BASICS ABOUT TORNADOES

FROM:  NOAA                                                          Waterspout (Tornado)  Credit:  NOAA 
What is a tornado? According to the Glossary of Meteorology (AMS 2000), a tornado is "a violently rotating column of air, pendant from a cumuliform cloud or underneath a cumuliform cloud, and often (but not always) visible as a funnel cloud." Literally, in order for a vortex to be classified as a tornado, it must be in contact with the ground and the cloud base.

Weather scientists haven't found it so simple in practice, however, to classify and define tornadoes. For example, the difference is unclear between an strong mesocyclone (parent thunderstorm   circulation) on the ground, and a large, weak tornado. There is also disagreement as to whether  separate touchdowns of the same funnel constitute separate tornadoes. It is well-known that a tornado may not have a visible funnel. Also, at what wind speed of the cloud-to-ground vortex does a tornado begin? How close must two or more different tornadic circulations become to qualify as a one multiple-vortex tornado, instead of separate tornadoes? There are no firm answers.

                                        Waterspout (Tornado) Credit:  U.S. Geological Survey  

How do tornadoes form? The classic answer--"warm moist Gulf air meets cold Canadian air and dry air from the Rockies"--is a gross oversimplification. Many thunderstorms form under those conditions (near warm fronts, cold fronts and drylines respectively), which never even come close to producing tornadoes. Even when the large-scale environment is extremely favorable for tornadic thunderstorms, as in an SPC "High Risk" outlook, not every thunderstorm spawns a tornado. The truth is that we don't fully understand. The most destructive and deadly tornadoes occur from supercells--which are rotating thunderstorms with a well-defined radar circulation called a mesocyclone. [Supercells can also produce damaging hail, severe non-tornadic winds, unusually frequent lightning, and flash floods.] Tornado formation is believed to be dictated mainly by things which happen on the storm scale, in and around the mesocyclone. Recent theories and results from the VORTEX program suggest that once a mesocyclone is underway, tornado development is related to the temperature differences across the edge of downdraft air wrapping around the mesocyclone (the occlusion downdraft). Mathematical modeling studies of tornado formation also indicate that it can happen without such temperature patterns; and in fact, very little temperature variation was observed near some of the most destructive tornadoes in history on 3 May 1999. .

What direction do tornadoes come from? Does the region of the US play a role in path direction? Tornadoes can appear from any direction. Most move from southwest to northeast, or west to east. Some tornadoes have changed direction amid path, or even backtracked. [A tornado can double back suddenly, for example, when its bottom is hit by outflow winds from a thunderstorm's core.] Some areas of the US tend to have more paths from a specific direction, such as northwest in Minnesota or southeast in coastal south Texas. This is because of an increased frequency of certain tornado-producing weather patterns (say, hurricanes in south Texas, or northwest-flow weather systems in the upper Midwest).

How long does a tornado last? Tornadoes can last from several seconds to more than an hour. The longest-lived tornado in history is really unknown, because so many of the long-lived tornadoes reported from the early-mid 1900s and before are believed to be tornado series instead. Most tornadoes last less than 10 minutes.

How close to a tornado does the barometer drop? And how far does it drop ? It varies. A barometer can start dropping many hours or even days in advance of a tornado if there is low pressure on a broad scale moving into the area. Strong pressure falls will often happen as the mesocyclone.

What is a waterspout?
A waterspout is a tornado over water--usually meaning non-supercell tornadoes over water. Waterspouts are common along the southeast U. S. coast--especially off southern Florida and the Keys--and can happen over seas, bays and lakes worldwide. Although waterspouts are always tornadoes by definition; they don't officially count in tornado records unless they hit land. They are smaller and weaker than the most intense Great Plains tornadoes, but still can be quite dangerous. Waterspouts can overturn boats, damage larger ships, do significant damage when hitting land, and kill people. The National Weather Service will often issue special marine warnings when waterspouts are likely or have been sighted over coastal waters, or tornado warnings when waterspouts can move inland.

DOES IT RAIN FISH AND FROGS? MAYBE

FROM:  U.S. LIBRARY OF CONGRESS                        PHOTO:   U.S. GEOLOGICAL SURVEY
Can it rain frogs, fish, and other objects?
There have been reports of raining frogs and fish dating back to ancient civilization. Of course, it doesn’t “rain” frogs or fish in the sense that it rains water - no one has ever seen frogs or fish vaporize into the air before a rainfall. However, strong winds, such as those in a tornado or hurricane, are powerful enough to lift animals, people, trees, and houses.  It is possible that they could suck up a school of fish or frogs and “rain” them elsewhere.

Many scientists believe tornadic waterspouts may be responsible for frog and fish rainfalls.  According to Complete Weather Resource (1997), “a tornadic waterspout is merely a tornado that forms over land and travels over the water.”  An especially strong kind of waterspout, they are not as strong as land based tornadoes, which can reach up to 310 miles per hour.  But tornadic waterspouts can reach 100 miles per hour, which can still be quite destructive.

