Impact of humidity, cloud cover, wind... on frost damage

[cousinfloyd]

I know temperatures definitely don’t tell the whole story of how bad a frost will affect plants, but I really don’t understand the rest at all. Looking at the forecast I wonder if I should be more or less concerned based on some of the other things in the forecast, like humidity, cloud cover, wind, barometric pressure… Does anyone understand these things well enough (or know of a good link) to explain how I can read these other things (besides temperature) in the forecast to foresee what kind of frost damage is likely?

[jcguarneri]

I do know that if there’s no cloud cover, you’re more likely to get a frost. The clouds act like a blanket to keep heat in. I remember seeing a post on here somewhere about radiative cooling; I’ll see if I can find it.

[jcguarneri]

Here we go:

Freeze tonight

Nice explanation of what is about to occur in my backyard… Radiation Frosts A radiation frost is probably the most common during “cold sensitive” times in Washington and is the easiest to protect against. Almost all frost protection systems/methods available today are designed to protect against radiant-type frost/freezes. Radiant frosts occur when large amounts of clear, dry air move into an area. There is almost no cloud cover at night. During these times, the plants, soil, and other obj…

[Boizeau]

Orchards in Eastern Washington use wind machines to stir the air. This brings warmer air down to the Orchard floor. Works well during a moderate freeze.
Bare soil also releases more heat at night than tall grass.
Mulch keeps the soil cooler, not a great idea in the Puget Sound lowlands, unless you grow Rhododendrons.

[Oepfeli]

The fruit farm I worked at would close the rain roof over the cherries and turn on the irrigation. The running water caused air movements so the cold air could not settle down. At least that’s how the farmer explained it to me.
This made a difference of 1 to 2 degrees Celsius.

[zendog]

No links or specific scientific explanations, but the ability of frost to settle into low sections when there is little to no wind was really brought home to me this spring. At the community garden where I have a plot, my neighbor has really built up the paths around the edge of his plot, so that they are about 6" higher than his central growing area. During our late Spring cold snaps, his seedling tomatoes and eggplants were killed twice by frost when those in plots only 20 feet away only had some light frost burning on the leaves. Just that little bit of low spot he’d created by mounding up the surrounding walkways was enough to collect the colder air during the still mornings. I imagine if he had electricity there (we don’t) just a single fan might have made a difference.