Tornadoes
Tornadoes are perhaps mother nature's most violent display of energy. Rotating winds up to and in some cases over 200 mph are possible in these swirling funnels of destruction. The United States, because of geographical features and location, is impacted by the most tornadoes a year out of any other country, with an annual average of close to 1200 reported. April, May, and June are the months when tornado activity is maximized with most occurring in the central plain's states and the Midwest. Fortunately, large destructive tornadoes in the Northeast are relatively rare but they can and do happen here. And sometimes the damage local tornadoes produce is catastrophic. From 1950 to 2005 there have been approximately 150 confirmed tornadoes in WRGB's twenty-one county coverage area. Damage surveys by National Weather Service meteorologists in the 50's, 60's, and 70's were not done as routinely as they are today which means many tornadoes in the earlier part of the record likely went unreported. This suggests that there certainly could be a much higher number of tornado occurrences in eastern New York and western New England than the record shows. Fortunately, most of the tornadoes that have been observed here have been the smaller ones lasting only a few minutes with winds generally of 100 mph or less.
Since the early 1970's tornadoes have been ranked on the Fujita Tornado Intensity scale, noted below.
Fujita Tornado Intensity Scale
F0 40-72mph Light Damage
F1 73-112mph Moderate Damage
F2 113-157mph Considerable Damage
F3 158-206mph Severe Damage
F4 207-260mph Extreme Damage
F5 261-318mph Complete Destruction
The scale was developed by Dr. Theodore Fujita as a way to categorize each tornado by its intensity and estimate a wind speed associated with the damage that it caused. To determine an "F" rating for a tornado , National Weather Service meteorologists conduct damage surveys after a tornado has passed. Therefore, tornadoes are ranked after they have occurred, not while they're developing or in progress. A moderate number of strong F-2 tornadoes have occurred locally with only a few of the very powerful F-3 or F-4 storms. Since 1950, only seven F-3 tornadoes and three F-4 tornadoes have been confirmed in this region, with no tornadoes ranked F-5. Nationally only 1% of all tornadoes in a year are ranked F-4 or F-5, but they account for the vast majority of tornado damage and fatalities.
Through much research and many storm damage surveys, particularly of the destruction left by the Jarrell, TX tornado on May 27, 1997 and the Moore, OK tornado of May 3, 1999, it has been determined that the F scale has a number of weakeness that tend to lead to an overestimation of wind speeds in tornadoes, especially those rated F-3 and higher. Specifically, the F scale is completely subjective, based soley on the damage caused by a tornado and a rating by a person or team that could interpret damage clues differently than another person or team. Most importantly, an accounting of the difference in construction types and techniques with the buildings in a tornadoe's path is not included in the F scale, which is important because a poorly built structure can easily be destroyed by a weak tornado. Also, the damage rating is generally based on the worst damage in the tornado path, even if it is to a single structure, not on the entire damage field.
As of February 1, 2007, an enhancement to the Fujita scale was made operational to correct the short comings of the original Fujita scale. The new "Enhanced Fujita Scale (EF) was developed by meteorologists and structural engineers and is a much more objective gauge of a tornado's strength. The EF scale uses 28 damage indicators ranging from types of structures to types of vegetation. Each indicator has associated with it a typical description of the type of construction for that indicator as well as a degree of damage category with a range of wind speeds (a lower bound and upper bound) found through research to cause differing levels of damage to different construction and vegetation types. The classification leaves little room for subjectivity with damage surveys allowing for a more consistent and accurate determination of wind speeds with tornadoes. A relationship was also developed between the EF scale and the original F scale which supports the past tornado database.
