What Is Thundersnow and How Does It Work

Thundersnow is a snowstorm accompanied by thunder and lightning. The phenomenon is rare, even in areas prone to snow. Youre not likely to get thunder and lightning during a gentle snowfall. The weather needs to be seriously bad. Examples of storms with thundersnow include the bomb cyclone of 2018,  Blizzard of 1978  (northeastern United States), Winter Storm Niko (Massachusetts), and Winter Storm Grayson (New York). Key Takeaways: Thundersnow Thundersnow refers to a snowstorm that produces thunder and lightning.Thundersnow is rare. It sometimes occurs on  plains, mountains, or coastlines, or  with lake-effect snow.The thunder of thundersnow is muted. The lightning appears whiter than usual and may carry a positive charge.Depending on the conditions, the precipitation might be freezing rain or hail instead of snow.   Where to Find Thundersnow Obviously, if it never gets cold enough to snow, thundersnow is out of the question. In any given year, an average of 6.4 events is reported worldwide. While thundersnow is uncommon  under any circumstances, some locations have more favorable conditions than others: Great plainsMountainsCoastlinesLake-effect regions Areas reporting higher-than-average thundersnow events include the eastern side of the Great Lakes of the United States and Canada, the plains regions of the midwestern United States, the Great Salt Lake, Mount Everest, the Sea of Japan, Great Britain, and elevated regions of Jordan and Israel. Specific cities known to experience thundersnow include Bozeman, Montana; Halifax, Nova Scotia;  and Jerusalem. Thundersnow tends to occur late in the season, typically April or May in the Northern Hemisphere. The peak formation month is March. Coastal regions may experience sleet, hail, or freezing rain rather than snow. How Thundersnow Works Thundersnow is rare because the conditions that produce snow tend to have a stabilizing effect on the atmosphere. In the winter, the surface and lower troposphere are cold and have low dew points. This means there is little moisture or convection to lead to lightning. Lightning superheats the air, while the rapid cooling produces the sound waves we call thunder. Thunderstorms can form in winter, but they have different characteristics. A typical normal thunderstorm consists of tall, narrow clouds that rise from a warm updraft leading from the surface up to around 40,000 feet. Thundersnow usually forms when layers of flat snow clouds develop instability and experience dynamic lifting. Three causes lead to the instability. A normal thunderstorm at the edge of a warm or cold front can run into cold air, changing rain into freezing rain or snow.Synoptic forcing, such as might be seen in an extratropical cyclone, can lead to thundersnow.  The flat snow clouds become bumpy or develop what are called turrets. Turrets rise about the clouds, making the top layer unstable. Turbulence causes water molecules or ice crystals to gain or lose electrons. When the electrical charge difference between two bodies becomes large enough, lightning occurs.A cold air front passing over warmer water can produce thundersnow. This is the type of thundersnow most often seen near the Great Lakes or near and ocean. Differences From a Normal Thunderstorm The obvious difference between a typical thunderstorm and thundersnow is that a thunderstorm produces rain, while thundersnow is associated with  snow. However, the thunder and lightning of thundersnow are different, too. Snow muffles sound, so thundersnow thunder sounds subdued and doesnt travel as far as it would in a clear or rainy sky. Normal thunder may be heard miles from its source, while thundersnow thunder tends to be restricted to a 2 to 3 mile (3.2 to 4.8 kilometer) radius from the lightning strike. While thunder may be muted, lightning flashes are enhanced by reflective snow. Thundersnow lightning typically appears white or golden, rather than the usual blue or violet of thunderstorm lightning. Thundersnow Hazards The conditions that lead to thundersnow also lead to dangerously cold temperatures and  poor visibility from blowing snow. Tropical force wind is possible. Thundersnow is most common with blizzards or severe winter storms. Thundersnow lightning is more likely to have a positive electrical charge. The positive polarity lightning is more destructive than usual negative polarity lightning. Positive lightning may be up to ten times stronger than negative lightning, up to 300,000 amperes and one billion volts. Sometimes positive strikes occur over 25 miles away from the point of precipitation. Thundersnow lightning can  cause a fire or damage a power line. Sources Patrick S. Market, Chris E. Halcomb, and Rebecca L. Ebert (2002). A Climatology of Thundersnow Events over the Contiguous United States. American Meteorological Society. Retrieved 20 February 2018.Rauber, R.M.; et al. (2014). Stability and Charging Characteristics of the Comma Head region of Continental Winter Cyclones.  J. Atmos. Sci.  71  (5): 1559–1582.