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Meghan's WEATHER CORNER |
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November 2009
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Recently by Meghan DanaheyI got a good question from Sheryl Arldt last week. I thought I would share my answer with her here in my blog. It might offer a bit more understanding on the topic of Jet Streams in the Northern Hemisphere and how they affect our weather. "It seems that we usually don't get cold fronts or bad weather coming from the east or northeast and I was wondering why?" The polar (or mid latitude) jet stream winds blow across the northern hemisphere from west to east all the way around the globe. It is the polar jet stream that drives our storm systems (cold fronts, low pressure systems, etc.).
Imagine you a little piece of wood floating down stream in a small creek. That wood will move downstream along with the current. Sometimes the current picks up, so the piece of wood moves faster. Sometimes the current is very slow, so the wood moves very slowly. In stagnant water, the wood would just float until more of a current came along to pick it up and move it back downstream. Low pressure systems bring unsettled weather. Low pressure systems are like the wood moving in that creek. The twists and turns in the jet stream, along with the jet stream position, determine the track of those low pressure systems. In the summer, the polar jet stream migrates up toward the Canadian border. That's why we don't see a whole lot of cold fronts in the summer! Most of the active weather in the USA is along the northernmost states in July and August. In the Spring and Fall, the jet stream migrates back to the south. We start to see cold fronts and periods of unsettled weather with this transition.
In some instances we do see weather come at us from the east or northeast. In those rare cases, it is usually a tropical feature, easterly wave, or other low pressure system sitting just off to our east. The circulation around those features can bring in showers or storms from the opposite direction. For more information on Jet Streams, cold fronts and pressure systems check out this article courtesy of the National Weather Service Office in Louisville, KY. I finally got to get out to visit some eager 2nd graders. It was a quick trip over to Cedar Park to Naumann Elementary. I started by reading Cloudy with a Chance of Meatballs to Mrs. McLaughlin's class.
We talked about my background, education, my job and how I forecast the weather. We also got to talk a bit about plain old thunderstorms vs. severe thunderstorms.
"I live in the Star Ranch subdivision near Hutto. Last night the storm was short, but severe. Hail and very strong twister like winds blew down my fence on both sides along with my neighbor's play house and patio furniture. It also picked up their big trampoline and it landed three houses away. My garage doors seemed to suck in and out." - Lynn Bryan We know severe wind gusts over 65 mph tore up homes and businesses in Hutto and Taylor a couple of nights ago, but were those wind gusts the result of a microburst or a tornado? What happened in Hutto was a severe downburst wind event. They often happen very quickly and without much warning. Below you will see a couple of images I found to help explain a microburst. This is the same type of an event that brought down the Cowboys practice bubble up in Irving back in May.
It is the same event that brought down Delta Flight 191 as it attempted to land at DFW International Airport on August 2, 1985. Sadly, 8 crew and 126 passengers lost their lives in that crash, but it was essential in the development of windshear detection equipment that keeps airplanes in safer environments today.
A downburst (or microburst) is a different process than a tornado, but severe wind damage is easily seen in both situations. Heavy rain-cooled air rushes down out of the base of the thunderstorm. Research has shown that melting of hail can play an important role in downburst formation. The rainshaft and winds in a microburst smash into the surface of the earth and spread outward from the point of impact. Hutto and Taylor were likely at that point of impact where winds were upwards of 65 mph.
In these pictures from the National Oceanic and Atmospheric Administration below, notice the surface curl soon after a microburst impacted the area. It is a real world example of the schematic above.
One of the things the meteorologists at our local National Weather Service offices are trained to do is observe damage patterns after severe wind events. The patterns can help determine and support what processes might have been occurring at the time the damage was sustained. The swirling and chaotic winds in a tornado will leave strikingly different damage patterns than straight-line wind or microburst events. Since the wind spreads outwards in all directions, the wind regime in a microburst is opposite to that of a tornado. The environment prior to thunderstorm development is also very important. Our atmosphere this time of year is not as favorable for tornado development, due to the lack of upper level wind support.
We need strong upper level winds moving from southwest to northeast and low level winds out of the southeast to create a rotating thunderstorm updraft. As that rotating updraft grows taller and turns faster, a tornado can spin up at the surface. We most often see this along strong cold fronts in the spring.
