Estimating the global distribution of severe thunderstorms and tornadoes
Severe thunderstorms are a hazard not just in the United States, but around
the world. Our understanding of their distribution in space and time is limited
by problems in our physical understanding of the processes, and in the observational
databases. Even the best severe thunderstorm database, the US record of tornadoes,
is incomplete and inconsistently collected. As a result, estimating the distribution
of severe thunderstorms from the reports is practically impossible.
One way around the problem is to use the kinds of relationships between large-scale environmental conditions and severe thunderstorm occurrence, originally developed to help in forecasting, to estimate where severe thunderstorms and tornadoes are likely. A popular method is to use observations from weather balloons and relate observed weather to the observed conditions in which the weather forms. Since the large-scale conditions are observed more consistently, the occurrence of severe thunderstorms can be inferred from the observation of favorable environments.
To extend this work around the world, scientists at NSSL used global reanalysis data from the National Center for Atmospheric Research and the National Centers for Environmental Prediction. This dataset estimates the global environmental conditions every six hours starting in 1957. Analysis of the distribution of environments favorable for significant severe thunderstorms (2 inch or larger diameter hail, hurricane force winds, and F2 or stronger tornadoes) and significant tornadoes (F2 or greater) shows where those events are more likely to occur. Severe thunderstorm environments are concentrated to the east of north-south mountain ranges, such as the Rockies and the Andes. The tornado distribution is dominated by the central part of the United States.
This work is the beginning of a process to look at possible
climate change effects on severe thunderstorms, occurrence and distribution.
