A lot of inland areas hit freezing as expected, but aside from ending the growing season probably not enough to cause damage because the ground is still warm. In town, the low was 38 F, not much colder than yesterday. Here is a plot of the temperatures over the last few days, along with the soil temperature (in green) …
It’s pretty clear when the cold front passed through! The soil temperatures are why I wasn’t too worried about the kind of freeze that can damage pipes, etc. That’s still very warm.
In winter, a key thing to watch when worried about freezing is the dew point. The Dew Point Temperature is the temperature at which the air would be saturated, and any lower than that moisture would have to condense as droplets. That simple statement carries a lot of implications. For one thing, in general, the actual air temperature normally can’t drop below the dew point. Why is that? Because the water changing from vapor to liquid is a phase change, and phase changes take energy – lots of it. Water is such an amazing substance. The energy required to change it from liquid to solid (drops to ice) is called the heat of fusion. So when you look at a temperature curve for air, you find that there seems to be a “pause” near freezing, as the freezing water releases energy back into the atmosphere and surfaces (very simplified explanation). This is why spraying water on crops to protect them from freezing works, a common practice in orange groves in Florida, as long as it doesn’t get too cold. The freezing water actually helps warm the plants!
Note that surfaces can be colder than the air. That’s why there was frost on the roofs in Savannah this morning. The air temperature was 38, the dew point was 35, but due to radiative cooling surfaces facing the sky were below 32. So the water vapor adjacent to the roof condensed into liquid at 35, then froze in contact with the surface that was below 32.
I’ve received a few messages from folks confused about how the National Weather Service does frost and freeze watches and warnings. They only do frost and freeze watches and warnings during the growing season. Once the first freeze hits, they consider the growing season over so they stop doing them until the growing season restarts in the spring (March 1st in climatology terms). During winter, they still do cold weather advisories, cold weather warnings, and other alerts (blizzard warnings, ice warnings, etc) but don’t consider going below freezing an event worth issuing a warning over.