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Snow squall

earth science Maturity 5-7 Next article →

A snow squall is a sudden weather event. It brings moderately heavy snowfall and strong, gusty winds. These winds blow the snow around. This often creates whiteout conditions. A whiteout is when visibility is very low. You might not be able to see the road or nearby objects. Snow squalls are similar to blizzards. However, they are different in two ways. They are localized in time or location. They may also have different amounts of snow accumulation.

Toronto lake effect frontal squall
Toronto lake effect frontal squall

There are two primary types of snow squalls. These are known as lake-effect snow and frontal snow squalls. Both types can reduce visibility significantly. They can also produce very heavy snow. Lake-effect snow occurs when arctic air moves over warm water. This happens during the winter months. The air moves over large expanses of open water. This process creates convective clouds. These clouds cause heavy snow showers because of the moisture.

Snowsquall line-Bourrasque neige frontal NOAA
Snowsquall line-Bourrasque neige frontal NOAA

To form lake-effect snow, specific conditions must be met. The temperature difference between the water and air is important. The surface temperature should be near the freezing mark. The lake must remain unfrozen. The path over the lake must be at least 100 kilometers long. Additionally, the directional wind shear with height should be small. This means the wind direction changes by less than 30 degrees from the surface to higher levels. These storms create narrow snow bands. These bands can produce many inches of snow per hour. The areas affected are called snowbelts.

Snowy Higddhway 4012
Snowy Higddhway 4012

Frontal snow squalls work differently. A frontal snow squall is an intense convective line. It is similar to a summer squall line. This happens when the temperature is near freezing at the surface. Strong convection develops in the air. This convection provides enough moisture for whiteout conditions. The wind causes intense blowing snow as the line passes. These squalls usually last less than 30 minutes at any single point. However, the moving line can travel over very large distances.

Snowsquall line-Bourrasque neige frontal NOAA
Snowsquall line-Bourrasque neige frontal NOAA

Forecasters look for specific signs to predict frontal squalls. They look for a sharp frontal trough. They also look for a wind shift. They watch for a low-level jet of more than 30 knots. The cold dome behind the trough must be at the 850-millibar level. It must also be at least 10 degrees Celsius colder than the air below it. Surface moisture also helps. Moisture from water or liquid precipitation raises the dew point. This helps saturate the boundary layer. This saturation increases convective available potential energy. This leads to deeper vertical growth in the clouds.

Snowsquall line-Bourrasque neige frontal NOAA
Snowsquall line-Bourrasque neige frontal NOAA

Both types of squalls can lead to thundersnow. Thundersnow is snow accompanied by lightning and thunder. This happens when there is large vertical growth and mixing. This can occur in lake-effect snow or frontal squalls. These storms are very dangerous for travelers. They affect motorists and airplanes. The change in weather is very sudden. Slippery roads and sudden whiteouts cause many accidents. In some cases, squalls can even become supercells. These powerful storms can form tornadoes.

Car into ditch bad winter weather hwy 404 south near stouffville rd Jan08
Car into ditch bad winter weather hwy 404 south near stouffville rd Jan08

History shows how dangerous these events can be. On January 9, 2015, a heavy snow squall hit Michigan. It occurred on the I-94 highway near Galesburg. The localized storm caused a massive pile-up. In this single event, 193 vehicles collided. This shows how quickly heavy snow can accumulate. It can also paralyze entire cities. Because they are so sudden, they are often more dangerous than blizzards.

Car into ditch bad winter weather hwy 404 south near stouffville rd Jan08
Car into ditch bad winter weather hwy 404 south near stouffville rd Jan08
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🖼️ Images & Media (4)
File:Toronto lake effect frontal squall.JPG
Toronto lake effect frontal squall.JPG
File:Snowsquall line-Bourrasque neige frontal NOAA.png
Snowsquall line-Bourrasque neige frontal NOAA.png
File:Car into ditch bad winter weather hwy 404 south near stouffville rd Jan08.jpg
Car into ditch bad winter weather hwy 404...
File:Snowy Higddhway 4012.jpg
Snowy Higddhway 4012.jpg
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