Snow Water Equivalent (SWE)

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Equation / Last modified by KurtHeckman on 2018/07/02 13:14
Titan.Snow Water Equivalent (SWE)

The Snow Water Equivalent (SWE) calculator computes of the volume (V) of liquid water contained in rain or snow pack defined by area, depth and snow type or rain.

INSTRUCTIONS: Choose units and enter the following:YardSnow.jpg

  • (a) area covered
  • (d) depth and 
  • (t) type of snow or rain (see table). 

Liquid Water Volume (V): The volume (V) is returned in gallons.  However, this can be automatically converted into other volume units (e.g. liters or cubic yards) via the pull-down menu.
In essence, this computes the amount of water in snow.  See YouTube video instructions HERE

Type of snow or ice(kg/m3)
Fresh New snow 50-70
Damp new snow100-200
Settled snow200-300
Depth hoar100-300
Wind packed snow350-400
Firn   (granular)400-830
Very wet 700-800
Glacier ice830-917

Water, Rain and Snow Calculators:

Calculating Area

The area covered by snow may be difficult to estimate.  Here are some simple calculators to help you compute the area.  To compute the size of your snow covered area, you must first identify the shape of the area. 

The Science

When snow melts, it becomes water.  This equations uses the approximate density of different types of snow (Snow Type) and the volume of snow based on the coverage area (a) and the average depth (d) to calculate the approximate volume of water contained in snow pack.  

   The areas entered can be small for things such as patios and roofs, and they can be large like a county.  Here is an equation that provides the areas for each county in Maryland -> Maryland County Areas  Use this equation to retrieve the area of the Maryland county, and then use that as input to the SWE equation to see how much water is contained in a snowfall on the county.

Density of Snow

Density of snow can range anywhere from 5% when ambient air temperature is 14 F, and can range up to 20% if the temperature is 32 F.  The snow density will increase after the snowfall due to gravitational settling, packing, wind effects, melting and refreezing.  The table below contains a generally accepted range of density (kg/m3) for different types of snow.    The equation will use a median value for the ranges in the density value column.