Freezing Rain Warning for Southern Ontario: Winter Weather


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Freezing rain is expected to fall across Southern Ontario on Sunday. Photo: Dendroica cerulea / CC by 2.0

As of December 9th, much of southern Ontario is under a freezing rain advisory as a low pressure system moves its way across the Great Lakes.

The freezing rain could continue until Monday, and it is possible that snowfall amounts in the Ottawa Valley may trigger a severe weather warning later today.

What is Freezing Rain?

Winter brings with it a host of eclectic weather, including ice pellets, hail, and freezing rain.

Freezing rain is rain that falls when the surface temperature is below freezing.

Although it seems that the higher in the atmosphere you go, the colder things would get, sometimes this is not the case.

When freezing rain occurs, air from a warm front is in the upper parts of the atmosphere, while cold air is trapped underneath.

Precipitation can change a lot as it moves downward through the sky. As precipitation falls through layers of cold and warm air, it might begin as snow, melt into rain, and then get supercooled into freezing rain.

Supercooling Leads to Icy Layers

What is supercooling? When water cools below its usual freezing point without turning into a solid, this is supercooling. Freezing tends to happen around a nucleus that allows freezing to begin, which might be a piece of dust or another impurity. When an impurity is not present in a drop of water, liquids can get cooled far below the temperature at which they would normally freeze. When the drops of freezing rain hit roadways, trees, and other objects, they abruptly change into a thick, solid layer of ice called glaze ice. This creates dangerous driving conditions and can damage trees.  An ice storm occurs when there is an especially large layer of glaze ice.

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