Temperature Formula HELP!!!
 

I'm having trouble in creating a temperature formula that will increase the
number of calls based upon a drop in the average temperature for the day.
There are other variables in the equation but I have factored those out, and
I'm left with temperature change. For example: the previous x number of days
is 65 degrees, but the next temperature is 47. The normal call volume is on
average 350, but with the decrease in temperature the call volume was 1363.
I tried to taking 65 minus 47 and applying a percentage (2.33%) based upon
the previous year but that only increased by forecasted call volume to 497
not 1363. Also, subsequent drops in temperature do not dramatically increase
call volume as the 1st drop in temperature (e.g. 55 to 40 call volume goes
from 450 to 710.) I coming to the conclusion that I must have a unique
temperature formula per time of year. Any help would be appreciated.