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.
video

Wednesday, February 25, 2009

Giant Hail..............



As we continue with severe weather awareness week today I will discuss large hail and the severe storms that have produced some of the largest hail on record. Hail is a type of precipitation which grows inside the thunderstorm due to strong updrafts suspending ice crystals in the storm cloud until they grow to a point where the updraft can no longer support them and they fall to the Earth. The largest know hail stone to strike the United States is in the photo below from a storm in Aurora, NE.



This hailstone is just over 7” in diameter and 18.75” in circumference. It was the largest stone in one piece from this storm however, there were reports of larger stones that broke apart on impact with the ground. In some places up 12” diameter creators were left on the ground. Below is a short movie of the volumetric radar return from the storm that produced this giant hail. What is amazing about this storm is not only the height, topping out over 61,000’, but the strong reflectivity near the top of the storm, 60dbz at nearly 46,000’.



Another powerful storm that produced very large hail was right here in East Texas last year when softball size hail was reported near Bullard on February 5th. Below is a short movie of the volumetric radar return from the storm that produced this giant hail. Notice the storm was nowhere near the height that produced the giant hail in Nebraska. This storm formed during the cool season so you do not need to have storms as high to produce very large hail because the mid levels of the atmosphere are much colder.



You can imagine that chunks of ice the size of softballs or larger can be very dangerous if caught outside. The last known death in the United States occurred in March of 2000 when a man in Lake Worth, TX was hit in the head by softball size hail. Now the Great Plains are known for very large hail at times but parts of south Asia and China are known for devastating hail storms. In July of 2002, 25 people lost their lives during a hail storm in the Henan Province of China. Bangladesh is also notorious for very large hail. In fact the heaviest hailstone on record fell there in April of 1986 and weighed just over 2.2 pounds. I have not seen the actual dimensions on this stone but I would have to imagine it would have been slightly larger than volleyball size.



So how can a storm suspend ice particles this size? It all has to do with the strength of the updraft. Once we start to see hailstones the size of softballs or larger, the storm’s updraft speed will exceed 100mph! This was the case back in October 2007 when a massive hail storm hit Santo Cristo, Brazil. In the photos you see stones over 10cm in diameter, or about the size of softballs.





So unlike with tornadoes, the United States is not the hail capital of the world. While we get our fair share, even here in East Texas, other parts of the world see this severe weather phenomenon as well. Large hail is commonly found along the front range of mountain chains with the storms along the Himalayas producing the most and largest hail on Earth.

Tuesday, February 24, 2009

Lightning The Underrated Killer!

Every second on Earth around 45 bolts of lightning occur. That amounts to a staggering 1.4 billion flashes of lightning per year. Of these total bolts about 20%actually hit the Earth’s surface meaning there are nearly 280 million cloud to ground or ground to cloud lightning sbolt from the blue,trikes each year. With a tremendous amount of electricity, an average of one terawatt or one trillion watts per bolt, and an extremely high temperature, around 50,000°F, it is no wonder lightning is such a great threat to life and property. The greatest know loss of life from one lightning strike was in Brescia, Italy in 1769 when 3000 people lost their lives because lightning struck a church containing 100 tons of gunpowder that resulted in a huge explosion destroying a sixth of the city.(source Wikipedia) To see how lightning strikes are distributed around the world, take a look at the image below. Notice there is a great concentration of lightning near the equatorial regions of the world where thunderstorms are very common. The lightning capital of the US would be the peninsula of Florida where 6 to 9 months of the year sea breeze fronts collide across the center of the State causing thunderstorms to develop most afternoons.



On average lightning kills 66 Americans each year. This number is greater than that caused from hurricanes and tornadoes. Here are some interesting statistics of lightning victims in 2007.

98% were outside

89% were male

30% were males between the ages of 20-25

25% were standing under a tree

25% occurred on or near the water

So what can we do to keep our selves safe during a thunderstorm? Some easy rules to follow would include finding indoor sturdy shelter during a thunderstorm. Stay away from windows. If you are on the golf course and hear thunder, return to the club house immediately. Standing in an open field holding a metal club makes you a lightning rod. If you are caught outdoors and cannot make it to a shelter the best advice is to crouch down, tuck your head, cover your ears, and only have your toes touching the ground. If you lay flat on the surface then you have a much better chance of being struck indirectly form lightning from an underground current. For more on lightning safety click here. When is it no longer safe to be outside? If you can hear thunder, your best bet is to move inside. To determine how far away lightning is from your location, count the seconds in between the lightning bolt and thunder. For every five seconds you count, a distance of one mile passes. So if you see a lightning bolt and 30 seconds later you hear the thunder, the lightning was approximately 6 miles away. Lightning has been known to strike and cause injury or death up to 10 miles away from the parent storm. This type of strike is known as a “Bolt From The Blue.” So staying inside 30 minutes after you hear the last clap of thunder is the best way to keep you and you family safe.



