Meteorologists are using a technique based on human observations to calibrate a Doppler radar method of predicting how much snow will fall in major storms.

In a new program sponsored by the National Oceanic and Atmospheric Administration (NOAA), several dozen volunteers will record information about the shape and size of snowflakes and measure the depth of snowfalls in the Denver, Colo., area. Handheld microscopes will allow t h em to determine the type of snow falling as heavy storms develop. Because large dendritic snow crystals are usually associated with deeper snow, while crystals laden with frozen cloud water droplets called graupel are characteristic of lesser accumulations, the morphology of the crystals can be used to guess where more snow will fall.