While vacationing in Idaho and Montana last week (blissfully off the grid), I experienced something beautiful: altitude. At 6,260 feet Stanley, Idaho is a mile higher than my home in San Diego. The skies there were a brilliant blue. There was daylight well after 10 PM. The mornings were a chilly 35 degrees. And I got sunburned.
How can this be? Montana is over 1,000 miles north of San Diego. Shouldn’t the sun be stronger down here?
Several things determine the sun’s intensity. The closer to the equator you are, the more intense the sun’s rays. But also, the higher up you are, the more intense the sun’s rays. Your UV exposure increases by 10% for every 3,280 feet in altitude; at 6,000 to 8,000 feet in elevation, you’re exposed to 25% more ultraviolet radiation than at sea level.
Also, snow (which fell during our mid-June trip) is an efficient reflector of sunlight. When skiing or hiking in snow, 80-90% of UV light is reflected at you, dramatically increasing your sun exposure. Grass in comparison reflects only about 3% of sunlight.
Water, especially when still, also reflects sunlight. Still lakes, including the beautiful Yellowstone Lake pictured above, can reflect up to 100% of UV light (hence the term mirrored lake), doubling your UV exposure.
So although you might feel hot lying on the beach in June in Southern California, you might be more vulnerable to sunburn on a chilly hike in Yellowstone after a June snowstorm, which is exactly what happened to me. (Hence the Stetson later in the trip…)
Photos: Madsit, Stanley, ID (top) Purticortico Yellowstone Lake, WY (middle) Dermdoc White Bird, ID (bottom).