Be prepared for snow, icy roads and trails, and possible road closures. Winter conditions on the South Rim can be extreme. However, late summer thunderstorms or early winter snow storms have been known to take place during this transition season, making for sudden changes to the weather. The summer rains typically diminish in mid September with a drier fall period the norm with fewer days of precipitation. Low temperatures will typically fall below freezing on the Rim, but still remain in the warm 50s and 60s (10-21☌) along the river. The summer heat gives way to a cooler but nonetheless pleasant fall period with average high temperatures gradually falling from the 60s (16-21☌) in September through the 50s (10-15☌) by November along the Rim, and from the 90s (32-37☌) in September to near 70 (21☌) by November along the river.
Some of these storms can reach severe levels, with large hail, damaging winds, and occasionally even a tornado. These thunderstorms are extremely variable in intensity and location and occur mainly between the hours of 11 a.m. Summer thunderstorms frequently occur during July, August, and early September with the potential for torrential rains, frequent lightning, and sudden flash floods. Overnight lows can still drop near to below freezing occasionally on the North Rim, although typically low temperatures range from the 40s and 50s (4-15☌) at the South Rim to the 60s and 70s (16-26☌) at Phantom Ranch. North Rim summer high temperatures are typically cooler than the South Rim due to increased elevation (8000 feet/2440 m), with highs typically ranging in the 70s (21-26☌). Summer temperatures on the South Rim, at 7000 feet (2135 m), are relatively pleasant with high temperatures generally in the 80s (27-32☌) (with temperatures typically warming to over 100 degrees (>38☌) at the river near Phantom Ranch (2400 feet/762m). Summer thunderstorms and winter snowfall adds to the weather variety in this region. This weather variety includes cold winters and mild pleasant summers, moderate humidity, and considerable diurnal temperature changes at the higher elevations, with hot and drier summers at the bottom of the Grand Canyon along with cool damp winters. With an elevation spanning from around 2000 feet to over 8000 feet (760-2440m), the Grand Canyon area experiences a variety of weather conditions. Climate Overview for the Grand Canyon Region