How to measure snow and ice

Measuring snow and ice can be tricky, especially if it is windy.  However, with some background information and understanding, severe weather spotters can do a good job of measuring snow and ice.

Basically, as a minimum, the National Weather Service (NWS) measures snow and ice once every 6 hours.  Some co-op observers measure snow once per day, usually sometime around 6 or 7 am local time.  The NWS then adds up the snow that fell in each 6-hour period to arrive at the total 24-hour snowfall for a calendar day, or from 6 am to 6am.  At the end of each 6-hour period the NWS then brushes the snow off the 6-hour snow board.  In order for snow measurements to be considered for the record books, the NWS can't use time periods less than 6 hours.

Granted, one can measure snow accumulations on an hourly basis, but for the official record books, we measure once every 6-hours on the 6-hour snow board.  Since snow settles as air is squeezed out due to the weight of new snow on top, the total of the hourly snow measurements during a 6-hour period will usually be greater that the "once per 6-hour" snow measurement.  However, we do not add up the hourly snow measurements during a 6-hour period to arrive at the 6-hour snow accumulation - we measure only once every 6-hours on the 6-hour snow board to arrive at the 6-hour snow accumulation.

Ice and sleet accumulations are also measured on a 6-hour basis, and we measure the thickness of the ice on exposed surfaces and the depth of the sleet, both in tenths of an inch.

Here's an example:

12 am to 6 am......4.2 inches of snow.       6am to 12 pm.....3.8 inches      12 pm to 6 pm.....2.5 inches      6 pm to 12 am.....5.4 inches.

Total snowfall for the calendar day equals 15.9 inches.

Here are some links that give you more background information on how to measure snow:

http://www.crh.noaa.gov/mkx/?n=coop

http://www.nws.noaa.gov/om/coop/training.htm

http://www.nws.noaa.gov/om/coop/snowguid.htm

http://www.mke-skywarn.org/snow.measure.htm

http://www.cocorahs.org/state.aspx?state=wi

If you have any questions about how to measure snow, please contact Rudy Schaar, our Data Acquisition Program Manager at:

rudy.schaar@noaa.gov

Thanks for your interest in providing snow measurements to the NWS!

...Rusty Kapela, WCM

 

 

 



Return to News Archive

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.