More tornadoes in the most extreme U.S. tornado outbreaks

Area of Science:

• Atmospheric science
• Climatology
• Extreme weather events

Background:

• Tornadoes and severe thunderstorms cause significant annual fatalities and property damage in the U.S.
• Severe thunderstorm insured losses in the U.S. reached $8.5 billion in the first half of 2016.
• Tornado outbreaks, sequences of closely occurring tornadoes, are responsible for the most substantial U.S. impacts.

Purpose of the Study:

• To analyze trends in the frequency of U.S. tornado outbreaks.
• To investigate the relationship between outbreak severity and frequency.
• To model the behavior of extreme tornado outbreak events.

Main Methods:

• Extreme value analysis was employed to study tornado outbreak data.
• Extreme value distributions with time-dependent parameters were used for modeling.
• Analysis considered indicators of multidecadal climatic variability.

Main Results:

• The frequency of U.S. tornado outbreaks with a high number of tornadoes is increasing.
• The rate of increase is steeper for more extreme outbreaks.
• Observed upward trends in extreme meteorological environments do not match global warming expectations.

Conclusions:

• Extreme tornado outbreaks are becoming more frequent and intense.
• The observed trends suggest factors beyond current global warming projections may be influencing severe weather.
• Further research is needed to understand the drivers of these increasing tornado outbreak trends.