Severe Weather Impacts: Winter Thunderstorms and Aviation

Thunderstorms occur in all 50 states and U.S. territories. At any given time, there are approximately 2,000 thunderstorms in progress worldwide—and lightning strikes the Earth an average of 100 times per second! Although thunderstorms can occur at any day and time, summer thunderstorms (May to September) are more frequent than winter thunderstorms (October to April). Winter thunderstorms have been less studied than summer thunderstorms, but scientists have documented differences between them. Winter thunderstorms are generally shorter in time and have lower lightning frequency. Warm air moves upwards (the updraft) at a slower speed to form clouds and rain in winter thunderstorms, and thunderclouds have a smaller vertical extent or height. Winter thunderstorms that occur when temperatures are relatively warm are called cold-season thunderstorms.

You’re probably familiar with many of the hazards that come along with thunderstorms, including lightning, flash flooding, hail, heavy winds and tornadoes that can damage property and pose health risks. But did you know that thunderstorms can impact aviation?

Winter thunderstorms are rare – they’re also more difficult to forecast because the procedures for detection and warning are designed for summer thunderstorms. It can be difficult for pilots to estimate the risk of flying through cumulonimbus clouds (associated with thunderstorms) in winter because they occupy less space and seem harmless. Flying into these clouds can produce lightning – in 90 percent of cases the lightning discharge is initiated by the aircraft itself. Studies in Japan showed that the majority of lightning strikes in summer occurred when aircrafts were at a height of 1.8 to 3.6 miles; in winter, lightning strikes occurred when aircrafts were at a height of zero to 1.8 miles. During winter, planes are more often struck during landing and takeoff. Lightning can produce direct damage such as holes in the skin of the plane, as well as indirect damage such as magnetic disturbance or damage to electronic systems. Winter thunderstorms occur more often in the central part of the United States, the Great Lakes region, and along the east coast all the way up to Canada.

(Source: Makela, A., E. Saltikoff, J. Julkunen, I. Juga, E. Gregow, and S. Niemela. 2013. Cold-season Thunderstorms in Finland and their Effect on Aviation Safety. Bull. Amer. Meteor. Soc. 94:847-858. and Slangen, A. 2008. Probabilistic Forecasts of Winter Thunderstorms Around Schiphol Airport Using Model Output Statistics. Koninklijk Nederlands Meteorologisch Instituut. 53 pp. and National Oceanic and Atmospheric Administration. Severe Weather 101: Winter Weather Basics. Accessed online 5 November 2013. http://www.nssl.noaa.gov/education/svrwx101/winter/  and National Oceanic and Atmospheric Administration. NOAA Study Finds Fishing Tops U.S. Lightning Death Activities. Accessed online 5 November 2013. http://www.noaanews.noaa.gov/stories2013/20130624_lightningsafety.html and Federal Aviation Administration. 2010. Thunderstorms and Interference. Air Traffic Bulletin. 1-3 pp. Accessed online 5 November 2013. http://www.faa.gov/air_traffic/publications/bulletins/media/atb_may_10sp.pdf and Federal Aviation Administration. Thunderstorms. Accessed online 5 November 2013. http://www.faa.gov/documentlibrary/media/advisory_circular/ac%2000-6a%20chap%2010-12.pdf)

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