Mike's Blog Archive: May 2010

In my 35 years in meteorology, I have been through many tornado watch and warning situations. I have walked through a small town in southern Wisconsin, named Barneveld, just hours after it was ripped apart by a massive tornado. Only one time have I seen a tornado, as most of the time I am right here in the 24/7 Weather Center issuing warnings and weather updates, so I do not get much of a chance to chase these storms. However, we do have a crew of storm chasers that go out in search of these deadly weather events and you can follow along with them as the blog for us here at 7News.

Storm Chaser Blog

The tornado season typically begin in May across Colorado, but peaks in June. Most tornadoes in the United States occur in the central plains, with the greatest likelihood of twisters in the southern plains around Kansas, Texas and Oklahoma. Colorado lies of the western fringe of "Tornado Alley", but our state still averages between 40 and 60 tornadoes per year.

The peak season for tornadoes is in the spring and early summer. From March through June, about 70% of all the tornadoes in a year will occur. This is due to the fact that the weather patterns that are needed for tornado development are most common in the spring and early summer.

Most tornadoes form from large rotating thunderstorms called "super cells". These monster storms tend to develop ahead of cold fronts that push southward from Canada across the central U.S. As the fronts sag into the warm and humid air that covers the southern plains, the colder air wedges under the warm air, creating lift. The lifted air rises up to form thunderstorms that can rapidly grow to heights of 40 to 50 thousand feet above the ground.

The storm pushes high into the sky, reaching into the jet stream - the band or river of fast moving air that flows around the world. It is the increase in wind speed with height that causes the thunderstorm to begin a large, slow counterclockwise rotation. This rotating thunderstorm is what is classified as a "Super Cell".

Once the super cell storm develops, the best analogy for thinking about how the tornado forms is to think of a figure skater doing a spin. The skater starts with their arms out, and is rotating rather slowly. As the skater brings their arms in, the rotation begins to speed up. In physics, this is called "the conservation of angular momentum". The rotation gets faster and faster as the size of the rotating column grows narrower. This is a very simplistic description, but eventually this narrow rapidly rotating column of air will drop to the ground as a tornado.

Tornadoes are classified by the wind damage that they cause. The scale was developed by Dr. Ted Fujita from the University of Chicago. Dr. Fujita based his "F scale" on a 0 to 5 basis for tornadoes. The F0 is a weak tornado, while the F5 storms are the most powerful winds ever observed on Earth.

F0 - up to 72 mph - light damage F1 - 73 to 112 mph - moderate damage F2 - 113 to 157 mph - considerable damage F3 - 158 to 206 mph - severe damage F4 - 207 to 260 mph - devastating damage F5 - above 261 mph - incredible damage

About 70 % of the annual average of 1000 tornadoes nationwide are classified as F0 or F1. About 28 % of all tornadoes fall into the F2 or F3 category. Only about 2% of all tornadoes are classified as F4 or F5. Often a severe weather season will come and go without a single F5 tornado reported. However, about 80% of all tornadoes deaths are the result of the F3, F4 and F5 tornadoes. These storms are much less common, but much more dangerous.

As of 2007 this scale was replaced by the enhanced Fujita (EF) scale. The EF attempts to rate tornadoes more accurately, taking into account that it often requires much lower wind speeds to create F5-like damage. The new EF scale is now the official standard to measure the strength of tornadoes.

EF 0 - 65 to 85 mph EF 1 - 86 to 110 mph EF 2 - 111 to 135 mph EF 3 - 135 to 165 mph EF 4 - 166 to 200 mph EF 5 - Over 200 mph

Tornadoes are not named like hurricanes are, but the strong or deadly tornadoes are usually remembered for the town or location that they affected. For instance, the infamous "Xenia Ohio Tornado" of April 1974, or in Colorado, the "Limon Tornado" in June of 1990 and now the "Windsor Tornado" in 2008.

Perhaps the single worst tornado on record was the great "Tri-State Tornado" of March 1925. This huge tornado started in southeastern Missouri and tore a path of destruction all across Illinois, before ending in western Indiana. The twister covered a distance of 219 miles and was on the ground for over 3 hours. In the days before adequate warnings, the storm caught everyone off guard. The Tri-State Tornado killed 689 people, injured over 2,000 and caused 17 million dollars in damage - a very large figure in 1925!

