What Is Frost ?

[jmsieglaff]

Where frost forms the temperature is freezing or less. Where your thermometer is it could be 35 or 40 or whatever. Have a frost prone spot put a thermometer there to see how it differs from your other(s).

Temperature inversions (coldest at ground level) and warming with height are most common on frost conducive nights (e.g.-calm and clear). It is common for
a 3-5F temperature inversion to exist from ground to standard thermometer height on nights like that (6 ft).

On calm nights small variations in terrain height matter, with the coldest air draining and pooling in the lowest spots due to gravity.

So frost can form "when the temperature is above freezing" because your thermometer isn't where the frost is.

Originally Posted by Gardeneer

Right. Radiation heat loss to the space is what happens in the deserts .
So that is what frost at 35F happened last night. It might even happen with tonights's low of 40 with clear starry skies.

[Worth1]

Frost happens when a witch flies close to the ground on her broom.
Back in 2001 we had our last witch hunt and burning and haven't seen a frost since.
So this is proof I am right.
It is witches that cause frost.

So if you have a garden and are worried about frost you better get in good with your local witches if you have any.
It is also a well known fact that they live in the north more than the south.

We have more witch doctors which are not to be confused with a witch.
Witch doctors cant fly on brooms and they do not cause frost.
There is also the voodoo queen but she cant cause frost either but can bring in plagues and bad luck.

I have been sitting on my hands for some time now reading all of this stupid garbage about temperature dew point and radiation till I just couldn't take it anymore.
Any idiot would know it was a witch not some stupid unproven modern science.

They really need to get back to basics in our schools and start teaching the right things.
Stuff like how to dunk a witch building a good witch burning fire how to attache a stake to a wagon and stack brush.
They need to start as soon as they can in our schools teaching how to organize a witch hunt too.
It is also a well known fact that around 80% of all redheads are witches.
Keep a sharp eye out for them.

Maybe we could outlaw brooms or have a witch test before people buy brooms.
Maybe even a dunking.
If they drown they weren't a witch if they float they are and cant buy a broom.

So anyway to wrap things up as long as we have witches and brooms we are going to have frost.


Worth

[henry]

From mid June to Mid August our witches trade in their frost brooms for fire brooms and take a vacation.

[Hoosier]

Originally Posted by jmsieglaff

Where frost forms the temperature is freezing or less. Where your thermometer is it could be 35 or 40 or whatever. Have a frost prone spot put a thermometer there to see how it differs from your other(s).

Temperature inversions (coldest at ground level) and warming with height are most common on frost conducive nights (e.g.-calm and clear). It is common for
a 3-5F temperature inversion to exist from ground to standard thermometer height on nights like that (6 ft).

On calm nights small variations in terrain height matter, with the coldest air draining and pooling in the lowest spots due to gravity.

So frost can form "when the temperature is above freezing" because your thermometer isn't where the frost is.

Not in all cases as you can get evaporative cooling that can form frost when it is above freezing even at the ground.

[jmsieglaff]

Originally Posted by Hoosier

Not in all cases as you can get evaporative cooling that can form frost when it is above freezing even at the ground.

The point is at the location where frost is forming the temperature is freezing or lower, whether it is at the ground or 6 inches or 12 inches above the ground, etc. Most often people place thermometers 3-7 feet above the ground and the temperatures at the thermometer doesn't depict what is happening where the frost is forming.

[Worth1]

I was driving to work the other morning and it said 47 degrees at my house with the truck thermometer and read this for some distance.
I looked up at one spot and it was 40 for about 1/4 mile and then jumped back up to 47.
Also when I go down the road to town there is a big cemetery on the tall hill.
At this exact spot it is always way cooler than the rest of the way.
It is like going through and air conditioner and back out again.
There are several of these cool spots around here even in the summer it is cooler big time and always in the same little spots.
I wish I would have looked for a home in one of them.

Worth

[jmsieglaff]

Originally Posted by Worth1

I was driving to work the other morning and it said 47 degrees at my house with the truck thermometer and read this for some distance.
I looked up at one spot and it was 40 for about 1/4 mile and then jumped back up to 47.
Also when I go down the road to town there is a big cemetery on the tall hill.
At this exact spot it is always way cooler than the rest of the way.
It is like going through and air conditioner and back out again.
There are several of these cool spots around here even in the summer it is cooler big time and always in the same little spots.
I wish I would have looked for a home in one of them.

Worth

Driving through a region of varying terrain on a calm, clear night/pre-dawn is interesting for that very reason. There is a small valley with a stream I drive through on the way to work, one time this winter it was -1F pretty much everywhere except as I drove through, the temp dipped to -11F.

Our backyard, while small is graded ever so slightly as to have a low spot that goes through the middle of it. On those borderline frost nights, the back edge of the yard and the part closer to the house will be dewy, but the middle low region will have spotty frost.

[wxcrawler]

With just the right conditions (clear, calm, right moisture content), you can have the temperature at the surface be 31. And just 2 or 3 inches above that level, it can be 33. And at the same time, a properly sited thermometer at 6 ft. might be 38. The lapse rate is almost always highest right at the surface. You can get frost if even the lowest centimeter is at freezing or below.

Lee

[Worth1]

The best thing to do is fire up a sprinkler in the garden or smudge pots but lots of luck finding one of those now in quantity.

[Gardeneer]

Last night my remote sensor ( outside on the north wall ) registered 39F. Again, we had a light frost. The frost must be right on the surface, not the air mass or higher. That is why we see it on the grass not on the trees and shrubs.
Anyway, it is over. Tonight's low will be 45F and there on the lows will be in 50s.
Time to plant out the okra seedlings. That is tomorrow.