Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 2:40 PM GMT en Marzo 05, 2012
A blanket of snow 2 - 4 inches deep fell yesterday on the regions of Southern Indiana and Northern Kentucky pounded by deadly tornadoes on Friday, adding to the misery of survivors. The violent tornado rampage killed 39 and injured hundreds more, wreaking property damage that will likely exceed $1 billion. Hardest hit were Kentucky and Southern Indiana, which suffered 21 and 12 dead, respectively. Three were killed in Ohio, and one each in Alabama and Georgia. The scale of the outbreak was enormous, with a preliminary total of 139 tornadoes touching down in eleven states, from southern Ohio to Northern Florida. The National Weather Service issued 297 tornado warnings and 388 severe thunderstorm warnings. At one point, 31 separate tornado warnings were in effect during the outbreak, and an area larger than Nebraska--81,000 square miles--received tornado warnings. Tornado watches were posted for 300,000 square miles--an area larger than Texas.
Video 1. Spectacular video of the EF-4 tornado that devastated Henrysville and Marysville, Indiana on March 2, 2012. You can see small satellite vorticies rotating on the side of the main vortex.
Video 2. Another video of the EF-4 tornado that devastated Henrysville and Marysville, Indiana on March 2, 2012, taken from a gas station.
The deadliest and most violent tornado: an EF-4
The deadliest and most violent tornado of the March 2, 2012 outbreak was an EF-4 with winds up to 175 mph that demolished much of Henryville, Chelsea, Marysville, and New Pekin, Indiana. Ten minutes after that tornado demolished much of Henryville, a weaker EF-1 tornado hit the town. The twin tornadoes killed twelve people. The Henryville tornado was the only violent EF-4 tornado of the outbreak.
Figure 1. Radar reflectivity image (top) and Doppler velocity image (bottom) of the two tornadoes that hit Henryville, Indiana on March 2, 2012. The first (rightmost) hook echo on the reflectivity image belonged to the only violent tornado of the outbreak, an EF-4 with winds of 166 - 200 mph. Ten minutes after that tornado demolished much of Henryville, a second tornado hit the town. These tornadoes also caused severe damage to the towns of Chelsea, Marysville, and New Pekin, and killed twelve people.
At least eleven other tornadoes in the outbreak have been classified as EF-3s with winds of 136 - 165 mph. Capitalclimate.com reports that the EF-3 tornadoes that crossed three Eastern Kentucky counties were the first tornadoes that strong ever observed, since tornado records began in 1950. The deadliest of the EF-3 tornadoes hit West Liberty, Kentucky, killing eight. Here's a summary of the deadly tornadoes of the outbreak taken from Wikipedia:
EF-4, 12 deaths, Henrysville, Indiana
EF-3, 8 deaths, West Liberty, Kentucky\
EF-2, 5 deaths, East Bernstadt, Kentucky
EF-3, 4 deaths, Crittenden, Kentucky
EF-3, 2 deaths, Holton, Indiana
EF-3, 3 deaths, Peach Grove, Ohio
EF-3, 2 deaths, Blaine, Kentucky
EF-3, 2 deaths, Salyersville, Kentucky
EF-2, 1 death, Jackson's Gap, Alabama
Figure 2. Damage in West Liberty, Kentucky after the March 2, 2012 EF-3 tornado. Image taken from from a Kentucky National Guard Blackhawk helicopter, while landing in West Liberty, KY (Morgan County).
Figure 3. Radar image of the West Liberty, Kentucky EF-3 tornado of March 2, 2012, showing a classic hook echo. The tornado carved a 60-mile-long path through Eastern Kentucky, causing extreme damage in West Liberty. The tornado killed six in West Liberty and two near Frenchburg. At least 75 people were injured. It was the first EF-3 tornado in Eastern Kentucky since 1988.
Video 3. A woman prays for deliverance of West Liberty as the ominous wall cloud of the developing tornado approaches the town.
Incredibly fast-moving storms
The speed with which some of the storms moved was truly exceptional, thanks to jet stream winds of up to 115 mph that pushed the thunderstorms forward at amazing speeds. A number of the tornadoes ripped through Kentucky with forward speeds of 70 mph, and two tornado warnings in Central Kentucky were issued for parent thunderstorms that moved at 85 mph. NWS damage surveys have not yet determined if one of the tornadoes from the outbreak has beaten the record for the fastest moving tornado, the 73 mph forward speed of the great 1925 Tri-State Tornado, the deadliest U.S. tornado of all-time.
Video 4. A family gets in their car in an attempt to flee the Borden, Indiana tornado of March 2, 2012. Unless you know what you're doing, fleeing a tornado in a car can be extremely dangerous, especially when the tornadoes are moving at speeds of 50 - 70 mph, as many were doing during the March 2, 2012 outbreak. Most tornado fatalities occur in mobile homes and cars.
Largest 5-day and 2nd largest 2-day tornado outbreak for so early in the year?
