Frost

[Billy]

If those are dark scud clouds, I wouldn't sweat the garden. Shelly never could read well.

[Dioclese]

I agree most of what you're saying.

What I do disagree about it airflow in lowlying areas. Your final perception is correct, low spot is colder. You have to understand that heat is what's being lost, not cold gained. Cold is the LACK of heat energy. The heat is moving uphill, rather than cold moving downhill

If "cold" was moving downhill, it would have point of origin. Which it doesn't if the ambient air temperature is warmer that the cold pocket in the low spot you indicate.

Kind of reminds me of "hole flow:" vs. "electron flow" in electronic circuitry theory. Both theories work, but the former ignores what is actually moving. But, that's another story.

[David Hare-Scott]

Yes

Some where between these two extremes, air

Maybe, but how much? I am not saying you are wrong but what effect will it have and is it worth worrying about? In what situation would this effect make a practical difference?

I think we all agree on that.

David

[David Hare-Scott]

Yes because it reduces radiant heat loss like cloud cover

I won't say anything else. I'm just dazzled by some of

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

[David Hare-Scott]

I find this odd that you tell us you are an expert and that much of this discusion is wrong but you won't say what is right. I am not trying to have an argument but to learn.

David

[Pat Kiewicz]

"Cold" doesn't move, but cold air most certainly does. And cold air drainage to low lying areas makes them more prone to frost.

$department/deptdocs.nsf/all/agdex9

Cold air drainage On calm nights, the shallow layer of cold dense air that forms near the ground surface will tend to flow downslope if the ground is not completely level. This phenomenon is known as cold air drainage. It has a major influence on the distribution of minimum temperature, rendering some areas much more frost-prone than others nearby. The coldest air settles in depressions commonly called frost hollows or frost pockets, or it collects in other areas where cold air drainage is obstructed by some kind of barrier.

On a small scale, the effects of cold air drainage may be visible in the widely variable frost damage observed within a medium sized garden. The lowest areas are hardest hit while higher portions may escape all frost damage. This underlines the importance of considering topography when choosing garden sites. On a larger scale, entire fields may be affected. Even if the slopes involved are very gradual, some fields are much more suited to cold-sensitive and long-season crops than others nearby.

[brooklyn1]

Most of the responses are for the most part correct, just not entirely accurate in every detail because it would require an entire library to describe the frost phenomena with exquisite detail, whereas most folks on newsgroups do not tend towards verbosity. Ommission and condensation do not necessarilly equal erroneous information, which is why discussion is ongoing and no one gets the final word, not ever. One should always be wary of self proclaimed experts; self praise is no recommendation. Those who enter discussion claiming expertise typically know the least... belittling other's knowledge and abilities is a mechanism whereby one attempts to disguise their own insecurities regarding their lack of ability and knowledge. The farblondzhet when questioned react with funfeh.

[Dioclese]

Cold air does move down in elevation. Heat moves up. Heat is lost pretty uniformly on cool, non-windy nights/early morning at the ground surface. And the coolest air settles in low pockets. Got it, thanks.

[Dioclese]

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.

[brooklyn1]

When fog (visible water vapor near the ground) freezes it's called frost... snow is different, snow is the inverse.

[Pat Kiewicz]

One of the most amazing things that can happen on a cold morning is a freezing fog leading to rime frost on trees. I've most often seen this in the river vally just north of my house.

It's staggeringly beautiful, but usually quite ephemeral, when the sun is shining; millions of rainbow crystals glittering in the morning light.

Some photos:

articles (with illustrations):

[brooklyn1]

Thank you for the lovely photos and very informative articles.

Your pictures remeinded me that I have some similarly depicting the frost phenomena, not nearly as artistic:

"Fat Albert" Colorado blue spruce's first Christmas (2008): it is at night... at first I was suprised, until I realized the flash made the otherwise invisable water vapor appear, eerie: new spruce is now covered with buds that weren't there last fall, albiet still tightly closed, very exciting waiting to see the progress.

[Pat Kiewicz]

You are most certainly welcome.

I wish I had done more than found them on the web. I did pick them out of thousands, though.

I finally found a crocus blooming near the SE corner of the garage. April already, and the snowdrops are still in bloom. The buds are finally showing some sign of swelling on the amelanchier.

We had one warmish day last month. Today is supposed to be warm, but I have commitments all day. And this weekend it will be turn COLD again. So the outside gardening is running behind.

Meanwhile, inside I'll be gearing up to start the tomatoes, eggplants, and peppers (and here's hoping we don't have a repeat of the late May hard frost this year).