With the first summary from the next set of Intergovernmental Panel on Climate Change (IPCC) reports about to be released, I thought I'd reflect on the role global warming has played in my life.
Old curmudgeon that I am, resistant to change and new ways, I find it surprising -- looking back -- that I once jumped on a bandwagon before it even showed up.
Long ago and far away I became acquainted with the late Dr. Hurd Willett, a professor emeritus at MIT. Dr. Willett was a recognized authority on the correlation between solar activity and the earth's weather. He'd developed some convincing relationships between long-term solar cycles and climate. In the 1970s he foresaw a trend toward colder winters in the eastern U.S. through the end of the 20th century.
Interesting stuff. I wrote a book about it. But in the course of researching the book and talking with other scientists, I came across a theory which back then was known as an enhancement of the "greenhouse effect," global warming caused by man injecting increasing amounts of CO2 into the atmosphere.
I asked Dr. Willett about the increased greenhouse effect and he essentially pooh-poohed it. "Don't worry about it," he told me, "it's not an important factor." I wasn't sure about that, however. It seemed to me a bigger deal than Dr. Willett and a number of other researchers at the time believed.
Maybe worth another book, I thought. I developed a questionnaire and mailed it off (this was long before e-mail, kiddies) to a couple of dozen researchers in the field. Plus, I read a lot about the greenhouse effect.
Like most operational forecasters, I didn't really want to believe that human activities could change our climate and perhaps eventually doom one our favorite things in the whole world: wild winter weather -- snowstorms and arctic outbreaks.
Alas, as the questionnaire responses came back and I continued to review books and technical papers, the preponderance of evidence seemed to me to favor global warming. The clincher was a graph by Dr. Wallace Broecker of the Lamont-Doherty Geological Observatory suggesting that CO2-induced warming would completely overpower Willett's cooling cycles by the beginning of the 21st century.
Thus I wrote The Greenhouse Effect, published in 1980. I followed it up with Global Warming Unchecked in 1993 at which point the evidence for human-caused climate change had become overwhelming. (By the way, don't run out and try to buy these books. They're out-of-print and out-of-date.)
In both books I presented what I felt were convincing double-barreled arguments for weaning ourselves from fossil fuels. We could stem the tide of global warming and simultaneously become less reliant on imported oil, much of which was coming (and continues to come) from countries that aren't going to sit down with the U. S. around a campfire and sing "Kumbaya."
For my efforts, I was called a charlatan by a Fellow of the American Meteorological Society. The guy obviously was clueless about the economics of publishing (and, as it turns out, clueless about global warming).
You don't make money writing books unless, for instance, your name is John Grisham or Al Gore. And more power to Al Gore for his efforts. My books were only modest sellers and I understand why. People didn't know who I was. Just a weather forecaster. Not a researcher. Not a Ph.D. Not a politician. (I've often said that unless an author's name on the cover of a book is bigger than the title, he or she isn't going to make money.)
But believe it or not, I had my chance. One brief, golden opportunity to gain national recognition. It was undone by world events. The Bernard Curse, my dad later told me.
Good fortune doesn't run in the family.
I'll tell you about it in my next blog.
In my blog of January 26th, I indicated that despite the occurrence of a moderate El Nino this winter, California and Florida have not been getting a lot of wet weather. I wanted to make the point that other factors can overwhelm the influence of El Nino.
Several readers asked for more details about those other factors. They can be pretty complicated and easier to recognize than to predict, but I'll try to give you a sense of them. They aren't my specialty.
During winter, the key factor is quite often if and where amplified waves (north and south meanderings) in the jet stream get locked into place across the mid- and high-latitudes. Making things difficult is that these waves can rather suddenly amplify, de-amplify, or shift position, as they are to a large degree an instability that develops within the upper-level jet stream.
The nature of the instability is that rather subtle, small changes in the jet stream can sometimes result in dramatic changes in the whole jet stream pattern around the hemisphere that may then persist for several weeks. Our numerical models of the atmosphere often can predict this about a week ahead of time, but there isn't nearly as much skill in predicting these pattern changes months ahead of time.
Here's an example of such a change, for the 500 mb level (about 18,000 feet above sea level). The top diagram is from January 1, the middle one from January 14, and the bottom one from January 25 (all courtesy of NOAA).
