Mike's Blog Archive: April 2010

Another huge change in the weather has taken Colorado from a taste of summer, back to a chilly reminder of winter. A strong cold front roared across the region Wednesday night and will now keep Colorado cold for several days. Along with the drop in temperatures, a messy mix of snow and rain greeted many folks on the north side of Denver, north to Fort Collins and Greeley early Thursday.

Severe weather is likely farther east with this front and tornado chasers will be deployed across the Midwest over the next few days. You can follow along with some of the best weather chasers in the business on our Storm Chaser Blog.

Storm Chasers Blog.

We have some great features on the website to help provide you with the latest information during severe weather season.

THE 24/7 WEATHER CUSTOM FORECAST

We offer the only personalized web page that is powerful enough to generate an hour-by-hour forecast for your specific location. We actually use your address to design a specific forecast for exactly where and when you need it. You'll have access to data from the same advanced computer models that we use to prepare our on-air forecasts here on 7News.

Sign up for your FREE 24/7 Weather Custom Forecast today and start planning your week! CUSTOM FORECAST

You can also choose to allow us to alert you by e-mail or on your mobile device when severe weather is threatening your area. Get your school closing information automatically sent to you in a e-mail or text message. A downloadable desktop weather icon is also available that shows current weather conditions, warnings and radar!

INTERACTIVE RADAR

You can also use our simple "point and click" 24/7 Weather Interactive Radar to get a real-time look at storms anywhere in the country. Just click on the Interactive Radar tab on our top of our weather navigation bar. Our new 24/7 Weather Interactive Radar uses super high resolution mapping to let you zoom right down to your neighborhood! You can even find your house – check it out!

INTERACTIVE RADAR

You can switch the map between a street map view, or add topography for a more detailed look! You can view lightning strikes, clouds, and storm specific information. You can even view the National Weather Service official watches and warnings directly from this product!

EXCLUSIVE FUTURECAST

The Futurecast is another product that you will only find on TheDenverChannel.com! View the forecast for the state or the nation using the same forecast products we use on air! The Futurecast updates 4 times a day with the latest forecasts on approaching storm systems! FUTURECAST

Great fun and lots of learning this Saturday at the National Center for Atmospheric Research (NCAR) in Boulder!

Join NCAR and Wild Bear Center for Nature Discovery for a fun family event!

Wild Earth Saturday will be held on April 17th from 10 AM to 4 PM at NCAR's Mesa Lab. Join the scientists and researchers at NCAR as they celebrate the beginning of Earth Week and the coming of Earth Day. This action-packed event is free to the public and features hands-on exhibits and activities plus food and music.

Understand the constellations in the night sky Learn the language of the Raptors with Hawk Quest Meet the reptiles Engage in Earth Magic Dance to the music of Emmy-award winning songwriter David Williams Realize the power of alternative energy sources Explore NCAR’s Mesa trails Perform your own weather broadcast with Channel 7 Weather

Visitors to Wild Earth Saturday are encouraged to leave a “light touch” on the Planet by using alternative means of transport such as carpooling or biking to the event. NCAR’s cash-only cafeteria will be serving food all day and visitors can enjoy indoor and outdoor dining.

Wild Earth Saturday promotes a healthy environment and mobilizing people through awareness of the world around us.

The event is sponsored by the Scientific and Cultural Facilities District (SCFD), and Radiance Corporation. Media sponsors include the Boulder Daily Camera and KGMH (Channel 7).

The 24/7 Weather Experience will again be there in the main lobby at NCAR. The 7News portable weather studio allows you to be the weathercaster! You can appear on TV in front of a variety of stormy weather! Do the weather in the middle of a tornado outbreak, ahead of a severe thunderstorm or in the grip of a blizzard! Meet the 7News Meteorologists and Weather Interns at the 24/7 Weather Experience.

Wild Earth Saturday is designed to promote sustainable living through an awareness of our world and it's limited resources. We hope to see you there for this annual celebration in honor of our home planet, Earth, and to learn more about our responsibility to be good stewards.

