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May-June 2014

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The 2013 Tornado Season: Local Devastation Defies Below-Normal Numbers

There were 903 tornadoes reported in the United States in 2013. The annual count was well below the 10-year annual average of 1,350 tornadoes (2003-2012). It has been 25 years since a year with fewer tornadoes (1989 had 856). It was also the second year in a row with lower than normal activity, and the past two years now stand in stark contrast to the level and intensity of tornado activity experienced in 2011 (see “Tornadoes 2011: An Unprecedented Year,” Weatherwise, May-June, 2012).

Tornadoes occurred in 43 states on 152 days during 2013. The first tornado of the year hit Saint Martin Parish, in southwest Louisiana, at 5:30 a.m. local time on January 10. No injuries or deaths were reported with this EF1 tornado, but estimated winds around 100 mph damaged rooftops along a two-mile path. The final tornado of 2013 was reported in Bourbon County, Kentucky, just before midnight local time, on December 21. The EF1 tornado destroyed or heavily damaged a number of outbuildings, and was one of 13 tornadoes reported during this year-ending mini-outbreak of severe storms that stretched across 10 states.

The 55 fatalities and over 700 injuries directly related to tornadoes in 2013 belie the overall low tornado count, and suggest a continuing vulnerability due to increased population density in those areas of the country most prone to strong and violent tornadoes. The deadliest day of the year was May 20, when 24 lives were claimed by a violent EF5 tornado that struck Moore, Oklahoma, during the afternoon. This was the third day in a row with a strong to violent tornado (EF4-5 with estimated winds between 150-200 mph). An EF4 near Rozel, Kansas, on May 18 was followed on May 19 by a killer EF4 tornado in Shawnee, Oklahoma (two fatalities), and then the incredibly devastating Moore tornado on the 20th. Before 2013, there is no record of three consecutive May days with strong to violent tornadoes being reported in the United States.

A chart depicting the daily tornado counts and annual trend line in 2013, compared to the past decade, is shown in Figure 1. The chart displays the odd nature of a year where the biggest tornado days fall outside of what is traditionally considered tornado season (March-May). Until November 17, 2013, the most prolific tornado day of the year had been January 30, with 44 tornadoes. The November 17, 2013, outbreak pushed passed January 30 for the title of most active day of the year, with a total of 74 tornadoes. The last year featuring a November day as the most active tornado day of the year was 2005.


Figure 1. Daily tornadoes and running annual total for 2013 in red and 10-year averages in black/gray.

 

January

The month ended with more than double the 10-year average level of activity. There were 75 tornadoes on five days compared to a 10-year average count of about 34 tornadoes on six days. Most of the tornadoes occurred at the close of the month, in a two-day outbreak spanning January 29-30. The 65 tornadoes reported in 12 states during this event came about as a powerful large-scale trough in the jetstream plowed east into very moist air from the Southern Plains to the Southeast. Many of the tornadoes raced east-northeast as part of a larger thunderstorm squall line. The strongest tornado of the event developed from a supercell storm ahead of the squall line on the second day, January 30. That's when an EF3 moved into parts of Adairsville, Georgia, just before noon, killing one person and injuring nine others. This killer tornado ended a stretch of 219 days without a fatal tornado in the United States. The property damage inflicted by the Adairsville tornado was estimated by the National Weather Service at $75 million.

February

An average number of 39 tornadoes was reported across eight days and eight states in February. The most significant tornado of the month occurred on February 10, when Hattiesburg, Mississippi was struck in the early evening by an EF4 packing winds estimated at 170 mph. This tornado was on the ground for over 20 miles across Lamar and Forrest Counties in southern Mississippi. Hundreds of homes were either destroyed or seriously damaged by the tornado according to emergency management officials. While 71 injuries were reported, there were, remarkably, no fatalities with this tornado. Total damage in the Hattiesburg area was estimated at over $38 million. The only fatality of the month occurred in the east Texas town of Plainview on February 21. A weak EF1 tornado felled numerous trees on a five-mile track, and one of the trees crushed a mobile home, killing the occupant. Four other weak tornadoes occurred on this day across Louisiana and Texas.

