Kansas City, Mo. ? Even expert storm chases would have struggled to decipher the difference between the tornado warnings sent last May before severe weather hit Joplin and, a few days later, headed again toward downtown Kansas City.

The first tornado was a massive EF-5 twister that killed 161 people as it wiped out a huge chunk of the southwest Missouri community. The second storm caused only minor damage when two weak tornadoes struck in the Kansas City suburbs.

In both cases, the warnings were harbingers of touchdowns. But three out of every four times the National Weather Service issues a formal tornado warning, there isn’t one. The result is a “cry wolf” phenomenon that’s dulled the effectiveness of tornado warnings, and one the weather service hopes to solve with what amounts to a scare tactic.

In a test that starts Monday, five weather service offices in Kansas and Missouri will use words such as “mass devastation,” ”unsurvivable” and “catastrophic” in a new kind of warning that’s based on the severity of a storm’s expected impact. The goal is to more effectively communicate the dangers of an approaching storm so people understand the risks they’re about to face.

“We’d like to think that as soon as we say there is a tornado warning, everyone would run to the basement,” said Ken Harding, a weather service official in Kansas City. “That’s not how it is. They will channel flip, look out the window or call neighbors. A lot of times people don’t react until they see it.”

The system being tested will create two tiers of warnings for thunderstorms and three tiers for tornadoes, each based on severity. A research team in North Carolina will analyze the results of the experiment, which runs through late fall, and help the weather service decide whether to expand the new warnings to other parts of the country.

Laura Myer, a social science research professor at Mississippi State University, said people she has interviewed want more advance warning about a potential tornado strike and more information on the specific locations where the storms are expected to hit.

“We have found in Mississippi and Alabama and various other Southern states that people feel they would constantly be going to a shelter if they heeded every tornado warning,” she said. “For people in mobile homes, that’s the craziest thing.

“To get to a shelter, they have to leave home,” she said. “They feel like if they left during every watch or warning, they would be on the road all the time.”

The primary audiences for weather service’s written bulletins are broadcasters who issue warnings on the air and emergency management agencies that activate sirens and respond to the storm’s aftermath. In the event of a Joplin-like tornado, the new-look warning would have an urgency hard to ignore.

Andy Bailey, a meteorologist with the National Weather Service office in Pleasant Hill, Mo., said it might look something like this: “THIS IS AN EXTREMELY DANGEROUS TORNADO WITH COMPLETE DEVASTATION LIKELY. … SEEK SHELTER NOW! … MOBILE HOMES AND OUTBUILDINGS WILL OFFER NO SHELTER FROM THIS TORNADO — ABANDON THEM IMMEDIATELY.”