btw, thanks for reminding me of the pleasant places map -- I think it must have been an unconscious influence on this.
Given an air temperature (T) in °F and a relative humidity (rh).
Indexheat = − 42.379 + (2.04901523 × T) + (10.14333127 × rh) − (0.22475541 × T × rh) − (6.83783×10−3×T^2) − (5.481717 × 10−2 × rh^2) + (1.22874 × 10−3 × T^2 × rh) + (8.5282×10−4 × T × rh^2) − (1.99×10−6 × T^2 × rh^2)
The equation came later - the output of that article is just a table, and the equation was derived to be a nice fit over the table's values.
AT = Ta + 0.33×e − 0.70×ws − 4.00
where:
Ta = Dry bulb temperature (°C)
e = Water vapour pressure (hPa) [humidity]
ws = Wind speed (m/s) at an elevation of 10 meters
The vapour pressure can be calculated from the temperature and relative humidity using the equation:
e = rh / 100 × 6.105 × exp ( 17.27 × Ta / ( 237.7 + Ta ) )
where:
rh = Relative Humidity [%]
Not to 'steal' ideas from the other site, but having that little year avg chart pop up on click is a really killer feature for showing which months are best. For example, I'd much rather live somewhere with 4 solid "uncomfortable" months and 8 solid comfortable, than somewhere with 2 on, 1 off.
But yeah, as others mentioned, rainfall, storms, cloudiness, etc, are all things that would be great to include.