Snow and sleet are measured several different ways.  One method is to simply take a ruler or measuring stick and measure the depth of the snow on a flat board called a snowboard.  The snowboard consists of a perfectly flat, white (reflective) surface.  The snowboard is white so that it does not absorb solar radiation and heat up, thereby melting snow that falls on its surface.  This measurement is done very soon after the snow has fallen so as to get a measurement before any settling takes place, and with snow a very large amount of settling can potentially take place depending on the temperature at which the snow formed.  If it formed at very cold temperatures, it is more likely to have a higher settling rate because the crystals are more dendritic in nature and tend to allow much more room for air to gather in between flakes as it lands on the surface.
 
 

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• Dendritic is a word that means "tree-like" and this is very much what a dendritic crystal or dendrite looks like.  The tip of a dendrite  grows and side branches grow outward as supercooled water freezes onto the existing ice.

 
 

• Other forms that snow/ice crystals can take on include: needle, plate, and columns.  As you can see from the figure below, there is much less space for air to become trapped among accumulated crystals of these types.  Therefore, the effect of settling on snow comprised of these crystals is much less than the settling that would occur within a dendritic snow.

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Snow and sleet can also be measured for their liquid water equivalence.  This is done by collecting the snow in a bucket similar to a rain guage except it is heated to melt the snow as it lands so that its depth can be measured as if it were rain.  This method can be much more useful and is typically a more consistent method----it allows meteorologists to determine a liquid to snow ratio, which can be as high as 15:1 for very cold snow and as low as 1.1:1 for sleet that piles up with much less room for air in between the particles.

 

• In a standard rain gauge where measurement of liquid equivalence is taken with a scaled ruler, anti-freeze or oil is used to prevent the liquid from freezing.

Another instrument used to measure the liquid equivalence of snow depth is a snow pillow.  A snow pillow usually consists of around 4 stainless steel panels that are plumbed so that they are all level with eachother.  The panels are filled with an antifreeze solution so that snow melts into them and the added weight due to the liquid puts pressure on the panels, sending the fluid to a pressure transducer that converts the pressure into a liquid equivalence and liquid depth.  Snow pillows are sometimes used at remote sensing stations so that the signal from the pressure transducer is sent via antenna to a computer that can analyze the data.

 

The sonic range sensor is an instrument used on weather observation towers to measure snow depth.  This sensor sends out pulses of ultra-sonic sound waves (sound waves that can not be heard by the human ear) and records how long it takes for the echoes to come back to the sensor.  Knowing the speed of sound allows the distance from the sensor to the top of the snow to be determined.
 

 
 
 
 

Click here to learn about freezing rain measurements!

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Click here for the Main Precipitation Page!