Snow depth should be measured to the nearest inch and reported to the NWS.  Ideal measurements are on a flat surface in an open area - snowboards work great.  Measurements should be taken every 3 to 6 hours, but not more than every hour.  Always report if snow falls faster than 1" per hour, or if you observe thunder.  If sleet has fallen, include the sleet with your snow measurement.  If snow has drifted, take several measurements including bare areas but not the highest drifts.  You should then take an average of these measurements for your final report.