There is some indication that parts of eastern Colorado see more precipitation during the late fall and spring during El Nino years.  This can be seen in the box and whisker plots shown here. The forecasts you reference however, include other tools, such as trends, model forecasts, and statistical tools.

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ENSO/box_whiskers/i…