ~ 0 w Ul 0 0 o~ ~ = .....~ ~ 0 :3 "'Cl ~ ~ Figure 14. NRCS outlook for natural streamflows for spring and summer in the Intermountain West region as a percent of average streamflows (data through January 1, 2008). On the Web For more information about NRCS water supply forecasts based on snow accumulation and access to the graph on this page, visit: http://www.wcc.nrcs.usda.gov/wsf/. The official NOAA streamflow forecasts are available through the following websites of individual River Forecast Centers: · Colorado Basin (includes Great Basin): http://www.cbrfc.noaa.gov/ · Missouri Basin (includes South Platte and North Plate: http://www.crh.noaa.gov/mbrfc/ · West Gulf (includes Rio Grande): http://www.srh.noaa.gov/wgrfc/ · Arkansas Basin: http://www.srh.noaa.gov/abrfc/ The NOAA CBRFC has a new interactive website that shows streamflow forecasts as inputs to reservoirs: http://www. cbrfc. noaa. gov /westernwater/ FORECASTS 11 7