In Colorado, the peak season for tornadoes is in early June. At that time, the almost daily dose of thunderstorms can easily rise up to the jet stream level and begin to rotate into a super cell. These storms tend to form along the Front Range, roll over the Denver metro area and then really get severe over the eastern plains of the state. About 90% of all Colorado tornadoes occur east of I-25. Although tornadoes can form in the high country, the rough terrain tends to disrupt the rotation needed to form a super cell.

Tornadoes have done some very unusual things. The powerful winds can pick up a railroad locomotive, lift a water tower off the ground, and drive blades of grass into walls just like a hammer and a nail. At the same time, there have been reports where tornadoes have picked a refrigerator off the ground, tossed it several hundreds of yards, dropped it back on the ground and not even broken an egg inside the refrigerator!

Tornadoes usually form on the back edge of the thunderstorm cloud, meaning that most of the storm has already passed overhead. Often the rain, hail, thunder and lightning have mostly gone by and then the tornado occurs. That is why you will often see the sky looking very bright behind the tornado - a dramatic contrast to the very dark funnel. After the tornado, the sky often quickly clears as the storm moves away. There are, however, no hard and fast rules for tornados, so sometimes the twister occurs in the midst of a large area of thunderstorms, so after the tornado occurs, it just rains and rains.

A new service that will provide you and your family with fast and accurate warnings for tornadoes, severe thunderstorms and flash floods!

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24/7 Weather ALERT CALL

Forecasting weather involves extensive areas of studies including high level mathematics and physics, tools, instruments, and many research scientists. It is done in steps: first measurements and readings are made by instruments; next using those data and numerical methods (mostly on the computer these days), basic forecasts are made and third, the final results are plotted on the maps. When these maps and numerical analysis are done, they are sent to various agencies and TV stations as well as radio stations where forecasts interpret the information and translate them into viewer friendly form and broadcast them.

The weather maps are created at different pressure levels such as surface, 300 mb, 500mb, 700mb and higher levels. For the forecasting purpose, one incorporates all of those maps to understand the whole state of the air masses and flows since the air aloft and surface air interact to create dynamics or motion.

The maps used for forecasting are mostly on a synoptic scale which involves continents and oceans to give a whole picture of the air movements. By observing the air movements, one can see the cold fronts, warm fronts and stationary fronts which show the temperatures and flows. In addition, the maps show the wind speed and direction as well as precipitation. All of this information is drawn on the map with symbols and line. Lines indicate constant air pressure and symbols indicate different information.

Predicting the weather involves figuring out how a massive thermonuclear reactor nearly 100 million miles away will affect a complex mix of gases on a swirling, irregularly shaped planet. In addition to the rotation, throw in factors like huge bodies of water that can store vast amounts of heat and release it into the atmosphere. Also, change the axis of the spinning planet so that different parts of the surface get more heat than others at different times of the year. The result is a churning witch's brew of clouds and storms that we try to track and project into the future.

I would guess that if the purpose of our news and sports reports were to predict the following day’s events, or perhaps the events to come in the next 3-5 days - we would have a lot of folks frustrated about the accuracy of our news and sports.

Sometimes a forecast will undergo a dramatic change over the course of a couple of days. The reasons can be as simple as an air mass taking a different track on its journey over North America. That is a fairly straight forward process, but it plays heck with the resultant forecast. If an arctic air mass shifts in its path by a hundred miles, Denver and the mountains may never get in the cold air, while Limon and the eastern border counties turn very cold. In that light, it is possible and fairly common that an extended outlook can change from mild and dry to cold and snowy. Now we could couch all of our forecasts by saying "this might occur, or it could be just the opposite", but that would not serve our viewer very well either. So, we give you our best estimate of what is going to happen - just like a stock broker or a mortgage banker will do.

An analogy in longer range prediction might be that early in a sports season, a certain team is picked to win the championship, but halfway through the season, the star player is injured. That certainly changes the course of the season and the potential outcome for the team.

Some of the equipment that we use includes: 24/7 Doppler radar, our very powerful live radar that enables us to see strong thunderstorms and pinpoint areas of damaging winds and tornadoes. Our satellite equipment allows us to watch the skies from 22,000 miles above the Earth and keep a close watch on storm systems that will be moving into the Rocky Mountain region. We also have some of the newest technology in computer weather graphics, allowing us to craft high quality maps that show our audience what is happening right now, and - more important - what is going to happen next!

