Canada Wheather Facts
December 19, 2007
Visit http://www.weatheroffice.gc.ca/mainmenu/faq_e.html for more information on this topic.
How is rain measured?
A.
Rain, drizzle, freezing rain, freezing drizzle and hail are usually measured using the standard Canadian rain gauge, a cylindrical container 40 cm high and 11.3 cm in diameter. The precipitation is funnelled into a plastic graduate which serves as the measuring device. The liquid precipitation is normally measured in millimetres.
How is snow measured?
A.
Usually, the snow amount or the depth of accumulated snow is measured using a snow ruler. The measurements are made at several points which appear representative of the immediate area, and then averaged. Snow is normally measured in “centimetres”.
How do you calculate the water equivalent of snow ?
A.
To calculate the water equivalent of snow, we melt the snow captured in snow gauges like the Nipher snow gauge. This Nipher gauge is designed to diminish the turbulence around the opening of the gauge and positioned high enough above ground to prevent most of the blowing snow from entering the gauge.
In many snow events a ratio of 10 to 1 can be applied to the amount of snow to determine its water equivalent. In other words, 1 centimetre of snow is equivalent to about 1 millimetre of water once the snow is melted. This means that in many snowfall situations (on days when only snow fell), you can simply change the units from millimetres to centimetres on the “Yesterday’s Precip. Total” on a specific location’s weather page to get a reasonably good idea of how much snow fell.
However, this 10 to 1 snow to liquid ratio is not exact. Exceptions include very fluffy snow (snow that has less water once melted) where the snow to liquid ratio could be 15 to 1 or higher (i.e. 1.5 centimetres of snow would melt to provide 1 millimetre of water). At the other extreme, the snow can be heavy and wet resulting in a snow to liquid ratio of around 5 to 1 (i.e. 0.5 cm of snow would melt to provide 1 mm of water).
We also have a map giving snow depths (snow on the ground). It is available from http://weatheroffice.gc.ca/analysis/index_e.html.
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