What are snow ratios and how are they determined?
Who likes to shovel?
I didn’t mind as a kid, but now, it’s not so much fun.
Besides being a chore, the snow we’re shovelling here in Atlantic Canada is often wet and heavy and can be dangerous for our health.
However, not all snowfall events produce heavy, wet snow. In some cases, it can be light and fluffy. This all leads to something known as snow ratios.
The snow ratio, also known as the snow-water equivalent, is the amount of liquid water in the snow, which can be determined by melting it.
The average snow ratio is considered 10:1.
This means if you were to melt 10 cm of snow, it would produce one centimetre of water, or 10 mm. However, when temperatures
are just above freezing, wet snow can produce a snowfall ratio of 5:1 – then meaning melting five centimetres of snow would produce one centimetre of water.
On the other hand, some of our heavier snow events occur when temperatures are colder. Suppose the temperature is at or below -7 C.
In that case, we can see a snowfall ratio of 20:1, where 20 cm of snow equals one centimetre of water.
So, what does this all mean and how does it fit into forecasting? Colder temperatures lead to higher snow ratios.
Often, a snow ratio of 15:1 or 20:1 will produce more snowfall than a ratio of 10:1 or 5:1.
Temperatures and wind speed are also critical and can impact the snowfall ratio.
Since temperatures aloft and at the surface fluctuate with our storms, the ratio can change several times during the event.
Most models use the 10:1 ratio, but forecasters can use equations to adjust it as necessary.