Enhanced Fujita Scale
EF0 65-85 mph Light Damage
EF1 86-110 mph Moderate Damage
EF2 111-135 mph Heavy Damage
EF3 136-167 mph Severe Damage
EF4 168-200 mph Extreme Damage
EF5 Over 200 mph Complete Destruction
Some Local Notable Major Tornadoes (Rated on the F Scale)
June 24, 1960: Schenectady County: F3
August, 28 1973: West Stockbridge, MA, Berkshire County: F4
July 10, 1989: Montgomery, Schoharie, Albany, and Greene Counties: F3 to F4
May 29, 1995: Great Barrington, Massachusetts, F3
May31, 1998: Mechanicville/Stillwater: F3
TORNADO DEFINITION
A tornado is defined as a violently rotating column of air in contact with the ground that extends from the base of a thunderstorm, often, but not always, visible as a funnel. Most tornadoes in the Northern Hemisphere rotate in a counterclockwise direction, but some rotate clockwise. Tornadoes are fickle, most lasting only a mater of minutes, some surviving for up to an hour. Tornadoes can range in size from a few yards in width to over a mile in diameter. The majority of tornadoes in New York and New England are small and short-lived. However, big ones sometimes do occur. On June 9, 1953, an extremely violent tornado leveled parts of Worcester, MA killing 94, injuring over 1000, and leaving 10,000 homeless. On August 28, 1973, a large tornado hit West Stockbridge, MA in Berkshire County killing four, and inuring forty. More recently, on May 12, 1984 a moderate tornado injured eleven people on the Altamont fairgrounds and one in Schenectady as well as damaging property. On November 16, 1989, a tornado, which had dissipated into a straight-line wind gust, crumbled a wall at the East Coldenham Elementary school in Montgomery, NY killing seven children. On Memorial Day, 1995, a devastating pair of tornadoes struck Columbia and Berkshire counties killing three and producing millions in property damage. Three years later a violent outbreak of severe thunderstorms and tornadoes on May 31, 1998 produced the destructive tornado which left parts of Mechanicville and Stillwater in Saratoga county, NY in ruins. And on July 21, 2003, a series of tornadoes spawned by a single supercell thunderstorm moved through New York’s Hudson valley and up into Vermont.
THE OUTLOOK, WATCH, WARNING SYSTEM FOR TORNADOES
The National Weather Service uses an OUTLOOK, WATCH, WARNING system to alert you to the potential and the occurrence of widespread significant severe weather that includes tornadoes. The system seems to confuse many people, but it really is very simple
Severe Weather Outlook
Severe weather outlooks are issued by the Storm Prediction Center in Norman, Oklahoma out to three days in advance of severe weather in the form of severe thunderstorms and tornadoes, for all regions of the country. The outlook products are designed more for meteorologists rather than the public in that they give a general and somewhat technical overview of the prevailing patterns that could lead to severe weather in a given region. However, the outlooks issued by the Storm Prediction Center are publicly available on the Storm Prediction web site, at http://www.spc.noaa.gov In cases when a widespread and particularly dangerous severe weather outbreak is forecast, a special public outlook statement is written and disseminated on both the Storm Prediction Center web site as well as through local NOAA weather radio.
Tornado Watch
A TORNADO WATCHis issued in advance of a major severe weather outbreak of damaging thunderstorms which are expected to produce straight line winds, large hail, and tornadoes in a given region. A WATCH covers a large multi-county area in one or more states, and is normally in effect for six hours. When a TORNADO WATCH is issued by the Storm Prediction Center, meteorologists at the center have determined that the atmosphere will support tornado producing severe thunderstorms. The WATCH is your first line of defense because it alerts you to the potential of damaging thunderstorms and tornadoes in your area during a given time period. A TORNADO WATCH, however, does not mean that a tornado is happening now.