Scattered thunderstorms that we see over the next couple of days, will be in a favorable environment for severe downburst or microburst winds. As in the case of Hutto and Taylor, no severe thunderstorm warning was in effect at the time of the microburst. They can happen suddenly and with very little warning, so keep an eye to the sky the next couple of days. Thank you, thank you from the bottom of my heart! I appreciate everyone who made a donation. Thanks to the volunteers, too, who gave their time and sweat to make this year's For the Children school supply drive a huge success. Distribution Day was this last Saturday at Sanchez Elementary School in southeast Austin. Administrators and employees from at least 10 area districts came by to load up supplies for the start of the school year next week.
Thanks to your generosity, we were able to provide supplies to over 50,000 students from K to 4th grade. It was the 20th year For the Children has been working hard to see that area school children succeed right from the very first day of class. Since 1989, For the Children has helped over 363,000 students in Central Texas. For the Children is an all-volunteer non-profit organization, so 100% of all cash donations go to the purchase of school supplies. Since it can buy in bulk, For the Children can really make that dollar stretch! Under $4.00 can supply one child. $20 can supply 6 students. Area H-E-B stores made a huge difference this year with the $1, $3 and $5 scan cards. Thank you H-E-B for all of your help. We hope to partner with you again next year!
Ready for a little late summer fireworks? Earth is entering into a trail of dust from the Comet Swift-Tutle and the debris can give us quite a light show each year. We will be in the densest part of this dust on Wednesday, August 12th. The best time for viewing will be late Tuesday night into the pre-dawn hours that Wednesday morning. At it's peak, this year's Perseid shower could produce 100 meteors per hour. We might have to deal with a few morning clouds that day, but sky conditions should be pretty good. There will be some bright light from a 55% Gibbous moon. For more information, check out NASA's website or take a look at this article in the Los Angeles Times. Last week, I got a chance to take a long weekend and escape the brutal Central Texas heat. I flew out to Charlotte, NC and met one of my best friends from Texas A & M. Stephanie and I had a great evening, then did a yummy brunch the next day in Uptown Charlotte. We figured out it had been 5 or 6 years since we had seen each other. Way too long! The weather was very nice. Quite a break from the record heat we have been dealing with here for weeks now. Upper 70s to low 80s on the mountain, with lows in the mid 60s. We did run into some of the heaviest rain I have ever seen and flash flooding on the drive from Charlotte to Landrum. Couldn't go more than 20 mph on a little 2-lane highway and finally had to pull over and stop. I wish I could have bottled up all that water and brought it back to Central Texas with me! Thanks to ALL involved for the love and laughter. What a great trip! I'm a meteorologist. I am not an architect or a concert critic. That said, I AM a native North Texan, and I've been to my fair share of Cowboys games and concert events at the recently retired Texas Stadium in Irving. And there is big buzz all around about the history-making inaugural event at the new Cowboys Stadium in Arlington this past Saturday night. I was lucky to be in the audience and just had to share. If any of you found yourselves there, too, please weigh in! THE EVENT: 5:30pm, Saturday, June 6th. A star-studded country concert headlined by the "King of Country" George Strait. Fellow artists Reba McEntire, Blake Shelton and Julianne Hough were also on the bill. Lee Ann Womack stepped in at the last minute for Julianne Hough, who was suffering from a yucky bout of strep throat. THE ATTENDEES: My group numbered about 12 and included folks from Austin and Georgetown to Graham and Dallas/Fort Worth. People in the audience drove from Fort Stockton, Lawton, Louisiana and Kansas (and that's just the people that I talked to!). Some of them flew all the way from England! Cowboys owner and general manager, Jerry Jones, was joined by ex-Cowboys coach, Jimmy Johnson. Governor Rick Perry and Senator Kay Bailey Hutchison were in attendance, while Troy Aikman and other ex-Cowboy sightings happened here and there all night long. 60,188 was the offical tally. And even with all those people milling about, it never really felt terribly crowded! THE GOOD: Wow. That stadium is simply state-of-the-art. It is a mammoth structure as you make your way to its front doors. It has a beautiful glass skin that reflected the rich blue Texas sky and those giant steel arches seemed so strong and endless when standing underneath them. Through the front doors you'll see the whole place just laid out in front of you in the very open mezzanine breezeway. There seemed to be digital t.v. screens everywhere. Even the vendors were using them for menus and pricing. It's all concrete and steel, with a silver and blue color scheme... of course! There doesn't seem to be a bad seat in the house, thanks to the two much talked about enormous HD screens above midfield. Measuring 