"When the dew is on the grass
Rain will never come to pass.
When grass is dry at morning light
Look for rain before the night."
Dew forms when the air is cooled to its dew point, when it overflows with moisture. At night this happens in clear, cloudless weather, which (as it did in Sausalito last month) allows the day's heat to escape into the atmosphere. If a cloudless night cools the air, a cloudless day heats it and creates thermals. A heavy dew at dawn, therefore, may promise a fresh sea breeze that afternoon.
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