It was briefly mentioned in one of the longer threads that a contact
approach requires 1 sm reported ground visibility. It reminded me that
I had flown a contact approach some 8 months ago to an airport about 15
minutes after the tower had closed (there is no automated weather
available) and couldn't land because fog and low clouds had rolled in.

So did approach control screw up? I'm sure they had the last ATIS
report some 70 to 80 minutes old at the time of my request, and the
weather was good in that report.

Interestingly, both the AIM and the 7110.65 say that a requirement for
ATC authorization of a contact approach is that "The reported ground
visibility is at least 1 statute mile."

But the AIM starts out by saying: "Pilots operating in accordance with
an IFR flight plan, provided they are clear of clouds and have at least
1 mile flight visibility and can reasonably expect to continue to the
destination airport in those conditions, may request ATC authorization
for a contact approach."