Here the violet-shaded areas represent the coldest cores of the troughs. Note how the shape of the pattern changed between these maps. On the first, there was a big elongation from the Aleutian Islands across Alaska to near Norway, left to right across the diagram. By the fourteenth, that orientation had changed to one from upper-left toward lower right: from near Kamchatka to Hudson Bay and Greenland.
With that trough just north of the Great Lakes on the 14th, the pattern became favorable for driving cold air masses out of Canada into the United States. The previous pattern was a mild one that generally kept Pacific air across the continental U.S. Also note the green-colored area plunging across the western U.S. As it developed it pulled enough cold air into the central U.S. to allow for the major ice storm that weekend. With that trough having developed inland, California got dry northwest winds aloft rather than a moist southwest flow if the trough had developed offshore.
By the 25th the cold trough surged even farther southeast over the Great Lakes and into New England, bringing bitter cold surface temperatures with it. The diagram also shows that an upper low and cold pocket have begun to reform over the North Pole.
There are several indices that monitor these types of patterns or related ones in the sea-level pressure. One is the North Atlantic Oscillation (NAO) that relates to the strength of low-pressure near Greeland and Iceland and high pressure over the subtropical North Atlantic. When these are strong, as in the positive index pattern below (from http://www.ldeo.columbia.edu/NAO/ ), the westerlies blow strongly across the Atlantic and it is stormy in Europe, mild and wet in the eastern U.S. When both features are weak, the index is negative and the eastern U.S. is colder and snowier. The index value was positive at the start of January but has become negative in the latter portion of the month, coinciding with the cool-down in the weather across the U.S.
There are other indices that relate to the mid- and high-latitude weather pattern, including the Artic Oscillation (AO) and the Pacific/North America (PNA). Current and forecast conditions are available from NOAA's Climate Prediction Center (CPC).
One reader mentioned the Madden-Julian Oscillation (MJO). This phenomenon emphasizes that periods of enhanced rain associated with deep clouds in the Indian Ocean and west Pacific regions can have broader impacts. Disturbances in the upper-level winds move eastward from these areas and bring about a cycle with 30-60 day period as they move across a region. The disturbance enhances rain during one part of the cycle and suppresses it in another. CPC indicates that the MJO is currently rather weak.
The bottom line is that, yes, meteorologists are a lot more skilled in predicting the weather for the next several days than for the next few months or longer. The sloshings of the atmosphere associated with the various indices mentioned above remain a challenge!
The start of the winter was quite warm along the east coast, but the cold air has finally settled in and will be hanging out for a bit. It has even made it into Florida! There are freeze warnings from south Georgia through the Sunshine State!
So are you happy the cold air is here and here to say or are you bummed out? All I have to say is it takes a little extra effort on my part to get up early and workout or run errands when it is cold. Do you find yourself doing less and staying indoors more when it is frigid?
Much attention has been given by the media to the development of a moderate El Nino late in 2006. In particular, this led to expectations that the winter weather might be rough on California.
The presence of El Nino has often meant a wet, stormy winter in California and wet conditions in Florida and other Gulf Coast states. With the exception of Texas and Louisiana, that has not been the case so far this winter! In this season of the Academy Awards, The Weather Channel Senior Meteorologist Tom Moore made the analogy "if this winter's weather was a movie, El Nino would have only had a bit part, and would certainly not be in the running for an Oscar as lead or supporting actor."
Put another way, thus far in January, Los Angeles, San Diego, and Sacramento, California have each had less than 0.10" of rain in what normally one of their wettest months. Instead, they have had only 2 to 4% of the average January rainfall.
What is going on? Well, for one thing, this hasn't been a particularly strong El Nino. And it has noticeably weakened between November and January, as shown by the pair of sea-surface temperature anomaly maps below. It has weakened between November and January, as shown by the pair of sea-surface temperature anomaly maps below. Notice that the size of the areas with red anomalies (water more than 2 degrees Celsius above average) and brown (1-2C above average) have shrunk. (Images courtesy of NOAA Climate Prediction Center.)
In simple terms, El Nino is often able to affect weather conditions across the United States because the warm waters warm the air, which tends to subsequently promote a stronger-than-average jet stream that blasts eastward across the subtropical Pacific Ocean into southern California and northern Mexico. This is shown in the schematic diagram below (courtesy of NOAA Climate Prediction Center).
