Despite Arizona's desert environment, cold, snow, rain, and wind are commonplace on mountains and also canyons at certain times of year. Mountain weather is notoriously unpredictable. Temperatures can plummet to well below 0ºF, winds can become fierce, and whiteouts can disorient you.
Heat stroke and hypothermia are possible on the same hike if the weather changes. Hypothermia is the cooling of the body's inner core. It is the primary killer of outdoor recreationists. Warm and dry clothing including hat and gloves, high-energy foods, water, a good night's sleep, and avoidance of alcohol all can help ward off hypothermia.
Symptoms of hypothermia include uncontrollable shivering, poor coordination, loss of manual dexterity, drowsiness, disorientation, slurred speech, and exhaustion. The recommended treatment is to get back to your car or shelter as quickly as possible, keeping dry, getting out of the wind, eating fast-energy food, and slowly rewarming the body externally. Do not give hypothermia victims liquids because they may be in shock.
Check the weather conditions before you leave, but keep in mind that thunderstorms are common in Arizona from June to September, and their occurrence is unpredictable.