An inch of rain does not always equal 10 inches of snow — See how meteorologists forecast snow

Youngstown Weather
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Winter weather is on the move and snowflakes are in the forecast. Snow forecasting can be very tricky and many factors are involved in producing snowfall forecasts.

Three big factors determine the majority of ingredients needed in a snowfall forecast.

1.) How much liquid will fall?
2.) How long will the precipitation last?
3.) How cold/warm is the air that the snow is falling through?

There are other factors that come into play as well. Is the ground above freezing? Is the ground wet? Will the sun help melt the snow? These are just a few of the items a meteorologist needs to keep in mind when producing a snow forecast.

You need cold temperatures to produce snow. In fact, cloud physics deals with supercooled water droplets. These are droplets that are well below freezing at times. The temperature plays a big role in the snow shape and size. The amount of moisture has has a role too.

Snow can come in shapes like plates and columns. It can form thick and thin in these plates or dendrites. There are even needle-shaped snow crystals. Again, this is all due to the amount of moisture in combination with temperature that will create the different shapes and sizes.

The different shapes and sizes will also play a role in how the snow accumulates. This is a very important factor when forecasting snow for a meteorologist.

Think of it this way. The colder the air, the more the snow can accumulate. It is typically a drier snow. The warmer the air, the less the snow can accumulate. This is typically a wetter snow. This also has many factors that can influence the amount of snowfall, including snowfall intensity and time of snowfall. Compaction of any snow will also play a role in the end result of a snow forecast. The heavier the snow, the more it will compact and look like less snow has fallen in a given location.

Temperature plays a big role in the snow to liquid ratio. The “snow to liquid ratio” is a tool that meteorologists use to plug into their snow accumulation equation when putting together a forecast.

Back to the title of this article. An inch of rain does not always equal 10 inches of snow. This is very true. Remember, the colder the air is, the higher the snow ratio is. The warmer the air is, the lower the snow ratio is.

If the air temperature was 34°F to 28°F, a 10:1 ration would be used.

An example: The forecast knows that 1.00″ of liquid precipitation will fall in a given time. The forecast also knows that the air temperature is going to be between 34°F and 28°F. The forecast can expect that the 1.00″ of liquid precipitation can create 10.0″ of snowfall. Keep in mind, this is just a scale to use to start a forecast. The other factors talked about earlier in this article can influence the snowfall accumulation.

Using the same example with colder temperatures would result in higher snowfall out of the same amount of liquid precipitation. The same 1.00″ of precipitation falling in a region where the air temperature is between 14°F and 10°F would result in 30.0″ of snow! That is a big difference that is created due to the change in the crystal structure of the snow.

Our part of Northeast Ohio and Northwest Pennsylvania will average around 13:1 to 15:1 ration through the winter.

You can see a few of these snow to liquid ratios below:
Air Temp = 34° to 28°F
Liquid of 0.01″ = 0.1″ of Snowfall
Liquid of 0.25″ = 2.5″ of Snowfall
Liquid of 0.50″ = 5.0″ of Snowfall
Liquid of 1.00″ = 10.0″ of Snowfall

Air Temp = 27° to 20°F
Liquid of 0.01″ = 0.2″ of Snowfall
Liquid of 0.25″ = 3.8″ of Snowfall
Liquid of 0.50″ = 7.5″ of Snowfall
Liquid of 1.00″ = 15.0″ of Snowfall

Air Temp = 19° to 15°F
Liquid of 0.01″ = 0.2″ of Snowfall
Liquid of 0.25″ = 5.0″ of Snowfall
Liquid of 0.50″ = 10.0″ of Snowfall
Liquid of 1.00″ = 20.0″ of Snowfall

Air Temp = 14° to 10°F
Liquid of 0.01″ = 0.3″ of Snowfall
Liquid of 0.25″ = 7.5″ of Snowfall
Liquid of 0.50″ = 15.0″ of Snowfall
Liquid of 1.00″ = 30.0″ of Snowfall

Air Temp = 9° to 0°F
Liquid of 0.01″ = 0.5″ of Snowfall
Liquid of 0.25″ = 10.0″ of Snowfall
Liquid of 0.50″ = 20.0″ of Snowfall
Liquid of 1.00″ = 40.0″ of Snowfall

Air Temp = -1° to -20°F
Liquid of 0.01″ = 0.5″ of Snowfall
Liquid of 0.25″ = 12.5″ of Snowfall
Liquid of 0.50″ = 25.0″ of Snowfall
Liquid of 1.00″ = 50.0″ of Snowfall

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