The next map shows an actual map of the upper-level winds during a strong El Nino event in February, 1998. Note the strong jet stream (yellow and orange-shaded strong speeds) blowing across the Pacific Ocean into southern California and northern Mexico. It looks just like the schematic diagram above.
Contrast that with the average upper-level wind pattern from January 1-22, 2007, shown below. The jet stream heads northeast from the central Pacific Ocean into southwest Canada. Weak northwest winds are offshore of California.
The relatively slight amount of energy contributed this winter by a weak El Nino has not been enough to overcome much stronger jet stream processes at high latitudes that have kept the jet stream far north of California. In other words, by itself El Nino can't overcome other processes if they set up in a pattern too unfavorable. El Nino, even at its strongest, plays the role of a supporting -- not lead -- actor.
Actually, this shouldn't come as a surprise. Anywhere from 15% to about 40% of the past California winters have had below-average precipitation during El Nino events.
This is shown in the figures below (courtesy of NOAA Climate Prediction Center). The top diagrams show precipitation in the Los Angeles area during past El Nino events, for December through February (left) and January through March (right). The bottom diagrams are for the Sacramento area. The brown bars indicate that anywhere from 15% to 40% of the winter periods have been below average, while about 40-60% have been above average (green), and about 15-20% have been near-average (yellow).
Given the dry, wildfire-prone conditions in California, residents would probably like for El Nino to play its wet role a little more forcefully this winter!
What ever happened to the good old days when football fans used to brings signs to the game that poked fun of the quarterback's masculinity, or joked about the coach's mama, or just gloated about how great their team was? I miss those days. Did you happen to see the Bears vs. Saints this weekend? I think I saw the most despicable and truly classless sign I have ever seen.
I understand what signs are all about, demoralizing the other team and a little trash talking. That's cool, but how on earth do you go to Soldier Field with that sign and think it is ok? Have we forgotten how one of our most charismatic cities was reduced to almost nothing, how 1300 people lost their lives, how hundreds of thousands of people suddenly became homeless in the matter of a day?
Chicago is one of my favorite cities and the sports fans there are, in my opinion, the best in all of sports, but it only takes a few heartless, idiotic fans to ruin the image of a proud city. I wish it was illegal to be stupid because these guys would be locked up for life.
In President Bush's State of the Union Address Tuesday night he spent a good chunk of time talking about climate change and reducing the country's dependency on oil. As a meteorologist, he got my attention. Reducing oil consumption by 20%? Raising vehicle emissions standards? Investing in alternative and renewable energy? That a way Mr. Bush! Other countries have been leading the way for years in all of these categories. It's good to see that The U.S. is finally taking a stand and moving forward to make this a better place for all of us to live.
I particularly liked the comments President Bush made regarding improving battery power (which may eliminate the combustion engine one day) and clean nuclear energy. These are both viable options to fossil fuel. The cost of converting to these types of energy sources is going to be expensive but I truly believe that the end result will pay tenfold and we will all be able to breathe easier...literally. Imagine cities like Los Angeles, Dallas, and Atlanta without smog.
It can happen if we all do our part to reduce pollution. President Bush's speech should inspire us all to do whatever we can to save this planet, because once it's gone, so are we.
It's the dead of winter. Snow is on the ground. The sky has been gray for what seems like forever now. It's enough to get you down, and it does. Millions of Americans suffer varying degrees of SAD (Seasonal Affective Disorder). SAD is linked to a biochemical imbalance in humans that reacts to lack of light...remember the daylight hours are shorter in the winter. Symptoms can include fatigue, lack of interest in normal activities, social withdrawal, craving high carbohydrate foods, and weight gain. These symptoms usually subside in the spring.
Increasing your exposure to light can help improve your symptoms. The American Psychiatric Association recommends walking outside and rearranging your home or office so that you are exposed to more window light. Severe cases of SAD can be treated with light therapy. It has proven to be an effective treatment for SAD. It usually involves exposure to bright light for 30-90 minutes a day.
If you have any tips on overcoming the winter blues, let me know. You can email me too at email@example.com Beating SAD can be a tough thing. Good luck. Remember, spring is just 2 months away.
Last week it was clouds in Cali, this week it's ice I encountered in San Antonio, where nearly 2,500 meteorologists are gathered at the Annual Meeting of the American Meteorological Society.
