Thursday, May 26, 2011

Tornadoes of 2011

May 26, 2011
6:29 P.M.

I actually started writing this on May 13, 2011 at 9:32 A.M., but I never got around to finishing it. But, let's go onwards and talk about the tornadoes and severe weather we have seen this year. We have, as of May 24th, seen 1,208 tornadoes this year, and there was a significant tornado outbreak yesterday and another smaller one today. That is absolutely incredible. The average for the entire year in the U.S. is 1274, a record we will surely break. At this rate, it is also highly likely that we will surpass the record for the highest number of tornadoes in one year, which was 1,817, set back in 2004. April alone had 875 tornadoes. The previous record for tornadoes in April was 267, which was, not surprisingly, set in 1974, the month with what was then the largest tornado outbreak ever recorded (The "Super Outbreak" of April 3-4, 1974).

Let's chronicle some of the major tornado events so far this year around the nation...

The 2010 New Year's Eve Tornado Outbreak:

 A low-precipitation (LP) supercell from this particular outbreak

This outbreak, which occurred from December 31st to January 1st, stands as one of the strongest December outbreaks ever recorded, but I will include it because there were some tornadoes that were observed into the wee hours of New Year's morning. A total 36 tornadoes were reported, with 7 of them reaching EF-3 status with winds from 135-165 miles per hour. EF-3 tornadoes are very large tornadoes, with the vast majority of twisters being EF-0 or EF-1 with occasional EF-2 tornadoes being mixed in. Unfortunately, nine people were killed by this outbreak.

Less action occurred from the rest of January up to the beginning of April, but there were still some decent outbreaks. In January, there were 29 reported tornadoes, with 63 in February and 95 in March.

February 27-28th Tornado Outbreak

Surface analysis from 6 A.M. GMT on February 28, 2011

This particular outbreak was the largest one of February, with 35 tornado reports. One person was killed by an EF2 tornado, which was the first fatality of 2011 (the other fatalities were still in 2010). A EF-3 was also observed.

March 8-9th Tornado Outbreak
A rain-wrapped EF-2 tornado in a high-precipitation (HP) supercell near Clarksville, Texas.

This moderate outbreak stretched from north Texas to the Florida panhandle, with Louisiana receiving the most damage. There were 20 tornadoes, with 5 reaching EF-2 status.

April 2011 (875 tornado reports)

This month holds the record as having the most tornadoes of any month, beating, as previously stated, 267 in 1974 (record for April) and 542 in May 2004 (record for any month). The two largest outbreaks occurred from April 14-16 and April 25-28, with the latter being the largest tornado outbreak ever recorded.

April 14-16th Tornado Outbreak

Visible satellite image of the storm on April 14th @ 23:45 GMT, which is early evening for the Midwest.

Tuskha, Oklahoma multiple vortex tornado, April 14th

Radar image (around 3 PM on April 16th) of Raleigh supercell with a clear hook echo, the tornado is denoted by the yellow triangle. 
Animation of the outbreak

The April 14-16th tornado outbreak was one of the largest tornado outbreaks in recorded histor until it was dwarfed by the outbreak that would take place a week and a half later. In total, 162 tornadoes were confirmed, with 43 EF-0, 75 EF-1, 30 EF-2, and 14 EF-3. There were no EF-4 or 5 tornadoes. The outbreak started in the southern plains in places like Oklahoma and Texas, and it crossed the southern United States as the outbreak progressed, with tornadoes reported in 16 different states. 
Some tornadoes of note were the Tuskha, Oklahoma tornado, which was a strong EF-3 with multiple vortices. It caused 2 deaths and shifted an entire house 6-8 feet off of its foundation. The Raleigh/Sanford area also experienced a significant tornado from a supercell with a very well-defined hook echo, which is formed when precipitation and debris is wrapped around the tornado by the mesocyclone, which is the deep, rotating updraft that makes a supercell thunderstorm a supercell. Hook echos form with "classic" supercells (neither HP or LP ones) and are often indicative of a very powerful storm.

But now for the largest tornado outbreak in recorded history...

The April 25-28th Super Outbreak

Storm Prediction Center (SPC) severe weather reports over the four days. Green = hail, blue = wind, and red = tornado. April 27th was by far the most destructive day of the outbreak.

 Severe weather warnings on April 27. Green = flood, yellow = severe thunderstorm, red = tornado

Severe weather reports for April 27 only.

This April outbreak had 327 confirmed tornadoes and 426 reported tornadoes, This obliterates the previous record of 148 tornados in the 1974 outbreak, although it is important to point out that the 1974 figure may be low because of more sophisticated technology nowadays to confirm tornados, particularly weaker ones. Nevertheless, the 2011 outbreak is the largest the U.S. has ever witnessed. The 1974 “Super Outbreak” was once thought to be a once in 500 year event (.02 % chance of occurance any particular year), but this recent outbreak has shown us that these tornado events are likely less rare than we previously thought.
I was recently comparing satellite imagery between the two storms, and I noticed they looked pretty similar in size and form.

