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More on frost.  RSS feed

 
Emerson White
Posts: 1206
Location: Alaska
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A few times I've heard (read) Paul and Sepp talking about draining frost away, treating it like a liquid, but I think that is only one part of the frost story. No matter where you are cold air is slightly heavier than warm air at the same pressure , but I'd encourage you to look at some mountains in the fall. Here we call it termination dust, as the summer comes to an end the snow creep further and further down the mountains. This occurs because the air up higher has lower pressure and there for lower temperature, since the low pressure air cannot push down below the high pressure air with out being squeezed (and rising in temperature and pressure) you end up with what is called a temperature inversion. In the winter that freezing line will continue to lower in elevation until it hits the ground, and suddenly you have a frost that is on top not on the bottom. Now a raised bed will heat up during the day, and cause things to germinate and buds to break, but if that happens and then the temperature inversion descends on your plants the frost will ravage them (unless they are peas, I love peas), in that way a raised bed can be a plant death trap instead of a plant life raft like it is in Montana and Austria, and probably most places.

Some season extending measures do not do enough to extend the season.

And additional problem is night sky radiation. Some of you will notice that clear nights are cold nights, even with out a problem with frost pooling it is possible for more radiation to leave the tissues of a plant than comes in to them, in that case the tissues will freeze and a raised bed does nothing to prevent it (and may make it worse by holding the plant further away from the radiant heat from the ground.
 
Rob Sigg
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Location: PA-Zone 6
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Interesting thought. Apparently its not an issue for Sepp in practice?
 
Emerson White
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Location: Alaska
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Well the pressure gradient is not so extreme at altitude (it's an exponential thing) so I'd expect Sepp and other people at altitude to have less of an issue with it.
 
maikeru sumi-e
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Inversions suck. We get them every winter where I am along the Rockies and they're pretty horrible. They also trap air pollution in the valleys. Like you mentioned, some of the coldest nights are the clear sky nights, and the warmest ones in the winter when it's cloudy or even snowing.
 
Brenda Groth
pollinator
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Location: North Central Michigan
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the inversions wouldn't apply to where I live we have no mountains, but we do get nightime radiation on clear nights when there is no cloud, wind, or moisture to hold in the heat..like the full moon we have had the last two nights..however, generally it is early on before we have bud break.

I always have said I won't plant my tender plants outside until AFTER the full moon in June here in Michigan as the full moon on a clear night will always bring a frost..we had a couple summers where we had a frost each month all summer long cause of the full moons..and that sucks bigtime.
 
Mekka Pakanohida
Posts: 383
Location: Zone 9 - Coastal Oregon
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"Smart Permaculture Design" by Jenny Allen has a passage and illustrations on how you can use this to your advantage to protect frost sensitive plants.

"A Frost Diversion Arc deflects frost. It is on a hill, with the highest point at the top and sides going around the plants that need protection.  As cold air drains down the hill it flows to either side of the arc.  When it reaches the bottom of the hill it pushes warmer air up into the arc to those plants that need it most.  If the slop is northerly facing ((Aussie book, flip for norther hemisphere)) the arc can double up as a sun trap.  Sun traps increase and store heat in the soil, water and structures with a high thermal mass.  This also helps prevent frost." Pg112


I don't think of it as water, more like molasses. 
 
Jordan Lowery
pollinator
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Location: zone 7
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i agree Emerson, i watch the frost here all winter. study its actions and how to deal with it. raised beds in the wrong spots are basically like you said a death trap.

also like mentioned, cold clear nights after a storm has passed is the worst. everything gets frozen solid. except my peas too haha.
 
Rob Sigg
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Location: PA-Zone 6
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Im curious as to what altitude you all are at that you get this reversal?
 
Emerson White
Posts: 1206
Location: Alaska
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I live at 82 feet above sea level.
 
Mekka Pakanohida
Posts: 383
Location: Zone 9 - Coastal Oregon
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Rob S. aka Blitz wrote:
Im curious as to what altitude you all are at that you get this reversal?


180' here above and I see it on a daily basis, it's a great morning show to watch over chai, coffee or tea
 
John Polk
steward
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Location: Currently in Lake Stevens, WA. Home in Spokane
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On a cool, calm and clear night, water can freeze at temps well above 32° F (0° C).
The clear skies can suck heat so quickly out of the water that it freezes, even though the surrounding air might remain @ 35°.
Similar experiments have shown that on a 30° F night, two dishes of water, side by side, one at 33°, the other at 38°, the warmer dish will freeze first.  The more rapid temperature change needed to "equalize" the warmer dish is what causes this phenonoma.
 
Emerson White
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Location: Alaska
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It happens at all altitudes, it's just a matter of degree. It also happens in areas with no mountains. The effect literally exists over the entire globe. If you got in a space ship and flew high into the air you would notice that the pressure drops and the temperature rises as you fly into the air. pV=nRT
 
Rob Sigg
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Location: PA-Zone 6
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Strange, I live at 600 above according to a website that calculates it based on your address. There are hills and mountains around, and I live on top of a hill and I haven't seen this yet. Im keen to keep on eye on it now.
 
Emerson White
Posts: 1206
Location: Alaska
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Well You won't necessarily see it if you haven't got an aerial with a bunch of thermometers on it.
 
John Polk
steward
Posts: 8019
Location: Currently in Lake Stevens, WA. Home in Spokane
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Regardless of your altitude, you should be slightly warmer than the folks "downhill" from you.  Temperatures decrease with altitude, but since cold air "falls", they should be getting frosts, while you remain slightly warmer.  This is all presuming no wind.
 
Emerson White
Posts: 1206
Location: Alaska
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What I'm saying is that that isn't always true, it all depends on the pressure gradient vs. the heat lost to night sky radiation. On a cloudy day less heat will be lost to radiation, so the temp will drop more slowly, so there will be less of a temperature differential and the frost will not run off down hill. Just think about a naturally vegetated mountain, maybe somewhere like california. At the base of the mountain it could be tropical, with ferns and palm trees. While the top might be alpine, with super hardy plants. It might never ever frost at the base, while the peak could get snow 10 months of the year.
 
Walter Jeffries
Posts: 1095
Location: Mountains of Vermont, USDA Zone 3
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"raining the frost away like a liquid"

This is how I setup our farmstead. Our neighbors down in the valley get frosts later in the spring and earlier in the fall than us because the frost settles down there. I setup all of our gardens and terraces so the cold air drains down and away from us. It makes a very big difference. This gains us weeks of frost free time on either end of the growing season for things like pumpkins, tomatoes, etc.

Unfortunately we have much deeper snow cover due to our altitude so we get snow up here much earlier and it lasts much later than for pastures down in the valley. This means our grasses, our fields, open up later in the spring. I combat this by changing our albedo  by spreading wood ash using the wind. The wood ash darkens our snow fields and causes the sun to melt them sooner. Timing is critical as is wind direction. Think Local Warming!

Cheers

-Walter
Sugar Mountain Farm
Pastured Pigs, Sheep & Kids
in the mountains of Vermont
Read about our on-farm butcher shop project:
http://SugarMtnFarm.com/butchershop
http://SugarMtnFarm.com/csa
 
Emerson White
Posts: 1206
Location: Alaska
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I really like the albedo idea.
 
                                              
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this is a very interesting thread, and touching subjects Ive not encountered before... i will have to research this some more. thanks!!!
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