Let me add to the good points JohnJ makes. Some will tell you (jokingly) "Don't shoot in hot weather", but that's not always the case. It's not the temperature that causes heat haze, but rather the temperature difference between the air and the surface. A couple of weeks ago, when I was shooting the US A320 in the Hudson River, I ended up with significant heat haze when shooting across the river from Jersey City. It was 15F air temperature, but the water was around 35F, and with that difference, there was heat haze coming off the river.
KC-135 - Passing gas and taking names!