Radar works very simply by sending out a beam of microwave energy from the radar unit and bouncing that signal off of a distant object. By timing the radar signal from when it leaves the radar, hits the object and returns to the radar, we can determine how far away the object is.

Doppler radar does one additional thing and that is to send out even more radar signals spaced very closely together so that they can tell if an object is rapidly moving toward or away from the radar unit. This is how a police "speed gun" works - it not only "sees" your car, it can tell how quickly the car is moving toward or away from the radar - hence determine the speed of the object. In weather forecasting, we use this same principle to look for motion within the storm cloud - in other words, signs of damaging winds and possible tornadoes.

It is important to understand that any radar, no matter how powerful or where it is located will have its limits. Radar energy cannot "see" through solid rock, so the mountains of Colorado can be a very effective barrier to the radar. In the winter months, snow clouds tend to be rather low, so the radar beam can either be blocked by the nearby mountains or the radar signal may "shoot over the top" of the clouds. This is caused by the fact that the radar beam goes straight, but the Earth curves, thus the radar beam can be looking 20 to 30,000 feet into the air by the time the signal is about 150 miles away from the radar site. For these reasons, even some of the much hyped "mega doppler" radars used by some TV stations cannot "see" all of the precipitation in the state of Colorado. Summer thunderstorms do "stick up" higher in the sky, so they will show up better, but even then we need to combine our 24/7 LIVE Doppler radar with a network of National Weather Service NEXRAD radars.

We will use both the 24/7 Live Doppler and the NEXRAD radars in tandem to help locate the precipitation areas statewide. I must admit, however, that even with our radar and the NEXRADs we share, there are still some mountain areas that are pretty well blocked out by the terrain and will rarely show up with radar echoes, even if it snowing or raining in those places. It is not a failure of the technology, we just need to have even more actual radar units scattered across the state because of all the mountains. For that reason, we will also always rely on satellite observations and surface weather reports from local trained spotters to fill in the gaps.

Closer to the Denver area, the location of our LIVE radar will greatly aid us in "seeing" developing precipitation, but the radar has much more than that going for it! As television evolves into the high definition format we are poised to use our very detailed radar mapping to get "up close and personal" and show our viewers where the storms are and where they are heading with greater resolution and definition than ever before. 24/7 LIVE Doppler has high-res mapping that enables us to zoom down to the street level anywhere in Colorado and show our viewers exactly where dangerous storms are, how they are developing and moving.

As we get more people moving into beautiful Colorado, the newcomers often wonder what the "Palmer Divide" is. If you check a topographical map of Colorado, you will notice a west to east "spine" of higher terrain running from just north of Colorado Springs out to around Limon. This is the "Palmer Divide" or the "Palmer Ridge". This region of higher elevation has very different weather conditions as the winds blow over and around it. Northerly winds often push moisture to the Monument Hill area north toward the southern Denver Metro area as the air "piles up" a bit against the ridge. A wind from the south can bring rain and snow to the Colorado Springs side, leaving the north part drier. The Palmer Divide also creates swirling wind patterns that can help stir up severe weather in Denver, especially when the winds are blowing in from the southeast.

In addition, I get number of viewers asking what is the "Denver Cyclone?" I discussed the "Palmer Divide," a west to east ridge that extends from just north of Colorado Springs to near Limon. This ridge runs about 1,000 to 2,000 feet higher than the surrounding plains and can create some unique local weather conditions. When the surface winds are blowing from the southeast across the plains, the air must blow up and over the Palmer Divide as it moves toward Denver. This motion can cause a large scale swirling movement in the air as it drops downs toward Denver and curls slightly toward the mountains to the west. This counter-clockwise rotation of the winds is known as "The Denver Cyclone". When the Denver Cyclone develops, we often get stormy weather as the winds push up against the mountains west of Denver, the air is lifted and moisture condenses out - creating clouds and rain.

When southeasterly winds swirl down from the Palmer Divide south of Denver, the air over the greater Denver metro area will develop a large gentle counter-clockwise rotation. This spinning of the wind field around Denver helps to create areas where the air converges, or comes together.

When the surface air converges, the air is forced to rise and can form clouds and thunderstorms. The thunderstorms sometimes will actually develop a slow rotation as well, due to the Denver Cyclone. This spinning can help to form small, short lived tornadoes in the Denver area. As the thunderstorms move farther east across the plains, they often grow much stronger.

