BrrrrrOctober 5th, 2011 at 5:38 pm by Sam Kantrow under Weather, WTNH Blogs
If you happen to make your way outside tonight, you’ll notice that temperatures are going to be downright cold! Right now, we’ve got a frost advisory and a freeze warning in effect for Litchfield County tonight from Midnight-10AM tomorrow morning. With light winds, and clear skies overnight, we’ll see temperatures sharply fall as the sun goes down tonight.
We’re forecasting temps in the 40s by midnight, and for many inland spots, dropping down into the 30s by daybreak. The ingredients for unseasonably cold temperatures are there, so it should be interesting to see how cool it gets tonight. This has caused the alarm bells to ring at the National Weather Service, and they’ve issued the first freeze warning of the season! Now with that being said, lets get meteorological!
There are many factors that can cause unseasonably cool temperatures including clear skies, dry air, a long night, light wind, and even snow cover. All of these factors combined increase what meteorologists call radiational cooling. This is the main reason that temperatures fall overnight! The earth is constantly emitting radation, and thus is constantly losing heat. The heat needed to maintain the earths daytime temperature is mainly received by the sun, which is radiating towards the earth. At night, there is no radiation coming from the sun, because the sun is not in direct line of site with our side of the earth, so the earth is therefore resulting in a net loss of energy. When this energy is lost, the temperatures cool, and tend to fall throughout the night with the coolest temperature being right around sunrise.
On a night like tonight, clear skies are one of the main factors allowing for us to get as cold as we’ll get. When there are no clouds at night, the longwave radation that the earth is emitting has a much easier time escaping into space. If the night is cloudy, temperatures can struggle to fall because the radiation that’s being emitted by earth will be relected back to earth, and is then absorbed again. The clouds form a big blanker over us when we’re cloudy!
Clear skies aren’t enough to let our temperatures to get to record cold…you need dry air also! Even when the skies are clear, the water vapor in the air is doing the same thing as a cloudy sky. It’s allowing us to remain blanketed and not letting the energy that the earth is emitting to escape as easily. So when the air is very dry, it will help allow the temperatures to get cold.
Finally, another important factor that will allow our temperatures to get so cool tonight is light winds. When the wind is light, it doesn’t allow the air near the surface to mix as much. Why is this important? Because the ground surface is the source of all of the cooling, the coolest temperatures will be right at the surface of the earth. When the wind is very light, this lack of mixing with the warmer air aloft will let the cool temperatures to reach their full potential!
Don’t worry about the wintertime cold tonight, by this weekend temperatures are forecast to get above 80 again with lots of sun! Gotta love the weather in New England