As the climate continues to warm, we expect a greater fraction of winter precipitation to fall as rain instead of snow. Areas of “at-risk” snow with winter air temperatures near freezing are likely to be most sensitive to losses in snow accumulation, changes in snowmelt rates, shifts in streamflow volume and timing, and shifts in the frequency and magnitude of rain-on-snow events. However, these at-risk snow areas are also most affected by fundamental uncertainties in modeling rain-snow partitioning and observational challenges from both in situ networks and remote sensing platforms.

Our inability to predict rain versus snow at air temperatures near freezing is most pronounced in the very areas expressing the greatest sensitivity and vulnerability to climate warming. This simple fact calls for a project that performs enhanced monitoring of the rain-snow transition zone across the western US.

The primary goal of collecting these observations of rain, snow, and mixed precipitation is to improve satellite-derived estimates of precipitation phase from the Global Precipitation Monitoring (GPM) mission, which will allow GPM to better quantify rain and snow across the western US and snowy regions globally. This will advance our knowledge of the water cycle in mountain regions and improve NASA’s Earth observational capabilities for winter storms, including rain-on-snow events. Project data will also enhance representation of rain vs. snow in land surface and atmospheric modeling systems such as NLDAS-2 and MERRA-2 as well as operational and experimental weather models.

Mountain Rain or Snow is supported by NASA.

The full title of this project is “Using Citizen Science Observations to Monitor the Rain-Show Transition of the Western US and Improve Satellite Estimates of Precipitation Phase”. It is funded by a grant from the  National Aeronautics and Space Administration (NASA) ROSES Earth Science Research Program. Any opinions, findings, conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of NASA. For more information about NASA citizen science, visit science.nasa.gov/citizenscience or  www.nasa.gov/solve.