Moreover, I often speak of "upslopes" and "downslopes" during my weather reports on 7News, but what exactly do these terms mean?

Much of the weather in Colorado is determined by the topography. Our spine of tall mountains that divide the state can create all kinds of havoc with our weather.

The winds that blow across Colorado cannot go under the mountains or through them, so the air must move over the mountains. As the winds blow against a mountain, the air is forced to rise up and over the peak. This rising air is moving "up" the slope of that mountain. When air rises, it cools at a rate of about 5.5 degrees Fahrenheit for each 1,000 feet that it goes up. This temperature change is called the "dry adiabatic lapse rate". The cooler air cannot "hold" as much water vapor as warm air, so the vapor condenses out to form clouds. If the air continues to rise up the mountain, more and more moisture will condense and the cloud will thicken and eventually produce precipitation.

To put this into an example, let’s take a situation where a westerly wind is pushing into western Colorado; the air will be forced to rise up as it travels into the mountains. This rising air will cool, the moisture will condense out, clouds will form and rain or snow will develop over the west facing slope of the mountain.

A "downslope" is just the opposite, as the air reaches the crest of the mountain and begins to move downhill, it will begin to warm up, due to the air being compressed as it descends (the molecules of air are being pushed closer together as the air moves down into the thicker atmosphere at lower elevations). This compression warms the air; warmer air can "hold" more moisture than cold air so the humidity drops and the clouds evaporate. Thus a downsloping wind will generally bring clearing skies and warmer temperatures.

The same weather pattern that can bring snow to the western side of a mountain can bring dry and mild weather to the opposite side of the mountain. That is why it is sometimes snowing on the west side of the Eisenhower Tunnel, but not on the east side. In fact, it can be sunny, breezy and warm in Denver with a strong westerly wind, while the mountains west of the Divide are getting hammered with snow.

In Denver, our "upslope" winds are from the east. An easterly wind will have to travel "up the hill" from the 4,000 foot elevations near the Kansas border, to our Mile High elevation here in Denver. Easterly winds will bring an increase in clouds and often a chance for rain or snow to the Denver area, especially since that air moves west of Denver and backs up against the mountains, gradually forming the clouds and precipitation over the foothills and then out across the eastern plains. In this instance, the upslope winds will often cause rain or snow here, but dry weather will hold west of the Continental Divide (remember, they would have an easterly "downsloping" wind there as the air blows down from the Divide).

It may sound a little confusing, but that is why Colorado weather is such a challenge to predict! Just remember, "upslopes" tend to bring clouds and precipitation - "downslopes" tend to bring windy, dry and mild weather. If you would like to learn more about our wild weather, I have written a book about it - THE COLORADO WEATHER ALMANAC is available from Amazon.com or at many Front Range bookstores

Nolan Doesken, the State Climatologist for Colorado has just announced a free seminar for the public about our changing climate. This workshop is titled - Making Sense of Colorado's Climate and will be held on May 14 on the campus of Colorado State University

On May 14th there will be an all-day class focused on the basics of global climate, Colorado climate and fundamental concepts and issues about climate variability, extremes and change. This class is geared for general audiences who want to have a better understanding of climate and how it works.

According to Doesken "we've never done this particular class before, but we think it should be interesting, useful, and somewhat entertaining."

This course was developed first by the State Climate Office of Oklahoma and then adapted to Colorado as a part of a National Science Foundation grant they received for climate education and outreach.

Lunch will be provided (free) and some handouts as well, so they will need to know ahead of time who and how many are coming. If you might be interested or need a better background in Colorado climate, please have contact Nolan Doesken by noon on Tuesday May 11th to reserve a place in the class. The class will be taught here at the CSU Department of Atmospheric Science on the CSU Foothills Campus.

Mr. Doesken can be reached by e-mail at this address - nolan@atmos.colostate.edu

Here is some background on this very important subject and some of my thoughts on climate change.

We have been blessed to have such a beautiful, bountiful and life-giving planet. It is our duty, to take the best care of this gift that we have been given.

In the world of truly peer reviewed science, the degree of controversy about anthropogenic global warming is not as great as you might believe. Here are a few thoughts about things you may hear or read about global warming. Unfortunately, the recent e-mail issue (some call it Climate-gate) has now called into question the validity of "peer review" - this is very unfortunate in the short term, but may actually serve to make us more diligent about these things in the future.

