Some people have the theory that the mosquito season depends on the dampness of the ground surface and how much standing water is there, like from snow melt. Others have the theory that the season depends on the air temperature. I think it is both. Mosquitos aren't too bad when everything is still frozen snow, and they aren't too bad when everything is dry and warm. It is the transition season that is so unpredictable. I take long clothing, a headnet, and a few ml of DEET, and I am good.
Highs and lows? Geez, I don't know. There is an automated snow monitoring station very close to Bishop Pass, just west, and you might be able to see the data online. California Department of Water Resources, I think.
When I am chugging uphill toward one of these passes in the middle of a day, I expect the air to be around 55-70 F, and seldom higher. When I am camped overnight in some high valley, I generally expect the air to be around 25-35 F.