Doppler radar is a great tool to display the saturation occurring in the atmosphere. The National Weather Service meteorologist can place the radar in an operating mode that slows down the rotation and limits the elevation scan. When revolving in this volume scan, wear and tear on the radar is reduced. With regard to atmospheric surveillance, it allows for detection of growing ice particles. Meteorologists refer to this mode of operation as clear air mode.
Ice crystals dominate the cloud structure during the cold season. When the radar is rotating in clear air mode, meteorologist can view atmospheric saturation as moisture laden clouds blossom on the radar monitor. Due to the curvature of the earth; the radar beam properly detects ice crystals multiplying between eight to ten thousand feet, about 90 miles from the transmitting radar.
On occasion this mid level precipitation fails to reach the ground; often being displayed in a donut shape encircling the radar site. So when viewing the radar imagery on the MPR website this winter, curb your enthusiasm for accumulating snow until you see that donut hole dramatically shrink in size.
Meteorologists constantly match ground observations to the radar imagery to gage the intensity of the snowfall.
Radar is invaluable, but it takes a skilled meteorologist to formulate and communicate the critical details of impending snowfall.
Check out the Doppler radar imagery.