Drought Effects on Fall Foliage

With October just around the corner, our expectations grow with the thought of the upcoming fall foliage. This year though, may be a tough one. The April freeze and continued drought conditions may not allow some leaves to even make it to the peak of the season in late October. The remaining leaves might even be delayed in changing due to the late season heat. Fall foliage is indeed hard to predict because of so many different weather conditions that can occur near the peak of the season. The peak is usually from late October to early November in the Tennessee Valley. In the higher elevations, the peak is usually in mid-late October. Here is a link to a very interesting article which sheds some light on what could occur with the fall foliage this year.

http://www.herald-citizen.com/NF/omf.wnm/herald/news_story.html?rkey=0046029+cr=gdn

Thank You Humberto!

In so many of my past posts, I mentioned the fact that it would take a few tropical systems to give us some much needed rain. Humberto is just what we needed. Now, of course, I hate to see anyone experience damage like the folks did on the Texas/Louisiana coast, but the inland rain is welcome. The heaviest rain will be to our south over central Alabama and Georgia, but even here in the Tennessee Valley we should see rainfall amounts from 1/2 inch to an inch in many spots. A few areas could see more, especially south. A cold front should sweep in late Friday pushing the rain out of here and setting the stage for a drier and cooler weekend. Clouds might linger early Saturday, but sunshine should return for the afternoon. with a brisk north wind, high temperatures should only be near 80 and morning lows Sunday in the middle 50s. Most of next week should be dry again, so Humberto, we say thank you!

La Nina Effects on the Tennessee Valley

I have used the term "La Nina" in several past posts especially relating to the tropical season. With NOAA making it official that a La Nina pattern should persist for at least the next 3 months, I thought I would do a little research on the effects a La Nina pattern could have on our local weather.

La Nina is a global pattern that results from the cooling of the ocean water off the coast of South America. It is just the opposite of the El Nino pattern of warm water in the same region. The upwelling of water in the equatorial region off the South American coast leads to this effect. Now, El Nino and La Nina episodes are nothing new, both have been occurring at alternate periods for centuries. However, with each episode we are learning more about the global ramifications that take place. In simplest terms, a La Nina pattern usually equals mild and dry winters in the U.S. and increased hurricane activity in the western Atlantic. El Nino episodes usually relate to wetter patterns over the southern U.S and slightly decreased hurricane activity in the tropical breeding grounds of the Atlantic. Now, that is a broad scale view of the two patterns. With a developing La Nina, here is some research on how our local weather has been effected by past La Nina episodes.

I took a look at La Nina episodes that have occurred since 1980 and there were 5 of them. The most recent was in 2000-2001. Other years include, in order: '83-'84, '88-'89, '95-'96, '98-'99 and '00-'01. Each set of years had some differences as would be expected. But, there were some similarities. I will start with tropical weather. With the exception of '83-'84, each La Nina set of years had above normal tropical activity late in the season (mid Sept-November). The average was 4 September storms, 3 October storms and 1 November storm. There was also an average of at least 2 major hurricanes during the late part of the season. As for our local conditions during the time frame of October-March, here is what I found. Octobers were warmer and drier than normal. Novembers had near normal temperatures and above normal rainfall (yipee!). The December's during these years were quite interesting. Decembers average below normal for temperatures and slightly above normal for rainfall/snowfall. Snowfalls of 2.3 inches (2000) and 3.5 inches (1998) occurred. The months of January and February both had above normal temperatures with at or above normal rainfall. Some light snows occurred in the January years, but not as much in February. One month that really stood out was the month of March. In each La Nina year, March was cooler and drier than normal.

Only time will tell what transpires over the next 6 months. But, based on the averages, we could be looking at a milder, but slightly wetter than normal winter (December could be the cold month), followed by a cooler March. At the very least, the prospects of rain are looking a little better than last winter. We shall see how 2007-2008 turns out!

Weekend College Football Weather

Ah yes, the first week of college football really wet our appetite for the second week of action this weekend. So, for all you tailgating fans, here is a look at the weather conditions for area teams Saturday.

UTC at Jacksonville State (3:30pm) - Partly Sunny 90

Southern Miss at Tennessee (7pm) - Partly Cloudy 84

South Carolina at Georgia (5:45pm) - Partly Sunny 90

Alabama at Vanderbilt (11:30am) - Partly Sunny 84

Samford at Georgia Tech (1:30pm) - Partly Sunny 89

South Florida at Auburn (8pm) - Partly Cloudy 85

Sewanee is off this week

Felix Ashore.....Another System Closer to U.S. to Watch

Major Hurricane Felix roared ashore at Category 5 strength along the northeast coast of Nicaragua close to the Honduras border. Felix strengthened during the predawn hours as it went through an Eyewall Replacement Cycle. During this cycle, the sustained wind initially dropped late yesterday, but then rapidly strengthened during the completion of the cycle just before landfall. This marks the second category 5 landfall this season. Both Dean and Felix fed off nearly perfect surface and upper level conditions to pull off such feats. There is a lot of talk about the warm water being the main ingredient. Well, it is one important ingredient, but not the only one. The Caribbean waters are always going to be warm, it is a low latitude body of water. So, yes, during the height of the hurricane season, you can bet on the warmest water of the season. Upper atmospheric conditions play a huge part in a storms survival. During both Dean and Felix, a strong ridge of high pressure was situated north of the storm. The same ridge of high pressure that brought our region the extreme heat. The strength of that "high" allowed Dean first of all to be well ventilated and lacking of any shear to disrupt its development. A slightly weaker, but otherwise strong ridge again is positioned over the US southeast and Gulf which steered Felix and created similar perfect conditions for development. The developing La Nina conditions off the western South America coast plays a role in these upper level conditions. La Nina is the opposite of El Nino. It is a cooling of the waters off the South American coast which also affects global weather patterns and occurs on intervals opposite of El Nino. When a La Nina is developing or is in place, we expect hurricane conditions to be above normal. This occurs because La Nina creates a lack of wind shear in the tropical development region. With a lack of shear, storms can more easily develop and strengthen. During an El Nino episode, wind shear increase in the tropical development region and that can serve to prevent development or help weaken a developed storm. So, year in and year out, the Caribbean waters are plenty warm, but it's the upper level factors that go a long way in determining the outcome of a storm.

Another area to watch for development is off the southeast US coast. Currently, it is a non tropical low. But, should it continue drifting off the coast around the region of the warm, Gulf Stream waters, the "low" could become a warm core, or tropical system. Some computer model guidance shows this system drifting for 24-48 hours before gaining some strength and backing west toward the coast. So, as we enter the peak of the hurricane season there is a lot to watch.

Major Hurricane Felix Threatens Southern Caribbean

Felix is now a major hurricane reaching category 5 strength!

Hurricane Felix is slowly creeping westward through the southern Caribbean Sea. Aruba is feeling the effects of the south side of the storm. Felix should continue a westward motion gaining a little latitude north through early next week. Belize could be the next landmass Felix affects next week.
Elsewhere in the tropics, there are 2 areas being monitored. The first is off the Georgia coast. This is a an area of low pressure that is left over from a decayed frontal zone. With very weak upper level support, systems such as these have to be closely watched for signs of any tropical development. It should slowly drift east. The second area to watch is between the US and Africa. This tropical wave is not showing immediate signs of development, but could over the next few days. September is the peak month of hurricane season, with the peak day of the season on the 10th. The "peak weeks" of the season continue through October 15th. The season does not end until November 30.