The Wisconsin winter got off to a seemingly slow start, but it sure picked up in January and February. While the snow and cold can make getting places harder, John Perrin knows winter can also be beautiful.
Perrin, who lives in Milwaukee, was driving southeast on the Menomonee River Parkway the morning of Feb. 19, when he saw a sight he knew he had to capture.
“Something had coated virtually everything on the riverside and was much less pronounced on the other side. Looking into the sun I could tell [that] it was thick, and I knew it didn’t snow the night before. I had assumed it was some sort of deposition but had never seen anything like it,” he recalls to WUWM via email.
Perrin dropped his daughter off at school and hurried back to Menomonee River Parkway and Ridge Boulevard.
“I knew the sun would make it go away but didn’t realize how delicate it was until I was up close and a breath of air quickly cleared a small section. After that I was more careful,” Perrin says.
He arrived at the scene before 9:30 a.m. and about 45 minutes later, what he saw was gone. Thankfully, Perrin had his iPhone with him.
Perrin saw what he thought was rime — ice crystals that form on solid objects and then continue growing on themselves, according to Michael Westendorf of UWM’s Innovative Weather.
Rime forms in very high humidity environments below freezing with calm or semi-windy conditions, Westendorf explains.
"Stunningly beautiful, but we will also often see freezing fog conditions, which can make for some very icy travel, especially on bridges and overpasses," he notes.
But then there’s hoarfrost, which is similar to rime.
The difference between rime and hoarfrost is slight but important. Rime is the result of widespread, dense freezing fog and can form in windy or calm conditions. Hoarfrost often forms due to cold temperatures, calm winds and very localized high humidity, often near a moisture source, according to Westendorf.
An ideal setup for hoarfrost would be clear skies and no wind near an open water source, which leads to extremely cold temperatures and a saturated local environment — exactly what our photographer saw.
Why is it called hoarfrost? According to WeatherOps, the name originates from the Old English word "hoar," which means "showing signs of old age."
"My understanding it is an Old English word that is meant to describe the whiteness, like an old man's beard," Westendorf says.
So, what was it that Perrin captured — rime or hoarfrost?
"Because you took these near an open water source on a morning with partly cloudy to mostly clear skies, I'm thinking that this is most likely hoarfrost," Westendorf writes.
He went on to explain, "That morning, Mitchell airport dropped to 5 degrees at 7 a.m. with calm winds and clear to partly cloudy skies with a cloud base height of about 20,000 feet. No fog was reported, but visibilities dropped from 10 miles down to 8 or 9 miles — suggesting a bit of haze in the air."
At last, Perrin knows what it was that caught his eye.
“I have found that after 53 years, there is no shortage of things for me to learn," says Perrin. "I have never seen, heard of or read about hoarfrost. I am saddened — this means I must update my Facebook post calling it rime."
Editor's note: Thank you to John Perrin for sharing these photos with WUWM and the community.