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Tornado season: why so active?

By: Dr. Jeff Masters, 4:22 PM GMT on April 10, 2006

Friday's tornado outbreak in Tennessee featured at least 46 tornadoes across eight states. Three strong F3 tornadoes touched down (winds of 158 to 206 mph), including the Gallatin, Tennessee tornado that killed nine people and damaged or destroyed 700 to 900 homes in Sumner County. The April 2 outbreak had six F3 tornadoes among the 56 reported, and the March 9-13 outbreak had 11 F3 tornadoes and one F4 tornado among the 84 that touched down.

Figure 1. Departure of Sea Surface Temperature (SST) from normal in early April for 2005 and 2006. SSTs were near normal in 2005 in the Gulf of Mexico, but were about 1-2 degrees C warmer than normal this year. Other things of interest: the cool water signature of La Nina is obvious in the Eastern Pacific in 2006 but not 2005; water temperatures in the Caribbean and tropical Atlantic are cooler this year than last year, which may mean a delayed onset to this year's hurricane season compared to last year. Image credit: NOAA.

Why has this year's tornado season been so violent? According to NOAA,, "The difference this year is the abnormally warm temperatures and dry conditions during the winter throughout the southern and central United States that kept water temperatures warm in the Gulf of Mexico." If we look at a plot comparing this year and last year's change ino Sea Surface Temperature (SST) from normal (the anomalies, Figure 1), we see that the Gulf of Mexico is indeed significantly warmer this year. Plenty of warm moist air from the Gulf of Mexico certainly doesn't hurt, but the primary reason that this year's tornado season has been so bad is that we've had an unusually active and strong jet stream. The reasons for this are complicated and not well-understood, but have more to do with large scale global circulation patterns such the the presence of La Nina and the negative phase of the North Atlantic Oscillation (NAO) that has predominated this Spring.

The latest 2-week forecast from the GFS model shows that the jet stream is now expected to grow less active for the next 10 days, and no further major tornado outbreaks are expected during that period. A more active pattern may return late in the month, however.

Jeff Masters
Tornado Damage
Tornado Damage
Automobiles at car dealership in Gallatin, Tennessee, resulting from toranado which hit April 7, 2006.
Tonado North of Winona Mississippi
Tonado North of Winona Mississippi
Taken from McDonald's on Highway 82 at 5:35pm on April 7, 2006


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

Hate this time of year because of all the tornados!!! Scary stuff!
My tunnels will stop the Jet Stream

Sorry, just had some sort of identity problems. Anyhow, that low on the tail end of the cold front doesn't look to be developing, and the one on the GFS isn't forming.
Okay people place you bets on went the first Tropical System of the season is going to appear. I think we overdue for a mid-May system..

And I am also betting based on previous up and downs of the hurricane peaks. This year will be above average but no where near the mind-blower of last year. However I don't think we seen the last of a mind-blowing year like last year. I have a feeling almost all those records (save the greek alphabet) ones will one day be shattered.
Agreed, orion. Have you looked @ my seasonal forecast yet?

No can you throw me a link (normally I would dig for it, but I got a short week at work and above average amount of stuff to do. Add on that more meetings than usual to boot)
It's been months since I've checked in (since the end of hurricane season). I'm already getting wound up for the 2006 season. Anyone know when to start watching for systems coming off Africa? I see a little coming off the west coast of Africa and I'm assuming the season's getting ready to roll...

Hope you're all doing well and getting ready!

Wow, I guess there are weather problems no matter where you live. Not looking forward to the summer/fall in the Florida Keys dodging huricaines. Guess we're lucky though, at least we know they are coming and can get out of the way.Link
We just had 6.3inches of rain in the last 48mins in Georgetown, up to 48mins ago we had had 4 inches all year. No warning and half way to the shops at the time, lovely!!!

