On the afternoon of April 27, 2011, a large, long-tracked, and violent high-end EF4 multi-vortex tornado, known by most as the Cullman–Arab tornado, moved across north-central

Alabama Alabama ( ) is a U.S. state, state in the Southeastern United States, Southeastern and Deep South, Deep Southern regions of the United States. It borders Tennessee to the north, Georgia (U.S. state), Georgia to the east, Florida and the Gu ...

, in the United States, striking numerous towns along its track, including Cullman, Fairview,

Arab Arabs (, , ; , , ) are an ethnic group mainly inhabiting the Arab world in West Asia and North Africa. A significant Arab diaspora is present in various parts of the world. Arabs have been in the Fertile Crescent for thousands of years ...

and

Ruth Ruth (or its variants) may refer to: Places France * Château de Ruthie, castle in the commune of Aussurucq in the Pyrénées-Atlantiques département of France Switzerland * Ruth, a hamlet in Cologny United States * Ruth, Alabama * Ruth, Ark ...

. The tornado killed 6, injured over 40, and impacted hundreds of structures. It occurred as part of the largest tornado outbreak in modern history, and was the second violent tornado of the outbreak, touching down after the Philadelphia, Mississippi tornado. The tornado first touched down in

Cullman County Cullman County is a county located in the north central portion of the U.S. state of Alabama. As of the 2020 census, the population was 87,866. Its county seat and largest city is Cullman. Its name is in honor of Colonel John G. Cullmann. C ...

before entering the city limits of Cullman, where EF4 damage was recorded to numerous buildings, including a large church in the downtown area. The tornado then left the Cullman area, moving through Fairview and heavily damaging multiple buildings located in the town. As the tornado tracked through

Morgan Morgan may refer to: Arts and entertainment * ''Morgan – A Suitable Case for Treatment'', also called ''Morgan!'', a 1966 comedy film * ''Morgan'' (2012 film), an American drama * ''Morgan'' (2016 film), an American science fiction thriller * ...

and

Marshall Marshall may refer to: Places Australia *Marshall, Victoria, a suburb of Geelong, Victoria ** Marshall railway station Canada * Marshall, Saskatchewan * The Marshall, a mountain in British Columbia Liberia * Marshall, Liberia Marshall Is ...

counties, it struck several smaller villages, including Ruth, where heavy damage was documented. Shortly after crossing the

Tennessee River The Tennessee River is a long river located in the Southern United States, southeastern United States in the Tennessee Valley. Flowing through the states of Tennessee, Alabama, Mississippi, and Kentucky, it begins at the confluence of Fren ...

, the tornado dissipated. The tornado devastated downtown Cullman, inflicting an estimated $13.5 million (2011

USD The United States dollar (symbol: $; currency code: USD) is the official currency of the United States and several other countries. The Coinage Act of 1792 introduced the U.S. dollar at par with the Spanish silver dollar, divided it int ...

) to the city and causing widespread power outages throughout Cullman County. The tornado had maximum estimated windspeeds of , classifying it as violent. Several buildings, many made of brick, in downtown Cullman were leveled by these winds, and the tornado directly preceded several other violent tornadoes that would touch down shortly after, including the Hackleburg–Phil Campbell tornado 20 minutes before the Cullman tornado dissipated.

Meteorological synopsis

Setup

The environmental conditions leading up to the 2011 Super Outbreak were among the "most conducive to violent tornadoes ever documented". On April 25, a vigorous upper-level

shortwave trough A shortwave or shortwave trough is an embedded kink in the trough / ridge pattern. Its length scale is much smaller than that of and is embedded within longwaves, which are responsible for the largest scale (synoptic scale) weather systems. Sho ...

moved into the Southern Plains states. Ample instability, low-level moisture, and

wind shear Wind shear (; also written windshear), sometimes referred to as wind gradient, is a difference in wind speed and/or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical ...

all fueled a significant

tornado outbreak A tornado outbreak is the occurrence of multiple tornadoes spawned by the same Synoptic scale meteorology, synoptic scale weather system. The number of tornadoes required to qualify as an outbreak typically are at least six to ten, with at least ...

from

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

Tennessee Tennessee (, ), officially the State of Tennessee, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Kentucky to the north, Virginia to the northeast, North Carolina t ...

; at least 64 tornadoes touched down on this day. An

area of low pressure In meteorology, a low-pressure area (LPA), low area or low is a region where the atmospheric pressure is lower than that of surrounding locations. It is the opposite of a high-pressure area. Low-pressure areas are commonly associated with inclem ...

consolidated over Texas on April 26 and traveled east while the aforementioned shortwave trough traversed the

Mississippi Mississippi ( ) is a U.S. state, state in the Southeastern United States, Southeastern and Deep South regions of the United States. It borders Tennessee to the north, Alabama to the east, the Gulf of Mexico to the south, Louisiana to the s ...

and

Ohio River The Ohio River () is a river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing in a southwesterly direction from Pittsburgh, Pennsylvania, to its river mouth, mouth on the Mississippi Riv ...

valleys. Another 50 tornadoes touched down on this day. The multi-day outbreak culminated on April 27 with the most violent day of tornadic activity since the

1974 Super Outbreak The 1974 Super Outbreak was one of the most intense tornado outbreaks on record, occurring on April 3–4, 1974, across much of the United States. It was one of the deadliest tornado outbreaks in U.S. history. It was also the most violent t ...

. Multiple episodes of tornadic activity ensued with two waves of

mesoscale convective system A mesoscale convective system (MCS) is a complex of thunderstorms that becomes organized on a scale larger than the individual thunderstorms but smaller than extratropical cyclones, and normally persists for several hours or more. A mesoscale conv ...

s in the morning followed by a widespread outbreak of

supercell A supercell is a thunderstorm characterized by the presence of a mesocyclone, a deep, persistently rotating updraft. Due to this, these storms are sometimes referred to as rotating thunderstorms. Of the four classifications of thunderstorms (su ...

s from

North Carolina North Carolina ( ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, South Carolina to the south, Georgia (U.S. stat ...

during the afternoon into the evening. Tornadic activity on April 27 was precipitated by a 995

mbar The bar is a metric unit of pressure defined as 100,000 Pa (100 kPa), though not part of the International System of Units (SI). A pressure of 1 bar is slightly less than the current average atmospheric pressure on Earth at sea ...

(

hPa The pascal (symbol: Pa) is the unit of pressure in the International System of Units (SI). It is also used to quantify internal pressure, stress, Young's modulus, and ultimate tensile strength. The unit, named after Blaise Pascal, is an S ...

; 29.39

inHg Inch of mercury (inHg, ″Hg, or in) is a non- SI unit of measurement for pressure. It is used for barometric pressure in weather reports, refrigeration and aviation in the United States. It is the pressure exerted by a column of mercury in h ...

) surface low situated over

Kentucky Kentucky (, ), officially the Commonwealth of Kentucky, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Illinois, Indiana, and Ohio to the north, West Virginia to the ...

and a deep, negatively tilted (aligned northwest to southeast) trough over

Arkansas Arkansas ( ) is a landlocked state in the West South Central region of the Southern United States. It borders Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, Texas to the southwest, and Oklahoma ...

and

Louisiana Louisiana ( ; ; ) is a state in the Deep South and South Central regions of the United States. It borders Texas to the west, Arkansas to the north, and Mississippi to the east. Of the 50 U.S. states, it ranks 31st in area and 25 ...

. A strong southwesterly surface jet intersected these systems at a 60° angle, an ageostrophic flow that led to

storm-relative helicity {{Short pages monitor