The SnowCast app analyses the atmosphere data provided by the National Weather Service to estimate the amount of snow likely to start falling above a specific geographical area. However, once a snowflake forms, there is no way to predict it's final landing location. Wind, updrafts, turbulence, etc. resulting from topography can result in large variances.
A 2" snowfall forecast could easily result in more than 2" being deposited on one side of a valley and somewhat less on the opposite side.
Actual snow accumulation is typically a physical measurement and such data is not available to the app. Consequently, and to maximize the app's performance on mobile devices, the app has been limited to forecasting only and does not include historical tracking.