PSS

Storm Chasing in the Scale of F

by Andrew Wickenden ’09

Because measuring tornado wind speed during the event itself is not only dangerous but often impossible, Tetsuya Theodore Fujita developed the Fujita Scale, or F-Scale, in the early 1970s to categorize the storms based on the amount of damage they caused.

Since 2007, the Enhanced Fujita Scale (EF-Scale) — a revised version of the original — has been the standard for estimating tornado severity in the U.S., which can see more than 1,000 tornadoes each year.

“The F-Scale was revised because it became clear that the damage-based wind speed estimates weren’t totally accurate,” explains Nick Metz, assistant professor of geoscience. “The EF-Scale was the next logical improvement. Engineers and meteorologists slightly adjusted the scale and the wind speeds associated with damage.”

Each level of the scale — from EF0 to EF5 — corresponds to a level of damage and the theoretical range of wind speeds associated with this damage, from 65 miles per hour at the lower end of the EF0 range, to more than 200 miles per hour at EF5. Like the F-Scale, the EF-ratings are assigned to tornadoes after the storms have dissipated, when meteorologists survey the damage on the ground and estimate the range of wind speed.

“Are there trees down? Which direction did they fall? If a structure sustained damage, what was the quality of structure? What kind of damage? Were there rotating winds or straight line winds? In terms of damage surveys, meteorologists are investigators, piecing together evidence, trying to tell the story of the storm,” says Neil Laird, associate professor of geoscience.

For nearly two weeks this summer, as part of the Colleges’ geoscience curriculum, Metz, Laird and eight students forecasted and tracked storm systems across the Midwest and Central Plains, chasing severe supercell thunderstorms that had the potential to produce tornadoes.

After a three-day intensive on-campus workshop to prepare students with details about severe storms, storm-chasing simulation scenarios, and field-testing of the HWS mobile weather balloon system and other instrumentation, the group hit the road. Each morning a separate pair of students was tasked with providing a weather briefing to the rest of the group while identifying the best route to take to locate the day’s most promising severe storms.

After 11 days, the group had traveled through 14 states and covered 6,300 miles. Using handheld instruments, balloons rising from the ground to the upper atmosphere, instrumented kites collecting data in the lower atmosphere, radio-transmitted realtime weather information, and time-lapse photography, the students predicted how the atmosphere’s ingredients — moisture, temperature, and wind — would come together to produce storms most afternoons. This rich suite of measurements and data, along with the visual observation of the explosive development of cumulus clouds, allowed the group to witness multiple incredible storms and a tornado.

“It’s hard to fathom actually being up close and personal with severe storms until you are out there experiencing all aspects of the chase,” says Caitlin Crossett ’15, who is working toward her major in geoscience with a concentration in atmospheric science.

It was the mystery of the storms — and being able to see the weather and storms develop up close — that enticed Jeffery Rizza ’15.

“There are still many unknowns in the area of severe weather associated with supercells such as tornadoes and extreme hail,” says Rizza, a physics and environmental studies double major and a geoscience minor. “There are so many subtleties and details that went into predicting the development of a storm. It’s amazing that thousands of these severe storm events occur in the U.S. every year and yet we aren’t completely clear on the processes that produce them.”

 

Preparing Students to Lead Lives of Consequence.