4/13/09 This Morning's Winds Explained in Today's Weather Outlook.

This morning was a bit hectic with the strong winds in the area. The peak wind gust in Chattanooga was 43mph at 4:53am. Just moments before, we lost power at the station. I have noticed reports of over 50mph in spots. This highest wind gust I found was on top of Lookout Mountain with a gust of 65mph at Covenant College!

These winds were caused by either what is known as a "gravity wave" or a "wake low". The disturbance that gave us the light rain this morning actually created a somewhat rare phenomenon. As the disturbance entered the area, it force very stable air to rise, more or less against it's will. Once the shield of rain passed, that upward forced air was pulled down quickly by gravity creating a “wave” in the atmosphere. Some of the winds reached the surface as a mini area of high pressure developed. A great example would be when we throw a rock in the water, the water is forced up, and gravity then pulls it down creating the ripple or waves we see in the water. I know, it’s a bit confusing.

Below is video of clouds during a gravity wave in IA. Once the rain/clouds passed, the stable air was forced down, even clearing the sky at times, but you can see the "waves".

Video Here:

Another explanation from a former Professor of mine.

Another possibility, is that the winds were caused by what is called a "wake low". These are somewhat caused by a gravity wave, in that air that is forced up as a shield of rain OR a thunderstorm passes, must come down. In some cases, as the air on the backside of the precip comes down quickly due to evaporative cooling of rainfall, it forms a "mini" area of low pressure or a mesolow and the winds race to it, with speeds of up to 70mph.  The soggy ground from the rainfall also led to the numerous trees blown over. 

Now for the rest of today’s weather. The winds we have now are out ahead of yet another area of low pressure that could lead to more storms later this afternoon and evening. For the rest of this morning and early afternoon, look for a mostly cloudy sky and breezy with winds from the SE at 10-20mph. A few showers will develop at any time, however they will remain light as storms to the south are robbing our moisture. Highs will reach the mid 60s.

As a cold front approaches tonight, a line of storms could roll through the area, some strong, however due to cloud cover, storms to the south, and time of day, storms may not be as strong. I do look for rain in the late night hours, ending before sunrise. Rain totals look dismal with an average of less than a quarter inch.

The SPC has us in a slight risk for later today-tonight…just in case.

Cloudy, cooler for Tuesday with highs in the 50s to around 60. Some clearing will take place late, but more sunshine is expected on Wednesday through Saturday with seasonable temps. Average High is 71, low 46.

See you soon,

Brian