6.3 in of rain in 48 minutes?Only in the tropics incredible,I have seen rasin rates of 6 inches per hour in the summer in stronger storms,and 7 inches per hour in hurricanes but it wasnt able to last long enogh for it to accumulate like that!I guess because it isnt fully in tropics here lol.But only in tropical regions will you EVER see rain that heavy.Up north of here in the northern U.S.
Up in the northern U.S. they call an inch per hour rain rates "very heavy downpours" lol ya right that is nothing for us down here.
the weather page is down at your Cayman link, but the cam still works... Looks like it's still falling.
13. F5
My aunt and uncle live in Hendersonville TN. They saw the tornado that struck parts of Hendersonville, while driving in their car. Fortunately, their house was not damaged, but they had to go 12 miles out of their way to get into their neighborhood due to the heavy damage on the edges. Their old neighborhood in Hendersonville was pretty torn up.

Meanwhile in TX, we are back in a hot/dry pattern with no significant precip chances for the next 10 days. Last week, there were good chances every day for 6 days in a row, and yet we got a grand total of 5 minutes of rain.
The site seems to work for me, but takes a while to load, and is quite comprehensive with rain rates, etc and a live lightening screen (although can't understand that one), we hit 920w/m2 of sunshine before the rain hit, so summer seems to hve started early
I haven't seen rain like that outside a hurricane. Water was going over my shoes on the pavements.
Going to dry off in the office for the afternoon.
it's working now, your up to 6.7"
By the way, it is possible to get intense rainfall outside of the tropics; in fact, the world record rainfall rate occurred in my state on June 22, 1947 when Holt, Missouri, got 1 foot of rain in 42 minutes (17 inches per hour). Link
Yeesh. I saved this radar image while watching the storms rip through TN. This cell is moving through Sumner county headed right for Gallatin. It's probably the one that caused all the damage and deaths. It looked very intense on radar. It's a shame people had to lose their lives.

Good afternoon and Thank you, Dr Masters, for the update.

We actually got a little rain here in my area of Broward County Fl this afternoon after that teaser yesterday. NO a lot; maybe 1/4 inch...not what you would call a soaking.

only 1 1/2 mos until June 1st!!!
get ready.
a little weather news


Truck Struck By Lightning On Alligator Alley~ guess the vehicles these days aren't completely immune to lightning's effect.

Japan got a lot of snow~ killed 71

NOAA explains rainbows

Killer Tornado Packed Winds Near 170 mph

Storm story~Recent storms carries things 3 hours away

That 250 acre fire less than a mile from me in town is still smoldering

here's 1 for Gamma:)
if any one gets time come to my blog and i am going to see rain for the next 10 days or longer
F5:"Last week, there were good chances every day for 6 days in a row, and yet we got a grand total of 5 minutes of rain."

same thing happened in KC...even as towns 60 miles east get hammered by repeat tornadoes, we haven't seen more than 1/3" of rain any day this spring.
buster it looks doubtful with the shear. Tis interesting that it still calls for the favorable enviroment E of Fl, passing back over SFL. Alotta convection hanging out around there.
There's not even a depression yet. Let's at least get a depression before we start calling for Alberto.
I have updated my blog; it is about a historical event that occurred in my area 5 years ago.
Buster, i'm not even sure which "thing" you are talking about...is it that upper-level feature sinking southwest toward the Yucatan? nothing i see looks even remotely like it's even thinking about developing.
Colby, you tease, you talk about your seasonal prediction but where is it? I didn't see it on your Forecaster Colby WU blog...
The only invests on this site are in the Indian Ocean. Also, this does not show snything developing.
I have a lot of doubts about an April tropical storm--only 1 has ever formed that we know about and I wonder how many times in the past models have made spurious forecasts like that.

That the gulf is warmer than last year this time worries me, however.
You're right St Simons. The chances of an April storm are remote at best. I know people are thinking that anything can happen after last year, but be realistic...it's April.

