Interesting wind shear

Peter wrote:

The interesting thing is that the shear happens at the cloud layer.

Here goes another pop-corn thread
Please define “extreme” as in the title of the thread?
Now, why do you think the shear happens at the cloud layer, or, for a better understanding, why is the cloud layer on the same level as the shear?
Ever heard of inversion?
Last question, is MET part of today’s PPL syllabus?

Peter wrote:

The interesting thing is that the shear happens at the cloud layer.

What you call interesting is absolutely normal. But, interesting is that you can see the turbulence in the PBL (topped by the shallow cu clouds) vs. the more or less laminar flow above.
PBL=planet. boundary layer

Well, I must be a QB-warrior like Peter Is a change in direction of wind at an inversion a given?

Peter wrote:

I know it is more turbulent below clouds, but the change in wind speed at the cloud layer is amazing. What is the physics behind that? Why does the cloud layer block the wind?

It is not the cloud layer, but the inversion that blocks the wind. An inversion is a strongly stable layer, i.e. it blocks vertical air movement. That has two effects:

1) The wind direction and speed above and below are pretty much independent as there is very little “friction” between the layers.
2) Moisture tends to accumulate in the inversion, forming clouds.

The physics between the blocking is the adiabatic temperature change of vertically moving air, e.g. the temperature change caused by rising air expanding as the air pressure decreases or by descending air compressing as air pressure increases. This temperature change is in the order of 3°/1000 ft of vertical movement. Whenever the static temperature drop is less, rising air gets cooler than the surrounding air so vertical movement stops. Similarly for descending air. In an inversion the temperature actually increases with altitude so this blocking effect is very strong.

Yes it’s weird. We have lots of this weirdness at Meråker (ENMO). It was the cause of a fatal accident some 4 years ago. It’s up in the mountains, and rather unpredictable. It can be zero wind at the airfield, but 20-30 knots or more 100-200 feet up in the air. It can also be the opposite. It’s the same thing at Oppdal (ENOP), and I guess in all mountainous areas.

Last time I flew there a month ago, it was zero wind at the ground and also at 1000 feet agl. Then I flew close to a mountain, and all of the sudden I was at 3000 feet agl in a matter of seconds (less than a minute), like an elevator. Then out of the updraft and into an equal downdraft.

When landing again, completely calm. I have found no way to predict this, or even to know when such things occur. Be prepared for anything is the only thing that works. Which basically means always be prepared to set the nose straight down and apply full throttle. The real danger is when taking off and suddenly head into a tailwind at 30 knots. That’s wat killed the guys 4 years ago. The danger of climbing at Vx in the mountains.