Calm Before The Storms

The recent severe weather in the southeast and midwest has subsided, at least for now. Here in Colorado, we have not seen many violent storms so far in 2011. What is the reason for this? One probable culprit is La Nina. While most of us meteorologists caution against blaming local weather patterns on global phenomena, in this case I feel the need to point to La Nina for our unusually calm and cool May.

NOAA and the National Weather Service do an amazing job of tracking the El Nino/La Nina pattern. The latest data shows that La Nina is continuing to weaken, and sea surface temperatures in the eastern Pacific are rising. For most of the early spring 2011, the Jet Stream was draped across California and on through the southern parts of the USA. This gave Colorado some much-needed moisture, and cool temperatures. All that is about to change.

As La Nina continues to weaken, we can expect the Jet Stream to be pushed farther north, with expanding high pressure over the Great Basin. For Colorado, this has several important implications. First, we should see temperatures begin to warm rapidly. This will melt the significant snowpack in the mountains, and could cause river flooding. Second, weather disturbances may dip across northeast Colorado from the Pacific Northwest, causing an increase in thunderstorms over the plains. This means wind, rain, hail and possibly tornadoes.

Colorado's peak severe weather season is late May through the end of June, however we can experience severe thunderstorms all the way into October. Most of the latest data on La Nina points to more precipitation over Colorado as we head into June.

This is good news for storm chasers, such as myself. Those of us who venture out onto the plains in the spring and summer to photograph and video severe weather are looking forward to the month of June. One important caveat to this is my personal hope for the safety of everyone on the plains. Most storm chasers do not want to see people hurt or killed, or property destroyed. I even worry about livestock exposed to hail and lightning.

If you've been intrigued about this year's EF-5 tornadoes in the south and midwest, you may be thinking about going out on your own to chase thunderstorms this summer. I'm going to repeat some information I posted here in 2009 about "Safe Chasing":

1.) Learn all you can about severe weather before you go out.

2.) Chase with an experienced partner.
3.) Do not stop on the road. Slow down and pull way off to the side.
4.) Use your flashers when stopped on the roadside.
5.) Do not speed through small towns. Besides the possibility of running over a
small child, local law enforcement is usually wary of storm chasers and they will bust you.
6.) Avoid eating while driving. This is an unnecessary distraction.
7.) Do not text or blog while driving. Yes, I have seen chasers doing this!
8.) Get a hands-free cell phone headset or earpiece. You need both hands to drive.
9.) Don't core punch your first time out.
10.) Save your camera and video recorder for when you stop.
11.) Watch the other chasers and drivers around you.

12.) If someone is driving recklessly, report them.

Those of us who have years of storm chasing experience are not trying to discourage new chasers. What we are trying to do is keep you, and everyone else, safe.

Whether you are interested in chasing storms or not, you should be very aware how fast Colorado's weather can change. If you check the forecast once a week, you are going to miss some important information. We at Channel 7 keep a very close eye on changing weather, and we encourage you to watch our weathercasts, and check our website every day for the very latest information and safety tips. I can be reached at steve.hamilton@mac.com if you have any questions at all.

Thanks!

What Happened In Joplin, MO?

The strength and violence of the Joplin, MO tornado that hit last Sunday raises some important questions for safety planners and residents who live in tornado-prone areas. These questions are: Finding adequate shelter, and believability of tornado warnings.

The National Weather Service issued a "Tornado Warning" for the Joplin area 23 minutes ahead of the first reported touchdown. This gave residents a decent amount of time to find adequate shelter. The questions then become, "What is adequate shelter?" and "Is this a real tornado, or another false alarm?"

In my opinion, the NWS did a great job of providing adequate lead time for the local residents. Sirens were blaring over 20 minutes ahead of the disaster. We can explore the above issues a bit further by simply looking at the images of the devastation. One challenge is, how often does this magnitude of tornado hit any one particular area? We haven't seen one single tornado do this kind of damage, with so much loss of life, since the 1950s. For every EF-5 tornado that hits a populated area, there are hundreds of others that pass harmlessly around big towns and cities. This fact can cause disbelief or denial amongst people in highly-populated areas. I saw one interview on CNN where the victim said "I never thought this could happen to me."

As a meteorologist, and a broadcaster, this is one of the most troubling things to hear from people. Now we know, these things can happen to anyone living in a tornado-prone area.

So, those of us who communicate severe weather warnings to the public have to keep in mind how we address the issue to those who are listening and watching on radio and TV. My observations have shown the range of human emotions in life-threatening weather, including fear, apathy, wonder, disbelief and denial. It's important that people facing powerful weather understand the dangers, and understand that tornadoes do not choose who they affect. Tornadoes are pure acts of Nature, indiscriminate in their destruction. Getting people to believe this fact is another story, and raises an entirely new set of issues, which I will address in my next posting.

The other point that has been on my mind is 'adequate' shelter. At least some of the broadcasters and meteorologists in the Joplin area were telling people that they must seek shelter underground. EF-5 tornadoes have wind speeds of over 200 mph. We are talking about winds that are moving debris at the speed of an Indy race car. Humans cannot survive such an environment without 'adequate' protection. What is adequate protection from an EF-5?

Tests have been done for years with cannons and 2x4s against various types of housing. A piece of wood propelled at 200 mph easily penetrates drywall, press-board, most housing siding and even brick walls. The typical home is constructed of exactly these same materials. Additionally, the power of EF-5 winds will often completely remove residential homes from their foundations and destroy them in-flight, along with anyone in them.