March

Only 18 tornadoes were reported in March. This is less than 20% of the 10-year annual average of 100 tornadoes. The month was the most inactive March in over 35 years (17 tornadoes during March of 1978), and only 10 more tornadoes than the least active March on record (eight tornadoes in March of 1969). As can be seen from Figure 1, the running annual count would normally double during a normal March, climbing from about 100 to 200 tornadoes as the atmosphere reconfigures from winter to spring seasons. The 2013 annual count (red line on Figure 1) remained nearly flat through March 2013.

April

Despite the near-normal number of 18 tornado days during the month, April continued the inactive trend established in March. There were 86 tornadoes in 20 states, which is well below the 10-year average of 234. The 10-year average for April is skewed by the incredible tornado count of 757 that occurred in April 2011. However, even without 2011 included in the long-term average, April 2013 marked another month of well below normal activity.

The most destructive tornadoes of April 2013 hit the middle and lower Mississippi Valley areas on April 10-11, ahead of a strong cold front. Potent wind shear contributed to an EF2 tornado in Saint Louis, Missouri, on April 10, with damage to nearly 400 structures. The activity level ratcheted up on April 11. As low pressure intensified across the Midwest, powerful storms swept east from Louisiana to Georgia. A particularly long-lived supercell tornado tracked over 60 miles from Kemper County, in eastern Mississippi, to Pickens County, in western Alabama. Maximum wind speeds with this tornado were estimated at 145 mph (EF3) in Kemper County, where five injuries and a fatality were reported. There were 34 tornadoes reported over this two-day April episode with property damages estimated to exceed $10 million.

May

An inactive first half of the month contributed to a slightly below average number of May tornadoes (265). However, this would be overshadowed by a devastating last half of the month, particularly for the state of Oklahoma. As a more active pattern began to evolve by the middle of the month, supercell thunderstorms brought large hail and tornadoes to north-central Texas on May 15. Six fatalities occurred in association with an EF4 tornado in Granbury, Texas.

As part of a multiday severe weather outbreak across the Plains and Midwest, 73 tornadoes occurred between May 18 and May 20. An EF4 tornado occurred near Rozel, Kansas, on May 18. On May 19, Wichita, Kansas, had a close call as an EF2 tornado dissipated southwest of the Wichita airport. Other tornadoes occurred on May 19 near the Oklahoma City, Oklahoma, metro area, including an EF4 tornado that resulted in two fatalities near Shawnee.

Even greater devastation would ensue across central Oklahoma the following day. On May 20, a tornado formed just before 3:00 p.m. southwest of the Oklahoma City metro area in the town of Newcastle. This tornado quickly strengthened and tracked east-northeast into Moore, Oklahoma. This strong to violent tornado tracked for around 14 miles and resulted in 24 fatalities, many of them young children. Over 300 homes experienced EF4/EF5 damage along the tornado path. The May 20 EF5 tornado was the third violent tornado (EF4-plus) to strike the heart of Moore since 1999. In the aftermath of the May 20 devastation, President Barack Obama visited the area to tour the damage path and meet with survivors. Ten representatives of the National Weather Service met with the President prior to his departure on Air Force One at Tinker Air Force Base.

For the third time in less than two weeks, the Oklahoma City metro area was particularly hard hit by intense tornadoes on May 31. Shortly after 6:00 p.m., a tornado developed just south of the El Reno, Oklahoma, area. This tornado grew to be very wide (2.6 mile maximum width) while taking a complex path and rapidly changing in speed and direction. The El Reno tornado gained additional notoriety, as three of the eight tornado fatalities included well-known severe storm researchers who lost their lives as the tornado overtook them. An additional 13 fatalities occurred in Oklahoma City, Oklahoma, when excessive rainfall produced flash flooding through the evening.

The May 31 El Reno tornado was sampled by two separate mobile research radar teams. In particular, a mobile X-band Doppler radar (RaXPol) measured nearly 300 mph winds very close to the ground. While these wind speeds are in excess of EF5 strength, comprehensive ground surveys found no damage warranting more than an EF3 rating for the tornado.

June

There were 123 tornadoes reported in June, which was about half the 10-year average number of 230. As Tropical Storm Andrea moved from the eastern Gulf of Mexico across north Florida and to the Eastern Seaboard on June 6, the stronger winds associated with the tropical circulation aided in the development of several weak tornadoes. There was roof damage and at least one injury reported early on June 6, in Palm Beach County, Florida, from an EF1 tornado associated with Andrea. Ten additional weak tornadoes occurred in Florida on this day.

