What instruments are used to measure a blizzard?

First of all, to measure the snow in a blizzard, you can find a flat open area away from trees and buildings.  Take several measurements with a yardstick and average your reading to the nearest 1/10 of an inch.

Secondly, forecasters can use radiosonde balloons, which are balloons that measure various atmospheric parameters.

Radiosonde Balloon

Last but not least, we have remote sensing platforms which satellite imagery and radar.

Satellite