And whereas last week there was barely a snow flurry at 8000' elevation in the Sierra where I was staying, this week there is not only ice on trees such as those in the photo above (taken with a camera phone again!), there's been massive disruption to travel in South Texas. That includes for a number of those aforementioned meteorologists, who have had their flights canceled. (Yeah, I know, you're thinking, "Serves them right for all those times we got 6" of partly cloudy!)
The freezing rain, sleet, and snow that fell in this part of the country and the bit of sleet pinging not far from Atlanta at this hour represent a continuing series of inclement weathermakers that the wind in California last week was the first sign of. The stuff now in the southeast U.S. will join up with a more northern disturbance to create what is expected to be an intense cyclone in southeast Canada by Friday night and Saturday.
Meanwhile, there was a potent mid-to-upper-level low -- the swirl of which I circled in red on the water vapor image from earlier today below -- that brought snow and graupel in the hills not far from Los Angeles today. That disturbance will tap into a persistent moisture plume (see green arrow on the image) to cause precipitation to spread back across the central states by Saturday.
Even though the "hose" of moisture from the tropical Pacific to the U.S. Gulf Coast is a classic signature of a January pattern influenced by a moderate El Nino, SoCal continues to run well below average in precipitation this winter -- the feisty weather today notwithstanding -- contrary to what is typical when El Nino is present at this time of year.
Don noted the lack of precip there in a comment on 1/16 to my entry on the Cali trip, and no, there's not a lot of precip in the offing there in the near future.
The past few days, from Friday to Tuesday, 12-16 January, brought quite an ice, sleet, and rainstorm to a strip of the United States from Texas to New England, beginning in the central United States and then spreading to the Great Lakes and Northeast.
The most devastating aspect of the storm, in general, was a swath of freezing rain that accumulated on just about everything and made transportation nearly impossible. The accumulation of ice on power lines, and on trees and branches that fell onto power lines, brought power outages to hundreds of thousands of people in many states, including Texas, Oklahoma, Missouri, Illinois, Michigan, New York, New Hampshire, Vermont, and southwest Maine.
Up to 2 inches of ice accumulated in southwest Missouri near Springfield, resulting in the largest power outage from an ice storm there since 1987. The National Weather Service office there has a web page summarizing the storm there. St. Louis, MO, had lots of power outages from ice accumulation and also has a web page summarizing the event. The storm generally did not bring a lot of snow, but brought unusual accumulations of sleet to some areas. Three to five inches of sleet, with one report of six inches, accumulated in southwest Missouri, just west of the region of heaviest freezing rain.
Oklahoma City had sleet accompanied by thunder on Sunday morning, an unusual event. How is that possible? The map below shows surface weather conditions at the time, courtesy of the National Center for Atmospheric Research (NCAR).
The cold front, in blue, had driven 300 miles southeast of Oklahoma City by that time and was located over Houston, Texas. Ahead of the front, temperatures (shown by the number to the upper left of the weather station circles) were mostly about 70 or 71 F, while the temperature at Oklahoma City (red arrow) was 25F !
The cold air behind the front was in a shallow layer, only about 3000 feet thick. This allowed the temperature at that altitude above the ground at Oklahoma City to be about 50F. Thunderstorms were forming in that warmer air aloft, and then their raindrops were freezing into ice pellets (sleet) by the time they reached the ground.
The figure below shows the small red-cored thunderstorm cells that were generating the sleet over central Oklahoma, courtesy of the National Center for Atmospheric Research (NCAR).
To give you another picture of this situation, the map below shows the weather above the ground at the 850 mb pressure level, which is approximately 5000 feet above sea level. Here the cold front is farther northwest, located from southwest Texas to near Dallas and northeastward into Illinois and Indiana. These temperatures are in Celsius; generally about 13C (55F) south of the cold front, but 7C (45F) at Oklahoma City.
The warm, moist air from the surface over southern and coastal Texas was being lifted up over the cold slab of air behind the cold front. In some places it was unstable enough that thunderstorms developed. In northeast Texas and Arkansas - not so far back into the cold air as Oklahoma City -- heavy rains developed. One location in Arkansas got 9.17 inches of rain from the storm!
