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All the right ingredients to make a tornado

Posted on 05/17/2018
All the right ingredients to make a tornadoStory by Baker Geist Weld County Communications Specialist, photos from Greg Hanson

Anyone familiar with Weld County weather knows that tornadoes occur often, but they’re usually small, predictable and happen in the afternoon and out in the open plains. In contrast, the Weld County tornado that occurred on May 22, 2008, was unique in its direction, timing, power and size.

In general, most tornadoes in Weld County track eastward; however, the Weld County tornado traveled in a strange direction, from the southeast to the northwest. This was due to a low-pressure system that formed in the days before May 22. The system moved along the southwestern United States before eventually traveling north through Colorado.

Meteorologist Greg Hanson began working for the National Weather Service in 1988. “It was the powerful low-pressure system that actually helped spawn the storm and created the jet stream pattern that made it curve back a little more northwest than we would normally see,” said Greg Hanson, Warning Coordinator Meteorologist for the National Weather Service.

The timing of the tornado was also odd as it first touched down in the Platteville and Gilcrest area shortly before noon. Of the 263 Weld County tornadoes recorded by the National Oceanic Atmospheric Administration (NOAA) since 1950, only six have occurred in the 11 o’clock hour.

On May 22, weather activity began with a thunderstorm southeast of Platteville. Hanson said the thunderstorm contained all the necessary elements to create a rotating supercell thunderstorm. Those elements included changes in wind speed and wind direction which combined with the low-pressure system to bring a large tornado so early in the day.

“The dynamics, the big low-pressure area to the west and the jet stream were all strong enough to make the storm kick-off way earlier than it should have,” Hanson said. “We were actually expecting very strong thunderstorms in the afternoon but further east out on the plains. This was one that happened closer to the mountains because the weather in the upper layer of the atmosphere was so powerful.”

The supercell thunderstorm that spawned the tornado was also responsible for the storms’ power and speed, allowing it to track 39 miles and impact the communities of Gilcrest, Platteville, Milliken, Johnstown, Greeley and Windsor before dissipating north of Wellington in Larimer County. Hansen explained that while only 10 to 20 percent of supercells produce tornadoes, when tornadoes do form, they are the most powerful.
In addition to traveling a great distance, the tornado’s power also came from its size, something not normally seen in the weaker tornadoes that form in the plains. The tornado’s wind speed was so great — reaching 150 miles per hour — that it created funnels a mile wide.

A meteorologist with the weather service since 1988, Hanson has seen almost everything when it comes to tornadoes. While he admits there’s not a lot about them that surprises him, one word comes to mind when describing the Weld County tornado from a meteorological point of view - unusual.

“It was a very powerful storm and a big day overall,” he said.

Technological Improvements to spotting tornadoes

Just as the weather is constantly changing, so too is the technology that the weather service uses to monitor it. In preparation for the next tornado or significant weather event in Weld County, the following additions to weather service equipment will help identify storms sooner and increase public awareness and safety.

• Updated Radar – Features to an updated radar system allow the weather service to better define tornadoes and the debris caused by it, allowing meteorologists to see if a storm is causing or turning into a tornado.

• New Satellite – A new satellite launched last year, provides a better look at storm clouds and gives minute-by-minute snapshots and higher resolution photos.

• Computer Modeling – Hanson said the computer models used to forecast storms have improved, allowing for a clearer picture of when and where storms will form; technology that wasn’t available in 2008.

 The above graph shows the time of day for the 263 Weld County tornadoes reported to the National Oceanic and Atmospheric Association. Most tornadoes happen in the afternoon. The 2008 tornado was strange in that it occurred just before noon.