just below 3 feet Northern city covered in snow Indiana Thanks to an impressive snow whirlwind in the sky last week. lake michigan.
residents of great lakes region Heavy snowfall is common in January, but Friday's snow was anything but ordinary. blizzard.
That's because the snow comes from rare bands of low pressure called mesovortices that form over Lake Michigan. More than a dozen people formed a tight band that looked like they were woven together, and in the end, the lake caused a huge amount of snow to fall.
So what exactly happened on Friday and why were meteorologists so surprised?
What is lake effect snow?
lake effect snow Not uncommon in the area the Great Lakes. Cold air from Canada falls as it moves across the Great Lakes, forming clouds that can dump 2 to 3 inches of snow per hour.
The severity of the lake's impact is related not only to the difference between Canada's cold air and the lake itself, but also to the lake's warmth and lack of ice, according to a study by Tom Di Liberto of the United States. National Oceanic and Atmospheric Administration.
Lake effect snow is par for the course, but Friday's system was anything but a normal weather phenomenon.
Why did this whirlwind of snow form on Lake Michigan?
On Friday, more than a dozen medium eddies formed in a braided band over the lake.
Kyle Brown, a meteorologist with the National Weather Service in northern Indiana, said two complementary weather conditions led to this series of heavy lake-effect snows.
These factors include winds from both the northwest and northeast that push the system into a single band, and just the right wind speed that is fast enough to propel the whirlwind further, but slow enough that the whirlwind doesn't break up. was.
„So we can create this kind of delicate environment where these mesovortices can rotate, for example, in a process similar to that of a thunderstorm on a hot, sunny day in a flat area. ” he said. Brown said. Independent.
Those winds tightened the band, said TJ Turnage, science and operations officer for the National Weather Service in Grand Rapids, Michigan.
„The key point is that the wind is blowing in different directions on each side of the band, in fact somewhat opposite directions,“ Turnage said. independent person.
This created a “roll-up” effect in the mesovortices.
„Imagine holding a rag between your hands and moving your hands back and forth in opposite directions,“ he continued. „That rag can curl up, and that's what happened Friday. But it wasn't one thing, it was a series.“
Just the right temperature also helped promote the intensity of the mesovortex. The lake was just above 0 degrees Celsius, while the air above the lake was close to -20 degrees.
„This is a very large temperature difference in a short layer of the atmosphere,“ Brown said.
If lake-effect snow occurs so frequently, why did this system garner so much attention?
Turnage said Friday's system wasn't unprecedented, but it was highly unusual.
What made this phenomenon so special was a confluence of subtle factors.
„Yes, you can get lake-effect snow, but you really have to have the right combination of ingredients to get a band of lake-effect snow as strong as we had in this event.“ Mr. Brown said.
„The reason they don't always show up is because they actually require fairly specific conditions, such as wind direction,“ Turnage added.
Friday's system was more dangerous to drivers than the average lake-effect snowstorm because it consisted of many small intermediate vortices rather than a single dominant system.
Turnage said when such clusters occur, snowfall amounts can vary significantly over short periods and distances, making road conditions unpredictable.
„The bottom line is that this is rare and what we saw is something that many people didn't really notice,“ Turnage said.