Stratus clouds in Nilgiri valleys

Stratus clouds seen in one of the valleys of NBR (Photo P.A. Vinayan)

Clouds form in a valley mostly related to the temperature inversion. Mountain areas often produce morning valley fog after a clear night where air near the damp ground has cooled by radiation. As the cool air is heavier it stays in the valleys, leaving the tops in clear warmer air. The sun will normally destroy this effect within a few hours of rising.

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