At least 33 people were killed as a tornado outbreak slashed across the South on Sunday and Monday, destroying hundreds of homes and businesses and leaving numerous towns with widespread, severe damage.
While tornadoes can and have occurred in every month in the United States, the most active months are typically April and May, with an average of 11.6 and 23.2, respectively, since records began in 1950. April tends to average about 170 tornados and has often been the most dangerous month. May typically averages about 270 tornadoes, making it the most active month of the year. The top 10 states for tornadoes are as follows, in order from high to low: Texas, Kansas, Oklahoma, Florida, Nebraska, Illinois, Colorado, Iowa, Alabama, Missouri, and Mississippi. Below are some more interesting facts:
How Does a Tornado Form: Tornadoes form where warm moist air is trapped underneath a layer of cold, dry air. This instability is upset when the warm bottom layer gets pushed up — either by heating near the ground, or by an influx of cold air. As the moist air rises, it cools, forming clouds and thunderstorms. If the conditions are right, the rapidly rising air will spin around a central funnel, at speeds sometimes exceeding 250 mph.
Wind Speed Matters: The original Fujita scale is named after Dr. Ted Fujita, a University of Chicago severe storms research scientist who came up with the scale in 1971. Dr. Fujita’s scale, which ranges from F0 (the least violent) to F5 (the most violent), is based upon the type and severity of damage the tornado produced. F4 and above, account for less than 1 percent of all tornadoes but account for 70 percent of tornado-related deaths. The Enhanced Fujita (EF) Scale was devised by a panel of meteorologists and engineers convened by the Wind Science and Engineering Research Center at Texas Tech University. The Weather Channel’s severe weather expert Dr. Greg Forbes was on the team of experts who determined the revised wind speed ranges. Since 2007, the EF Scale has been used to rate tornadoes.
EF-0 – estimated wind speeds: 65 to 85 mph. Light damage. Peels surface off some roofs; some damage to gutters or siding; branches broken off trees; shallow-rooted trees pushed over.
EF-1 – estimated wind speeds: 86 to 110 mph. Moderate damage. Roofs severely stripped; mobile homes overturned or badly damaged; loss of exterior doors; windows and other glass broken.
EF-2 – estimated wind speeds: 111 to 135 mph. Considerable damage. Roofs torn off well-constructed houses; foundations of frame homes shifted; mobile homes completely destroyed; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.
EF-3 – estimated wind speeds: 136 to 165 mph. – Severe damage. Entire stories of well-constructed houses destroyed; severe damage to large buildings such as shopping malls; trains overturned; trees debarked; heavy cars lifted off the ground and thrown; structures with weak foundations blown away some distance.
EF-4 – estimated wind speeds: 166 to 200 mph. Devastating damage. Whole frame houses Well-constructed houses and whole frame houses completely leveled; cars thrown and small missiles generated.
EF-5 – estimated wind speeds: Over 200 mph. Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 m (109 yd); high-rise buildings have significant structural deformation; incredible phenomena will occur.
States with the Moist E5 Tornados: The states with the highest number of F5 and EF5 rated tornadoes since data was available in 1950 are Alabama and Oklahoma, each with seven tornadoes. Iowa, Kansas, and Texas each are tied for second-most with six. The state with the highest number of F5 and EF5 tornadoes per square mile, however, was Iowa.
Deadliest Tornadoes: March 18, 1925 Tri-State Tornado, Missouri, Illinois, and Indiana killed 695 people; Worst Modern-Day May 22, 2011 Joplin, Missouri killed 158 people. The deadliest outbreak came on April 3, 1974, when a two-day “Super Outbreak” of 147 tornadoes killed 308 people in 13 states.
What Time of Day? For some strange reason, tornadoes are most likely to occur between 3 pm and 9 pm, but can occur at any time.
What is the heaviest thing a tornado has ever picked up? The Pampa, Texas, tornado moved machinery that weighted more than 50,000 pounds.
Directional Changes: Most twisters or cyclones travel from southwest to northeast and can move in the opposite direction for short periods of time. A tornado can even backtrack if it is hit by winds from the eye of the thunderstorm.
Sky Changes Color: The sky typically turns to a characteristic greenish color when a tornado is on the rise.
How the Tornado Ends: Like anything else on this planet, everything that takes birth, must die, even the tornadoes have a definite lifecycle. They last up to 1-2 hours. The down pouring rainfall drags a rapidly descending region of air which is known as the rear flank downdraft (RFD). It drags the super cell’s Meso cyclone (area of organized rotation) to the ground with it. This RFD, when becomes cool, chokes the tornado, stopping its power source of warm air and finally dissipates the vortex.