Are there precise met circumstances where you do and don't get wind shear or
CAT ? I wonder if it was due to vortex shedding by previous craft like that
USA crash 5 years or so ago, packing them in too close.

The term CAT (Clear Air Turbulence) means just that, no cloud nor
ground induced turbulence.

Vortex shedding is normally only a factor when there are fairly calm
conditions (eg cold, calm early morning) or at altitude - it was
probably too windy today.

Windshear could occur in conditions such as today.

However, the circumstances of the accident are now becoming clearer
and not weather related.

Jack (retired airline captain)