#MEwx Today's weather proverb

Now that summer is over, this proverb may be a bit late, but is still informative.

“When dew is on the grass, rain will never come to pass.”

Dew forms when grass gets colder than the dew-point temperature (the temp at which dew forms). At night, grass cools when heat from the ground radiates upward. In a clear, dry atmosphere, this heat escapes the atmosphere and rises into outer space.

In a moist and humid atmosphere, water vapor absorbs some of that heat and can redirect it back down to the ground, warming up the grass, and thus keeping it dew free.

Dew on the grass is therefore a sign of a high pressure system, and good weather.