Resources to determine temperature probability for a given location on a given date What tools or resources are available (free) on the web to determine the probability of a given point on the earth to be at or above (or below) a specific temperature on a specific date.

Some [extreme] examples:

At the South Pole, the probability of it being > 90-F on June 1 approaches 0% (I'm guessing).

Conversely, the probability of it being &lt; 32-F on the equator (at or near sea level) on Dec 1 approaches 0%, as well.

Another way to phrase what I'm looking for:  On what date in the calendar year does the probability of the air temperature being above (or below) X approach 0% for a given location/city?  

So, say, for Washington, D.C.-- after (or before) what date in the year is it virtually impossible for the temperature to be above, say... 80-F?
The most basic way to measure probability is to look at historical 
records. There are several sources for this data, including: 


http://wunderground.com 
ftp://ftp3.ncdc.noaa.gov/pub/data/noaa/isd-lite/ 


This assumes no climate change. If you believe in climate change, you 
will need to factor that in.