Weather leading up to Peshtigo Fire of 1871 was ideal fire weather
On Oct. 8, 1871, a massive wildfire engulfed 1.2 million acres of Northeast Wisconsin.
Directly in its path was the city of Peshtigo, which was all but incinerated in its wake.
A huge contributor to this disaster was the weather.
But according to Green Bay National Weather Service meteorologist Kurt Kotenberg, re-examining this bit of history can be difficult.
"It's kind of like trying to piece things together because there wasn't this this surface observation network that we have today. Standing right behind me is a bunch of weather sensors-- that didn't exist back in 1871. So really, it's trying to piece together past records," says Kotenberg.
And from what we have pieced together about this day, it was a classic fire weather setup.
You have to go back to the prior winter to start painting this picture.
That winter had been extremely dry, so there was very little snow pack and very little soil moisture to begin with in the spring.
The dry weather persisted all summer in 1871.
And it was also a warmer summer than usual.
This caused any vegetation, and especially cleared trees from the booming logging industry, to dry out and become extremely flammable.
All summer, smaller fires had been a problem, leading to smoky skies and poor air quality that year.
But on October 8th, everything came together in the worst way possible.
Strong low pressure developed in the central plains states and pushed up against high pressure near the Carolinas.
Between these two pressure centers, the atmosphere got squeezed together, and strong southwesterly winds cranked up.
The air was warm and dry.
Sustained winds of 20 to 30 miles per hour took the numerous small fires across Northeast Wisconsin and whipped them up into a single wall of fire that marched to the northeast.
Peshtigo was far from the only community impacted, but it was where by far the largest loss of life was.
Something else to discuss with the Peshtigo Fire of 1871 are some the witness accounts of howling winds hurling debris and even trees into the sky, and blowing down structures.
Some have referred to it as a fire whirl or a fire tornado or a fire storm.
Those are all plausible, but it's impossible to know exactly what the circumstance might have been since so few people actually made it through the fire.
What we do know is that when a wildfire becomes hot and intense enough, all that hot air rising from the middle of the fire starts pulling in cooler, oxygen rich air from around it into the fire.
Those localized winds move inward, which can actually hold the fire in place for longer periods of time, burning everything until the fuel is spent.
These winds rushing into the fire can easily achieve gale strength, which would have been enough to knock down burned trees or weakened structures.
Additionally, if these winds tap into any sort of rotation in the atmosphere, there have recently been documented cases of actual tornadoes forming because of intense fires.
Not just smaller fire whirls or fire devils-- true tornadoes.
So, again, it's unclear what exactly happened in the Peshtigo Fire of 1871-- whether it was a fire tornado, or a more broad fire storm.
But either way, it was a perfect combination of conditions that we have thankfully never recreated since.