Now, with the warm Gulf, a late May or June storm would not be surprising at all.
The NHC updated the 2005 Hurricane Season Track Map today to include the unnamed subtropical storm 19 that occurred on Oct. 4-5. No report out yet on the system though.
that's wild...busiest season ever, plus an unnamed storm to boot.
Well I say this, we still have the westerly winds and that will stay for the rest of April. Now I still say it will be mid June for our first Storm to form. With the Gulf getting warmer does bother me some and I have already started getting my supplies for this season but taken it slowly...:0)

Someone please do a Rain Dance for the Gulf Coast...

While an April storm is unlikely from the disturbed area around Cuba, there is something interesting on the GFS in about two weeks.

I know the GFS flip-flops and shows odd things that never materize, but it has been rather persistent in showing marginally-favorable upper level winds in the deep tropical Atlantic (7N to 12N), with an active ITC, in about two weeks.

The GFS occasionally gins up a low, which disappears on the next run and then reappears again. The specifics are poor but the pattern is interesting.

Link for 360 hr GFS of the low-latitude North Atlantic
grizzled, I see the active ITCZ, but that low is heading into South America! lol. Thank you though, that is interesting. It see some activity in the Carribean too.
redefined, how do you save an image and then post it? I know how to post an image from the internet, but how do you save it to your desktop or something and then post it?
Wow look at the low shear in the Carribean in 72 hours! Alberto still has a chance!
This seems to indicate that we should be looking at the East Pacific:

Also, look at how the shear is dropping (tropical Atlantic; other charts can be found here):

We need a rain dance for the Denver area too! Red Flag Warning up for all of the Colorado Front Range and eastern plains. Humidity in the single digits here today and winds picking up.

I remain concerned about the warm GOM temperatures this year. It certainly doesn't hurt to get prepared early.

Public Service Announcement
There will be no Alberto in the next 72 hours. Or for that fact, in the next two week. Thank you and have a nice evening.
I'd agree with you, it's really hard for a tropical system to form in April, don't think it's going to happen. But I'll stick with my May 20 prediction, especially with the warmer than normal GOM.
Yeah, I am going for end of May too!..LOL But right now, there is nothing. Every little spin is not going to form into something tropical, especially in April!
Yeah, nothing to see here folks.

My forecast can be found in the tropical discussion or amateur discussion sections of my site. After the plagarism a while back I made it so you can't see them as a guest. If you have any problems with the alphanumeric confirmation let me know, it's buggy sometimes.

I here ya we had rain on saturday morning but it was only about 2 tenths of a inch and before that was in Febuary... So I'm getting the Tomb - Tomb out ( Drums that is )...LOL and where you live it looks like it might be at least another week to 10 days... (sorry)

and as for GOM we here in Mobile have not had a direct hit with a major hurricane since 79 so I think we might be on target for one, although I wish that on no one... Heck I just got my roof back on from Katrina and she hit LA & MS... so on that note it is never to early to be ready if you know what I mean...
Taco, Katrina was pretty significant, a dead-on strike on Mobile isn't terribly likely because of the way the steering currents are.
come on in my blog and join the fun
Everybody sure seems anxious for the hurricane season to start.
Yeah Lou...people are hyped because the weather is hyped. Actually everything to do with humanity is sort of in a state of flux, ie. global warming, war, finding enough switch grass to make gas.
Wouldn't it be great if the tropics just produced 50 knot tropicals storms all season!!
In order for that to happen, there would have to like 100 tropical storms in a season to dissipate the energy normally released by several intense hurricanes and prevent any one storm from getting too strong (due to interactions between multiple storms at one time).
Hey Orion,

I have already posted my date of June 2nd for Alberto's formation on my blog a couple of weeks ago.:)

Naturally, it is only my best GUESS and any date from late May to even as late as July 1 seems plausable in my humble opinion.:)


Has anyone realized that if that unnamed subtropical storm had been named then Wilma would have been Alpha and the theoretical issue of what to do if a greek letter storm should be retired would no longer have been theoretical!
Yeah, I'd considered that. What really gets me about it is that it hit LAND as an STS, and the NHC didn't say a word!
good morning to Dr Master's Blog!

got a little Shower very early this morning around 5:30am... now getting sunny outside.

