Vail Daily column: As the world turns
Vail, CO Colorado
The one thing that you can always count on during this time of year in the mountains is the unpredictability of the weather. Fall football games in Denver are a blast, but driving back through these first fall storms is not. During this time of year, it’s not uncommon to hear predictions of gray skies and snow flurries only to find that the day actually brings clear, blue skies and warm temperatures – or vice versa. Unfortunately, you have already driven into work wearing your snow boots, ski socks, and wool sweater in preparation for the cold, wintery day predicted on the morning news. So it goes.
Weather in the mountains is always somewhat fickle and tremendously variable. This is due to global and local factors related to the Earth’s orbital path and to mountain topography. Starting with the big picture, we all know that the Earth is tilted on its axis. During the lazy days of summer, the Northern Hemisphere is tilted towards the sun, receiving the most direct sun’s rays at 23.5 degrees north latitude. At our latitude of approximately 45 degrees north of the equator, we are relatively close to this line and receive the most direct sunlight we will receive all year long. As summer fades, and the Earth continues on its path around the sun, the Earth’s tilt is now neither towards nor away from the sun. Instead, the Earth is tilted sideways relative to the sun, with the most direct rays hitting the Equator, leaving us northerly folks to feel only the faint heat from slanting rays.
To understand the impact of slanting versus direct rays, imagine the beam of a flashlight. When the center of the light is shining directly on the Equator, the rays that hit us up north are faint and diluted. This means that there is less incoming heat radiation at our latitude. In addition, all summer long the Earth has been absorbing heat from the more direct sun’s rays. As we proceed through fall and the air cools, the Earth radiates heat into the air, creating warm rising air currents. The result is that we get air masses of different temperatures coming together. Since air masses of different temperatures don’t mix, this results in all kinds of turbulent weather from their various boundaries (fronts) and interactions.
Weather in Colorado is strongly influenced by air masses that originate in the Pacific Ocean. During the fall months, these air masses are warm relative to the land, because the ocean water releases its absorbed summer heat slower than the land. These warm, moist air masses are blown inland by the Prevailing Westerlies, winds that blow from west to east across the United States. The Jet Stream also flows from west to east, but at a much higher altitude. When the Jet Stream is over Colorado, it blows the big storms along with it. At other times, the Jet Stream carries the big storms north or south of us and we can only enviously watch the flakes on the news and wait for the winds of change to blow again.
Finally, our mountain topography also dramatically affects weather patterns. Mountain weather patterns are characterized by orographic precipitation. This precipitation occurs when moist, warm air moving across the landscape encounters a mountain. The air cannot go through the mountain, anymore than you or I could, and as more and more air collides with the mountain, it begins to push itself upwards, along the slope of the mountain. As it rises, the air cools as it encounters cooler temperatures above. Cool air cannot hold as much moisture as warm air and the water vapor begins to condense into droplets, forming rain or snow, depending on temperatures.
The unique weather influences present in our region combine to give us a variety of unpredictable and seemingly erratic weather. Ever wonder why the weather predictions are so often wrong? It’s because of the tremendous number of factors that come into play to influence our weather. James Gleick described what he termed The Chaos Effect, where the influence of a butterfly flapping its wings can influence the direction an air mass takes, dramatically changing the weather in a far off place. Predicting the weather is a science, but despite tremendous knowledge and technological advances, it is still a science plagued with uncertainty and unpredictability.
Jaymee Squires is the director of graduate programs at Walking Mountains Science Center. Jaymee lives in Eagle and enjoys playing outside with her family in all sorts of weather.
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