THUNDER BAY – WEATHER – The extreme cold weather on February 13, 2020, created a rare and unusual weather phenomenon on Lake Superior. “Cloud Streets” were formed.
There were several factors that were involved to make this happen.
First, the frigid Arctic front brought the coldest weather of the Northern Ontario winter. Second, only about 10 percent of Lake Superior is covered by ice this year.
The Arctic air and the unfrozen lake water created an approximately 30°C difference between the water and the air temperature an extremely unstable atmospheric situation.
This is what created the “cloud streets”.
The science is complicated. Wikipedia states, “Although horizontal convective rolls, also known as cloud streets, have been clearly seen in satellite photographs for the last 30 years, their development is poorly understood, due to a lack of observational data. From the ground, they appear as rows of cumulus or cumulus-type clouds aligned parallel to the low-level wind. Research has shown these eddies to be significant to the vertical transport of momentum, heat, moisture, and air pollutants within the boundary layer. Cloud streets are usually more or less straight; rarely, cloud streets assume paisley patterns when the wind driving the clouds encounters an obstacle. Those cloud formations are known as von Kármán vortex streets“.
Still, the science behind this is complicated
The Weather Network offers these insights:
- Cloud streets are always aligned with the wind, gravity waves are not (perpendicular to wave crest)
- Water vapor condensation happens on the upward side of the roll, and evaporation typically happens on the downward side
- The thought is rotation and friction are the primary cause of these weird formations
- A narrow part of the atmosphere allows these to form, unstable lower levels with daytime heating, but stable air aloft keeps these circulations organized