Why don't cities that receive lake effect snow in the winter also receive lake effect rain in the summer

The cold air that passes over the lake is much colder than the lake itself. As a result the lake water heats the air passing over it and causes it to rise, making the lake effect snows (there are a couple other factors involved, but I'll keep it simple). In summer the air is typically warmer than the lake waters, thus the instability is not created since there is little if any heating of the air passing over the water.

Answerequatorial guinea,gabon, and western sahara;

Well, a and b together would be negative. b alone would also be negative.