Freezing Point

[derrynoose]

Why do weather forecasters warn us of the possibility of frost when temperatures fall to around 3 degrees since freezing point is 0 degrees.There is often mention of a wind chill factor. I assume that wind chill will lower temperatures but, if so, why don't the forecasters state an anticipated temperature level which includes an allowance for wind chill.

[seniorgrumpy]

The temps that weather forecasters give are for the air. The ground cools much faster than air and so an air temperature of 3c will often result in a ground temperature of 0c or below.
The second part of your question should be aimed at the forecasters themselves who are inconsistent about wind chill information - sometimes they give it but sometimes they don't. Note that wind chill only affects warm blooded creatures as the wind removes the layer of warm air with which they surround themselves to keep warm.

[Teddio]

Wind Chill is really a measure of the rate at which heat energy is removed from the human body. For instance at an air temperature of 4 Celsius it would be quite comfortable to go for a walk in light clothing if there was no wind. However, it it was windy it would feel much colder because the moving cold air would remove heat energy from your body much quicker.
Rainwater or condensation (dew) is impure and will freeze at zero Celsius. Irrespective of the windchill factor, for water to freeze the actual air temperature must be at or below zero Celsius.