Climate.gov has your answer with the article Winter so far has people out west asking, Where’s the snow? (Feb 15, 2018) by Tom DiLiberto.
Farther south in Arizona, snows across the Rockies and in the Upper Colorado River Basin have been extremely low so far this year. Snow water equivalents—the amount of liquid water that would result if the snow melted in an instant—are between 0 and 30% of the median for this time of year for a broad region. In fact, the “best” areas for snow this season lie along the Front Range in Colorado and are only just around normal.
Why does this matter?
For areas in the Upper Colorado River Water Basin along the southern Rockies which rely on snow melt for water resources later in the year, snow amounts this low bring fears. Particularly, is there going to be enough snowmelt to fill Lakes Mead and Powell, which provide water to major cities like Tucson and Phoenix?
What is the cause? A second La Nina year in a row is part of the explanation, but (as their graph here shows)
As we continue to warm the planet due to emissions of greenhouse gases, mountain snowpack out west will likely continue to dwindle. Assuming we continue to increase global emissions of greenhouse gases (A2 scenario), the snow water equivalent of the snowpack in California by the end of the century will be 43% of what it was from 1971-2000. In Colorado, the snow water equivalent will be 26% less than that observed from 1971-2010.
A smaller and earlier-melting snowpack means less water to runoff into streams and tributaries in lower elevations. For places in the Sierra Nevada Mountains, Upper Colorado, and Upper Rio Grande River basins that rely heavily on a melting snowpack to provide the bulk of their annual runoff, climate change will have profound impacts on reservoir levels, water storage, and the people and ecosystems who rely on them.
There is enough quantitative information to use this article in a QL based course.