A table showing location and year of the IRE conference, as well as the monthly average temperature in June for that city.
Temperatures are from http://www.usclimatedata.com/ for average high in that city in June, based in most cities off of the 1981-2010 temperatures. DC and San Antonio are 1961-1990.
Years with avg temp => 85: 10 since 2003.
Why'd I choose 85? Because that's the temperature where I, personally, stop feeling comfortable outdoors.
The "South?" criterion is true if a city is south of the Mason-Dixon line. Denver was given a pass, since it's pretty much on the line. San Francisco is south of that line, but calling it and Phoenix "south" will depend on whether we're looking at cultural south or just geographic.
Years south of the Mason-Dixon line? 12 since 2003.