What makes the difference between freezing rain and sleet? Both occur when there is a layer of cold air near the surface, an above-freezing layer above it, and a cold cloud layer above that near 10,000 to 20,000 feet (see the figure below). Snow forms in that upper cold layer, melts to rain in the warm layer, then gets chilled in the near-surface layer. If that surface layer is very cold or very deep, the raindrops tend to freeze into ice pellets (sleet) before they reach the ground. A warmer, more shallow cold layer tends to give droplets that freeze into a layer of glaze ice on the first things they hit (trees, utility lines, houses, vehicles, roads).
Small variations in the depths and temperatures of those layers, and a few other factors, can cause rapid changes in precipitation type from one location to another and from hour to hour or minute to minute. Because some of these variations are above the ground and are very small in scale, we don't always have enough weather data to detect or anticipate them. That makes it very difficult to pinpoint when and where it will be rain, freezing rain, sleet, and snow.
There's a scene in the classic Western movie The Magnificent Seven where a bad guy is making a run for it. Britt, one of the good guys, played by a young, lanky James Coburn, means to stop him. Trouble is, Britt is on foot. The bad guy, already a couple of hundred yards away, is on horseback.
No matter to our hero. He takes a two-handed grip on his revolver, extends his arms, aims carefully and squeezes the trigger. BLAM! A couple of seconds pass. The evildoer, just topping a distant ridge, topples from his horse.
Britt's sidekick, Chico, played by Horst Buchholz, turns wide-eyed to Britt and says, "That was the greatest shot I've ever seen."
"The worst," says Britt, staring straight ahead, "I was aiming at the horse."
And so it goes with extended range forecasting. We don't very often hit the horse. (It's a metaphor, horse lovers, I've nothing against horses -- well, other than marching behind them in parades.)
The reason we frequently miss the horse is the same reason Britt missed his. The barrel of his gun probably was pointed just a sliver off the correct trajectory. (NOTE: forecasters use numerical models, not .45s.) A tiny error such as that doesn't matter if the target is only a few feet away. But a shot that's an inch off true trajectory at close range can end up a couple of feet askew by the time it arrives at a target on yon ridge. Result: dead horsey, live bandido.
Or in our case: busted forecast, embarrassed meteorologist.
The point is that a tiny error in the data jammed into a numerical weather prediction model probably won't make a big difference in tomorrow's forecast. But seven days down the road, for instance, it can balloon into a huge error. Maybe in the speed of a weather system. Maybe in its strength. Maybe in its location.
Thus we have the Bernard Three-Day Theorem: if you plan an activity based on a forecast beyond three days, you'd darn well better have Plans B, C and D in the hopper. Besides, do you really want to base a decision on an icon (e.g., sun, cloud, shower) whose genealogy is a smiley face?
Now before my superiors suggest I consider Plan O (Out-the-door), let me say there are redeeming values to extended range forecasts. Notwithstanding the tongue-in-cheek suggestion of one of my colleagues that such outlooks come with a warning label For Entertainment Purposes Only, they're perfectly safe when used according to directions.
1) Look for trends, not specifics. 2) Track day-to-day changes in the forecast relative to the day(s) in which you're interested; don't accept a six- or seven-day outlook as chiseled in stone.
For example, let's say it's Monday and you've got a family picnic planned for Sunday. But since Uncle Jake usually shows up at these affairs three sheets to the wind and starts a fight, you're hoping for a rainout. The outlook for Sunday, however, indicates cloudy, but no rain. Things don't look good.
On Tuesday, things appear better. The forecast indicates isolated thunderstorms. Maybe there's hope. On Wednesday, there's even more hope; the outlook now calls for scattered showers and storms. On Thursday, hallelujah, Sunday's forecast is for rain. The day is saved. Well, assuming the forecast is correct and Uncle Jake doesn't show up at your house.
So remember: Trends, not specifics.
Oh, and one more thing. Temperatures are much easier to forecast than precipitation. Thus, temperature trends are much more reliable than are precipitation trends. And the bigger the predicted temperature change (i.e., the stronger the trend) the more likely it is to occur. Models generally do pretty well with major temperature shifts, although they may struggle with the timing of such changes until the event is near.
Which, of course, supports the Bernard Three-Day Theorem.
