The Grand Canyon region is semi-arid, with great variation in temperature and rainfall due to elevation. Average annual precipitation is less than 10 inches at Phantom Ranch, 15 inches on the South Rim, and more than 20 inches on the North Rim. Most of the moisture arrives during the late summer monsoon season or during the winter. Temperatures vary from below zero to higher than 100°F in the inner canyon. Rims are often windy, and the inner canyon breathes, with upstream winds during daylight and downstream winds at night.

The seasonal descriptions below are general and hardly a guarantee. Expect the unexpected: snowstorms in June, 90°F temperatures in October, dry winters when the North Rim is accessible for stretches at a time, and long, cool springs when wildflowers seem to be in constant bloom.

In late March, when the calendar says it’s spring, the North Rim will still be tucked under a blanket of snow. On the South Rim, it may be cold and windy, but if you find a sunny, sheltered spot, you can already feel the power of the sun’s rays. During the next couple of months, spring creeps up from the inner canyon, as wildflowers bloom along trails and birds go about the business of establishing territories and nests.

Lingering Pacific storm patterns may dump inches of snow on the South Rim into April, though the snow melts quickly as the sun gains strength. By May, inner canyon temperatures are already reaching into the 90s, and winter loses its grip on the North Rim.

May and June are dry and cloudless. While the North Rim begins to experience spring, inner canyon temperatures edge toward the century mark as the dry desert foresummer tightens its grip. The South Rim is pleasant, with highs in the 70s and 80s, perfect for hiking. The intense sun quickly dries the forests surrounding the rims, and by the end of June, fire danger may trigger camping and hiking restrictions in the national forest lands surrounding the park.

As southern Arizona deserts heat up and weather patterns shift, pulling in moisture from the Gulf of Mexico, clouds begin to build, heralding the arrival of the annual monsoon. Hot, dry air may evaporate moisture before it reaches the earth, creating dry storms that spawn dangerous lightning.

By mid-July, the rains arrive at last in the form of brief, powerful thundershowers that sweep across the canyon, usually in the afternoon. The monsoon pattern lasts through August, the month when the inner canyon receives the most rain. A second bloom of wildflowers begins with the rains.

By mid-September, the monsoon retreats and cloudless skies return. Inner canyon temperatures moderate. Birds begin to migrate south, and on the North Rim, the aspens turn gold as October approaches. Sometime in November, the first heavy snowfall may close the road to the North Rim.

In December, Pacific storms again march their way west, bringing winter moisture to the canyon in the form of rain or snow. The North Rim can receive as many as 120 inches of snow; the South Rim, 65 inches. Ground squirrels hibernate, while deer and elk sink into winter sluggishness, conserving energy by browsing the piñon-juniper woodlands near the village and West Rim.

Snowpack is important in the West, providing a slow release of moisture as the weather warms, recharging springs and maximizing Colorado River flows. Glimpses of spring begin as early as February in the inner canyon, when brittlebush sends up its golden blooms and the cycle of seasons turns again.