A popular misconception is that waterspouts “rise out of the sea.” In reality, they begin in the air and descend toward the water’s surface. The first visible sign of a tornadic waterspout is usually a dark spot on the water’s surface, which is caused by a spinning column of low-pressure air stirring up the water from overhead.  As the spinning column of air, or vortex, gains momentum, the surrounding water is pulled into a spiral pattern of light and dark bands. Eventually a ring of spraying water, called the cascade,forms around the base.  The characteristic funnel extending from the sky toward the water’s surface becomes visible in the fourth stage of the waterspout’s development. At this point, it is considered a mature storm.

Like a tornado, a mature waterspout consists of a low-pressure central vortex surrounded by a rotating funnel of updrafts.  The vortex at the center of these storms is strong enough to “suck up” surrounding air, water, and small objects like a vacuum. These accumulated objects are deposited back to earth as “rain” when the waterspout loses its energy.  Most of the water seen in the funnel of a waterspout is actually condensate —moisture in the air resulting from the condensation of water vapor.

Professor Ernest Agee from Purdue University says, “I’ve seen small ponds literally emptied of their water by a passing tornado. So, it wouldn’t be unreasonable for frogs (or other living things) to ‘rain’ from the skies” (Chandler, 2004).  Most scientists agree that salt, stones, fish, or frogs can be pulled into a waterspout’s swirling updrafts and deposited once the waterspout hits land and loses its energy.

Although waterspouts are the most commonly offered explanation for animal rainfalls, some scientists, such as Doc Horsley from Southern Illinois University, theorize that any unusually powerful updraft could lift small organisms or organic material into the sky during a storm (Chandler, 2004). An updraft is a wind current caused by warm air from high pressure areas near the earth rising into cooler, low-pressure areas in the atmosphere. Because the cooling causes water in the air to condense, updrafts play an important role in cloud formation and storm development.  During thunderstorms, updrafts can reach speeds of more than 60 miles per hour— comparable to the winds of moderate-intensity waterspouts.

When it rained frogs in Kansas City in 1873, Scientific Americaconcluded that it must have been caused by a tornado or other land-based storm, since there were no swamps or other bodies of water in the vicinity (Cerveny, 2006).  Similarly, when it hailed frogs in Dubuque, Iowa on June 16, 1882, scientists speculated that small frogs were picked up by a powerful updraft and frozen into hail in the cold air above earth’s surface. Although no one has actually witnessed an updraft lifting frogs off the ground, the theory is scientifically plausible since updrafts regularly pick up lightweight debris and carry it considerable distances.

What is unusual in reports of animal rainfalls is the uniformity of the deposition.   When it rains frogs or fishes, witnesses reportonly fish or only frogs falling. According to William Hayden Smith of Washington University, this makes sense since objects of similar size and weight would naturally be deposited together. As winds lose their energy, the heavier objects fall first and smaller objects drop later.

                                                                     PHOTO:  NOAA 

Despite the numerous reports of raining animals, scientists still approach the area with skepticism. Many historical reports are provided by second or third-hand accounts, making their reliability questionable. Also, because of the popularity and mystery surrounding stories about raining animals, some people falsely report an animal rainfall after seeing large numbers of worms, frogs, or birds on the ground after a storm. However, these animals did not fall from the sky. Instead, storms fill in worm burrows, knock birds from trees and roofs, wash fish onto the shores of rivers and ponds, and drive frogs and other small animals from their habitats. People who live in suburban or urban environments tend to underestimate the number of organisms living around their homes. Therefore, they may suspect that animals came from the sky rather than their natural habitat.

Despite the cautious skepticism of the scientific community, a number of eyewitness reports strongly suggest rainfalls of frogs, fish, and other materials on occasion. For instance:

On October 23, 1947, A.D. Bajkov, a biologist with the Louisiana Department of Wildlife, was eating breakfast at a restaurant in Marksville, Louisiana when the waitress told him and his wife that fish were falling from the sky. “There were spots on Main Street, in the vicinity of the bank (a half block from the restaurant) averaging one fish per square yard. Automobiles and trucks were running over them. Fish also fell on the roofs of houses…I personally collected from Main Street and several yards on Monroe Street, a large jar of perfect specimens and preserved them in Formalin, in order to distribute them among various museums.”

On June 7, 2005, thousands of frogs rained on Odzaci, a small town in northwestern Serbia. Climatologist Slavisa Ignjatovic described the phenomenon as “not very unusual” because the strong winds that accompanied the storm could have easily picked up the frogs.

At the end of February, 2010, residents of Lajamanu, a small Australian town, saw hundreds of spangled perch fall from the sky. Christine Balmer was walking home when the rain/fish started to fall. “These fish fell in their hundreds and hundreds all over the place. The locals were running around everywhere to pick them up,” she reported.