Tornado Warning
A TORNADO WARNING is issued when Doppler weather radar is indicating strong rotation inside a thunderstorm suggesting that it either is or is about to produce a tornado or when ground spotters sight a tornado or funnel cloud. A WARNING is issued for a county or part of a county and means you should take cover immediately because the tornado is occurring. In a tornado warning there will be little time to seek shelter. Although, with Doppler radar, meteorologists have increased tornado warning lead times, the time still may be as little as five to fifteen minutes or in some cases less. In the case of the Great Barrington, MA tornado on Memorial Day, 1995, a warning was issued twenty-one minutes before the storm struck. Warnings were issued almost thirty minutes before the tornado struck Mechanicville and Stillwater on May 31, 1998. But in many cases, due to the fast developing and fast moving nature of tornadoes, there may be little or no time between the official warning and the storm hitting your location. This makes it very important for you to make your storm preparations during the WATCH period when there is time. DO NOT wait for an official WARNING before you take precautions. If you see threatening weather approaching your location and a weather WATCH is in effect, take the weather seriously and head for cover. You can find the latest National Weather Service WATCHES and WARNINGS on this site, by listening to NOAA weather radio, or by watching WRGB Channel 6. The WRGB Channel 6 weather facility is the most well equipped broadcast weather operation in upstate New York and western New England. Our severe weather diagnosing and coverage equipment includes an advanced severe weather information crawl alert system that instantly triggers upon receiving a warning. When a warning is issued the system immediately displays an on air text alert as well as animating the warned county or counties, that the severe weather either is or will be affecting. To diagnose and track severe weather meteorologists at WRGB Channel 6 use the first live broadcast Doppler radar in the area, Instant Doppler 6, along with the Instant Doppler 6 Storm Alert street level mapping and storm tracking system, as well as the WeatherScan analysis system.
TORNADO SAFETY
When a TORNADO WARNING is issued:
* Immediately get to the basement of the building you are in. If a basement is not available the next best place is an interior bathroom or closet on the lowest floor of your building. Put yourself in a position where there are the most walls between you and the tornado and cover yourself with cushions or a mattress. This will help protect you from flying debris.
* If you live in a mobile home, evacuate it immediately to a place offering stronger shelter. Most tornado fatalities occur in mobile homes and automobiles. A mobile home will crumble under the powerful winds of a tornado and in many cases the powerful straight-line winds severe thunderstorms produce.
* Do not try to outrun a tornado in your car. Vehicles can easily be picked up by a tornado and tossed some distance. Three people were killed in Great Barrington, MA in 1995 when their car was picked up by the tornado and tossed 600 feet.
* If caught outside, find the lowest area near you, lay flat, and cover your head to protect it from flying debris. Watch out for flooding of the low area in this case. The heavy rains thunderstorms generate can produce flash flooding.
TORNADO SAFETY MYTHS
"Opening the windows in my house will help equalize the pressure and save the house from the tornado?"
MYTH! Opening the windows will allow strong winds and debris to enter your home causing considerably more damage to the structure than if the windows were closed. Opening windows wastes valuable time, which you need to get to your shelter.
"Hiding under a highway overpass to escape a tornado is safe?"
MYTH! The overpass will serve to constrict the flow of the wind, causing the wind speed to increase under the bridge. If you are travelling in your car as a tornado approaches, quickly seek shelter in a strong building. If there is no building available, seek shelter in a ditch in an open field, away from trees and tall objects. DO NOT try to outrun the tornado! The tornado can easily catch up to you.
TYPES OF TORNADOES
The Supercell Tornado
The supercell tornado is the most common and most violent type of tornado. These storms are formed from the rotating supercell thunderstorm, due to a clockwise change in wind direction and speed with height in the atmosphere. This changing of the wind direction and speed with height causes horizontal tubes of spinning air to form. A thunderstorm updraft then tilts the horizontally spinning tube of air into the vertical and stretches it out forming a small area of low pressure called a meso-low or mesocyclone which enhances the low level winds which ultimately leads to the formation of the tornado. Supercell tornadoes can exist for up to six hours, grow to diameters greater than a mile, and produce winds up to 300 mph. The visible funnel cloud forms because of the significant air pressure drop in the region of the meso-low and tornado. The lower air pressure allows water vapor to condense into cloud droplets at a lower altitude, forming a cloud around the spinning funnel of air. In areas of the country, such as Colorado, where low level moisture may be lacking, a tornado may occur with no visible funnel cloud at all.
