Emergency Preparedness for TORNADOS

Transcription

1 Emergency Preparedness for TORNADOS What Should I Do Before a Tornado? Make sure that you review your Family Emergency Plan with your family and that everyone knows what they should do. Make sure that your Emergency Kit is fully stocked and that your family knows where it is. Be prepared to be self-sufficient for several days, in the event of widespread power outages or disruption of public utilities. Establish a safe zone in your home and place of work (preferably in the basement or in a small interior room or hallway) and make sure that everyone knows where to go. Have a NOAA Weather Radio (a special radio that provides around-theclock weather information) or an AM/FM Radio in your house that everyone knows how to use. Make sure that your radio is battery-operable and that you have a fresh supply of batteries on hand. Monitor weather forecasts before you go on a trip or spend an extended period of time outdoors. Learn tornado warning signs. Although tornadoes vary greatly in their appearance and can offer little or no warning, it can be helpful to be aware of signs that a tornado could be imminent. o A dark, often greenish sky. o A wall cloud, particularly if it is rotating. o Large hail. Although not always, storms that produce tornadoes frequently produce large hail as well. o A loud roar, similar to the sound of a freight train. o Tornadoes may occur near the trailing edge of a thunderstorm and be quite visible. They may also be embedded in rain and not be visible at all. What Should I Do During a Tornado Watch? Listen to battery-powered NOAA Weather Radio, your local radio or television stations and Brighton Alert for updated information. Be alert to rapidly-changing weather conditions. Watch for signs of a possible tornado. Know where your family members are. Use this opportunity to review your Family Emergency Plan. Even if a tornado does not strike, there is still a likelihood of severe weather conditions.

2 Listen for warning sirens. During a weather emergency, the City of Brighton may use its Emergency Warning System. This a series of allhazards, outdoor sirens spread throughout the city. Because of the unpredictability and sudden appearance of tornadoes, it may not be possible to provide advance warning. However, if you hear the warning siren, immediately seek shelter and tune into a local radio or television station. What Do the Sirens Mean? The system uses one siren tone. When they are activated during an emergency, the sirens will be activated for 5 minutes. Siren Test: Please note that the City does perform a semi-annual siren test to ensure all sirens are functioning. The testing occurs in the month of October and April. Citizens will be notified prior to the testing date. What Should I Do During a Tornado Warning? Listen to your battery-powered NOAA Weather Radio or a your local radio, television stations, and the Brighton Alert for updated information. If the electricity should go out, you will still be able to receive emergency information on a battery-operated device. If you're at home, go to your pre-identified safe zone to protect yourself from glass and other flying objects. If possible, seek shelter under a piece of large, sturdy furniture, such as a large table or workbench to protect yourself from falling debris or flying objects. Stay away from windows. Do NOT open them. If you're not in your home, seek shelter in the basement or an interior room of a nearby, sturdy building. Do not try to outrun a tornado in your car; instead, leave it immediately. If no shelter is available, lie flat in a low spot with your arms and hands protecting your head. Contrary to popular belief, seeking shelter underneath a highway or railroad overpass does not provide any measurable safety. Remain in your safe zone or shelter until you have received an all-clear signal from your radio, TV or Brighton Alert. What Should I Do After a Tornado? Continue listening to your local radio or television stations, Brighton Alert, and your NOAA Weather Radio for updated information. Review your Family Emergency Plan and follow through with your communications plan. If all of your family members are not present,

3 report to your family's pre-designated meeting point, unless emergency officials direct otherwise. Assess any damage to your home or immediate surroundings. Be aware of any potential hazards (ruptured gas lines, structural damage to your home, downed electrical lines, localized flooding, etc.) Immediately report any injuries or hazards via 911. Advise your family and neighbors as well. Help injured or trapped persons. Call 911. Give first aid where appropriate. Do not move seriously injured persons unless they are in immediate danger. Never enter any building that appears to have suffered significant structural damage, or that poses any other hazards. Do not enter any disaster area. Your presence there will simply add to the confusion and may hamper emergency response efforts. A public message will be sent in the event that volunteers are needed. Only use the telephone for emergency calls. Once you have notified your pre-identified emergency contact person that you are okay, let them notify other family or loved ones. Telephones are frequently overwhelmed in a disaster situation and need to be clear for emergency calls to get through. THE BASICS ABOUT TORNADOES 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 a 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. 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 a Storm Prediction Center (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. Supercells 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.

4 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. For example, hurricanes in south Texas, or northwest-flow weather systems in the upper Midwest. Does hail, rain, lightning, silence always come before the tornado? Not necessarily, for any of those. Rain, wind, lightning, and hail characteristics vary from storm to storm, from one hour to the next, and even with the direction the storm is moving with respect to the observer. While large hail can indicate the presence of an unusually dangerous thunderstorm, and can happen before a tornado, don't depend on it. Hail, or any particular pattern of rain, lightning or calmness, is not a reliable predictor of tornado threat. How do tornadoes dissipate? The details are still debated by tornado scientists. We do know tornadoes need a source of instability (heat, moisture, etc.) and a larger-scale property of rotation (vorticity) to keep going. There are a lot of processes around a thunderstorm, which can possibly rob the area around a tornado of either instability or vorticity. One is relatively cold outflow - the flow of wind out of the precipitation area of a shower or thunderstorm. Many tornadoes have been observed to go away soon after being hit by outflow. For decades, storm observers have documented the death of numerous tornadoes when their parent circulations (mesocyclones) weaken after they become wrapped in outflow air - either from the same thunderstorm or a different one. The irony is that some kinds of thunderstorm outflow may help to cause tornadoes, while other forms of outflow may kill tornadoes. Do tornadoes really skip? Not in a literal sense, despite what you may have read in many older references, news stories, or even damage survey reports. By definition (above), a tornado must be in contact with the ground. There is disagreement in meteorology over whether or not multiple touchdowns of the same vortex or funnel cloud mean different tornadoes (a strict interpretation). In either event, stories of skipping tornadoes usually mean there was continuous contact between vortex and ground in the path, but it was too weak to do damage; multiple tornadoes happened; but there was no survey done to precisely separate their paths (very common before the 1970s); or there were

5 multiple tornadoes with only short separation, but the survey erroneously classified them as one tornado. 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 1900s and before are believed to be tornado series instead. Most tornadoes last less than 10 minutes; however a tornado traveling at 60 mph, lasting for 10 minutes, would cover 10 miles. What is the original F-scale? Dr. T. Theodore Fujita developed a damage scale (Fujita 1971, Fujita and Pearson 1973) for winds, including tornadoes, which was supposed to relate the degree of damage to the intensity of the wind. This scale was the result. The original F-scale should not be used anymore, because it has been replaced by an enhanced version. Even with all its flaws, the original F- scale was the only widely used tornado rating method for over three decades. The enhanced F-scale takes effect 1 February 2007.