WSET.com - ABC13Frosty Fall Nights by Matt Ferguson

We are rounding out the month of October and still have not seen a widespread frost across the entire region. As my grandmother would say, "Jackie Frost has yet to make a visit!" I guess this is not too surprising since this fall is following a very warm summer.

There was some spotty frost early Sunday morning (10/16/10), especially in outlying locations, but for most of us the growing season continues. You may be wondering: on average when is the first frost of the season? Usually it occurs for Central and Southside Virginia between October 9 and 15.

It's only a matter of time before the first significant frost occurs. In fact, Saturday morning (10/24/10) lows will be the 30s and conditions look favorable for some frost then. In the past people have asked. "How can you have frost when temperatures only fall into the mid 30s? Actually the temperature must be at 32 or below, however the official temperature is taken around 5 feet off the ground. While it may be 35 at the sensor, surfaces such as blades of grass or the hood of your car can drop to or just below freezing. Frost usually occurs when you have clear skies, calm winds and of course, temperatures at 32 or below. At night when the temperature falls through the 40s and 30s, the air gets to a point where it can't hold any more moisture.

This is what meteorologist often refer to as the dewpoint. Keep in mind, warm air can hold much more moisture than cold air. So as air cools closer and closer to the dewpoint, it must condense onto objects, such as grass, flowerbeds, cars, houses and etcetera. Now you have dew, then as temperatures drop below freezing overnight dew turns to frost. Sometimes when it's much colder the process is a little different. On evenings when temperatures are already below freezing as the sun is setting and continues falling all night well into the 20s and teens, deposition occurs. This is when the water vapor in the atmosphere goes straight to solid frost form.

Ok, now you have your Meteorology 101 lesson in frost development. Remember a killing frost or freeze is just around the corner! Be ready to bring your plants inside for the winter months, at least the ones you intend to keep year round.