Storm spotters are local eyes on the sky for NWS

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By Audrey Posten, North Iowa Times Editor

The National Weather Service (NWS) has 122 offices around the country, all tasked with providing their service areas with weather forecasts and hazardous weather notifications.

“At the National Weather Service, we try to tell the potential of hazardous weather,” explained Todd Shea, warning and coordination meteorologist with the NWS office in La Crosse. “We’re not hypers or storm chasers.”

The main goal, he said, is to create a weather ready nation.

The La Crosse office, which covers a 28-county area in southeast Minnesota, northeast Iowa and southwest Wisconsin that includes Clayton County, has a staff of 23. At least two to three people work each shift, providing a 24-hour, continuous weather watch.

When severe weather threatens, Doppler radar is a valuable resource for the NWS, offering information about storm location, wind gusts and the type of precipitation involved. It can’t supply every detail, however. That’s where volunteer storm spotters come into play.

“A spotter observes weather happening locally,” said Shea. “That helps us get warnings going. That real-time report also gives residents more confirmation that something is happening, so they can take action. We all work together to get the word out and protect people.”

In order to prepare volunteers for storm spotting, the NWS holds free training sessions throughout the service area. Attendees are briefed on the types of hazardous weather they may encounter, as well as when and how to report it.

Shea instructed a group of over 77 people, comprised mainly of local firefighters, at the Luana fire station on March 9, just three days after a thunderstorm with hazardous winds whipped across the county.

“We try to get trainings in before severe weather hits,” Shea remarked. “That storm was a bigger event than normal for March.”

In northeast Iowa, Shea said late spring into early summer is typically the most active time for severe weather.

“Overall, the most severe weather occurs in June, then the frequency tails off,” he commented.

While tornadoes often instill the most fear in residents, flooding and flash flooding are the bigger threat, Shea said. Since he started at the La Crosse NWS office in 1994, he said 16 flood-related fatalities have occurred in the service area. There have been no fatalities due to tornadoes.

When gauging storms, Shea said there’s no cookie cutter blueprint.

“Each storm and event are different,” he said, “and cloud formations are never quite the same. We try to show you the basics and go from there.”

Shea said all spotters can begin by finding a good weather source, so they know if severe weather is coming. 

“Take advantage of technology,” he stated. “There are a lot of ways to track weather.”

The NWS provides weather outlooks several days in advance, which can be helpful to spotters. Watches are released two to six hours in advance, while warnings are released 10 to 60 minutes beforehand.

The watch stage, Shea cautioned, is often too early for spotter deployment. The storm might be several hours away yet. However, the warning stage is likely too late.

“You want somewhere in between,” Shea noted. “Be pro-active and try to stay ahead of it. Monitor upstream weather and weather in other counties.”

The NWS has designed a spotter notification system that sends out messages when staff feel they need spotter reports or when the weather appears to be strengthening. Spotters can be notified via text or email, or by checking the NWS website.

When selecting a spotting location, Shea said spotters can choose to be either stationary or mobile, as long as the spot is upstream of the community and offers good visibility. It’s also important to have shelter and a good escape route.

The first type of weather Shea touched on during the training session was thunderstorms. Thunderstorms, he explained, form when updrafts of warm air rise and meet downdrafts, or surges of cool air coming to the ground. Updrafts sustain thunderstorms and determine their strength. There are six thunderstorm risk categories, with one or two being the average storm, Shea said. Lightning, hail and wind are all by-products.

“In thunderstorms, wind is the most frequent type of severe weather,” Shea said, with gusts over 58 mph considered severe.

When reporting, measure the wind speed if you can, otherwise make a conservative estimate. Avoid using words like “heavy” and “strong.” Shea said the La Crosse office has heard descriptions like “it’s dang windy out there” and “a blast of wind.” But what exactly does that mean?

“You’re better off describing damage or what the trees are doing,” he said.

Hail equal to or greater than one inch in diameter (quarter-sized) is considered severe. Report the size and compare it to a common object, such as a specific coin or ball. Do not compare the size to marbles, Shea quipped, as marbles come in a variety of sizes.

Shea said there are several storm types and features, including single cell, multi-cell cluster/line and supercell. 

A line, he said, is like what occurred March 6. Squall lines can be widespread and extensive, with strong, damaging winds, heavy rain and hail. They can occasionally produce weak tornadoes.

Supercells are isolated, big weather-producing storms.

“Supercells are what tornadoes are built on,” Shea noted. “They’re the strongest, longest-living storms, with hail and damaging winds.”

A tornado is described as violently rotating air that makes connection with the ground, Shea said. An EF scale is used to rate tornadoes, with most being EF0 or EF1. 

One of the limitations of Doppler radar, explained Shea, is that it cannot confirm tornadoes, especially those lower on the EF scale.

“That’s why spotting help is really crucial,” he said. “You guys are the first detectors of these.”

EF4 and EF5 tornadoes are the rarest, but most deadly, with winds greater than 165 mph. The destructive tornado that hit Parkersburg in 2008 was the last EF5 tornado detected in Iowa, Shea said.

An average of 46 tornadoes touch down in Iowa each year, but Shea said northeast Iowa sees few of them.

Spotting tornadoes can be challenging. Tornadoes, Shea said, often spawn from wall clouds, which produce heavy rain on the front half that often obscures views. Spotters on the backside/updraft area have better views, since there is a rain-free base.

“Sometimes you’re not in a good position to see,” Shea said, “so you need to get views from different parts of the county.”

Other cloud formations can also resemble tornadoes. For example, said Shea, non-supercell storms can produce scud clouds, which are loose, low-hanging cloud fragments. Virga, or curtains of rains, can look similar, as well.

“The shape doesn’t mean it’s a tornado. Look for debris and rotation for the ultimate determination if it’s a tornado,” Shea stated. “A tornado will be rotating wildly.”

It’s important to only report what you see, to not assume, Shea said. Be confident and do not exaggerate. On the flip-side, though, if severe weather has been spotted, it’s equally important not to assume the NWS already knows about it, he added.

Ultimately, experience makes storm spotting easier.

“Hopefully, with all the work we’ve done, with the precautions and trainings, it will save lives,” Shea said. “We can’t stop the weather, but it gives people a heads-up.”

— — —

Weather Reporting

What to Report

  • Tornadoes
  • Funnel Clouds
  • Wall Clouds
  • Hail (size and amount)
  • Wind Gusts (40 mph-plus)
  • Shelf or Roll Clouds
  • Flooding and Mudslides
  • Heavy Rain
  • Damage
  • Injuries/Fatalities

What to Say

  • Who you are
  • What was observed
  • Where you are
  • Where weather occurred
  • When it occurred

Contact the NWS La Crosse Office

Phone: (608) 784-7294


Facebook: US National Weather Service La Crosse Wisconsin

Twitter: @NWSLaCrosse

Learn more about the NWS Office in La Crosse at March 27-31 is Severe Weather Awareness Week in Iowa. The state tornado drill will be held Wednesday, March 29, at 10 a.m.

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