Much of the world’s water resource infrastructure is experiencing rapid shifts in climate and snowmelt. Changing snowmelt regimes are responsible for rain-on-snow river flooding, putting communities at risk. Our study uses a new Snow Regime Classification system as a proxy for tracking climate driven changes in hydrology across the contiguous US over 40 years (1981-2020). Snow regimes are calculated annually, with changes evaluated across decadal and 30-year time scales. Our Snow Regime technique designates areas across CONUS as: (1) rain dominated (RD), (2) snow dominated (SD), (3) transitional (transient mix of rain and snow; R/S), or (4) as perennial snow cover (PS). Class thresholding ratios involve snow water equivalent (SWE) over cumulative cool-season precipitation (October through March).