Summer temperatures are pleasant along the rim, but increase rapidly as you descend into the canyon. Low humidity causes significant temperature differences between day and night. The low humidity and high elevation also means that it is important to drink water frequently. Afternoon thundershowers are common in July, August, and early September. Windy conditions prevail in April and May. Snow may fall as early as November. Winter snowstorms continue into March. Roads are plowed frequently, so closures seldom last long. For more information about the Grand Canyon's South Rim visit www.nps.gov/grca/.