Friday, April 29, 2011

Tornado Paths From Space

Extreme long track violent tornadoes as seen from space.

Thoughts on Wednesday's Outbreak

As the National Weather Service Offices across the country continue to conduct damage surveys from Wednesday's tornadoes, it is certain this will go down as one of the deadliest tornado outbreaks in U.S. history. At the writing of this article the current death toll stands at 297, only 38 short of the Super Outbreak of 1974, the last time the U.S. saw a tornado outbreak take over 300 lives.

What is not known is the exact number of tornadoes that hit the Southeastern United States. Many national media outlets have been stating that according to the National Weather Service there have been 164 confirmed tornadoes. This is just not the case. There have been 164 official “Reports” of tornadoes (now the official report is up to 211) from Wednesday.

The word report continues to be left out during the reporting of these large tornado outbreaks. Last week it was stated over 240 tornadoes touched down when in reality the number was closer to 113. Now this is still an incredible amount of tornadoes but you see how the actual amount of tornadoes is much less than the reports.

Wednesday’s 164 reports (now 211) of tornadoes will probably be much lower in the actual count. To give you an example, there were 20 tornado reports in Alabama from just Lawrence, Limestone, and Madison Counties. This was more than likely one continuous long track EF-4(with a possible upgrade to EF-5) tornado. Six tornado reports in Alabama come from Tuscaloosa and Jefferson counties where by looking at video, it is apparent this is one long track violent tornado, more than likely an EF-5.

Now I am in no way trying to take away from the incredible outbreak that occurred on Wednesday. I was alive during the Super Outbreak but have no recollection, I was only 2. So this is by far the worst tornado outbreak in my memory. Once all the damage surveys are complete this outbreak could come very close to the Super Outbreak. But until we know for a fact, I wish National media outlets would stick to the facts and not leave out key words making their statements false. I really have to believe that in 1974 if we had the communication abilities, numerous spotters and chasers, and population density that we have now, the actual tornado reports would have been closer to 500.

One thing is certain. This was a tragic event that took many lives. This one hit close to home for me. If the Madison County tornado would have veered off its course by only 200 yards, I very well could have lost my parents. A couple of houses down the street are swept clean and lives were lost. Feeling helpless here in Texas I had to watch this event on radar, knowing I did all I could by informing them they needed to take shelter. The longest five minutes of my life were the time it took to get a call to go through on my Mom’s cell phone once I saw the tornado moved off to their East. Thankfully they are still with me but my thoughts and prayers are with everyone who lost loved ones in this tragic event. I have a very bad feeling the death toll will eclipse the Super Outbreak of 1974 when everyone is accounted for……I hope I’m wrong.

Sunday, April 24, 2011

An Active Two Days Ahead

The next two days across East Texas could be very active weather wise, potentially life threatening. Two mid level disturbances will be moving through the area over the next 48 hours. The first is progged to move through Monday afternoon and evening and the second 24 hours later late Tuesday. As these systems move through the area strong to severe storms will develop across the area with a few of these storms producing very large hail and isolated strong tornadoes. So, I thought I would give a detailed look at how the atmosphere is setting up for what could be a historic weather day.

Monday the first mid level disturbance will swing through the Red River Valley by the evening hours dragging a dryline into the western counties of East Texas. Along this dryline thunderstorms will develop as peak heating provides plenty of instability. MLCAPE values will approach 2500 J/kg and combine this with 0-6km shear between 50 and 60 knots, the atmosphere is primed for robust rotating updrafts capable of producing strong supercells. By looking at the sounding for Tyler at 7PM Monday,
we can see there is ample instability for storms along with a fairly decent amount of low level turning of the winds with height. This will increase the tornado threat with any supercell that develops. Right now it appears that isolated supercells will develop wets of the Trinity River around 3PM and make their way across East Texas during the late afternoon and evening hours. In addition to a tornado threat, the amount of instability and shear will combine to make very large hail a significant threat. I would not be surprised to see a few reports of hail between baseball and softball size Monday afternoon and evening.

Now normally when we see a significant severe weather event here in East Texas the following day is usually calm. With this event, another mid level disturbance is forecast to move through the area. This system will develop a surface low near the Metorplex. This low is forecast to move northeast towards Texarkana during the overnight hours. This will bring another dryline through East Texas followed by a cold front. By looking at the forecast sounding for Tyler
we once again see an ample amount of instability but this time the low level turn of the winds with height is much stronger thanks to the aforementioned surface low. 0-1km SRH is forecast to be over 300 Tuesday afternoon making significant tornadoes a threat. In fact the significant tornado parameter is peaking at 13.6 Tuesday afternoon just north of Tyler.
Whenever we see values this high we become very concerned about the possibility of EF-4 and EF-5 tornadoes. The last time I saw a STP value actually that high was the day of the Yazoo City EF-4 tornado last year.

A lot could change between now and late Monday and Tuesday. Tuesday significant tornado threat is dependent on the actual track of a low pressure that has yet to develop. But right now it does look like a very active day for areas east of I-35 Monday and Tuesday and that includes all of East Texas. The Storm Prediction Center has all of East Texas under a slight risk of severe weather including a hatched outlook, meaning significant severe weather is a threat. More than likely much of East Texas will be under a moderate risk of severe weather come tomorrow. As for Tuesday's official forecast. Most of East Texas again is under a slight risk but if the current forecast holds true, I think we will once again be under a moderate risk if not a high risk on Tuesday afternoon.