 April 3, 1974

April 27, 2011

They aren’t exactly the same of course, but they are pretty darn close. Both have similar orientations and both have the southernmost point of the cold front at essentially the same location; in the Gulf of Mexico southwest of New Orleans. They both have strong bent back occlusions, although  the 1974 one is more well-defined and there appears to be two in the 2011 storm. There are also a higher number of tornados in the northern U.S. in the 1974 outbreak, while there were more in the southern U.S. with the 2011 outbreak. All in all though. these storms strongly resemble each other. Compare these images to the satellite image further above of the April 14th outbreak

Why did these outbreaks occur? Several things came together at once to make both of these outbreaks happen. By April 25th, it was clear that there was a distinct possibility of a severe tornado outbreak occurring. There was an upper level low pressure system moving in from the West, and as it entered the plains, it strengthened, fed by stark differences in the air masses north and south of the jet stream, with hot, moist air coming off of the Gulf of Mexico and cool, dry air coming south from Canada. The atmosphere was also very unstable, but there was just enough stability to have a "capping inversion" to help explosive supercells develop. I explained how a capping inversion acts as a "pressure cooker" in my previous blog post. On April 27th, the 5th deadliest tornado day in history, the system interacted with an incredibly strong mid-level jet stream, with winds at the 850 millibar level in the atmosphere in the range of 85 to 100 knots. This created wind shear, allowing for strong, long lived thunderstorms to develop by blowing the downdraft away from the updraft in the storm so that the storm is not "choked off" by the downdraft, allowing for a continuous updraft to support the storm for many hours. The wind shear also helped get air spinning within the thunderstorms, forming mesocyclones (rotating updrafts - in order for a thunderstorm to be a supercell it must have a mesocyclone) and tornadoes. Although the following day was quieter as far as tornado development goes, there were still a large number of tornadoes before the storm finally headed out to sea.

With 327 tornadoes total, 105 were EF-0, 134 were EF-1, 51 were EF-2, 22 were EF-3, 12 were EF-4, and 3 were EF-5. All three EF-5 tornadoes occurred on April 27th, only the second time three of more F or EF-5 tornadoes have been recorded in one day (there were six in on April 3, 1974, but it is widely accepted that it was easier to attain F5 status then than EF-5 now). Both of these tornado outbreaks are unique not only in the number or tornadoes that they produced but the number of strong tornadoes they produced (F-3 / EF-3 and up)

I also found some fascinating animating satellite and radar imagery of the storm. Look below!

radar (best I could find)
radar showing Tuscaloosa, Alabama EF-5 tornadic supercell

The EF-5 tornado in Tuscaloosa... these guys are WAY too close!!!

The Tuscaloosa, Alabama tornado was a very large one. This outbreak will never be forgotten. At the height of the outbreak, there were 188 confirmed tornadoes in 24 hours. 344 people died. And April 2011 will go down in history as one of the most violent tornado months in history.

Total severe weather reports for April

Man, I've been working on this thing for about four hours now... but it is worth it.

While May has been a calmer month, it has been a tragic one. In Joplin, Missouri, a 3/4 mile wide EF-5 tornado obliterated 1/3 of the entire city of Joplin, resulting in at least 125 deaths. This was the deadliest tornado since 1947.

May 21-25 Tornado Outbreak

May 22nd, 2011

After a very quiet first part of May, tornado activity ramped up again at the latter part of the month. During this outbreak, there were 30 EF-0 tornadoes, 25 EF-1 tornadoes,  17 EF-2 tornadoes, 8 EF-3 tornadoes, no EF-4 tornadoes, and 1 EF-5 tornado. 

The EF-5 tornado, occurring on May 22, was the Joplin tornado. This particular tornado was incredibly strong and it directly hit a city with 50,000 residents. The results were catastrophic.

Joplin one day after the tornado with a strong thunderstorm in the distance. The hospital withstood a direct hit although it still received heavy damage.

The tornadic supercell over Joplin

The Joplin tornado

Thankfully, the forecast for the future shows a period of calmer activity for severe weather. Hopefully these communities can rebuild themselves, but they will need a lot of help. This tornado season has already cost us over 10 billion dollars, which is the highest amount ever (even when adjusted for inflation).

On a side note, April was the coldest on record for Seattle. The U.S. had the most tornadoes on record last April. It is not a coincidence. I explained it in my previous blog post.

Also, I wrote an article on the strength of extratropical storms a ways back and included the Super Outbreak of 1974, which was the biggest outbreak ever at the time. There is a lot of great stuff on this blog, take advantage of being able to search for previous posts!

Thank you so much for reading! Good night, it is 11:48 P.M.


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