There's very little difference in weather between the north and south rims, cemeterybird (interesting name, by the way). It's probably not the best time of the year, but expect cool, windy days. The temperatures may reach 50 degrees F and at night you'll want a fairly heavy coat. The altitude in the area runs about 6,000 to 7,000 feet above sea level! it's likely to be near 10 degrees F and that's in good weather.
St. George is much lower in elevation... in fact it's considered to be a resort and retirement area for the rest of Utah's citizens.
Sedona, is beautiful about anytime of the year, but it is high desert with similarly cool to cold temperatures. It should be dry though! Best of luck!