To learn more about NCAR and this event click ! NCAR Wild Earth Day

The inclement weather date is April 24.

Severe weather season gets into full swing in April as the increase in daytime temperatures means the first thunderstorms of the year arise over Colorado. Thunderstorms that can produce large hail and tornadoes.

This year, Severe Weather Awareness Week will be observed in Colorado April 11-17. The National Weather Service will initiate a statewide tornado drill on Wednesday, April 14, between 9:00 a.m. and 11 a.m. using EAS and NOAA weather radios.

For television stations such as KMGH, a crawl will appear on the screen notifying viewers that this is a tornado warning. Viewers should be aware of this and know that it is only a test. This event is a test to determine the readiness of EAS equipment and emergency radio receivers located in broadcast facilities, schools, hospitals and other public buildings. All EAS receivers and weather radios that are set to receive tornado codes should receive the drill message between 9:00 a.m. and 11:00 a.m. on April 14th.

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.

In my 30 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 an F5 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 Channel 7.

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.

I thought since we are on the subject of storms, you might like to have a little information about rain and hail, some things that usually accompany a tornado...

Here are a few facts about rain and hail. Most of the rain that we get in Colorado forms from a mix of water droplets and ice crystals in the clouds. Under certain conditions, water will remain in liquid form even with temperatures that are well below freezing. This type of water is called "super-cooled". In most of our summertime clouds, we have a mix of super-cooled water and ice crystals floating around high above us. The ice crystals rapidly grow as they "feed" off of the super-cooled water and they basically form big fat snowflakes. These snowflakes fall slowly to Earth and begin to melt as they reach warmer air closer to the ground. The resultant raindrops will fall to Earth at about 15-20 mph.

In stronger thunderstorms, the tiny ice crystal gets bombarded by the super-cooled water thanks to the extreme turbulence in the storm cloud. The ice crystal forms a small stone of ice which is the beginning of a hailstone. If the storm is quite strong, there are intense updrafts of wind that can keep the growing hailstone suspended in the cloud for a long time. A hailstone that is the size of a golf ball needs an updraft of nearly 60 mph to stay aloft. A baseball sized stone requires a 100 mph updraft to keep it "afloat".

When the hail falls to Earth, they come zipping down at 70 to 100 mph. That is why it is a good idea to stay indoors during a major hailstorm!

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

You can follow along with some of the best weather chasers in the business on our Storm Chaser Blog.

http://Storm Chasers Blog.

We have some great features on the website to help provide you with the latest information during severe weather season.

THE 24/7 WEATHER CUSTOM FORECAST

We offer the only personalized web page that is powerful enough to generate an hour-by-hour forecast for your specific location. We actually use your address to design a specific forecast for exactly where and when you need it. You'll have access to data from the same advanced computer models that we use to prepare our on-air forecasts here on 7News.

Sign up for your FREE 24/7 Weather Custom Forecast today and start planning your week! CUSTOM FORECAST

You can also choose to allow us to alert you by e-mail or on your mobile device when severe weather is threatening your area. Get your school closing information automatically sent to you in a e-mail or text message. A downloadable desktop weather icon is also available that shows current weather conditions, warnings and radar!

INTERACTIVE RADAR

You can also use our simple "point and click" 24/7 Weather Interactive Radar to get a real-time look at storms anywhere in the country. Just click on the Interactive Radar tab on our top of our weather navigation bar. Our new 24/7 Weather Interactive Radar uses super high resolution mapping to let you zoom right down to your neighborhood! You can even find your house – check it out!

INTERACTIVE RADAR

You can switch the map between a street map view, or add topography for a more detailed look! You can view lightning strikes, clouds, and storm specific information. You can even view the National Weather Service official watches and warnings directly from this product!

EXCLUSIVE FUTURECAST

The Futurecast is another product that you will only find on TheDenverChannel.com! View the forecast for the state or the nation using the same forecast products we use on air! The Futurecast updates 4 times a day with the latest forecasts on approaching storm systems! FUTURECAST

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