In a special report called ‘The Copenhagen Diagnosis’, the 26 researchers, most of whom are authors of published IPCC reports, concluded that several important aspects of climate change are occurring at the high end or even beyond the expectations of only a few years ago.

The report also notes that global warming continues to track early IPCC projections based on greenhouse gas increases. Without significant mitigation, the report says global mean warming could reach as high as 7 degrees Celsius by 2100. This may be a high and alarming figure, but many of the projections given in the past 10-15 years have actually been rather conservative in terms of CO2 emissions and the decrease in Arctic ice.

The Copenhagen Diagnosis, which was a year in the making, documents the key findings in climate change science since the publication of the landmark Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report in 2007.

New evidence was presented at this conference and can be found on the Copenhagen website at http://www.copenhagendiagnosis.org.

There was a recent commentary in the New York Times that puts this issue into great perspective.

Back to Basics on Climate Change. Global ice-sheets are melting at an increased rate; Arctic sea-ice is disappearing much faster than recently projected, and future sea-level rise is now expected to be much higher than previously forecast, according to a new global scientific synthesis prepared by some of the world’s top climate scientists.

There is an often quoted issue of 1997 being the warmest year and that global temperatures have cooled since that time. This information is misleading. In 1997, the world climate was influenced by one of the strongest El Nino events ever recorded. This pool of very warm Pacific Ocean water bumped global temperatures higher. At the present time, the Pacific in is the midst of a slight La Nina - cooler sea surface temperatures. These periodic warming and cooling episodes need to be taken into consideration in the the overall global temperature trend.

There is much discussion about the fact that the sun has by far the largest impact on our climate. The sun has certainly not been overlooked by the many experts worldwide that contributed to the most recent IPCC Assessment on climate. The periodic changes in solar output and the orbital changes are taken into account in the climate studies and modeling.

Another comment often heard is that CO2 is just a tiny fraction of the atmosphere. Just because CO2 is a trace gas does not mean that it is not important in the equation. Small amounts do matter - I weigh 200 pounds, but it certainly does not take 200 pounds of arsenic to kill me. Another way to look at the impact of trace amounts is to consider the same amount of carbon monoxide (CO) in the atmosphere (about 385-390 ppm) - that level of CO would be lethal!

The majority of climate scientists remain in agreement that the overall warming of the planet (about 1.5 degrees Farhenheit since 1900), has been caused in part by mankind. This warming is due to the increase of so called "greenhouse gases" - such as CO2, methane and CFCs (chloro-fluorocarbons). These gases absorb outgoing heat from our planet and "reflect" it back to Earth. When this happens, energy from the Sun is trapped in our atmosphere and warms our climate.

As often noted, the Greenhouse Effect is normal and natural, in fact if not for this effect, the Earth would be about 60 degrees Farenheit colder - a lifeless ice planet. The problem we face is that the delicate balance of temperature may be upset by a change in atmospheric chemistry. In the past 200 years (since the Industrial Revolution) the increased burning of fossil fuels has released vast amounts of carbon dioxide into the atmosphere. The concentration of CO2 has risen about 25% in the past two centuries from 280 parts per million to over 385 parts per million. Here are two links to an excellent description of the roll of greenhouse gases in the atmosphere.

NASA Scientist Explanation part 1.

NASA Scientist Explanation part 2.

Human activity releases about seven billion metric tons of carbon dioxide into the air every year - adding to the 750 billion metric tons that are already there. Of the 7 billion tons, only about three billion tons stays in the atmosphere; the rest is absorbed by plants and the oceans. This "carbon sink" capacity complicates the issue of global warming, because the oceans have had a vast holding capacity for CO2. The oceans are becoming more acidic, however, and there is concern that this carbon sink capacity may reach a limit.

Some scientists feel that the increase in atmospheric CO2 will be offset by the ability of plants and the oceans to absorb this gas. In fact, some experts believe that the increase in CO2 will be a good thing - improving crop yields and making more parts of the world able to support crops. At the same time, others worry that warming will cause more severe droughts in key agricultural areas. In addition, which plants will benefit most - will it be useful crops, or weeds!

