Overrunning: How the 'cool clouds' formed

By: Tom Coomes Facebook | Twitter
Posted: May 8, 2023 10:33 PM EDT
Overrunning: How the ’cool clouds’ formed
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My inbox was flooded with photos Sunday evening, even more were shared on social media. Many posts were in awe and wonder of what were these clouds? I knew after seeing the first photo what was going on, as there was a front nearby, overrunning. 

Sunday was a warm day but by the evening the cool air had started pushing southward, displacing the warm air. Cold air is heavier than warm air, so it wedges along the surface. The warm air is lighter and rides over colder surface air. 

Surface temperatures 9:00 SUN May 7, 2023

The surface boundary between warm and cold air, is lift mechanism for the atmosphere, and storms started forming along it. In fact, with the convergence of north / south wind along this stalled boundary, a stagnant line of flooding thunderstorms formed. 

Satellite & Radar 8:44 PM SUN May 7, 2023

The clouds however kept rolling up over the wedge of colder air northward across Michiana.

Simplified example of overunning.

The roll-up is not a smooth process, especially with storms, the wedge isn't exactly a knifes edge. The waves in the clouds were the evidence of folding of the atmosphere as it was forced to a higher altitude. 

Rolling turbulence in the clouds, some mammatus clouds (sinking bubbles) are observed. But mostly lines of distinct crinkles. Josie Slunder


While pulling into my driveway, a better example hit me as I pressed the remote to open the garage door. As each panel rises is eventually bends at the hinge before turning horizontal. That's essentially what the atmosphere did, those ripples and crinkles were the atmosphere hinged higher. 


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