The organ builder's bible, Audsley: The Art of Organ-Building, gives
a table that relates the pitch of a flue pipe to the air temperature.
This is abbreviated below showing only the two end temperatures of the
scale.

A nominal pitch of a1 = 439 Hz at 68 deg. F. (20 C.) will change to
435 Hz at 59 deg. F. (15 C.).  A graphical representation of this table
will allow one to extrapolate at either end.

Audsley also gives details of the various pitch standards that existed
in 1899 prior to the standardisation of 'Concert Pitch', which may or
may not be a1 = 440 Hz at 20 C.!

As already stated by Robbie, you need to watch your reeds as they do
not change with temperature.  This gives problems to fair organs in hot
weather.  When very hot I switch off my organ's trombones in order to
preserve my sanity.

I hope this helps.

Nicholas Simons, GB