Travis Credit Union
Travis Credit Union

At the field level, even the smallest weather change matters

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One of my retirement hobbies is playing in a senior softball league “the Creakers” sponsored by the city of Walnut Creek.

Weather conditions are always a factor when we play. At a game a few weeks ago, we observed air motions ranging from the smallest scale to the largest.

Meteorologists divide the scales of atmospheric events into three broad categories: microscale, mesoscale and macroscale. These groupings are based on both the time and space scale of wind and weather patterns.

Microscale circulation

At the field level, even the smallest weather change mattersAs I was patrolling right field in the first inning, a high fly ball came in my direction. While waiting for my “can of corn,” a surge of wind hit my back. In a mini-second, the gust altered the course of the ball and it hit the ground after grazing the tip of my glove. It was an error in the scorebook and a good example of microscale wind motion.

Microscale circulation is the smallest scale of air motion. These air currents are often chaotic in nature, lasting from seconds to minutes. We can observe them for distances ranging from several feet to several miles. Because of the short space and time scales, they are nearly impossible to predict. The turbulence you experience in an aircraft and dust devils are other examples of microscale flow.

Mesoscale weather event

Later in the game, the sky suddenly grew dark and a strong shower developed. For about 20 minutes, wind-driven rain pelted the field as we escaped to the meager shelter of the dugout. A mesoscale-sized event caused the weather delay.

Mesoscale weather events last from minutes to hours. They can be transitory or stationary. Showers, thunderstorms and tornadoes are transitory mesoscale events. Stationary examples include the Bay Area sea breeze and the daily upslope/downslope wind flow cycles in the mountains.

Macroscale patterns

By the time the game ended, the skies had mostly cleared. However, we could see smooth bands of slightly arching cirrus clouds high overhead. These clouds formed a small part of a macroscale circulation pattern known as the polar jet stream.

Macroscale winds represent the largest circulation patterns in the earth’s lower atmosphere. These wind patterns last from days to months and have distance scales that range from hundreds to thousands of miles.Trade winds and the jet stream are good examples of planetary scale wind patterns.

The synoptic scale is a subcategory of macroscale events. Synoptic scale weather patterns typically last from days to weeks. Examples include hurricanes that develop near the earth’s surface and the anticyclonic (highs) and cyclonic (lows) circulations at the jet stream level.

Even though each scale of atmospheric wind pattern has defined time and space bounds, there are often interconnections between the scales. For example, the synoptic scale storms that deliver winter rains to California are embedded in the global jet stream circulations.

As a meteorologist, I enjoy observing all the scales of motion in our atmosphere. As a ballplayer, I could live without the microscale winds that twist and turn a sailing softball out of reach.

Woody Whitlatch is a meteorologist retired from PG&E. Email your questions or comments to
clayton_909@yahoo.com

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