What Is Thundersnow? How It Works and Where to Find It


Thundersnow
Thundersnow is a thunderstorm when it’s snowing. (Jeremy Bishop and Todd Helmenstine)

Thundersnow is a snowstorm with lightning and thunder. It’s also called a thunder snowstorm. Thundersnow is rare, even where snow is common. It only occurs during serious snowstorms and blizzards. Examples of storms that produced thundersnow include the Blizzard of 1978, the 2018 bomb cyclone that hit the eastern United States, Winter Storm Grayson (New York), and Winter Storm Niko (Massachusetts).

How Thundersnow Works

Thundersnow requires the same general conditions as an ordinary thunderstorm. Warm, moist air rises toward a cold air mass. In a normal thunderstorm, tall and narrow clouds rise from a warm updraft at the surface to about 40,000 feet. This creates atmospheric instability and the separation of electrical charge that produces lightning. Lightning superheats the air, with rapid cooling causing sound waves known as thunder.

Thundersnow is rare because the ground temperature needs to be warmer than the clouds, warm enough to hold enough moisture, yet cold enough for water to freeze into snow. The problem is that in the winter both the surface and the lower troposphere of the atmosphere are cold and have low dew points. Snow, when it falls, usually stabilizes the atmosphere so there isn’t enough convection to produce lightning. Instead of the tall clouds of a regular thunderstorm, thundersnow forms from flat snow clouds that become unstable and experience dynamic lifting. Three situations cause thundersnow:

  1. A normal thunderstorm runs into cold air at the edge of a warm or cold front. Alternatively, a thunderstorm can run into a region of cold air at high elevation, like a mountain. The rain changes into freezing snow or rain.
  2. A cold front passes over warming water, charging it with humidity and providing lift. This is the type of thundersnow most often found near the ocean or Great Lakes.
  3. Synoptic forcing causes flat snow clouds to get bumpy or develop what are called turrets. The turrets are subject to different conditions than the lower layers, producing instability. Turbulence causes friction between ice crystals or water molecules, resulting in a gain or loss of electrons. When the electrical charge difference between two bodies becomes large enough, lightning strikes. This type of thundersnow can arise in an extratropical cyclone.

Difference From Normal Thunderstorms

Obviously, a normal thunderstorm is associated with rain while thundersnow has snow. There are other differences, too. Lightning looks different during a snowstorm. In a regular thunderstorm, lightning is often blue or violet. Lightning in a snowstorm often appears white or golden and is brighter than normal because it’s reflected by snow. Thunder sounds different, too. Snow muffles thunder, so it sounds muted and isn’t heard as far away as regular thunder. Thundersnow thunder is heard within 2 to 3 miles (3.2 to 4.8 kilometers) from its lightning strike, but regular thunder may be heard many miles from its source.

Where to Find Thundersnow

On average, only 6.4 thundersnow events occur worldwide in any given year. Obviously, a place has to get cold enough to snow, but other factors affect the likelihood of thunderstorm formation in the winter. Geography plays a big role in thundersnow formation. Areas with favorable conditions include:

  • Mountains
  • Coasts
  • Great Plains
  • Lake-effect regions

Cities with thundersnow include Halifax, Nova Scotia, Canada; Bozeman, Montana, US; New York City, US; and Jerusalem. Areas reporting more thundersnow events than average include Mount Everest, the Sea of Japan, all of Great Britain, the Great Salt Lake, the Great Plains of the midwestern United States, the Great Lakes of the US and Canada, and higher elevations in Israel and Jordan.

The time of year matters, too. Thundersnow is more common late in winter, ranging from March to May in the Northern Hemisphere. The peak month is March. Coastal regions may get thundersnow with sleet, freezing rain, or hail instead of snow.

Thundersnow Hazards

Thundersnow may be more dangerous than the average thunderstorm. It’s usually associated with severe winter storms and blizzards, so it may be accompanied by poor visibility, dangerously cold temperatures, and sometimes tropical force wind. High wind introduces a windchill factor, making frostbite a serious concern. Snowfall rates tend to be heavy, with rates between 2 to 4 inches (5 to 10 centimeters) per hour. Because conditions are drier than during rain, there is an increased chance lightning can cause a fire. The lightning produced during thundersnow is more likely to have a positive electrical charge than normal lightning. Positive polarity lightning is more destructive than negative polarity lightning. It can be up to ten times stronger, delivering up to one billion volts and 300,000 amps of charge. Positive lightning strikes can hit over 25 miles away from the source of precipitation. They often damage power lines.

References

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