Chris W writes:

My dad drives along the south side of OKC to work every day and his OAT
in his car always goes a few degrees colder around the where the
extended centerline for the runways would intersect the road. Then it
goes right back up after he is through that area. He thinks this is
because the airplanes are descending from very cold air and bringing
down some of it with them.

I would not have thought of that, but it's certainly plausible. Aircraft
produce a massive downwash of air behind them that (at least in theory) drifts
downward until it encounters the ground. In the case of aircraft very near
the surface (as during landing and take-off), it's entirely possible that they
might produce gentle downdrafts of colder air that reach the ground. I think
it would take fairly constant traffic using the runway to make a clear
difference, though.

It's a bit like the constant wind that one often feels by the side of a
highway or major city street, always in the direction of traffic. Moving
vehicles do displace a lot of air.

He has noted that this isn't always the case
but it often is. You would think most of the traffic would be landing
from the north since our winds are mostly from the south, but it seems
like I see a lot of traffic coming in from the south, maybe because it
is easier for the traffic from DFW to just come strait in.

Things like noise abatement and other concerns might obligate the airport to
work against the wind, at least if the wind speed is low enough (less than 10
knots or so).

Anyway, any one here think it is really the case that the planes are
causing the temperature to be lower on the approach end of the runway?

I think it's plausible.

Also, if the extended centerline is mostly open area (not buildings or roads),
that could make a difference as well. An open field is often colder than a
large building, because it absorbs solar energy less rapidly and retains it
less efficiently, and because it doesn't generate any heat of its own.

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