How to predict frost or freeze

[Rocket]

For years I have listened and watched for frost warnings to protect plants in the fall. Often times a light frost comes through the area early in the season and does little damage. The "killing frost" or "hard frost" is the one that ends the growing season. How are they predicted? I hope it isn't just: when temps hit 32°F. What are the variables to look for? As a new wx station owner do I have the data to predict frost here?

Next is freezing. More specifically, road ice Is there a way to predict road icing other than measuring pavement temperature? We use lasers to read the temperature of the pavement. There seem to be a lot of variables that go into road icing. There can be icing just above the freezing mark or below. Is freezing the same as frost? Are the variables the same?

Where am I going with all of this? Ultimately, if at all possible, I'd like to have the weather station console or computer warn me when the conditions are ripe for either condition, so that the appropriate action can be taken.

Thanks for helping me understand this.

[ORH_wxman]

Frost occurs when the temp at ground level reaches freezing and the dewpoint is the same. This is not the same as the 2 meter temp reaching freezing. Sometimes, the layer near the ground below freezing can be so inverted, that the 2m temp can be 35F or 36F.

Best conditions for frost are clear, calm nights where the sfc can radiate extremely efficiently. The air right near the sfc will cool to below freezing and the surrounding air holding more moisture will condense on the sfc objects below freezing and produce frost.

As for road icing, its very difficult to predict unless you know if they have been pretreated. In colder climates, we often see roads pretreated with a brine solution in anticipation of colder weather and icing issues. If the roads have no treatment on them, then icing will occur whenever you have the sfc of the road drop below freezing and humidity it up near 100% (either actual freezing rain or freezing drizzle, or even just a saturated airmass below freezing which most commonly creates black ice because th elayer is so thin).

[Rocket]

What does it mean when you say

Sometimes, the layer near the ground below freezing can be so inverted, that the 2m temp can be 35F or 36F.

Does the cold air somehow get moved or is being "inverted" something else?

If I understand correctly, the ground is acting like a refrigerator of some type. It releases heat to the air and the process somehow drives down the surface air temperature. The warm air at 2m is capable of holding more moisture and when that comes in contact with the cooler surface air it condenses and creates frost—when the temps are low enough at the surface.

Am I understanding it correctly?

[WxUSAF]

What does it mean when you say

Does the cold air somehow get moved or is being "inverted" something else?

If I understand correctly, the ground is acting like a refrigerator of some type. It releases heat to the air and the process somehow drives down the surface air temperature. The warm air at 2m is capable of holding more moisture and when that comes in contact with the cooler surface air it condenses and creates frost—when the temps are low enough at the surface.

Am I understanding it correctly?

What he means is there is a temperature inversion. Warm air above colder air. The ground cools radiatively much more efficiently than the air. It can cool to freezing while the air just a few feet above the ground is 2-5 degrees warmer. If the dewpoint (measure of moisture in the air) is also at freezing (really just equal to the air temperature), frost will form on the ground.

[Rocket]

Ah, that makes sense. How low can the dew point get? If the dew point were lower than 32° but the sfc temp got to 32°F would we end up with frost? My elementary thinking is that there would not be enough moisture in the air to produce frost.