I was pleased to be home mowing the lawn Saturday afternoon when I saw a thunderstorm building toward Camden and Rockland. We've had a few thundershowers in the last week, and at least twice they moved east to west, eventually soaking us here in Union. Thunderstorms in late June and early July are not unusual, but the east-to-west movement is unusual. Typically, our weather moves west to east. On my trips, I often check the sky to the northwest to ensure no storm sneaks up on us.
Curious, I checked online and found out it's not unusual for thunderstorms to move in different directions or speeds than the surface winds. Thunderstorm motion is primarily determined by winds in the middle layers of the atmosphere, known as the steering winds, rather than surface winds.
These middle-level steering winds often have different directions and speeds compared to surface winds. Wind direction and speed can vary significantly with height, so thunderstorms are steered by these middle-level winds.
It turns out that thunderstorms moving against the surface wind direction is not unusual due to this vertical wind profile in the atmosphere. I suppose even an old guide can learn something new. I'll need to watch the sky in all directions for thunderstorms when I'm on the water.
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