All day Tuesday we watched cirrus clouds 10,000 to 15,000 above the ground over Central Alabama moving north next to a batch of cumulus clouds based around 4,000 above the ground hovering over North Alabama and Tennessee.
As the sun set on Tuesday evening, it was obvious how wind shear in the atmosphere was driving the clouds across the sky!
So how does this work?
The high, thin cirrus clouds are riding the upper-level wind flow pattern at the level of the jet stream (which is not terribly strong over Alabama Tuesday).
The cumulus clouds might be ‘affected by’ the jet stream (it enhances vertical development of clouds), but they are riding on the winds lower in the atmosphere. That wind happened to be coming from the west-northwest on Tuesday.
Why is wind shear important?
Wind shear on an average February day just makes for a pretty sky when the clouds come in layers like this; however, wind shear on a severe weather day is a critical piece of the forecast!
The wind would be different on a severe weather day, though. Lower-level flow is stronger and comes from the south (southeast/southwest). The middle and upper-level flows come from the southwest to west and sometimes ramp up to over 100 miles per hour just a few thousand feet above the ground.
Looking ahead to next week, we see a pattern that shows signs of this kind of wind shear and some healthy instability. The wind shear is the ‘muscle’ that creates the framework for powerful storms; the instability is the fuel that powers them.
We will keep you posted on the progress of that system. It’s too far in the distance to see how the true risk may pan out, but it’s something to keep an eye on through next week.