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Grant Petty, second from right, a UW-Madison professor of atmospheric and oceanic sciences, joins colleague Ankur Desai and a group of students in launching a helium-filled weather balloon Thursday.

It was dark with a wind chill of 25 below zero when they walked onto frozen Lake Mendota at 7 a.m.

Still, a group of UW-Madison’s weather scientists and students stood outside for a little over an hour to conduct their latest experiment as the sun rose Thursday morning.

“It was actually a beautiful sight even though none of us could feel our toes,” said atmospheric and oceanic sciences professor Ankur Desai.

The National Weather Service and meteorologists on TV forecast the polar vortex more than a week ago using computer models that spit out numbers similar to what appeared on thermometers across the Midwest this week.

But less attention is paid to what precedes the forecasts: the scientists at research universities such as UW-Madison who develop the models, crunch the data and improve forecasting technology that allows weather predictions to arrive earlier and more accurately than ever before.


UW-Madison's students in the Department of Atmospheric and Oceanic Sciences huddle around Grant Petty as he explains some of the data transmitting from the launched weather balloon.

While many bemoaned the bitter cold in the days leading up to the deep freeze, those in UW-Madison’s Space Science and Engineering Center building buzzed.

“When the weather gets bad, we run to the roof and go outside,” Desai said. “Everyone in this building loves weather. It diffuses into your pores.”

Grant Petty, a colleague of Desai’s, set out to launch a balloon during the cold snap. It would be by far the coldest launch Petty conducted, and he’s been doing launches since the 1970s. Thursday’s launch was an opportunity for students to observe the process during an exceptionally cold event.


A weather balloon released Thursday may travel as high as 20 miles above Earth’s surface and as far as 100 miles away before bursting and returning to the ground. The radiosonde transmits data that can be analyzed to determine atmospheric conditions above Madison on the unusually cold winter day.

The procedure involves filling a balloon with helium, attaching a sensor, sending it up into the air and hoping it doesn’t catch a tree. It’s still used by weather stations across the world twice a day, in conjunction with satellites and other technology, to help with model forecasting.

The balloon’s sensor, known as a radiosonde, records temperature and humidity as it floats higher.

Ground-level temperatures are what get forecast and reported. But higher up in the atmosphere is where scientists see what’s happening. Without instruments that can observe the atmosphere well above the surface, accurate weather predictions would be impossible, Petty said.

On the night before the launch, Petty fired off one final safety message to the group. He spelled out exactly what he planned to wear and urged others to opt out of the activity if they didn’t have proper gear.


Grant Petty explains to students how the balloon launch works. He recruited several students and colleague Ankur Desai to join him at sunrise on Lake Mendota. 

“I’m not completely confident that I can find a way to cover my nose without also fogging my glasses, so that’s the biggest wild card for me,” Petty wrote in an email to his group Wednesday evening. “If the cold proves too great an adversary, we’ll abort the measurements rather than risk injury.”

Petty worried he’d be the only one there at 7 a.m., a time he picked because some of the coldest temperatures are just before the sun rises.

A group of about 10 students braved the elements with him and Desai. An 11th would have joined, but the student’s car wouldn’t start in the minus 20-degree weather.

“It was hard to tell who was who with the ski gloves and face masks,” Desai said.


Icicles are visible on the eyelashes and clothing of Brian Zimmerman, a graduate student in the Department of Atmospheric and Oceanic Sciences. He and other graduate students in the department learned more about atmospheric conditions above Madison during the unusually cold weather. 

Icicles formed on eyelashes. Phones died within 30 minutes. A car kept running for brief retreats from the cold as extra warmer packets were distributed for hands and feet.

Petty’s laptop almost started a Windows update that would have added more minutes outside in the elements. A quick thinker canceled it just before the computer began to re-boot.

“Everyone was pretty hardy about it,” Desai said.

National distinction

Wisconsin is the birthplace of weather satellites. UW-Madison is one of three universities in the U.S. with a meteorological satellite institute collaborating closely with the National Oceanic and Atmospheric Administration and NASA.

Scientists in the university’s Space Science and Engineering Center have emailed each other back and forth about the weather for years, exchanging messages about snowfall and cold snaps and dry spells and floods. The group created a listserv allowing people to opt in and opt out of the messages. It was called the “Weather Weenies.”

A few years back, however, during a routine, campuswide information technology upgrade, Jordan Gerth, a weather researcher who oversees the listserv, changed the mailing list’s name to the “Weather Enthusiasts” to “class it up a bit.”

The group insists there’s no established leader nor is there a consensus on who among the roughly 100 members is the biggest weather nerd.

Petty said he had his “niche” but others knew more than him.

Cooperative Institute for Meteorological Satellite Studies director Steve Ackerman said, “I’m not really as fanatical as some others.”


Students in the Department of Atmospheric and Oceanic Sciences stand on frozen Lake Mendota ready to launch the balloon. Grant Petty checked that the instrument was transmitting data to his computer before giving students permission to launch. 

When a major weather event appears on the horizon, a flurry of activity on the listserv ensues. There’s model analysis. There’s conversation on computer scenarios.

“We’ve even had some deep discussions on school closure policies,” Desai said.

And then there’s the predictions for snowfall and temperatures that can be so close that winners are determined by a tenth of an inch or degree.

“It’s not a guessing thing,” Gerth said, describing how everyone arrives at their forecasts. He said some people probably spend their evenings going through all of the data before providing a prediction. He declined to share his own methodology.

Winners receive no prize, just bragging rights.

How many messages were exchanged on the listserv this week in anticipation of what forecasters called a “once-in-a-generation” deep freeze?

“Way too many,” Ackerman said.

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Kelly Meyerhofer covers higher education for the Wisconsin State Journal. She can be reached at 608-252-6106 or