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Minooka Community High School hosts weather spotting class

Jim Allsop trains potential weather spotters during a training held at Minooka Community High School - South Campus on Thursday night.
Jim Allsop trains potential weather spotters during a training held at Minooka Community High School - South Campus on Thursday night.

MINOOKA – It may not have looked or felt like spring recently, but that season officially is here – and it brings with it tornado season.

More than 160 people attended Thursday night a session at Minooka Community High School South Campus to learn about being a trained weather spotter.

The event – hosted by Channahon Police Department, Grundy County Emergency Management Agency and Will County EMA – was taught by Jim Allsop, formerly with the National Weather Service in Romeoville.

“We need ground truth about what’s going on to supplement radar,” Allsop said.

Attendees viewed a slide show and video presentation that demonstrated what to look for when potentially bad weather strikes. Allsop explained everything from a single-cell (pulse) thunderstorm to the potentially deadly supercell thunderstorm.

He talked about the difference in clouds, noting a shelf cloud – a low, horizontal wedge-shaped cloud – looks ominous but doesn’t have the threat of tornadic activity. A wall cloud – a localized, persistent, often abrupt lowering from a rain-free base – does. People often mistake the two, he said.

“As a spotter looks for a wall cloud, they look for damaging winds,” Allsop said. “A shelf cloud is really not a primary tornado threat.”

He explained shelf clouds signify an area of downdraft and outflow while wall clouds indicate an area of updraft and inflow.

“Swirly clouds freak people out,” he said. “But the downdraft is outflow, which some spotters call being in the whale’s mouth.”

He explained that less than 20 percent of wall clouds produce a tornado, and only 5 percent of thunderstorms are supercells, with the potentail for damaging winds and tornadoes.

He told the potential spotters where the safest place to be is when out spotting or chasing storms.

“When spotting a supercell try to position yourself with rain to your right and updraft to your left,” Allsop said. “This is called the Right Hand Rule.”

He said if you are south of the tornado in this area you are relatively safe.

Jim Lutz with the Grundy County EMA said that it’s important to be educated in order to stay safe.

“Not every tornado has a warning issued,” he said.

Sharon Alonzo of Morris attended with her son Nick, a sophomore at Morris Community High School. Nick, a self-proclaimed weather fanatic, had already taken an online training module.

“The course I took online was similar, but attending this two-hour training helps you to retain the facts better,” he said. “Weather happens every day, it can be dangerous and it’s better to know so you can plan for it.”

Allsop explained to the crowd that trained spotters should call the National Weather Service to report activity. A spotter should identify himself or herself, and be ready to report when and where a weather event occurred so the weather service can correlate it to radar data. Specifics matter, he added.

“When you are reporting, don’t exaggerate,” he said.

He said to use standard objects if reporting hail, such as a golf ball, a quarter or a nickel. Anything larger than a quarter and the NWS issues a warning.

“If it’s just wind gusts with damage report that,” Allsop said. “Be specific, if it broke a branch off the tree say how large the branch is.”

People interested in being trained weather spotters can check with Grundy County EMA or Will County EMA to find out when they are hosting a weather spotter class, or find one online.


• Shelf Cloud – A low, horizontal wedge-shaped arcus cloud, associated with a thunderstorm gust front (or occasionally with a cold front, even in the absence of thunderstorms). Unlike the roll cloud, the shelf cloud is attached to the base of the parent cloud above it (usually a thunderstorm). Rising cloud motion often can be seen in the leading (outer) part of the shelf cloud, while the underside often appears turbulent, boiling, and wind-torn.

• Wall Cloud – A localized, persistent, often abrupt lowering from a rain-free base. Wall clouds can range from a fraction of a mile up to nearly five miles in diameter, and normally are found on the south or southwest (inflow) side of the thunderstorm. When seen from within several miles, many wall clouds exhibit rapid upward motion and cyclonic rotation. However, not all wall clouds rotate. Rotating wall clouds usually develop before strong or violent tornadoes, by anywhere from a few minutes up to nearly an hour.

• Supercell – A thunderstorm with a persistent rotating updraft. Supercells are rare, but are responsible for a remarkably high percentage of severe weather events - especially tornadoes, extremely large hail and damaging straight-line winds. They frequently travel to the right of the main environmental winds.

• Tornado – A violently rotating column of air in contact with the ground and extending from the base of a thunderstorm. A condensation funnel does not need to reach to the ground for a tornado to be present; a debris cloud beneath a thunderstorm is all that is needed to confirm the presence of a tornado, even in the total absence of a condensation funnel.
Source: National Oceanic and Atmospheric Administration

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