The most active day of the month came on June 12 when 20 tornadoes were reported from Iowa to Ohio. The strongest, rated EF3 with winds estimated at 155 mph, damaged farmsteads and businesses along a six-mile track coming uncomfortably close to the town of Belmond, Iowa. Another strong tornado, with winds estimated around 135 mph (EF2), touched down in Carroll County, Illinois, before 6 p.m. These tornadoes were part of a larger developing straight-line wind system called a derecho. As the derecho spread east from Ohio to New Jersey between June 12 and 13, widespread damaging thunderstorm winds were reported across eight states. Another derecho formed on the heels of the first, across eastern Kentucky, early on June 13. This system produced over 500 damaging wind reports across the mid-Atlantic region through the day, along with about 10 weak tornadoes reported from North Carolina to Maryland.

July-August-September

The level of tornado activity through the summer of 2013 remained sub-par, with the three-month total of 138 tornadoes being about one-half the 10-year average for this period (273). This was the second year in a row without a tornado rated anything stronger than EF2 (winds to 135 mph) during July, August, or September. Prior to 2012, every year back to 2000 had at least one tornado rated stronger than EF2 during at least one of these months.

As the atmosphere warms through the summer months, the jetstream migrates north away from those areas of the Great Plains that are more accustomed to tornadoes through the spring and early summer. On July 15, across northeast Montana, a very moist air mass and daytime temperatures soaring above 90 degrees contributed to the development of strong instability. Thunderstorm development was focused along a trough of low pressure in the lee of the higher terrain, and a supercell erupted that sustained a 20-mile track tornado over mostly rural land in northern Roosevelt County. Isolated damage to buildings, power poles, and trees resulted in an EF2 rating for winds estimated at 115-120 mph.

October

Tornado activity climbed above normal levels during October, with 60 tornadoes reported across 16 states on 11 days during the month. The 10-year averages are around 54 tornadoes on 10 days in 12 states. The bulk of October 2013 tornadoes occurred on two days during the month; October 4 and 31.

On October 4, a strong low pressure system moved from eastern Colorado to South Dakota. As the dry line with this system swept into central and eastern Nebraska, a warm front lifted north across northeast Nebraska and western Iowa during the late afternoon. Unseasonably warm and moist air in the region contributed to the development of strong instability. The unstable airmass combined with strengthening wind shear and resulted in an environment very supportive of severe thunderstorms and tornadoes. Supercells developed near the intersection of the dry line and warm front across northeast Nebraska during the late afternoon. A number of tornadoes (17) occurred as these storms tracked northeast from Nebraska into Iowa and extreme South Dakota.

Two EF4 tornadoes were reported on October 4—one in Wayne, Nebraska, the other in Woodbury County, Iowa. At one point, the Wayne tornado was over a mile wide and producing estimated wind speeds over 165 mph (EF4). As the tornado tracked to the east of the small hamlet of Wayne, substantial damage occurred in an industrial part of town. Numerous metal buildings, some quite large, sustained serious damage and in some cases were reduced to nothing more than mangled debris. Fortunately, no one was killed by this monster tornado, but there were 15 injuries reported and property damage was estimated around $50 million.

Strong to violent October tornadoes in Nebraska or Iowa are rare, but not unprecedented. The last F4 tornado to occur in Nebraska in the month of October occurred on October 29, 1956. Incidentally, at nearly 150 miles in length, the 1956 tornado holds the record for the longest tornado track ever recorded in Nebraska. On October 14, 1966, the small town of Belmond, Iowa, was hit by a devastating F5 tornado that claimed six lives. (This is the same Belmond, Iowa, to experience the close encounter with an EF3 tornado on June 12, 2013, described above.)

The most prolific one-day outbreak of October tornadoes since 2010 occurred on Halloween Day, October 31, 2013. There were 32 tornadoes reported across seven states from Texas to Ohio. The majority of these tornadoes were weak and short-lived, and there were no injuries or fatalities reported. However, the National Weather Service estimated property damage from this single day outbreak approached $6 million.

November

November 2013 featured only three days with tornadoes. However, the 79 tornadoes reported during the month greatly exceeded the 10-year average of 53. Almost all of the tornadoes (74) occurred with a significant late-year outbreak on November 17. In terms of the tornado count, this day had more tornadoes than any other single November day on record, and the most tornadoes for any day in 2013.

