There are a series of questions you can ask yourself to aid in predicting the formation of frost for your own backyard:
• What is the temperature? If at sunset the temperature is close to freezing then there is a better chance for the formation of frost. Remember the temperature reported by your local weather station is measured 1.5 meters above the ground. So if the forecast is for a temperature of 39 degrees, the ground may be close to freezing.
• How fast is the wind blowing? A strong wind inhibits the cooling of the surface, and thus frost.
• What sort of cloud cover is there? Clouds are good emitters of infrared energy so they mitigate against the energy losses on the ground at night. If it is cloudy, and will stay cloudy, then the likelihood of frost is reduced. If it is to be a clear night then frost is more likely to develop.
• What is the condition of the ground? If the soil is warm and moist, then conduction will transfer heat upwards from below the surface and inhibit the development of frost. Also know your backyard. Cold air will drain into local low spots making them colder.
• How long will the night be? The longer the night, the more time the ground has to cool and so the colder it will get.
• What is the dew point? This is a very important question to ask yourself. A rule of thumb: If the dew point is above 45 degrees at sunset then you are probably OK. Below 40 degrees you will probably see a frost if the other conditions are good.