The weather can change rapidly. It can be 70 degrees F (21 degrees C) one day and 30 degrees F (-1 degrees C) and snowing the next, even in July.
Strong winds are common.
Thunderstorms move in rapidly. Seek shelter immediately. Avoid ridgelines and isolated tall trees.
Elevation
Monument elevations range between 6,600 ft (2012 m) and 8,000 ft (2438 m) in a desert. You will get sunburned and dehydrated more easily than at lower elevations. The air is also much thinner than at lower elevations and can put more strain on you.
Be aware of your physical limitations and drink water than you normally would to avoid the dehydrating effects of our dry desert climate.