As a powerful mid-level jet stream with winds over 150 mph spread east from the Great Plains, the lift and shear associated with the jet encountered a warm and unstable airmass developing north from the middle Mississippi River Valley. A family of supercell thunderstorms exploded near the Mississippi River between Missouri and Illinois before noon. The most violent tornado of the outbreak was an EF4 tornado that struck Washington, Illinois, in the early afternoon with peak winds of 190 mph. This tornado passed directly through a large residential area, where many homes were flattened to their foundation and trees were stripped of their bark. There were 125 injuries and two deaths with this tornado, and property damage was estimated at over $900 million.

The family of supercells congealed into an intense and extensive squall line across Indiana, and this set the stage for the second greatest Indiana tornado outbreak on record. The line of intense thunderstorms and embedded supercells moved east at an incredible 80-90 mph. Many brief tornadoes spun up along the line with nearly half of them producing EF2 or greater damage. One area across White County, Indiana, experienced widespread winds estimated at 100-120 mph that destroyed nearly every barn in the southern half of the county. The most significant tornado in Indiana was rated EF3 and touched down five miles south-southeast of the town of Lafayette, causing significant damage to two industrial facilities in the area.

The November 17 outbreak also produced two EF3 tornadoes in Kentucky, where widespread significant damage was reported in the region where the Ohio River meets the Mississippi River. One of the supercells that initiated across extreme southeast Missouri went on to produce a 42-mile-long track tornado that crossed the Ohio River from Kentucky into southern Illinois before it tracked into Kentucky, north and east of the city of Paducah. This tornado caused three fatalities in Massac County, Illinois.

By late in the evening on November 17, while the tornado threat was gradually diminishing, the extensive squall line with the larger intense weather system continued to produce widespread damaging winds from Michigan and Ohio into Pennsylvania and West Virginia. In summary, this was the most significant tornado outbreak of 2013 in terms of total tornadoes (74). However, the total tornado path length and/or death toll on this day were lower than prior November outbreaks occurring in 1992, 2002, and 2005. The estimated property damage, while substantial at over $1 billion, was still lower than the estimated $2 billion in damage from the EF5 Moore, Oklahoma, tornado of May 20.


Figure 2. 2013 Tornadoes by EF-Scale.

 

December

After an incredibly active November, December reverted back to below-normal levels of tornado activity, with only 18 tornadoes occurring on three days during the month—about one-half the 10-year normal of 34 tornadoes. Fourteen of the 18 tornadoes in December occurred on the 21st of the month, when a very intense storm system developed across the middle of the United States and then tracked northeast toward the Ohio River Valley region. There were two killer tornadoes with this outbreak, one in Arkansas and the other in Mississippi. Both tornadoes were rated EF2 with winds estimated between 110 and 130 mph. Both tornadoes also killed one person each, when mobile homes were struck by the destructive tornadic winds. Tornadoes also touched down in Texas, Louisiana, and Kentucky during the last tornado outbreak event of 2013.

In summary, 2013 was the second year in a row with fewer than 1,000 total tornadoes for the year. It was a year characterized by episodic and mostly locally concentrated outbreaks. The three most active days of the year were November 17 (74 tornadoes), January 30 (44 tornadoes), and May 20 (36 tornadoes). These three days account for nearly 90% of estimated property losses and over half of the 55 total tornado fatalities in 2013. After an uncharacteristically slow start in May, the devastation that was unleashed on parts of central Oklahoma on May 19-20 belies the lower-than-normal 2013 tornado totals. This serves to remind us that numbers do not always tell the whole story when it comes to these difficult-to-predict, small-scale atmospheric vortices of violence.

TABLE 1.

2013 SUMMARY TABLE

Month2013 Tornadoes2003-2012 Average2013 Tornado Days2003-2012 Average Days2013 Tornado Fatalities2003-2012 Average Fatalities
Jan75345612
Feb394085111
Mar18100713010
Apr862341819144
May26729821244130
Jun123230242713
Jul72106232400
Aug4581162001
Sep2186131501
Oct6054111001
Nov79533785
Dec18343621
Total903*135015217655109

* Preliminary total. Above/below 10-year (2003-2012) average. Source: NOAA/NWS/SPC.

All tornado numbers for 2013 remain preliminary pending further review by the Storm Prediction Center (SPC) and the NOAA National Climatic Data Center. The tallies indicated here are the best estimates at the time of publication.

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