The March 2 tornado outbreak spawned 128 tornadoes, according to preliminary reports as of 8 am EST March 7 from NOAA's Storm Prediction Center. An additional 11 tornadoes (preliminary) touched down on March 3, in Florida and Georgia; 3 additional tornadoes touched down on March 1 (Wikipedia does a great job tallying the stats for this tornado outbreak.) These preliminary reports are typically over-counted by 15%, but a few delayed reports will likely come in, bringing the total number of tornadoes from the March 2 - 3 outbreak to 115 - 125, propelling it into second place for the largest two-day tornado outbreak so early in the year. The top five two-day tornado outbreaks for so early in the year, since record keeping began in 1950:
January 21 - 22, 1999: 129 tornadoes, 4 deaths
March 2 - 3, 2012: 139 tornadoes (preliminary), 39 deaths
February 5 - 6, 2008: 87 tornadoes, 57 deaths
February 28 - March 1, 1997: 60 tornadoes, 10 deaths
January 7 - 8, 2008: 56 tornadoes, 4 deaths
Though the 36 tornadoes that occurred during the February 28 - 29 Leap Day outbreak were part of a separate storm system, the five-day tornado total from February 28 - March 3, 2012 is likely to eclipse the late January 18 - 22, 1999 five-day tornado outbreak (131 tornadoes) as the most prolific five-day period of tornado activity on record for so early in the year.
Figure 4. A key ingredient for tornado formation is the presence of warm, moist air near the surface, which helps make the atmosphere unstable. On the day of the March 2, 2012 outbreak, record warm air surged northwards into the tornado formation region, setting or tying daily high temperature records at 28 airports in Louisiana, Arkansas, Mississippi, Alabama, Tennessee, Kentucky, and Georgia.
Ingredients for the tornado outbreak
This year's unusually mild winter has led to ocean temperatures across the Gulf of Mexico that are approximately 1°C above average--among the top ten warmest values on record for this time of year, going back to the 1800s. (Averaged over the month of February, the highest sea surface temperatures on record in the Gulf between 20 - 30°N, 85 - 95°W occurred in 2002, when the waters were 1.34°C above average). Friday's tornado outbreak was fueled, in part, by high instability created by unusually warm, moist air flowing north from the Gulf of Mexico due to the high water temperatures there. This exceptionally warm air set record high temperatures at 28 airports in Louisiana, Arkansas, Mississippi, Alabama, Tennessee, Kentucky, and Georgia the afternoon of the tornado outbreak (March 2.) Cold, dry air from Canada moved over the outbreak region at high altitudes. This created a highly unstable atmosphere--warm, low-density air rising in thunderstorm updrafts was able to accelerate rapidly upwards to the top of the lower atmosphere, since the surrounding air was cooler and denser at high altitudes. These vigorous updrafts needed some twisting motion to get them spinning and create tornadoes. Very strong twisting forces were present Friday over the tornado outbreak area, thanks to upper-level jet stream winds that blew in excess of 115 mph. These winds changed speed and direction sharply with height,imparting a shearing motion on the atmosphere (wind shear), causing the air to spin. High instability and a high wind shear are the two key ingredients for tornado formation.
Figure 5. The other key ingredient for tornado formation is the presence of very strong winds aloft that change speed and direction sharply with height. This change of wind imparts a shearing motion on the atmosphere (wind shear), causing the air to spin. Here, we see the upper-level wind speeds at the peak of the March 2, 2012 tornado outbreak. The jet stream can be seen as the U-shaped belt of strong winds. Jet stream winds in excess of 100 mph (deep blue colors) were present over the tornado outbreak area in this analysis of data from the NOAA North American Model (NAM) from 7 pm EST March 2, 2012. Image credit: NOAA Environmental Visualization Laboratory.
Another bad year for tornadoes in the U.S.--what's going on?
Last year's tornado season was incredibly severe, and we are off to one of the worst early-season starts to tornado season on record now in 2012. However, it is too soon to ring the alarm bells on climate change being responsible for this. The tornado data base going back to 1950 doesn't show an increasing trend in strong tornadoes in recent decades. While climate change could potentially lead to an increase in tornadoes, by increasing instability, it could also decrease them, by decreasing wind shear. I'd need to see a lot more bad tornado years before blaming climate change for the severe tornado seasons of the past two years. One thing that climate change may be doing, though, is shifting the season earlier in the year. The 5-day total of tornadoes from February 28 - March 3 will probably break the record of 131 set in 1999 for the largest tornado outbreak so early in the year. Warmer winters, and an earlier arrival of spring due to a warming climate, will allow tornado season to start earlier--and end earlier. This year's early start to tornado season is consistent with what we would expect from a warming climate. I have a more extensive article on this subject that has just been published by Weatherwise magazine, and a 2008 post, Are tornadoes getting stronger and more frequent? Dr. Jonathan Martin of the University of Wisconsin-Madison is doing interesting research on the type of situation we saw with some of the recent severe tornado outbreaks, when two branches of the jet stream, the polar jet and the subtropical jet, merge to form a "superjet." In a December 2011 interview with sciencedaily.com, he said: "There is reason to believe that in a warmer climate, this kind of overlapping of the jet streams that can lead to high-impact weather may be more frequent."
I don't see any storm systems coming over the next 10 days that could cause a major tornado outbreak, though March weather is too volatile to forecast reliably that far in advance. There is a storm system expected to develop on Thursday in the Plains we will have to watch, but so far, indications are that it will not be capable of generating a major tornado outbreak.
Portlight disaster relief charity responds to the tornado disaster
The Portlight disaster relief charity reports that volunteers from colleges and churches made a strong showing in tornado-devastated Harrisburg, Illinois on Sunday. Team Rubicon and Portlight will push east to Indiana, where volunteer work is still restricted because of gas leaks and continuing SAR (search and rescue) operations.
I'll edit this post with new stats on the tornado outbreak as they become available, and have an entirely new post on Wednesday.
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