Central U.S. May Be in Store for a 3-Day Tornado Outbreak

What's This?

Homeowners look over the damaged a tornado-damaged home Wednesday, Nov. 20, 2013, in Kokomo, Ind. after intense thunderstorms swept across the Midwest.

Image: Darron Cummings/Associated Press

By Andrew Freedman2014-04-24 19:51:50 UTC

America’s tornado drought looks like it may end as early as this weekend, as a potent weather system moves into the Plains states and slowly lumbers toward the Mississippi River Valley. The storm system is likely to set off a multi-day severe weather outbreak, with thunderstorms capable of producing tornadoes forming on Saturday, Sunday and Monday.

If it occurs, the potential tornado outbreak would boost 2014’s tornado tally, which is currently in record low territory, and could end the long stretch without a tornado-related fatality as well.

See also: This Year May Be the Slowest Start to the U.S. Tornado Season, Ever

Bill Bunting, chief of operations at the Storm Prediction Center in Norman, Okla., told Mashable that the ingredients necessary for a large-scale severe weather outbreak are likely to start appearing on Saturday in the High Plains states. These ingredients include a strong low-pressure area in the upper atmosphere, which will trigger the development of a surface low in the Plains, as well as abundant low-level moisture and winds that vary in speed and direction with height.

Outlook for severe weather three days ahead (red) and four days (purple).

More specifically, the counter-clockwise circulation around the surface low will draw moisture from the Gulf of Mexico northward, and strong winds at altitudes of about 10,000 to 20,000 feet above ground level will provide the wind shear needed for tornadoes to form. (Wind shear refers to winds that change speed or direction with height, or both.)

“This is a very strong upper system with very strong wind shear,” Bunting said.

Bunting said people from Omaha to New Orleans need to watch weather conditions closely this weekend and be prepared to seek shelter.

“We are on track for at least a 3-day round of severe weather,” he said. “It’s difficult to say at this time just how significant” of an event this will be, Bunting said.

Computer model projection of jet stream winds on April 28, 2014. This shows the deep dip in the jet stream over the Plains, the huge High over Canada, and another dip or trough of low pressure off the East Coast.

Image: WeatherBell Analytics

The threat on Saturday likely will focus on the High Plains and Eastern Plains, affecting cities such as Omaha, Neb.; Lincoln, Neb.; Wichita, Kan.; Oklahoma City, Olka.; and Abilene, Texas. The storms’ target will shift east on Sunday, with cities from Omaha to Little Rock in the threat area.

On Monday, severe thunderstorms may threaten Columbia, Mo.; St. Louis, Mo.; Memphis, Tenn.; Little Rock, Ark.; Nashville, Tenn.; Birmingham, Ala.; and potentially as far south as New Orleans, Bunting said.

One of many tools that forecasters use to anticipate tornado outbreaks is analogs, which involve taking a look back at what happened in history when conditions were similar to what they are forecast to be.

In this case, the analogs for the upcoming weekend include some notorious severe weather outbreaks, including the May 3, 1999 tornado outbreak in Oklahoma. During that outbreak, an EF-5 tornado ripped through the Oklahoma City suburb of Moore, costing $1 billion in damage and killing 36. (An EF-5 tornado struck Moore again in 2013.)

However, Bunting said history won’t necessarily repeat itself this weekend.

"Using analogs to say that because something happened years ago with a similar setup it will happen again,” Bunting said, ignores the importance of small-scale details that will determine where thunderstorms form and how strong they are.

Such small-scale details include where frontal boundaries form, and whether the strongest wind shear is located above the areas that have the greatest chance for thunderstorm development.

Bunting said forecasters are concerned that the quiet tornado season so far may have lulled people in "Tornado Alley" and elsewhere into complacency, which is why they’re trying to get the word out early about this threat. “Having been so long since there’s been a significant severe weather event, people may not be thinking about it as they would’ve if we had had a couple of events,” Bunting said.

The storms will not only pose a tornado threat, but also flash flooding, since they will be slow-movers.

In fact, the entire weather pattern across North America will be temporarily blocked, or stuck, into the first week of May. An unusually sprawling and strong area of high pressure across southern Canada will prevent the storminess in the Mississippi River Valley from moving east and exiting the East Coast, keeping much of the U.S. cooler and wetter than average for this time of year, and accentuating the flood and severe thunderstorm threat.

Have something to add to this story? Share it in the comments.

Topics: Climate, severe weather, thunderstorm, tornadoes, U.S., US & World