Three questions about the devastating tornado outbreak last weekend

Three questions about the devastating tornado outbreak last weekend

On Friday night, an unusually violent and long-lasting tornado erupted across six states. It caused at least 88 deaths, damaged houses, and divided communities. Disaster relief workers continued to search for missing persons in the wreckage.

Tornado outbreaks-meaning a series or clusters of tornadoes that occur continuously-may be One of the deadliest record on file. Its 200-mile route through Arkansas, Illinois, Missouri, Mississippi, Tennessee, and Kentucky has almost no precedent.Tornadoes are also unusually strong, and the wind Speed ​​may be as high as 205 mphMeteorologists are still analyzing the data, but on the strength of the enhanced Fujita scale tornado (ranging from 0 to 5), it may be classified as an EF4 or EF5 storm.

In order to learn more about what caused this tornado to be so destructive, the state of the planet is Chiara Lepore, Who studies natural disasters at Columbia University’s Lamont-Dougherty Earth Observatory.

What made the tornado last weekend so unusual?

Chiara Lepore is an associate research scientist at Columbia University’s Lamont-Dougherty Earth Observatory.

It’s important to note that it’s too early to know exactly how many tornadoes actually occurred, or to learn more about the intensity of tornadoes and the size or length of their paths, but from Preliminary report The characteristics and destructiveness of the tornado outbreak last weekend were few, and there may even be no precedent.

From the preliminary report, it seems (again, we should be cautious until the National Weather Service office end Their Investigation work) We may be observing a three-state/four-state tornado, which may have stayed on the ground for more than 200 miles, and the parent supercell that caused the major tornado to erupt May have driven more than 600 miles. We are observing a number of high-intensity tornadoes, the intensity of which exceeds EF3 Enhanced Fujita Scale.

Fortunately, these statistics are actually not common, and definitely not common at this time of the year. In addition, this outbreak occurred farther north than the typical area where tornadoes erupt in winter.

What conditions caused the severity of the storm?

It’s really-like some Excellent scientist Say in front of me — An example of a “perfect storm” in severe weather.

Very warm and humid air with record-breaking high temperatures-for example, in Nashville, 83 degrees Fahrenheit, and the dew point in the 1970s. The situation in mid-December or autumn is indeed atypical, but it is more like spring.Coupled with very strong and continuous windshear, the conditions for severe weather outbreaks have matured, and the National Oceanic and Atmospheric Administration’s Storm Prediction Center has determined Two days in advanceThe powerful low-pressure system moving eastward interacts with these conditions, pulling the warm and humid air further north. All these ingredients gathered together, mainly producing a very big and strong storm. Moreover, the area with these conditions is very broad and can exist for a long time.

In addition to atmospheric conditions, this outbreak Untie at night And pass through Densely populated area, Thereby increasing its danger to humans.

Is it related to climate change?

The answer is complicated—or more complicated than the “yes” or “nos” of some other processes. I think we can split it in two: have we seen changes in tornadoes recently? Do we know whether we should anticipate changes in tornadoes in the future and in a warm climate?

Regarding the recent past, the changes in tornadoes are “subtle”. For example, we did not see “obvious” trends, such as annual totals.Until this outbreak, in fact, for 2021, we are Well below average In terms of tornado events. As we all know, storm reports have very large year-to-year changes in the occurrence of tornadoes. What seems to have changed recently is where these tornadoes occur– Shifting to the east of the U.S. — And their timely “gathering”, there may be fewer tornado days in a year, but More tornadoes will occur when they erupt.

On the contrary, regarding the possible link between climate change and tornadoes, one of the main challenges in understanding the prediction of severe storms in the future is to analyze how/when/where our planet will be in a warmer climate (i.e. climate model , For example contained in CMIP6) Cannot directly simulate severe storms, so tornadoes cannot be simulated.

The spatial scale of severe storms—producing hail, tornadoes, and destructive linear winds—usually represents only a small fraction of the typical grid size of these models. In a way, the model “can’t see them.”

What the model can reproduce is the large-scale atmospheric volume, when they appear in certain combinations, they are known to cause severe storms.

In fact, US climate model predictions indicate that as our planet continues to warm, the likelihood of conditions favorable to strong storms in general will increase. The main driving mechanism is temperature increase and moisture increase, which are some of the main components of storm updraft.One Recently Published My work with many other co-authors attempts to quantify these changes based on global CMIP6 data. The expected increase in conditions conducive to severe storms varies globally. For the United States, we expect that from now on, every 1 degree Celsius increase in global temperature will increase by 14-25%. However, there is a big caveat: these are an increase in the frequency of conditions conducive to severe weather, they are not real storms, only some of these storms will produce tornadoes. So the uncertainty is still great.