Heat haze can occur during all times of year. It's not dependent on absolute temperature, but rather on temperature gradients in the air. Basically, as it's usually created, the sun warms the ground, which then heats up the air immediately above it. That air is then hotter than the air above it, so you get convection, and hence heat haze as the differing air temperatures mix.
It tends to be worse in the summer, yes, but I've seen it pretty bad in the winter too (then again, winter in LA isn't exactly cold).
Technically, as long as you have any air between you and your subject, you can get heat haze. But it's more noticeable with greater subject distance, and with higher zoom. I've certainly noticed it at air shows at not too great a subject distance.
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JakTrax From United Kingdom, joined Jun 2005, 4936 posts, RR: 7
Reply 3, posted (2 years 1 month 2 weeks 3 hours ago) and read 3420 times:
There are two ways to reduce (but not always eliminate) the effects of heat-haze: getting as close to your subject as you can, and increasing your elevation.
Here in the UK we had an incredibly cold Mar/Apr, with early morning temperatures frequently dipping to -5C. However because the sun was rising quite high in the sky it was warming the ground nicely, giving us massive temperature variations between the air immediately above ground and that a little higher up. It produced some of the worst haze I've ever seen!
A primary reason why haze tends to be far less in winter is because the sun struggles to get high enough above the horizon to create the necessary temperature differences. Its rays can't penetrate enough of the atmosphere to do any real damage.
A good little trick I use for static aircraft is to wait for a large cloud to come over; the cloud casts its shadow and cools the ground, subduing any haze. When the cloud finally gives way I shoot the subject in the first hint of sunshine. Doesn't always work but effective 90% of the time, providing your subject isn't too far away.