Correlation of cold weather running speed to warm weather running speed?

At a given air pressure, and a temp swing of about 60 degrees F, there should be about a 11% difference in air density.  Shoot, I'll grab the link.  The point being that the air is actually less dense at the warmer temp.

http://www.engineeringtoolbox.com/air-temperature-pressure-density-d_771.html

I used the numbers of 30 to 90, in the first column of pressures.  I can't remember atmospheric pressure in psi, offhand.

Inside, outside, or both?

Ideal running temperature is around 50 degrees.  At my USATF seminar the endurance coach pointed out a study that showed for every 5 degrees above, you would expect a 0.5% decrease in performance.  There was NO loss below 50.

No references, sorry.  But it is also common sense.  Cooler air, more oxygen rich (dense), easier for the body to stay cool.  About 70% of the energy you produce is a waste product of heat because the body is not all that efficient.  So cooler temps allow that heat to dissipate better.

 I think it is way easier to run in the cold than the heat...I cannot run in the heat.

Just a guess, but is there any evidence that the uptake of oxygen is reduced at colder temps?

AG, like you, I am an outside exclusive.  No indoors at all though! 

I also run faster in the cold- that is when the ground is dry.

Today, in the snow, and with snow coming down I am sure I will be slow but it will be fun.  Friday's 2 runs were a perfect example for me - the mile repeats on the way to the gym were before the snow and the run home was in the snow....way slower - but I did not have my yak traks either....

 More effecient than anything else...

 Also, when running on compacted snow (a lot more for powder/slush) you should add about 1:30 - 2:00 to your mile time.  

I watched a video about the 2008 olympic marathon trials and Alan Culpepper (??) training run were on snow and he was running at 6:45 pace.  He siad on pavement he would have been going 5:45.  That's 1 min. difference and he's at the top, so I added more to the time you should add (above).

When the temps dropped this fall (70F to 50F), I dropped about 30 seconds per mile for the same HR

At lower temps, it takes longer to warm up and that shows up in my overall pace, but I'm not unhappy with where I am these days. 

Running in the snow or on ice does slow me down. 

There was something in a recent issue of either Runners World or Triathlete that said times get slower as temperatures increase, but elites experience more of a performance drop than age groupers.  I'll have to see if I still have the magazine to check the particulars.

Comparing running on snow in cold weather vs running on pavement in warm weather adds a variable other than air temp.  You need to compare "apples to apples", eliminating as many other environmental factors as possible.  Changing the condition of the running surface from pavement to snow would have a significant impact on times.  It also wouldn't work to compare a run at 90 degrees with a 20 mph tail wind and a run at 40 degrees and a 20 mph head wind if you're trying to determine the effects of temperature.