The issue is not a simple one because we must use computer models to predict future climate. These models are very complicated and must be run on a supercomputer. Even with today's technology, we cannot perfectly model something as complex as our atmosphere, so the models are simplified and do have errors. One of the undisputable facts is "we cannot even predict tomorrow's weather with 100% accuracy, how can we expect to predict the weather for the next 100 years! Of course, we are not attempting to forecast day to day weather that far in advance, just trends. There is no way to run an actual atmospheric simulation of the changes to come as we only have this one Earth - there isn't another similar planet nearby to run actual experiments.

My opinion is that we are indeed having a profound impact on the warming our climate, although this effect has been riding along side of a naturally occurring warmer period during the second half of the 20th century. It is vitally important that we study this topic with even greater effort in order to be able to take action for the future. This action may well be to use technology to bring ever increasing efficiencies to our society. Through a more efficient use of our fuels and energy resources, we will be able to limit the amount of greenhouse gases released, while still enabling our complex technological society to function and thrive.

No doubt this is a serious issue on all sides. My greatest frustration is when it gets torn down into quick sound bites and fractured thought strings.

We will need every bit of cooperation from all sides to truly solve the energy/environment issues that face us in the coming decades. I doubt that we will come to terms with reducing carbon emissions, the population growth alone will preclude that. In addition, the growing 3rd world does not want to live in a hut with one light bulb, they want the same things we enjoy.

Where will we get the energy? Fossil fuels are amazing, but the demand will only soar. We are tranferring so much wealth to other countries and there is no way that we could ever domestically replace what we must import. From a national economic and security point alone, we have to widen our energy portfolio. Wouldn't it be great to be able to tell OPEC, Russia, Venezuela that "we really don't need your oil".

Granted, we get much of our oil from Canada and some other "friendlier" nations, but it is a fungible commodity - that world oil price is still enriching the Middle East and that puts the U.S. in a position of weakness.

I am not opposed to coal - but we must burn it better, nuclear, natural gas, wind, solar. We need it all and we need to invest in a smarter grid.

I hate for America to not be at the energy forefront in the 21st Century. We can lead the world with better and cleaner ways to make power, we have done it before with major endevours. The Transcontinental Railroad in the 1880s, the Manhatten Project, The Interstate Highways, The Space Program, the Computer Revolution.

Instead of bowing down to special interests, we must, for our heirs, do the right things. To paraphrase JFK, "not because they are easy, but because they are hard."

In the unlikely event that we found out in 30 years that humans did not have the power to change the climate, we will be much better off to have taken the steps to use less fuel and conserve our resources. The research and discoveries that we make in the coming decades will enable mankind to whether the changes in climate and the increased demand for global energy reserves. A quote attributed to Albert Einstein is a favorite of mine, "the problems we face cannot be solved with the same level of thinking as at the time they were created".

The whole concept of somehow capping greenhouse gas emissions or even lowering them is growing less likely as the world population and global energy use continues to increase. It is much more likely that the CO2 and other green house gas emissions will continue to increase for decades to come. In that light, we may have to look more toward how do we deal with the changes that will likely result. I have serious doubts that we will be changing the CO2 content in our atmosphere, except to increase it.

Here are some likely results of a warmer climate in the western United States.

In the Rocky Mountains, a warming of the climate will likely mean hotter, drier summers and milder, but still perhaps stormy winters. The amount of snowfall may drop on the plains, aside from infrequent major blizzards, while the mountains may see the snow levels and the tree level rise to higher elevations. The biggest worry that climate scientists have is that the weather will become more extreme - more heatwaves, drought, but also more flash floods and severe local storms. These events have always been with us, but the concern is that they will occur with greater regularity.

I have written about this subject in far greater depth in chapter 6 of my current book - THE COLORADO WEATHER ALMANAC. The book is available at all local bookstores or from Amazon.com

There is also a local group of climate scientists, geologists, physicists and interested citizens that partake in a study group. If you are interested, check out http://www.denverclimatestudygroup.com. Another recommended website is http://www.climatecentral.org/

More than 100 researchers will be combing the Great Plains in the coming weeks, aiming to surround tornadoes with an unprecedented fleet of mobile radars and other cutting-edge tools in the second and final year of the most ambitious tornado study in history.

You can follow along with some of these tornado chasers on our Storm Chaser Blog.

http://Storm Chasers Blog.

A collaborative international project, involving scientists from the National Center for Atmospheric Research (NCAR) and a number of other organizations, will examine in detail how tornadoes form and the patterns of damage they cause. The findings will help lead to a greater understanding of tornadoes, and scientists expect they will ultimately improve tornado warnings and short-term severe weather forecasts.

