lower pressure in the rear is because the rear weighs considerably less than the front of the car - requres less air pressure to keep the tire's shape.
as far as cold tires, especially if kept at higher than normal pressures for the summer - they will get unpredicatble, so please be cautious.
Back on topic - for every 10 degrees F the temperature drops, expect to loose 1 PSI of tire rpessure - so if you last checked it in the summer at 80 degrees you'll be down 6 PSI simply from the drop in temperature.
more info here:
http://www.tirerack.com/tires/tirete....jsp?techid=73