The Ever-Changing Sky

Coming soon to a peak near you

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Frontal weather occurs when different air masses meet and cause a storm. The stronger the differences between the colliding air masses in temperature and moisture content, the stronger the front and the more severe the weather associated with it.

Fronts move across the United States from west to east, and clouds in the atmosphere often give us clues that indicate a front is heading our way. If you pay attention to the warnings, you can make an educated guess as to how much time you have remaining before the front arrives.

Indicators that a front may be moving toward you:

• Mare's tails: Thin, white to light-gray streamer clouds high in the sky (cirrus clouds). Isolated mare's tails aren't a strong portent of bad weather to come, but dense and widespread mare's tails can indicate the approach of a front from as far as 24 to 48 hours away.
• Uniform, featureless, white or gray clouds at high altitude covering most or all of the sky (cirrostratus): These clouds usually mean that a significant amount of moisture is moving into the area. They aren't spectacular, but they are important. Monitor the sky for a change in the weather.
• Halos: Rings of light around the sun or moon caused by light refracted through high altitude ice crystals. The old adage about halos preceding storms by 24 to 48 hours generally holds true in the moister regions of the United States, but in the drier climates, halos often pass with no ill-effects.
• Gray, water-droplet clouds at medium altitude (altostratus clouds): A solid coverage of these gunmetal-gray clouds usually precedes major weather systems by less than ten hours.
• A layer of dark clouds with noticeable blurring below the cloud bases (nimbostratus clouds): These clouds bring rain or snow, and in the warmer months can develop into thunderstorms. Typically associated with the arrival of a front. The weather is likely to stay bad for 24 hours.
• Frontal thunderstorms: These storms are formed when the leading edge of a cold-front wedges up warmer air in front of the moving cold front. This forms lines of thunderheads stretching from horizon to horizon (squall lines) and very severe weather.

Remember: This information is meant to help you make informed decisions. Weather forecasting is a very complicated discipline. When weather threatens, exercise good judgment and err on the side of safety.

Three months after our dousing in Eldo, Casey and I were halfway up the Longs Peak Diamond. When the puff clouds started swelling, we retreated. The sky became ever-more threatening as we descended. Peels of thunder echoed through the range as we rappelled the North Chimney. Just as we reached the snowfields, the swelling clouds passed overhead to reveal a calm, blue sky.