The field campaign, known as VORTEX2 (Verification of the Origins of Rotation in Tornadoes Experiment 2), runs from May 1 to June 15. It covers the most active part of tornado season on the Great Plains, where violent twisters are more common than any other place in the world.

"Tornadoes rank among the most destructive weather events on Earth, and it's imperative that we learn more about how they develop and why some are so powerful and long-lived," says David Dowell, an NCAR scientist who is a principal investigator on the project. "We're hoping to improve the lead time and accuracy for tornado warnings. If we can understand these forces better, that could ultimately save lives."

During the first phase of VORTEX2 last spring, researchers made key observations of a tornado in southeast Wyoming that was rated EF2 on the Enhanced Fujita tornado damage scale. They also collected data on several powerful nontornadic storms. Such information will help researchers distinguish between thunderstorms that produce tornadoes and those that do not. This year's study period is about two weeks longer than last year's, which enhances the odds of tracking down tornadoes.

The $11.9 million VORTEX2 program is funded primarily by the National Science Foundation, which sponsors NCAR, and by the National Oceanic and Atmospheric Administration (NOAA).

In addition to NCAR, participants include the Center for Severe Weather Research, Rasmussen Systems, NOAA National Severe Storms Laboratory, NOAA Cooperative Institute for Mesoscale Meteorological Studies at the University of Oklahoma, Pennsylvania State University, Texas Tech University, Lyndon State College, Purdue University, North Carolina State University, the universities of Oklahoma, Colorado, Massachusetts, and Nebraska, Environment Canada, and the Australian Bureau of Meteorology.

The first VORTEX project, conducted in 1994 and 1995, gathered critical data on supercells, the severe and long-lived thunderstorms that give birth to the most destructive and deadly tornadoes. VORTEX findings are credited with improving National Weather Service tornado warnings.

Building on that progress, VORTEX2 researchers are using an armada of enhanced mobile radars and other new weather-sensing tools to gather far more detail on the crucial zone where tornadoes develop. Rapidly changing contrasts in wind and temperature in this zone, which is only a few miles across, can spawn a tornado within minutes. However, this happens in only a small fraction of supercell storms, and standard observing networks and radars often fail to capture the atmospheric conditions that lead to a tornado.

Among the key questions that VORTEX2 researchers want to answer:

How do tornadoes form? Why do some supercell thunderstorms spawn tornadoes, while others do not? Why are some tornadoes violent and long-lasting while others are weak and short-lived?

How much detail can we see inside a tornado? How strong are winds near the ground? How do they cause damage?

Can forecasts be improved? Current warnings have a 13-minute average lead time and a 70 percent false alarm rate. Is it possible to improve forecast accuracy and warn residents a half hour or more in advance?

To capitalize on the unusual mass of mobile instruments, researchers will also look for opportunities to collect data on other major weather events in the region. A team of VORTEX2 scientists last year, for example, made unusually detailed observations of squall lines, which can produce damaging hail and lightning, and sometimes tornadoes as well.

"We have a vast collection of tools that can give us unique insights into the atmosphere," says George Bryan, an NCAR scientist and VORTEX2 principal investigator. "So we try to get the most out of them that we can."

Mega-fleet targets tornadoes

The radar fleet for VORTEX2, including 10 mobile radars, will track winds and precipitation in and near tornadoes in unprecedented detail.

The instruments will have a resolution as fine as 100 feet and time steps as small as 10 seconds. More than three dozen portable surface weather stations can blanket the area in and near a target storm. A robotic 12-foot propeller aircraft will probe the edges of severe storms.

The study area spans more than 900 miles, stretching from West Texas to southwestern Minnesota. On each day of operations, VORTEX2 teams will position equipment about an hour ahead of a potentially tornadic storm and remain in place until the storm passes. With no home base, the scientists remain on the road during the entire six-week study.

Meteorologists will provide detailed forecasts on short-fuse weather events as each day unfolds, using tools such as the Weather Research and Forecasting computer model, which proved its value during the 2009 campaign. WRF, pronounced "worf," was developed by NOAA, NCAR, and partners.

About half of the participants in the field will be undergraduate and graduate students. This is an unusually high percentage for a major field campaign and will provide a special learning experience for young researchers.