159 feet long and 71 feet tall, you can't miss anything from the north and south sideline seats and you could see every pore on Lee Ann Womack's face! The "hole-in-the-roof" was closed to keep out the hot afternoon sun, but it did allow nice natural light into the stadium. The sun shined brightly into the stadium from all around the mezzanine. The "hole-in-the-roof" was opened about three songs in to George Strait's set. It only took 12 minutes for the roof panels to fully open to the starry night sky. The luxury boxes and suites appeared to be quite cozy with every amenity right down to the Kobe beef and leather seating. Even the bathrooms were nice, with not-so-cheap toilet paper and rows and rows of brand new stalls. Everyone knows how important it is to keep THAT line moving! THE BAD: Let's go back to that "walk" up to the front doors. We stayed in nearby hotels, so we got as close as we could by taxi (about 1/2 mile). By personal car, the cheapest parking was $30-40 followed by a mile-long hike. At 4:30 in the blazing June Texas sun... ouch. Traffic was a bit of a mess, but city officials said that early patron arrival and good planning kept it from being the nightmare everyone thought it would be. While he praised Jerry Jones for "thinking of everything," singer Blake Shelton had some pretty cruel remarks when it came to the traffic issue and said he almost missed his set. When we walked in the west entry, Lee Ann Womack was already on stage about two songs into her set. The sound from the breezeway was terrible. Lucky for us, we had amazing floor seats in front of the stage set up on the east endzone. There the sound was good. But, just a short walk back toward the rear floor sections and that sound became muddled and reverberating. I felt sorry for anyone who had paid a steep price for west end tickets. Perhaps all the concrete and steel? All I know is that I want to go to the U2 concert there in October and I hope the sound quality is much-improved! It was the first event and finishing touches still have to happen before the Cowboys 2009 home opener. That was to be expected. Hour-long waiting times to get consessions were met with serious grumbles as patrons were told "we have hamburgers, but we're out of buns," or "I'm sorry, the only beer we have is hot and it's still $8.00." And those beautiful bathrooms... got a whole lot "less-than-beautiful" when all the toilet paper and paper towels ran out halfway through the 6-hour event. They need more trashcans around that place, both outside and inside, too. It seemed like trash was everywhere on the walk out. OVERALL: It was one amazing night!! The music was incredible and the songs legendary. The new stadium is a sight for sore Cowboy-eyed fans. It blows the old Texas Stadium out of the water. Even after 6 hours of being in there, most people left with jaws still gaping wide open. You can check out all of my pictures in the slideshow on KVUE.com.
Notice in these photos the orange and dusty sky. People in Iraq often have to deal with dust storms called Haboobs or Shamals. A Haboob forms from the outflow boundary of a thunderstorm and can happen frequently in the late Fall and Spring seasons. They can be very dramatic. It appears as a solid wall of flying dirt and dust moving across the landscape. The haboob may also occur in dry climates like Arizona or West Texas. This is a haboob blowing into Taji, Iraq taken in 2006. A Shamal is less dramatic, but can keep dust suspended in the air and reduce visibilities for four to five days. Check out the essay describing these dust storm events written by Michelle Moses, a forecaster at Balad Air Force Base, Iraq. And God bless all of our men and women serving the United States of America all over this world! Today we celebrate the 39th Earth Day. One of the reasons I love the Austin area so much is that Central Texans already do so much to help the environment and keep our earth green. It never hurts to start young! If we can get our children to start thinking about ways to reduce, reuse and recycle, then we have another generation of environmentally conscious and responsible adults to walk in our footsteps. I wanted to show off a few posters I got from my friends at Village Elementary in Georgetown. Mrs. Cothrin's 3rd grade students drew some very colorful pictures to help us talk about Earth Day this morning on KVUE News Daybreak.
It was my first visit to Florence and, wow, did the third grade classes at Florence Elementary ever make me feel welcome! I was greeted with lots and lots of smiles and good weather questions (as always!). The water cycle is a popular topic among second and third grade students. We talked more about it and how it specifically related to our sometimes volitile Texas weather. There was also a good discussion about regular air mass thunderstorms versus severe thunderstorms. Hail was a popular topic, thanks to the devastating hail storm on March 25th. One of the best things about visiting area schools is the wonderful "thank yous" I get from both teachers and students. Take a look at these. Awesome! |
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Meghan Danahey
Meghan Danahey can be seen Monday-Friday on KVUE News Daybreak and Midday. |
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