"David Hare-Scott" wrote in message
...
Jangchub wrote:
On Sun, 29 Mar 2009 01:29:42 GMT, "brooklyn1"
wrote:

"Denis Mitchel" wrote:

Does the temperature have to be at or below freezing for frost to
form on plants?

No. The dew on plants can freeze without the air temperature
dropping to below 32ºF... this often occurs with lawns and other low
growing plants because even though the air near the ground is heated
by the radiant heat to above 32ºF yet the fine droplets will
freeze... fog can freeze and settle on plants (like snow). But
just because the dew freezes on the plant doesn't mean the plant
freezes, many plants contain chemicals that act as antifreeze, and
many plants will suffer 'frost' damage above freezing, especially
young tender seedlings. There's good reason why weather forcasters
mention "dew point", has to do with barametric pressure/elevation.

Why do you ask?


First of all, fog creates a blanket and prevents frost more than it
causes it.

Yes because it reduces radiant heat loss like cloud cover

I won't say anything else. I'm just dazzled by some of
the inaccuracies in this whole thread.

I can understand that you may not want to dispute with people, do you
assume that a dispute will necessarily follow? If we never find out what
is wrong how will we learn?

David

Am guessing here, mind you. In the area of TX where Elizabeth and I live,
foggy and misty mornings are quite normal.

Fog mist is the result of water saturated air being cooled enough to wrench
a small amount of moisture from the air and make visibility a problem. It
creates more air temperature uniformity at the ground surface by slowing
heat loss at the surface. So, frost is an exception here. Such foggy/misty
mess in the dead of winter here are rare exceptions, does this foggy mist
freeze. Typically, the fog is dissipated by the morning sun later in the
day. And all is dry as a bone by the heat of the afternoon. This occurs
regularly here.

The rare times we get a frost, its from a high pressure area rolling
overhead, but hasn't leached all the moisture from the air to create such
frost. Usually, its very light.

Something I didn't see pointed out was thickness of brush, trees, and
ground-hugging plants is also a deterrent to frost on a typical no-wind
frost day. Another sort of blanket, it you will.
--
Dave
Confront and fight Obama zombieism