Seminole Crop E News

Agricultural News for Farmers and Agribusiness in SW Georgia

Frost – Nov 23, 2015

Posted by romeethredge on November 27, 2015

We had our first visual frost yesterday, Nov. 23 , 2015.  This is a little later than normal, we usually count on Nov 15 as our average first frost date. Today, Nov. 24th was a heavier frost but neither of them were very heavy and mostly in low shaded areas just as the sun was rising. Here’s a little on my roof, and below that some on some grass in a low area.

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Here’s what Pam Knox, UGA College of Ag Climatologist, says about frost and why we often see it but freezing temperatures aren’t reported by weather stations. “Weather instruments are usually located about five feet above the ground over sod.  There can be a significant difference between the temperature at that level and what is happening at the ground.   Also, the surface temperature depends on what it is made of.  For example, metal like the roof of a car is better at radiating energy to space and so it cools down faster than the ground, which is also feeling warmer temperatures from deeper down.  Dry soil cools down faster than wet soil because all of the energy loss goes to dropping the temperatures rather than freezing water.  Areas that are exposed to sky and space get colder than areas under trees because the trees help prevent the radiation from leaving.

Another thing that affects frost is local topography.  We have frost pockets, or low-lying areas that had cold air drain into them, causing locally colder conditions.  We know these areas that are most likely to see frost early in the fall.  Cold air is more dense than warm air, and so when it forms, it tends to move downhill and settle in the lowest areas.  There are some places in Wisconsin which see frost every month of the year because of this effect.  It doesn’t even take mountains; sometimes a low-lying place that is just a few feet lower can have this effect.

Of course, local temperatures do vary quite a bit due to differences in soil, how near they are to water, and how much sun they get, so the temperature at the weather station may not be a good representation for conditions somewhere else in the county.  Even from one side of the house to the other, you can get enough difference to affect the kinds of ornamental plants you might be able to grow, and master gardeners take advantage of that in planning their gardens.  These are called differences in microclimate.”

Here’s info from our UGA Weather monitoring network, http://www.georgiaweather.net , that shows the recorded first freezing temperatures of the fall at our weather station here at the Airport for the last 5 years.

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One Response to “Frost – Nov 23, 2015”

  1. […] type, soil moisture, and elevation.  Rome Ethredge discusses this in a Seminole Crop E News blog post from earlier today, including some of my thoughts on local […]

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