The Landspout Tornado
Landspout tornadoes are formed by thunderstorms that do not have rotating updrafts. In other words, a non-supercell thunderstorm produces the landspout. Wind shift lines in the lower atmosphere, such as the type sea breeze fronts or local topography may produce, cause very weak spinning vertical tubes of air. When a thunderstorm updraft forms over one of the weak spinning tubes of air, the tube is stretched. Stretching a rotating tube causes it to spin faster, forming a short lived and relatively weak tornado.
The Waterspout
Essentially, waterspouts are formed by the same mechanisms that form landspouts except that these funnels develop over water. Cold air funnels form on occasion when very cold air flows over the warm waters of the Great Lakes during the fall. The instability and wind shear due to the low level wind shift lines produce brief funnels over the water. Waterspouts are generally short lived and weak, rarely producing damage. However, supercell tornadoes that form over or move over water are also called waterspouts. Supercell storms, of course, are capable of producing great damage to property.
The Gustnado
The gustnado is an interesting whirlwind, forming on the leading edge of a thunderstorm gust front. Typically, gustnadoes are very weak and last less than a minute, rarely producing serious damage. Gustnadoes appear to be caused by the turbulence of the advancing wall of wind produced by the thunderstorm.
The Dust Devil
Dust devils are rotating columns of air that spin either in a counter-clockwise or clockwise direction, and have nothing to do with thunderstorms. Dust devils are formed over dry sandy areas on hot, sunny, calm, afternoons. Superheated air near the ground rushes upwards. Air surrounding the updraft spirals in at the base, causing a swirl, which develops from the ground up. The typical dust devil extends up to 200 or 300 feet and is generally several yards in diameter. The winds are normally insufficient to produce serious damage. Dust devils have been known to occur in the summer on the shores of the Great Sacandaga Lake.
LOCAL TORNADO HOT ZONE
Our local "Tornado Hot Zone" runs across the mid-Hudson valley to Berkshire County, Massachusetts and Litchfield County, Connecticut. Local research done by Albany, NY National Weather Service meteorologists strongly suggests that the local terrain in the primary hot zone is largely responsible for the higher number of tornadoes. The evidence currently implies that the north-south orientation of the Hudson and Housatonic valleys act to increase low level wind shear in cases when the surface flow feeding into a storm system producing thunderstorms in the Northeast, is out of the south. Observations during the Great Barrington tornado in May 1995 showed that the Hudson and Housatonic valleys turned the prevailing southerly wind into more of a southeasterly direction. The additional turning of the wind in the valleys consequently increases the low-level wind shear, which is a change in the direction and speed of the wind with height. As wind shear increases there is an increased likelihood for rotating supercell thunderstorms to form, which sometimes produce tornadoes. The southerly low level flow in the north-south oriented valleys also allows air with a higher moisture content (higher dewpoint air) to quickly move into the region, another ingredient for supporting severe convection.
In 1995, as a strong thunderstorm intersected the higher dewpoint air in the Hudson valley and the increased wind shear environment, it rapidly intensifying and produced an F-2 ranked tornado in Hillsdale, NY in Columbia County. As the storm moved into the higher terrain east of Hillsdale, it underwent considerable weakening, as the low-level flow became obstructed by hills. However, the storm rapidly intensified again when it arrived in the Housatonic valley as it again encountered higher dewpoint air and a more highly wind sheared environment. The thunderstorm then produced the killer F-3 tornado in Great Barrington, MA.
A similar effect is also observed in Montgomery County, NY in the vicinity of where the north-south oriented Schoharie valley intersects with the Mohawk valley. The weak tornadoes that occurred on June 16, 2002, in Florida, NY, and on May 1, 2003, in Tribes Hill, NY are both examples of how an increase in low-level wind shear over a very small area in Montgomery county possibly lead to storm intensification and the formation of the tornadoes.