I personally had the chance to view the damage done by the Greensburg, KS EF-5 tornado from May 4-5, 2007. Even though the death toll was much lower, the damage was just as great. I saw many concrete pads completely scoured, houses thrown into the air and dropped many yards away with vehicles on top of them, coins buried deep into tree trunks. Again, EF-5 forces are not survivable by humans, unless there is adequate shelter.

Simply put, being above ground during such a powerful tornado is a death sentence. Generally 'adequate shelter' from an EF-5 means being under ground, supposedly in a basement. Even this is no sure-fire guarantee of safety because the structure above the basement can collapse into it if the roof is removed. So, then we are talking about a basement with some sort of heavy structure in it, allowing the occupants to crouch under and avoid the wind-driven debris, and then whatever falls into the basement following the tornado.

Trailer homes and automobiles of any kind, including large trucks and SUVs are completely unsafe in almost any strong tornado, let alone an EF-5.

Many homes in the Joplin area, to say nothing of the rest of the Midwest, do not have basements. Some have crawl-spaces, but due to the high water table, sometimes a basement is not practical. What then? There are companies now that make 'safe rooms' that are designed to withstand the forces of 200 mph winds and debris, yet are located above-ground. Some people without basements are having these installed. They essentially consist of a large concrete block with a steel door. People get inside and ride out the storm. I've seen images of a concrete foundation with nothing else on it except the safe room. Unfortunately, these types of structures are not affordable by everyone, to say nothing of folks who occupy trailer homes in parks that do not provide concrete or underground safety areas.

It may seem that all I've done here is raise a lot of questions and concerns. This, to me, is a good place to start. In my next posting, I'll share some research on safe rooms and the power of strong tornadoes, and what makes them tick. Thanks.

2011: The Year Of The EF-5

Greetings, storm chasing enthusiasts. I hope you will understand that my excitement for the new storm season is tempered with the ever-growing casualty lists from towns across the South and Midwest. When I chase storms and tornadoes, at the forefront of my mind are the people under those storms who are losing property, and sometimes their lives. We must remember to keep everything in perspective about what we are doing out there. While storm chasers are vital in documenting meteorological occurrences, in my opinion it is critical for all storm chasers to maintain a certain level of stoicism regarding the destruction wrought by storms. (Photo credit: www.tornadovideos.net)

There has been much criticism of a video released last week documenting the Joplin, MO tornado, where chasers are heard yelling profanity-laced descriptions in the background. Granted, that tornado was huge, and bound to generate excitement. However, many professional and scientific chasers thought the verbiage was inappropriate, considering how many people lost their lives in Joplin, (125 as of this posting). I will tell you from personal experience that it is difficult to control one's emotions in the presence of such violent weather, so I see both sides of the issue. As storm chasers, we have to decide what is, and more importantly what is not, appropriate behavior, when we release storm video.

2011 is on track to become a record tornado year for the United States, not only in the number of tornadoes, but also in the number of EF-5s being recorded. The Joplin tornado was upgraded to an EF-5 yesterday (May 24, 2011).

If you are unfamiliar with the "Enhanced Fujita" or EF scale, please hit this link:
http://www.spc.noaa.gov/faq/tornado/ef-scale.html

Several EF-5s were recorded in last month's outbreak across Alabama, Tennessee and Georgia.

Why are this year's tornadoes so violent? First, the interaction between storm systems and the Jet Stream has made for several outbreak situations in recent weeks. Often in the early to mid spring, the Jet Stream is still far enough south to coincide with the passage of low pressure and frontal systems. The Jet Stream is a major player in thunderstorm evolution. If we get an active Jet Stream flow (50 knots or higher) above an area primed for thunderstorm growth, some of the major storm elements become enhanced. Speed and directional shear, and lift, are increased by strong Jet Stream winds. In the case of the recent tornado outbreaks, the Polar Jet, which circles the Earth at 7-12 km (23,000 - 39,000 feet) and separates major cold and warm air masses, was present. Digging further into this phenomenon, there were significant "jet maxes" crossing the prime thunderstorm areas during the outbreaks. A jet max is an area of particularly strong winds, embedded within the Jet Stream itself, say over 110 knots. In meteorology, we divide jet maxes up into quadrants, so picture an oval divided into quarters. In the left-front and right-rear quadrants of a jet max, we often see enhanced lift and shear.

The recent weakening of the La Nina phenomenon in the Pacific may also be a contributor. During La Nina springs, a large ridge forms over the western USA, serving to push the jet stream farther north. La Nina has weakened significantly in recent weeks, and the Polar Jet Stream has stayed far to the south. This means the Jet has been crossing the Deep South and the Southern Plains, and interacting with thunderstorms more frequently than usual.

Strong Jet Stream winds in the vicinity of large thunderstorms serves to enhance lift by evacuating air from the top of the thunderstorm. This air must be replaced with something, and often air is pulled from below, thereby enhancing lift. Shear is also enhanced because the Jet Stream usually provides strong southwesterly winds in the mid and upper levels. Combined with adequate surface winds from the southeast, the two wind vectors cross each other and give a "twist" to the atmosphere within a thunderstorm, enhancing growth and severity.

Many storm chasers I speak with are expecting a very active June for Colorado's eastern plains. We will be out there, providing images, video and accounts of whatever takes place.