While lightning can be a beautiful sight, it is best to take precautions to insure your safety during natures underrated killer.

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.

Monday, February 16, 2009

Valentine's Night Storm........


For all those lovers of exciting weather Cupid shot his arrow into the atmosphere and whipped up some elevated thunderstorms Valentine’s Night bringing a vivid lightning show and small hail to parts of East Texas. The lightning shots you see here were taken from my front porch as a strong storm moved out of Eastern Henderson County into Smith County.




This storm produced a large amount of small hail, covering the ground and causing hazardous travel along 346 from Flint to Whitehouse. The largest hailstone I found was penny size which technically is severe near the intersection of 346 and Oakbrook. These storms fired with a combination of many atmospheric conditions which came together over East Texas.



First, in the mid levels of the atmosphere a weak disturbance was entering West Texas causing the winds to diverge over East Texas. This causes the air to rise which could lead to clouds and precipitation. Second, a strong jet stream in the upper level of the atmosphere was moving just to our south. This put East Texas in what we call the left exit region of the jet stream which also adds in lifting the air.


Third, strong wind shear was noted in the atmosphere from 6,000’ to 30,000’. This will help aid in thunderstorm development by pushing the rain cooled air downstream, away from the storms updraft allowing the storm to become stronger.





The only thing missing for thunderstorm development, moisture. The low levels of the atmosphere where we normally find the moisture needed for thunderstorm development were too dry for surface based storm development. However, in the lower mid levels of the atmosphere a thin layer of moisture was moving into East Texas. This was all that was needed to help fire what we call elevated thunderstorms. Since the low levels of the atmosphere were dry, we were giving a vivid lightning storm with great visibility, giving many photo opportunities.





Thursday, February 12, 2009

Tuesday Night's Severe Storms!

A line of severe Thunderstorms raced across East Texas Tuesday night into Wednesday morning bringing strong winds, hail, and even an EF-1 tornado which touched down in Northwestern Smith County and traveled along the ground for 6.8 miles into Southern Wood County. This tornado was formed form a phenomenon we call a “bookend vortex.” If you look at the short radar loop(shown below) of the storms as they moved through parts of East Texas, you will notice they take on the shape of a bow, or “bow echo.” This is because near the center of the line of storms very strong winds are punching in causing the line to race forward in the center forming the bow shape. It is here where you usually find the strongest wind in some cases over 80mph. This is what caused the damage in the Sunrise Shores area of Henderson County. These strong winds continued to race east affecting parts of Smith County causing widespread power outages and tree damage.
video

In a highly sheared environment, which we had Tuesday night, sometimes on the ends of a “bow echo” will form an area of rotation called a “bookend vortices.” It is called this because the rotation is located at the ends of the bow shape. In a highly sheared environment winds will cause this rotation to strengthen. The environment on the northern counter-clockwise circulation in a highly sheared atmosphere can become favorable for tornado development.


Rear Inflow Notch

As the northern end of the bow echo entered Northern Smith County we can see a rear inflow notch or an area where winds are punching into the back of the storm. This is depicted in the radar image above with the air flow noted by arrows. The north and south ends of strong bow echoes will have these bookend vortices continuing to push are towards the center of the line helping create the widespread wind damage. The northern vortex began to tighten and eventually lead to the development of the tornado.


Precipitation Wraps Around The Circulation

In the next radar image taken five minutes later, you can start to see precipitation wrapping around the vortex similarly to what you would find in a mesocyclone found on the southwest side of a classic supercell.(Mesocyclone is a localized area of low pressure formed by the most severe thunderstorms called supercells. Mesocyclones are what give birth to the strong violent tornadoes like the one the struck Lone Grove, OK Tuesday.)

Rotation Becomes Streched In The Storms Updraft Forming A Tornado

Finally in the last image when can see the air rotation has tighten and eventually was stretched in the storms updraft causing the tornado to form near the intersection of CR 482 and CR 483 in Northwestern Smith County. At the time of the image it appears the storm has already moved past however, we must remember that in a highly sheared environment the precipitation is being pushed forward, away from the storm. Over this region of East Texas the radar beam which sends back and image is nearly 10,000’ in the atmosphere so the actual updraft of the storm lags behind the echo show by 5000’ or so.

