Forecasting Missouri’s severe storms
Posted February 22, 2012
Amanda Prasuhn
With weather events as varied as blizzards, heat waves, tornadoes and floods, Missourians rely on accurate forecasts to stay safe and informed. Luckily, atmospheric scientists and meteorologists have an ever-improving understanding of severe weather and reliable forecasting methods based on new technologies.
Severe weather formation
Anthony Lupo, an MU atmospheric science professor, says the North Atlantic and Arctic Oscillations, along with El Niño and La Niña, the systematic warming and cooling of tropical waters in the eastern Pacific Ocean, respectively, control weather circulation patterns over North America. Understanding these factors can help predict the severity of storm seasons in the Midwest.
“La Niña years tend to generate more tornadoes across the USA, for whatever reason,” Lupo says. Because last year was a La Niña year, there were a higher-than-average number of tornadoes. The Joplin, Mo., tornado of May 22, 2011 and the Mississippi-Alabama tornadoes of April 27 were some of the more memorable storms from last season, though they were unusual.
In reference to the Joplin tornado, Lupo says: “It’s very rare to have a tornado of that magnitude hit a city and move as slowly as it did. The average speed of a tornado is 25 miles an hour as it moves. This one was moving at about 10 miles an hour, so it had a lot more time to chew up things.”
Additionally, the Joplin tornado qualified as the most destructive category of tornado, an EF5.
The majority of severe storms are concentrated in the Midwest and the South because of a medley of ingredients that create perfect conditions for the formation of severe storms.
According to Lupo, geography is key. “No place else in the world has the conditions we have, and for that reason there are more tornadoes here and they’re more extreme.”
These conditions include the north-south Rocky Mountains, which funnel cold air into the plains, and the Gulf of Mexico, which provides warm, moist air.
The result, Lupo says, is instability, encouraging the formation of severe storm systems.
Spring is an optimal time for tornadoes and severe weather “because you get all the magic ingredients coming together,” Lupo says. Moisture, temperature contrast and strong winds are needed, but the element that creates tornadic thunderstorms is wind shear, which occurs when winds on the surface and winds aloft turn in different directions, sometimes with varying speeds.
Forecasting severe weather
Despite the magnitude of knowledge about how tornadoes form, forecasting any weather, let alone severe storms, is difficult “because the atmosphere is constantly changing,” says KOMU meteorologist Dave Schmidt. “It’s a living, breathing thing.”
“We can get out pretty accurately within two, three or four days. That’s improving all the time.”
Although viewers rely on broadcast meteorologists for forecasts and predictions, Schmidt says the raw data is available to anybody on the Internet, “but you have to know where to look” and how to interpret the data.
This information includes watches and warnings issued by the National Weather Service and detailed eight-day forecasts from the Storm Prediction Center in Norman, Oklahoma.
Michelle Bogowith, another KOMU meteorologist, relies on the National Weather Service in Springfield, Mo. Its balloon launches help with severe weather prediction by providing data from different levels of the atmosphere.
Meteorologists also look at CAPE, convective available potential energy, which is “a measure of how much ‘juice’ is in the atmosphere” to ignite severe storms, Bogowith says.
The problem with forecasting severe weather, according to Lupo, is that the “timescale of prediction is only as good as the timescale of the phenomenon itself.” For thunderstorms, the timeframe is around a half hour to two hours, which means that a prediction is only good for that long.
Predicting the 2012 season
The 2011-12 winter started out under the influence of La Niña, indicative of severe storms in the spring. However, conditions changed and the pattern weakened, resulting in a mild winter and a lack of moisture, which could hinder severe storm formation this season.
“I don’t think we’ll have an active season like we did last year,” Bogowith says. “That’s one of those freak incidences that happens every 40, 50 years.”
Lupo says that this year is more reminiscent of an El Niño year because of the Arctic Oscillation, which “tends to put more severe weather in the traditional Tornado Alley area, which is Oklahoma, Kansas, Texas, and, to some extent, Missouri.” Nevertheless, because of droughts in the Great Plains states, Lupo says to expect more tornadoes to Missouri’s east and south because those areas have more moisture to support severe thunderstorms.
Fortunately for Missourians, the National Weather Service in Missouri has offices that are “renowned throughout the country” for their forecasting abilities, Lupo says. “Missourians can be confident that we have a little extra protection that most people don’t have.”
Although tornadoes have received increased media attention in recent years, there are actually fewer, weaker tornadoes today than in the past. “There seems to be more tornadoes simply because we can capture more of them than ever before,” Lupo says.
Bogowith attributes this to increases in rural populations and improved communication technologies.
The weather is getting more variable, though, says Lupo, because 1950 to 2000 was a period of stable weather patterns. “People got used to the notion that the year to year changes weren’t so great, but that’s not the reality.”
Forecasts have drastically improved in accuracy, but there is still much to learn in the fields of atmospheric science and meteorology.
“We’ve learned a lot since the 1980s, when there was just beginning to be a push at looking at small-scale weather,” Lupo says.
According to Bogowith, forecasting accuracy has increased significantly in the past decade. “It had to be 20, 30 years ago that you could barely predict one day out. There’s so much that we don’t know, that we’re still learning every day.”
