Tuesday, October 05, 2010

Big Temperature Gap Over 1 Mile!

Last night I was driving home through Crowley's Ridge. I noticed the temperature was 52 degrees on my car thermometer. As I drove, I saw it drop 2 degrees real fast and I instantly grabbed my camera and snapped a picture. As I drove down the hill, I knew what was happening. I was driving into a "cold pool" of air in the valley. At the bottom of the valley, the temperature had dropped to 41 degrees! That's an 11 degree drop in about a mile of roadway!!! (Side note: I was really geeking out watching the temperature drop!)
Now, I know what you are thinking... You've always heard that the temperatures drop as you go UP and not DOWN. You're right! That's why there is snow on top of mountains while it is 50-60 degrees at the bottom.

This is a different phenomenon though. We had a radiational inversion with clear skies and calm winds. This prevented any mixing of the winds, the heat from the day radiated out into the atmosphere, and the colder (more dense) air pooled into the valley. This is the same reason we often see fog in the valleys.

Below is the NAM model for midnight last night. This is a skew T which shows the temperature and dewpoint as you go UP through the atmosphere. If you notice, the air is much colder near the surface than it is slightly above the ground... yet as you go up, the temperature (red line) starts dropping again. That's why it's colder on top of a mountain! (That's another subject though)...

So, if you live along Highway 358... in the area that ALWAYS drops phone calls, you were about 10 degrees colder than the higher points on the highway last night!

Have a great day!


Dan Satterfield said...

Hey Ryan,
We have some incredible variations here in Huntpatch as well. My weekend guy and I have been thinking of writing a paper on it.

The question is how do you convey this to the public in a forecast.

Interested in joining in on the paper??

Ryan said...

Conveying it to the public in 3 minutes or less with all of the other stuff "required" these days is impossible. ;)

As far as the paper, I'd have to think on that... I have not taken that plunge. I'm presenting some stuff at MEG's Media Workshop next week. We'll see how that goes... haha.