A Warmer Pacific Ocean Leads to More Tornadoes

Can warming oceans affect weather over landmasses thousands of miles away? In our highly connected globe, it would appear the answer is yes. Researchers from the University of Missouri have discovered that warmer sea surface temperatures in the Pacific Ocean play a role both in strengthening tornadoes, as well as influencing where they are likely to form.

Looking at data from over 56,000 "tornado-like" events over the past 60 years, the scientists discovered that when surface temperatures in the Pacific were warmer than average, during the warm phase of the Pacific Decadal Oscillation, the US experienced 20.3 percent more tornadoes rated 2 to 5 on the Enhanced Fujita scale.

The EF scale is a set of wind estimates for a given tornado, going from 0 to 5. A tornado rated as 0 will have a 3 second blast of wind in the 65-85 mph range. One with an EF scale rating of 2 will produce a wind gust of 111-135 mph. At the high end, an EF 5 tornado produces gusts of over 200 mph. For example, the 2007 tornado that destroyed about 95 percent of Greensburg, Kansas was rated EF5.

Warmer than average sea surface temperatures also led to tornadoes tending to occur in the west and north of "tornado alley" in Texas and Oklahoma. When temperatures are cooler than average, during the PDO cool phase, more tornadoes got pushed in Tennessee, Illinois, and Indiana.

This trajectory change comes down to shifts in the jet stream caused by the differences in ocean temperatures, the researchers say.

Now that the effects of warmer and cooler Pacific temperatures on tornado formation are known, researcher Laurel McCory points out, "weather forecasters have another tool to predict dangerous storms and inform the public of impending weather conditions." McCory also notes that this research can be inform budget and planning decisions at the state and town level for tornado season.

It also raises some intriguing questions worthy of further research. The big one is if sea surface temperature increases that are caused by climate change and not seasonal cycles will also affect tornadoes in a similar fashion.

As recent research has shown, the Pacific is soaking up vast amounts of carbon emissions, more than than initially thought, leading to a flattening in the amount of global warming that's happened. Which is shocking considering that the first decade of this century is still the warmest since modern instrumental records began being kept.

This temperature dampening won't go on for ever though. When it stops, much stronger warming is expected to happen. And when it does, what will it mean for the strength and location of tornadoes?

It's a question with very practical implications for the economy and preservation of life. In 2011, over 550 people died in the US from tornadoes.