CLOUDS IN CALI
I was in California this week. It's always quite a trip (figuratively, that is, as well as literally) going there. O the humanity and O the topography! And speaking of trips, it's not that long a one from one of the most populated places in the country (Los Angeles) to one of the most desolate (here east of Olancha just inside the west edge of Death Valley National Park, on top of the Acrophobia Road From Hell I noted in my entry on western U.S. weather).
The reason I was in the Golden State was to give a talk on global warming (MUCH more on that topic as soon as I get a chance) at the Operation Sierra Storm conference at spectacular Mammoth Mountain. While near that aforementioned remote spot on the way back to L.A. Thursday, I was able to witness a spectacular mountain wave cloud over the Owens Valley near the eastern escarpment of the southern Sierra, which is visible in the background near the bottom of the photograph above.
Pretty cool, eh? (Not only the cloud -- which looks kinda like a gigantic white funnel cloud -- but the fact that such photographs are possible with simply a small camera on a cell phone!)
Those atmospheric goings-on were associated with wind energy (not only at cloud level, but a gust almost blew me onto the shoulder of the road just north of the town of Mojave) provided by the first piece of the system that is creating, and going to continue to bring, a bunch of messy weather across a long stretch of the country ... now that finally some arctic air has built up in Canada and made its way south of the border, pushing against stubborn warm air in the southeastern third of the country, with an active jet stream and a bunch of moisture thrown in the mix.
On the satellite image below taken at the same time as the photograph, you can see the overall cloud (circled) -- the part above the low-hanging lenticular appendage in the photograph -- as well as streaks (pointed to by the arrows) cutting across the SoCal cloud field. That was indicative of the strong winds, which you'll be able to see even more clearly on this satellite loop as long as the link is still active for at least the next few days (slide the "Set Animation Speed" slider all the way to the right).
We noticed a dropoff in comments posted by readers during the past couple of months but suspected it was a technical problem and wasn't because less were being submitted ... it was vexing but our weather.com I/T folks were eventually able to find the cause ... so hopefully things'll be on track now ... our apologies if you had submitted comments but they weren't getting published, and thanks for your patience!
Happy New Year!
How about a bona fide winter storm to kick off 2007? This weekend is going to be disastrous for a few million Americans. Feel like driving on an inch of ice? Me neither.
The center of the country is already getting slammed with freezing rain and sleet. Tulsa is coated, St. Louis maybe soon, and Dallas is not out of the realm of possibility. Snow is blanketing a couple dozen metro areas too. Oklahoma City, Kansas City, Des Moines, Milwaukee, and Chicago will all get a couple of inches. Then, the heavy rain is going to push rivers and creeks well over flood stage in the Mississippi and Ohio Valleys.
All of that and I haven't even talked about freezing temperatures in Southern California that are threatening citrus crops. We may all be paying for that one.
Anyway, I'm sure many of you will be out taking photos this weekend. Email me some at firstname.lastname@example.org Be safe out there and have a good weekend.
Because there are few actual measurements of tornado winds, their intensity is estimated through after-the-fact examination of the damage that they produced. Until now, that has been done using the Fujita Scale (F Scale). Starting on February 1, the National Weather Service is adopting an Enhanced Fujita Scale (EF-Scale) for use in rating tornadoes.
The Enhanced Fujita (EF) Scale was devised by a panel of meteorologists and engineers convened by the Wind Science and Engineering Research Center at Texas Tech University. I was on the team of experts who determined the revised wind speed ranges.
The original Fujita Scale was devised in 1971 by "Mr. Tornado", Dr. Ted Fujita of The University of Chicago. It gave ratings of F0 to F5 based upon the type and severity of damage that the tornado produced. At that time there were very few actual measurements of tornado wind speeds that he could relate to the damage, but he used them -- together with a lot of insight -- to devise approximate wind speed ranges for each damage category.
In subsequent years, structural engineers have examined damage from many tornadoes. They use knowledge of the wind forces needed to damage or destroy various buildings and their component parts to estimate the wind speeds that caused the observed damage. What they found was that the original F-Scale wind speeds were too high for categories F3 and higher.
In particular, homes are not built so strongly that 250-300 mph winds are needed to destroy them. In some areas, building codes may only require that roofs withstand 70 mph winds. Once the roof is blown off, walls have less support and begin to fail. In other cases, the house frame may not be properly bolted to the foundation. Then it begins to slide off the foundation, perhaps partly lifted by strong upward winds in the tornado. By the early 1990s, even Dr. Fujita recognized these shortcomings and recommended adjusting the assessments down an F-Scale or more when such weaknesses could be identified.