The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Here are a few websites that you may wish to visit for more information on tornadoes...

www.tornadoproject.com www.usatoday.com/weather/wtorwhat.htm

A fun and educational website for kids:

http://www.ucar.edu/educ_outreach/webweather/thunderhome.html

Most tornadoes in the United States occur in the central plains, with the greatest likelihood of twisters in the southern plains around Kansas, Texas and Oklahoma. Colorado lies of the western fringe of "Tornado Alley", but our state still averages between 40 and 60 tornadoes per year.

The peak season for tornadoes is in the spring and early summer. From March through June, about 70% of all the tornadoes in a year will occur. This is due to the fact that the weather patterns that are needed for tornado development are most common in the spring and early summer.

Most tornadoes form from large rotating thunderstorms called "super cells". These monster storms tend to develop ahead of cold fronts that push southward from Canada across the central U.S. As the fronts sag into the warm and humid air that covers the southern plains, the colder air wedges under the warm air, creating lift. The lifted air rises up to form thunderstorms that can rapidly grow to heights of 40 to 50 thousand feet above the ground.

The storm pushes high into the sky, reaching into the jet stream - the band or river of fast moving air that flows around the world. It is the increase in wind speed with height that causes the thunderstorm to begin a large, slow counterclockwise rotation. This rotating thunderstorm is what is classified as a "Super Cell".

Once the super cell storm develops, the best analogy for thinking about how the tornado forms is to think of a figure skater doing a spin. The skater starts with their arms out, and is rotating rather slowly. As the skater brings their arms in, the rotation begins to speed up. In physics, this is called "the conservation of angular momentum". The rotation gets faster and faster as the size of the rotating column grows narrower. This is a very simplistic description, but eventually this narrow rapidly rotating column of air will drop to the ground as a tornado.

Tornadoes are classified by the wind damage that they cause. The scale was developed by Dr. Ted Fujita from the University of Chicago. Dr. Fujita based his "F scale" on a 0 to 5 basis for tornadoes. The F0 is a weak tornado, while the F5 storms are the most powerful winds ever observed on Earth.

F0 - up to 72 mph - light damage F1 - 73 to 112 mph - moderate damage F2 - 113 to 157 mph - considerable damage F3 - 158 to 206 mph - severe damage F4 - 207 to 260 mph - devastating damage F5 - above 261 mph - incredible damage

About 70 % of the annual average of 1000 tornadoes nationwide are classified as F0 or F1. About 28 % of all tornadoes fall into the F2 or F3 category. Only about 2% of all tornadoes are classified as F4 or F5. Often a severe weather season will come and go without a single F5 tornado reported. However, about 80% of all tornadoes deaths are the result of the F3, F4 and F5 tornadoes. These storms are much less common, but much more dangerous.

As of 2007 this scale was replaced by the enhanced Fujita (EF) scale. The EF attempts to rate tornadoes more accurately, taking into account that it often requires much lower wind speeds to create F5-like damage. The new EF scale is now the official standard to measure the strength of tornadoes.

EF 0 - 65 to 85 mph EF 1 - 86 to 110 mph EF 2 - 111 to 135 mph EF 3 - 135 to 165 mph EF 4 - 166 to 200 mph EF 5 - Over 200 mph

Tornadoes are not named like hurricanes are, but the strong or deadly tornadoes are usually remembered for the town or location that they affected. For instance, the infamous "Xenia Ohio Tornado" of April 1974, or in Colorado, the "Limon Tornado" in June of 1990 and now the "Windsor Tornado" in 2008.

Perhaps the single worst tornado on record was the great "Tri-State Tornado" of March 1925. This huge tornado started in southeastern Missouri and tore a path of destruction all across Illinois, before ending in western Indiana. The twister covered a distance of 219 miles and was on the ground for over 3 hours. In the days before adequate warnings, the storm caught everyone off guard. The Tri-State Tornado killed 689 people, injured over 2,000 and caused 17 million dollars in damage - a very large figure in 1925!

In Colorado, the peak season for tornadoes is in early June. At that time, the almost daily dose of thunderstorms can easily rise up to the jet stream level and begin to rotate into a super cell. These storms tend to form along the Front Range, roll over the Denver metro area and then really get severe over the eastern plains of the state. About 90% of all Colorado tornadoes occur east of I-25. Although tornadoes can form in the high country, the rough terrain tends to disrupt the rotation needed to form a super cell.

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