Skye, thanks for that link; saw where Coral Springs got very stormy weather.. I just live 3 miles south of Coral Springs and got nothing!
So funny how it all works out!!!

We're up to 59 tornadoes confirmed over the three-day period from April 6-8, including 37 on the 7th alone (that total is a three-day total). There are still more to be confirmed, including the Jackson office (which hasn't made any confirmations yet).
Ahh..Colby, the tracking map from the NHC never shows STS 19 making landfal.

Tracking Map
It would be instructive to generate a difference plot between the two SST anomaly maps shown. I notice, for instance, that the tropical and subtropical Atlantic regions and the Caribbean are noticeably cooler than at this time last year. I don't know why this would be so, but there it is. Perhaps this portends something in terms of what tropical pattern we may expect for 2006.
dr m any new updats today?
I can't believe people are already expecting to see a TS develop. Sure there are above average temps in the Gulf but overall the conditions are just not right this time of year, maybe this time next month you might be able to say there is a 1 in 10 chance but still doubt it. I am going to stick with my prediction from March 9, the first named storm will be June 17th. Here is the link to my complete prediction in the archived posting Link. My posting was very near the bottom.
Is there a nice link where one can go see the current state of the azores/bermuda high?
I believe it is parked just off the Florida Coast again, that is why we are seeing the high winds.
Here is a link to view the North Atlantic Surface Map
66. F5

I feel for you and know what you are going through. Despite a "rainy" period earlier this year, we are still in a severe drought. And of course, despite the rain amounts that "Some" areas around Dallas received, where I live received much less than some other areas. And we've had no rain since then. If the current forecast holds true, in about 8 days we will reach 30 days without significant rain fall. Considering the general lack of rain in the summer, if we don't get it now, in addition to all the fire danger we will have severe water restrictions. That is an issue because of the type of soil we have here. The clay needs to maintain a consistent moisture level. Too much rain and the soil expands, too little and it contracts. Most foundations are "floating" nowadays, so they can handle some expansion/contraction of the soil. And generally, too much rain is not an issue in Dallas. But too little rain, and the soil will begin to contract, pulling away from the foundation at uneven rates. This leads to cracks in the foundation, and then you have to spend many thousands of dollars on foundation repair, or eventually your house will become unlivable.

We desperately need the rain, but every system that comes through ends up with the main energy "too far north" and we miss out on any rain chances.
You can see it well in this image.
I thought it looked like 19 made landfall in the Azores on that map Myles
F5: if we don't get lots of rain this spring, it will also mean a hot summer...something yo in Dallas are probably dreading even more than I am.
For those of you in Florida, what was the tropical season like the last year you had a bone dry March like this past one?
I guess it did go very near the Azores. Cant really tell if it made landfall or not.
I see a small bit of T-Storms over Jamacia, however, no spin in the area.
Uhhh, Myles? *points at the Azores* :)

Cyclone, breathe. It's a vortex. I had one in my yard earlier that had more chance of becoming a TC than that does. It's north of the 26C isotherm, barely has a circulation, and is frontal. RELAX!
The SPC is beginning to indicate that another major severe weather outbreak may occur this weekend. Link
"I think tomorrow is the day not this weekend."

