Dorothy Couldn’t Get To Oz Without One.


They have been both a mystery and a curse to most people, especially those living in the “alley.” The alley I am talking about is “Tornado Alley.” The area of the United States most prone to being ravaged by tornadoes. Actually tornadoes can and have occurred in all 50 of the United States. There have been some recent tornado events that resulted in death and destruction. Thursday April 3rd a powerful storm ripped through the central US causing serious damage but no known fatalities. At around 7:00 pm Central Daylight Time a damaging twister with quarter-sized hail was reported near Washington, Missouri. A tornado was spotted about 50 miles to the east at 8:16 pm near Glendale, Missouri. That same day a tornado was reported to have touched down south of Krum in Denton County, Texas. Talk about strange, exactly 40 years ago 148 reported tornadoes killed 330 people over 143 states. Two people were killed and twenty were injured due to severe weather Monday April 7th. A tornado touched down in Beaufort County, North Carolina. All of this storm and tornado activity happened in the span of only one week.

We know that tornadoes exist and that they both kill and cause serious damage. Let’s take a look at how these twisters are formed. Here is how the National Weather Service defines the term tornado. “A tornado is a violently rotating column of air, usually pendant to a cumulonimbus, with circulation reaching the ground. It nearly always starts out as a funnel cloud and may be accompanied by a loud roaring noise. On a local scale, it is the most destructive of all atmospheric phenomena.”

Tornado Structure | Image by
Tornado Structure | Image by

They need certain elements to form including warm moist airflow from the south, cooler drier air from the north and a rotation that begins when a mesocyclone is formed. A mesocyclone is defined as a “storm-scale region of rotation, typically 2-6 miles in diameter and often found in the right rear flank of a supercell.” The mesocyclone’s circulation is much larger than the tornado circulation that can develop within it. Here is a video that shows a way the mesocyclone winds can spin into a tornado funnel. Research I have seen over the years has shown the tornado funnel itself can build in various stages sometimes starting high in the sky and dropping down to the ground or building from the ground level upward. Remember the difference between a funnel cloud and a tornado? The funnel cloud has the vortex rotation but is not touching the ground. In order for a funnel cloud to be called a tornado it must reach the ground.

Movie "Twister" | Image by
Movie “Twister” | Image by

There have been many movies made featuring tornadoes, but the most accurate depiction I have ever seen was “Twister.” I found two flaws in the details however. First of all if you are in a red Dodge Ram pickup truck you will be safe. At least it happened that way until the end of  the movie. That’s more tongue-in-cheek. The other flaw, if you will, is that the characters get all excited when one of them announces what they on the radio that they have an F-3 tornado on the ground. You can’t assign the number until after the tornado has passed and a lengthy ground check has been made and possibly even an aerial view has been examined. They should have said a possible F-3. Later on they say the weather service is predicting an F-5 tornado. That is what they would have said since the two cells were merging and they would very possibly create a massive F-5 tornado.

Enhanced Fujita-Pearson Tornado Scale | Image by
Enhanced Fujita-Pearson Tornado Scale | Image by

The way the wind speeds rotating around a tornado vortex are calculated was originally devised by the late Dr. Tetsuya Theodore Fujita who worked out of the University of Chicago in Illinois. The scale went from F-0 to F-5 with F-0 being the weakest causing minor damage and F-5 being the strongest causing total destruction. The scale has been updated (February 2007) and improved and is now called the Enhanced Fujita-Pearson Scale. The reasons for the updating of the scale are “that tornado wind speeds required to inflict the described damage were actually much lower than the F-Scale indicated, particularly for the upper categories. Also, though the scale gave general descriptions of the type of damage a tornado could cause, it gave little leeway for strength of construction and other factors that might cause a building to receive higher damage at lower wind speeds.”

Aumsville, OR EF-2 Tornado 12/14/2010 | Photo by The National Weather Service
Aumsville, OR EF-2 (cold core) Tornado 12/14/2010 | Photo by The National Weather Service

The whole state of Oregon averages over time about three tornadoes per year. From 1950 through 1995 there were 50 reported tornadoes in the state. Most were F-0 or F-1 in strength.  The type we see are called “cold core tornadoes.” The rising of very warm moist air into the higher reaches of the atmosphere is what gives tornadoes their strength. We rarely get very warm air and high relative humidity at the same time, so what happens here is the cold air aloft dives down to meet the warmer air. Simply put, shortening that distance makes a weaker tornado that, here in Oregon, usually causes very little damage and has resulted in no deaths or injuries during that 45-year period.

Believe it or not the best way we have to spot tornadoes is for people who see them to call the authorities and report the location and direction of movement. Doppler Radar is an amazing tool for helping to spot and track tornadoes. For a detailed explanation of how Doppler Radar works check out my previous column called “Doppler What?” If you see a tornado you need to take shelter immediately and once you are in a safer place call 911 and report it.

Let me know what you would like me to talk about or explain. You can comment below or email me at: [email protected].

Tim Chuey is a Member of the American Meteorological Society and the National Weather Association and has been Awarded Seals of Approval for television weathercasting from both organizations.

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