Cold Air in Low Spots – Fog, Dew and Frost

Morning fog, sun and sunrise

The sun has come up over the marsh and through a thick fog, making the trees and other plants in the landscape bathed in and orange glow.

Fog can slowly build up, or silently and slowly roll in during the night.  If may quickly burn off in the sun, or quietly drift away on the morning breeze.  Fog can come during any season, and any time of day.  Fog is a common sight in the low-lying areas of the landscape.  Cold air collects in the lowest areas, often wetlands.  The wetlands themselves retain the heat of the day and when the cold moist air and the warm ground meet, fog forms.

In the northern US and mountainous regions so much cold air can collect in certain low places it can freeze anytime of the year.  Frequent summer frosts can stunt trees and many species of plants can be killed by a mid-summer freeze.  Such areas are sometimes called frost pockets.  The small trees there may be as old as the large trees on nearby, higher ground.

Time-lapse of fog lifting in the marsh

August frost in the Rocky Mountain

An August frost in the Rocky Mountains

Most spring and summer mornings the conditions in wetlands favor dew when the temperature dips below the dew point at night.  When I conduct plant surveys in wetlands I go out as early as possible to avoid the high humidity and blazing summer sun.  I used to wear blue jeans, and they would become completely drenched with the condensed humidity that clung to the leaves of grasses, sedges and flowers.   By 10:00 the bright sun would completely dry them out.  After a time I switched to wearing rain pants for the morning and then took them off when I got hot. It is a sensible thing to do, but somehow it feels like disconnecting, if ever so slightly from nature.

Wisps of fog, crusty frost, and dew drops on spider webs are beautiful sights.  All appear so delicate.  Fog can’t be broken, but a slight brush against a plant brings a rain of dewdrops, and a little warm breath melts the icy fingers of frost.

Dead Tree Fog Pond

Dead trees in the pond, dark skies and fog give a spooky feel to this August morning.

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