Thursday, April 5, 2007

Lenticular clouds

I took this photo at dawn at the base of the Caps Ridge Trail in August, 2005. The summit is Mt. Jefferson in New Hampshire’s Presidential Range. Slightly above 5700 feet high, Jefferson is tall enough to obstruct the westward-moving airflow in the lower atmosphere. When the stream of air pushing against the mountain is moist and stable, lenticular clouds form because the mountain forces air molecules up into cooler strata, where condensation occurs.

The multi-layered aspect of the cloud indicates several distinct levels of humidity and is known as a pile d’assiettes—French for “pile of plates.” Lenticular clouds often forbode wet weather and have been mistaken for UFOs. On this day, we were lucky. We encountered nothing worse than a few cumulus on our traverse across to Eisenhower.

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