Hard Freeze

[polarisrider1]

What is meant by that?

 

[jd]

Typically it is issued when minimum temps of 28 degrees F or colder are expected. Most plant can handle temps at to just slightly below freezing, but may suffer damage with temps at to below 28 deg. F.

-John

 

[polarisrider1]

Typically it is issued when minimum temps of 28 degrees F or colder are expected. Most plant can handle temps at to just slightly below freezing, but may suffer damage with temps at to below 28 deg. F.

-John

Hope that don't take out the apple crop again like last year. Thank you for the info.

 

[polarisrider1]

So, at what temp does frost begin?

 

[jd]

So, at what temp does frost begin?

Frost is just ice accumulation on a surface. So you need to have the surface the ice is attaching to be at to below freezing. Air temps can be a few degrees above freezing and still have frost formation.

-John

 

[anonomoose]

Frost is just ice accumulation on a surface. So you need to have the surface the ice is attaching to be at to below freezing. Air temps can be a few degrees above freezing and still have frost formation.

-John

Here is a bit more detail on this process which is, rather interesting.

Every warm object loses energy by radiating electromagnetic energy which are, infrared photons. Normally things tend to equalize receiving and losing heat keeping the temperature at a relatively steady state. However, if it receives less such as you get on a still clear night, it loses energy very quickly and cools down. The earth, house top, car roof all are more dense than the air around it and radiate faster than the less dense air around it.

Space has an effective temperature of three degrees above absolute zero! Your metal car top is much, much warmer; so the roof of your car loses energy to space faster than the air around it. If there is moisture in the air just when and just like your glass of lemonade it will condense on the outside...be it the roof of your car or house or barn. As it continues to cool often faster than the air around it, frost forms as John says it is ice and to form is must be 0 c or below.

[FONT=arial, helvetica, clean, sans-serif]On a cloudy night, the clouds become a barrier to this process and the action is [/FONT][FONT=arial, helvetica, clean, sans-serif]interrupted[/FONT][FONT=arial, helvetica, clean, sans-serif] along with the fact that moisture in the clouds probably are above freezing too and act like an insulating blanket. So If the temperature stays above freezing little of this action occurs. Clear weather is important in this process. It should be stated that, it doesn't happen to objects under trees, canopies or other objects that block this process. You need open sky.[/FONT]

Two other heat transfer processes of conduction and convection move heat from one object to another also but it is radiative type transfers responsible for those frosty pictures in early fall we all wait for to get our juices flowing for the sledding season about to begin.