What We Look For With Tornado Damage

So how do we know it was a tornado? Well, the next photo paints the picture pretty clear. In the photo I have four points marked A, B, C, and D. “A” is a pine tree which was snapped in half. “B” is the top of the snapped tree which was blown to the east. “C” is another pine tree next to “A” which was blown down to the northwest. And finally “D” is another tree in the background blown down to the northeast. It is this scattering of debris which shows us it was a tornado. If we were looking at straight line wind damage, all the trees would be facing the same direction like we showed from “Chopper 7” in the Sunrise Shores area of Henderson County. Now just because the damage in Sunrise Shores was not caused by a tornado does not mean it was not as bad. In some cases it looked much worse than the tornado damage. We all seem to get caught up in the fact that anytime damage occurs from wind, a tornado must have hit us. 90 mph winds will do a tremendous amount of damage whether it is straight or blowing in a circle. This is why all severe thunderstorms should be taken very seriously.



Here are a few more photos I shot of the damage. The first photo shows tree debris down and scattered about. My daughter Halen is making sure Daddy gets all the information.



Halen Standing Among The Damage

The next photo is metal roofing or siding carried at least a ½ mile. There were no close structures this could have come from.


Roofing Metal Thrown 1/2 Mile

So what have we learned from this event. Bookend vortex tornadoes can and do form with very little or sometimes no warning at all. But you can be assured that the StormTracker Weather Team watches all “bow echoes” very closely and will break in to warn the public if we think a tornado is forming. You may remember us breaking into programming last year when a bookend vortex produced an EF-1 tornado took a 21 mile path through Gregg and Rusk counties. These events are something we have to live with in this part of the country and we will always be watching the skies to keep you safe.

Tuesday, February 10, 2009

Severe Weather Outbreak Possible!!!


We are watching a developing storm system that promises to bring some rough weather to parts of the Southern Plains, including parts of East Texas. Right now the Storm Prediction Center has most of East Texas under a moderate risk for severe weather, including the possibility of strong tornadoes. Looking at the latest data this morning, I would not be surprised to see a High Risk issued for areas north of I-20 this afternoon. We are just waiting to see exactly where the surface low will develop to get a better outline of where the greatest risk of severe weather will be this evening and overnight.

So here is the set up: At the surface, warm moist air will spread across most of Central and East Texas as well as Southeast Oklahoma and most of Arkansas. Later this afternoon an area of low pressure will develop near the Texas and Oklahoma Panhandles. This will force winds at the surface to the south southeast across most of the warm moist air.

Strong Southeast Surface Winds

Just above this surface layer, winds will be out of the southwest over 50mph at times. It is this turning of winds that will give the atmosphere enough spin for the possibility of a few tornadoes, some of which could be strong. Around 5PM this afternoon we will start to see a few storms fire along a dry line along the I-35 corridor, near Dallas. These storms will rapidly become severe and move east. One or two storms could move into East Texas. These storms have the greatest potential to produce strong tornadoes. Will these storms move into East Texas? There is a chance these storms could move into Oklahoma and miss East Texas.



Southwest Winds Just Above The Surface


Around 9PM this evening, I line of strong storms will begin to develop along a fast moving west of Dallas. This should be a solid line producing very strong winds and maybe an isolated tornado entering East Texas around midnight and exiting East Texas around 3AM, give or take an hour. Right now I am expecting widespread wind damage with these storms. We can expect tree damage and down power lines as this line moves through.

Forecast Squall Line Early Wed Morning

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.

Tuesday, February 3, 2009

Snow??????




Some places across East Texas awoke to what appeared to be snow yesterday. But if you were awake during the event, and most people were, you would know that a hail storm effected parts of the area Sunday night. I line of thunderstorms erupted ahead of a fast moving cold front Sunday night producing gusty winds and lots of small hail. We did receive reports of up to golf ball size hail in Montalba but most of the storms produced pea size hail. A storm that formed along the Rusk Panola county line produced a heavy dose of pea size hail which lasted for about 20 minutes. This caused an accumulation of small hail in some areas to reach 10” in depth. Now this occurs occasionally in western states but an accumulating hail even is very rare for East Texas. A big thank you to Rusty Nix for sending me photos of the hail accumulation.