Showing posts with label Tornado. Show all posts
Showing posts with label Tornado. Show all posts

Tuesday, March 3, 2009

Wild Weather Day in Alabama....

***UPDATE: RADAR LOOPS ADDED***

It was a wild 24 hours across parts of the Southeast Saturday into Sunday Morning. Severe weather and tornadoes followed by snow affected much of the southeast as a strong storm system moved from the Mid South to the Southeast Atlantic Coast. Three tornadoes touched down in East Central Alabama Saturday morning and ranged from an EF-0 to an EF-2 in intensity. I took a few snap shots from the FFC Doppler velocity data to show where the rotation was as it moved through Lee County. The first shot shows an area of rotation just east of Notasulga near the Macon-Lee County line. This area of rotation would eventually touch the ground near Salem, AL becoming the strongest tornado of the day. A second area of rotation is just north of Auburn. This rotation would lead to the EF-1 tornado near The Bottle at the intersection of highway 147 and US 280. Top winds in this tornado were estimated to be near 100mph. (source National Weather Service BMX) The next image shows a strong area of rotation near exit 51 on interstate 85 or near Chewacla State Park. I have not heard of any damage reports from this area so it appears the rotation was still in the air. The final image is the area of rotation as it passed through Salem. From the damage survey performed by the National Weather Service in Birmingham, an EF-2 tornado passed through at this time. Several buildings and homes were damaged and there were a few minor injuries. If you look closely at this image and compare to the last image, the rotation does not appear to be as tight. A large area of light blue color is becoming dominate in this image showing a strong outflow which eventually lead to the demise of this tornado. The Salem tornado was on the ground for 2.65 miles and had a maximum width of 500 yards. Top winds were estimated to be near 130 mph making this a strong EF-2 tornado. (source National Weather Service BMX) If you look closely again at the last image, the large area of light blue is showing the possibility of strong straight line winds over a large area. A few minutes later this area spread across Smiths Station causing wind damage to many building and trees. Normally having a day packed with severe weather is wild enough but Mother Nature was not done with East Central Alabama. A little more than 24 hours later this area received the heaviest snow it has seen in many years. Parts of Eastern Lee County received over 5 inches of snow. Below is a map from the National Weather Service in Birmingham showing the snowfall accumulations for Alabama on Sunday. A wild weather day indeed!





Friday, February 27, 2009

Tornado Development

With severe weather awareness week coming to an end, here is a short video on how wind shear can generate a spin in the atmosphere which can lead to supercells and tornadoes.

Monday, February 23, 2009

The Video That Started It All......................

Today starts Severe Weather Awareness Week here in Texas so I thought we would review the best practices for keeping you and your family safe during severe weather. Today we will discuss where to seek shelter from a tornado if caught outside or in your car. For years the meteorological community has been telling people if you are caught outside or in your car during a tornado the best place to seek shelter in and a ditch or ravine and to cover your head. This is still the best choice for protecting yourself during a tornado if caught outside without sturdy shelter nearby but during April of 1991, a large tornado outbreak hit Kansas and from this event, video of a news team first trying to outrun a tornado and then seeking shelter under an overpass changed the public’s outlook on where to seek shelter.




Unfortunately this misleading information caused three people to lose their lives as they sought shelter under an overpass during the Moore, OK F5 tornado on May 3rd, 1999. So why not an overpass? Well, the main reason is with most over passes, you are in an open area where debris from the storm can harm you as wind speeds increase, not only from increasing elevation but from the air flow being squeezed between the narrow opening of the overpass. Without going into the subject of fluid dynamics, the best way to explain what happens as winds hit an overpass is to relate the winds to water flowing out of a garden hose. If you put your thumb over the flow of water, what happens? The velocity of the water increases due to the same amount of volume being squeezed through a smaller opening. So the winds in a relatively weak tornado can increase dramatically causing more bodily harm to those who seek shelter under an overpass. Below is a graphic created by the National Weather Service on why Overpasses do not provide adequate shelter from tornadoes.

Thursday, February 5, 2009

One Year Ago Today!



One year ago today we were watching a serious severe weather episode unfold that would later be known as the “Super Tuesday Outbreak” By early Tuesday Afternoon the Storm Prediction Center placed most of the Mid South Region under a “High Risk” of severe thunderstorms and tornadoes with a moderate risk of severe storms as far west as East Texas. By the end of the day 131 reports of tornadoes and 126 reports of large hail pelted the country.



The atmosphere was increasingly becoming unstable throughout the early afternoon in East Texas as plenty of sunshine helped boost temperatures into the low 80s, almost unheard of for early February. By 4:00PM in the afternoon, a line of scattered supercells exploded along a fast moving cold front through East Texas. Three of these storms would end up producing a significant amount of damage across East Texas through the late afternoon.



By 4:30PM the city of Lindale was being pelted with golfball size hail causing widespread damage to cars and homes. Lindale ISD canceled classes through the end of the week to repair damage to Velma Penny Elementary School and E.J. Moss Intermediate School. This storm later moved north into Upshur County causing strong winds and quarter size hail.



At the same time the second supercell was about to unleash some of the largest hail seen in East Texas. The town of Bullard was crushed by hail up to the size of softballs. This hail damaged numerous cars; yours truly had his car totaled during this storm. While surveying the storm damage with the national weather service, we found houses along Lilly Lane in Bullard where holes were punched through the siding of the home.



Below are a couple a three dimensional views of this storm. Notice on the first image you can see a white core in the center of the cell. The next image it is gone. The first image is showing extremely large hail being held up by the storms updraft. Between the first and second image, the hail became too heavy to hold by the storm's updraft so it fell on the town of Bullard. In order for a storm to hold hail this large above the surface the updraft speed, or wind rising through the storm, to be over 100 mph.





The storm continued to move northeast producing large hail through parts of Smith County. Below is an image of 2.75” hail, or baseball size from my yard about 3 miles northeast of the softball size hail report. Of course I did not get these stones until about 30 minutes after the storm so, they were probably closer to 3 to 3.25” in diameter.



All three of these storms showed strong rotation in the mid levels of the atmosphere and we were under a tornado watch however, with these storms forming along a cold front, the warm surface air you need to produce a tornado was undercut by the rapidly moving cold air underneath these storms. However, as supercell #2 moved through Southeast Smith County, for a brief period of time the circulation of the storm was able to outrun the cold air from the front and produce an EF-1 tornado near Arp along Hwy. 64 East of Tyler. This tornado was on the ground for only about 30 seconds but in that time tore a mile long path of damage snapping trees and damaging a large barn, just missing a home. This is an interesting case of how a tornado can develop, touchdown, and then dissipate in less time than it takes our Doppler radar to make a complete scan. Another good reason to take all severe thunderstorms seriously.



The third supercell developed and moved through Cherokee County producing golfball size hail just east of Jacksonville. This cell also showed strong midlevel rotation however it too was undercut by cold air at the surface.



This storm system later developed into a massive tornado outbreak across the Mid South and Southeast. 2 EF-4 tornadoes touched town in Northern Alabama and dozens of people lost their lives across the Southeast. These storms formed from a combination of a cold winter storm interacting with very warm Gulf air which spread across the southeastern part of the country. With the cold midlevel temperatures combined with the record warmth at the surface, the air mass became very unstable allowing thunderstorms to explode.