Wednesday, April 13, 2011

Tornado Outbreak Possible Tomorrow

The 12Z NAM has come more in line with the other models and is painting a scary picture tomorrow afternoon. Right now it appears the cap will remain in place for most of the afternoon allowing temperatures to warm into the 80s. The cap will weaken by the evening hours but still be strong enough to only produce isolated convection. This means any storm that develops will be able to tap into all the energy available and quickly become severe. Wind shear is forecast to be very strong so supercells are likely. These storms will be able to produce baseball size hail and tornadoes. Again there will only be a few storms that develop so most areas will not see severe weather. The best chance of seeing severe weather including isolated strong tornadoes would be from I-30 north.

Below is the forecast sounding for 7PM tomorrow in Paris,TX. There is plenty of cape on the sounding and the hodograph on the right shows a tremendous turning of wind with height. Moisture is fairly deep here as well. You combine all these ingredents and if a storm develops near Paris it would likely be a supercell with hail and tornadoes.

The next image shows the forcast sounding for the sime time in Tyler, TX. here to we see plenty of CAPE on the sounding along with a large clockwise turning of wind with height on the hodograph. The moisture here looks deep enough as well to fire convection. The cap is a little stronger here meaning the chance of a storm developign is lower than in the Paris area but if it can form, watch out. It would likely be severe with very large hail and tornadoes.

The final image shows the forecast sounding for the same time in Lufkin, TX. You can see the amount of CAPE is a little smaller. Also the wind shear is not as strong. But the main limiting factor for storm development is the lack of deep moisture and two inversions, caps, the air parcel would have to rise through. SO for Deep East Texas the chances of severe weather appear to be very small. Storms will more than likely not form.

With this looking like it might develop into a fairly significant tornado event, I will be heading out tomorrow after my Midday show to see what develops. Tagging along will be our newest StormTracker Meteorologist Brett Collar. Stay Tuned!

Tomorrow's Set Up Much Like 04/09/09

A storm system will be moving through the Southern Plains tomorrow with the threat of severe weather for parts of the area. Much of Eastern Oklahoma has been placed under a moderate risk of severe storms with a slight risk of severe weather from I-20 north. But as I look at the forecast data it looks like this set up for severe weather is looking much like the set up we had on April 9th 2009. For those who may not remember what happened on this date four supercell thunderstorms developed across East Texas producing hail and tornadoes continuing on into Louisiana. A couple of these tornadoes were on the ground for over 30 miles producing EF-3 damage.

So what happened that day and how does it compare to tomorrow’s event? Well, a strong area of low pressure developed at the surface dragging a dryline through East Texas during the early evening hours. There was a conditional threat of severe weather across East Texas meaning storms may not develop but if they did, watch out! Why was the threat conditional? There was a warm layer of air around 5000 feet in the atmosphere we call a cap. This cap forces rising air back to the surface putting a lid on thunderstorm development. Because of this cap temperatures were able to warm well into the 80s producing plenty of instability. At the same time wind of different speed and direction at different levels in the atmosphere was producing strong wind shear across East Texas. This wind shear allowed for any storm that could develop to rotate, producing large hail and tornadoes. As the dryline was forced through East Texas, there was enough lift to cause this cap to break in a few locations causing severe storms to explode.

A very similar set up is being forecast for tomorrow across the Southern Plains. An area of low pressure will develop dragging a dryline through the area. The next few images below show the position of the cut off low in the mid levels of the atmosphere. First the actual cut off low front April 9th 2009 then form various forecast models.

You can see that the second image and last image both place the cut off low in nearly the exact location as April 9th 2009. The outlying model is the NAM which places the cutoff low farther north. This is important because if the NAM’s solution is correct, the formation of the surface low would be farther north placing less forcing across East Texas limiting the threat of thunderstorm development.

The next set of images show the actual 850mb level low pressure analysis for April 9th 2009 followed by the NAM and GFS forecast position of the 850mb low. Again the NAM has this low much farther north which would limit the threat of severe weather here in East Texas. However the GFS is pretty much positioning the low pressure in the exact location from April 9th 2009.

Usually I like to use what the NAM is showing for my short range forecasting. This high resolution model seems to do a fairly good job in predicting the position of weather features with 48 hours. However, today the NAM is the odd model placing the low pressure much farther north than all the other computer models. All models seem to have a pretty good handle on this disturbance in its current position but then send the energy in different directions. When you look at the forecast instability across East Texas, 2000+J/kg of surface based CAPE and Lifted Index Values around -5°C, there is more than enough energy to produce strong to severe storms. You combine that with nearly 70 knots of shear and 0-1KM Storm Relative helicity values over 240, any storm that develops would rapidly become severe, rotate, and more than likely produce golfball size or greater hail and an isolated tornado. Again with such a variance between the models we will have to watch the eventual path of this developing low pressure. If it moves farther north, the chances of severe weather will be very small. If it moves farther south tomorrow could be a very interesting day. Stay tuned!