If you are referring to my post, then you don't know what you are talking about. As you can very well see, this shows that no severe storms are forecast until this weekend.
Hawkeye, the very dry floridian pattern is charictaristic of a La Nina, though we're actually not much below average despite only having been rained on twice. One time was like the sixth wettest day in Tampa history, and as this front went through we got a bit more.
Last time it was getting this dry was 1998. But we are not even close to that yet. I know some people are trying to make that 1998 comparision, but its too early to say whether it will be as dry. We will see what the rest of April brings us, but right now its not looking to wet.
Cyclone went from tunnels to small vorts. Oh boy:)
cyclonebuster - you obviously don't have any understanding of what is needed to have a severe weather outbreak; there may be a few storm reports over the next couple days, but no more. As you can see here, instability is very limited; CAPE is only 250 and only a marginal threat of damaging winds is expected.
Of course, last Thursday, the SPC had a High Risk and expected a significant tornado outbreak... not much actually happened (until the next day).


look at this oh no
The SPC has updated their tornado stats:

Tornadoes: 472
Killer tornadoes: 15
Tornado Deaths: 48

Also, look at this graph; it now shows the 10 year (144 torandoes) and 30 year (169 tornadoes) averages for this time of the year.
MichaelSTL can you help me on my blog


i try to post this on my blog but it look like it did not work
Your link does not work - it has an extra http:// in it. Try this:

I think that there is an error in your link.

can you pos this in my blog


so i can add it on top
what is going on with the extra list to be named by the WMO?
buster: "There is to much of a temperature difference between the two air masses for it not to happen."

it takes more than just a temperature contrast to spark severe weather....it requires moisture, instability at the surface, upper air support, etc.
Yep think of the huge differences in temperature in northern California between the coast and the central valley in the summer--even through the gap at San Francisco and the Sacramento River where the airmasses come in contact without a barrier from coastal mountains, thunderstorms and severe weather are almost unheard of in summer. Upper support is needed, along with moisture, for severe weather outbreaks to occur.
I don't see much on the NWS national radar.
the moisture is not all that substantial. really. that's why KC probably won't get any rain today, again, despite the front coming through. and that moisture plume, such as it is, is coming from the pacific for now...

Well, I'll be darned! Shear's too high ATM, but it does look like it has more chance to develop into a TC than my knee hair.
Ack, what am I saying? I was reading the stupid shear map wrong *pokes self in eye*

We might see something kick up out of this.
boy it sure doesn't look impressive on the water vapor loop. looks like there is plenty of dry air and shear around.
If it develops on Tax Day, HeavySnow will win the contest (see Weatherguy03's blog).
it won't. even if it forms a TD, which is unlikely, it won't become a named storm.
Don't need a knee hair mental image, thanks.
globalize - I am curious about your screenname - if I click on it, I always get this message (everybody else's takes me to their blog):

Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, support@wunderground.com and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.


Apache/1.3.33 Server at www.wunderground.com Port 80
I, also, get that error. Mail WunderYakuza about it, he's the site's technical guy.
my blog is update
Remember that I said that I emailed Jeff Masters to ask if he could explain whether cyclonebuster's tunnels could work or not? Well, he sent me the following reply, saying that there will be a conference on April 26 that will talk about a different idea that also uses tubes/tunnels:

Sent by JeffMasters at: 6:14 PM CDT on April 11, 2006

I'm going to treat a different tube idea that is being presented April 26 at a conference I'm going to. I'm not an engineer, I don't know if cyclonebuster's idea will work.

112. RL3AO
I hope this doesnt add gas to the fire...
Michael STL..that's probably because I don't have a blog site..just like to visit this one now and then. I have a question about ocean water salinity and acidity and its relationship to heat absorption. I may do a few personal experiments in a week or two in the Keys. Somebody clue me in.
where is dr m update to day any way
Look at this map, which shows the probability of a tropical cyclone forming:

Notice the area northeast of the Bahamas.

With shear like this, I can't understand all the excitement. Until it drops below about 20kt where it matters, I wouldn't take all this too seriously.
There is a probability of formation if shear is less than 65 kts.
118. MZT
If anything shows up in these conditions, though - it'd be another shallow - 'Greek' type storm.

Just posted my first hurricane prediction on my blog:

Quoting Snowfire:

With shear like this, I can't understand all the excitement. Until it drops below about 20kt where it matters, I wouldn't take all this too seriously.

but this says 2008