"If it's wind shear without rain, there are no water drops to bounce the radar signal back off, therefore no detection."
I'm less than 2 miles immediately South of Pearson Airport and there was big time rain, wind and lightening at the 4:12 EDST point of impact. Suspect the plane was hit by lightening and its electrical system cut out.
If there's very heavy rain, you get the opposite problem -- the rain scatters and absorbs the radar microwave signal so badly that there is very little penetration into, and back out of, the storm.
Interestingly, the TS wind shear is due to a strong, cold downdraft from the storm clouds above. When it hits the ground it spreads out in all directions. As the plane approaches 'ground zero', there is a strong head wind, causing increased lift -- until the plane passes ground zero, when it becomes a tail wind, causing the plane to sink dramatically, into the ground if the plane is on late final.