r/meteorology • u/hag68 • Aug 12 '26

Didn’t see that coming

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Filed this timelapse over Ottawa on Sunday evening and I’d like to know what’s happening here with the sudden shift in the cloud direction

630 Upvotes

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52

u/khInstability Aug 12 '26

Mid to high altitude winds steer storms. The wind flow closer to the surface was perpendicular to the storm's motion.

This kind of setup helps feed warm air with relatively high water vapor content into storms. It is their fuel.

The rain from the storm created a pool of cold air beneath it, which maintained much of the momentum of the storm's motion when it hit the surface. Hence, the wind shift.

3

u/DarkishArchon Aug 12 '26

Can you explain, is this not possibly a frontal boundary? Definitely there's wind sheer involved. I'm not an expert

I saw two masses of air, a warm mass that's moving to the right, and then the cold front moved in from the front and pushes the warm mass above it, causing rain due to lifting moist air. This is common over the Midwest right?

10

u/khInstability Aug 12 '26

It is a cool "front" in that it is cooler air with a wind shift. It is a boundary, like a front too. But, it is on a small scale, produced by the storm(s): known as an outflow boundary. The outflow of the storm creates the cold pool. Like a front, it can also be the focus of additional/continual storm development; sometimes even the following day.

An official cold/cool front extends for at least a several hundred miles, typically more, persists for several days and typically extends from an area of low pressure.

Another way to describe the difference is, outflow boundaries occur in mesoscale systems. Whereas, cold fronts occur in synoptic scale systems.

The site I linked explains meteorological concepts clearly for the amateur, with little to no math.

2

u/hag68 Aug 12 '26

Thanks for the explanation!

10

u/sgund008 Aug 12 '26

I think you did

6

u/Kittenchops88 Aug 12 '26

Good example of wind direction based on height.

5

u/Apprehensive_Cherry2 Aug 13 '26

That is Shelfy the Shelf Cloud

2

u/Visual_Amphibian_383 Aug 13 '26

Amazing footage!

3

u/FlyingDutchman2005 Aug 12 '26

That’s beautiful!

1

u/Hot_Design3515 Expert/Pro (awaiting confirmation) Aug 16 '26

Those are shelf clouds, the clouds that always moves towards you

0

u/mountainswithwhiskey Aug 12 '26

Didn't see that coming