The table below compares the original Fujita (F) Scale winds to the Enhanced Fujita (EF) winds. The EF wind speeds are estimates of the strongest tornado wind gusts occurring at 10 meters (about 33 feet) above ground.
Guidelines in the original scheme lumped together homes, schools, mobile homes, vehicles, and trees in one short description of damage for each F-Scale category. In the enhanced scheme, detailed descriptions are given for examples of damage to 23 types of buildings and 5 additional objects like trees, towers, and poles. Wind speed estimates are then provided for each structure and type of damage. The National Weather Service web page gives details of the EF Scale scheme.
For a frame residential home, for example, shown below are the estimated wind speeds associated with various types of damage, listed by DOD -- degree of damage category. A range of estimated wind speeds are given, with EXP meaning "expected" or most likely, LB indicating lower-bound estimate, and UB indicating upper-bound estimate in miles per hour.
For houses, near-total destruction -- with only small interior rooms remaining (DOD9) -- will still rate a 3 on the new scale (EF3), but with winds now estimated to be about 152 mph (rather than 158-206 mph with the original F Scale). Total house destruction, however, will require winds of only about 170 mph, now EF4 rather than an F5 that was often previously assigned. Only the most strongly built homes might rate consideration for borderline EF5.
The actual tornado wind speeds, of course, have not changed -- just our estimates of them. Tornadoes are just as damaging and dangerous as ever! People still need to take tornado watches and warnings seriously and seek shelter in a safe place when a tornado is approaching.
Although the normally prime months for tornadoes, May through July, were quiet in 2006, December brought several unusual tornado events.
The most recent one was in Texas on Friday December 29th, where at least 23 tornadoes have been confirmed. One was a killer near Groesbeck in Limestone County, causing the first death there in any month since 1946.
Tornadoes are rare in Texas during the last week in December. Only one year in nine, on average, has had tornadoes in that week. In fact, this was the largest Texas tornado outbreak on record during the last week in December, with records going back to 1950.
The same weather system spawned two tornadoes in LA around sunrise on Saturday December 30th. Most of the tornadoes occurred from near College Station TX to south of Dallas-Fort Worth, as can be faintly seen in red triangles on the figure below.
The tornadoes occurred in a zone where a warm front, shown in red above, formed during the day. It's what I call a "limiting streamline" type of warm front. It formed where a cool, dry mass of air from the east collided with air from the southeast that had been warmed and moistened by passing over the Gulf of Mexico. That difference of staying over land or over water provided the air mass contrasts needed to generate a front. Arrows show the collision of these streamlines or air trajectories along that warm front.
This outbreak followed unusual Christmas-Day tornadoes in Florida (see my blog from December 28th), and an unprecedented outbreak of tornadoes in Pennsylvania on December 1st. The year ended with a bang!
As I write this on January 4th, another weather system is spawning tornadoes in Louisiana. Tornadoes there happen during the first week in January only in one year out of 10, on average. The last time was in 1999. I think we need a substantial cold-air outbreak to calm down this off-season tornado peril!
If you've ever caught the show before, you might have noticed that Steph and I have a little thing going...no no, not that kind of thing, a rivalry thing. We are both huge college football fans. She roots for the SEC and of course her Florida Gators. I root for the Big Ten and my Ohio State Buckeyes. It just so happens that they are playing each other for the national championship on Monday. We've kept the smack talk to a minimum so far but it is heating up. All I know is that she has given no love to the Big Ten all year and in head to head bowl games, the Big Ten is 2-0 against the SEC, so far. Not that I'm keeping track or anything.
With the most monumental of monumental games fast approaching, we decided to put a little wager on the game. If for some reason the football gods decide to allow Florida to slip past THE Ohio State University, then I will don Miss Abrams' Florida Gators hat while doing the Gator Chomp live on air. However, if the football gods decide that the best team shall win (OSU) then Miss Abrams will don my Ohio State sweatshirt live on air while chanting O-H-I-O! I can picture it now. It will be a Tivo moment for all time.
Who do you like in the game? Orange and Blue or Scarlet and Gray?