Severe Weather Events - When Weather Becomes More Than Just a Talking Point

I guess we all know what severe weather is. Fortunately there is no formal definition, so we can take it to mean, and include, just about anything that stops us in our tracks and makes us think "Now should I be going out in this?"

But I suppose I should be a little more specific.

Firstly, this is a big topic - too big for one page. So I'm restricting this page to severe weather events that mostly occur in the warmer months of the year. Check out Winter Weather for the storms, freezes and floods that are more typical of the cooler months. There is of course considerable overlap, but that's weather.

So let's include in severe weather anything out of the ordinary, expected range of daily events from Spring through to Fall that could, if we didn't prepare adequately, be hazardous to our lives and property. Our definition is still wider than National Weather Service's definition of severe thunderstorms - storms which produce any one of

• A tornado
• Damaging winds, or winds measuring 58mph (93kph) or more
• Hail 3/4 inch (1.9cm) in diameter or larger

If you have a good home weather station, among the most interesting projects are observing the often rapid changes in wind speed and direction, air pressure, humidity and temperature in advance and during an extreme or severe weather event. The rate and total of precipitation can also come up with some surprises.

Even more worthwhile is being able to predict severe weather in advance of the weather office. That's not all that easy these days, with the improvements in equipment, facilities and modelling available to meteorologists, but it's fun trying. And it's not cheating to step beyond your own home weather resources and consult the fascinating information derived from weather radar and satellite images.

Remember also that the average person today has access to more information than was available to professional meteorologists only a decade ago. You, of course, being above average and possessing your own weather station, are even better off.

But you can do far more than just record the changing weather. Numbers on a screen tell their own story, but that story becomes far more interesting and dramatic if accompanied by descriptions of what is happening outside.

And I'm not talking about just words. Just imagine how much more interesting the record of a passing severe weather event, such as a storm would be if it included descriptions of cloud types, the effect of wind, rain and hail, and a summary of any damage to your area.

Take it a step further and include photos, video, on the spot audio recordings, and screen prints of critical radar or satellite images and you have a fully documented multi media coverage.

Now this may get you a reputation as a weather geek, but I guarantee that you'll get a much greater adrenalin rush than you are ever likely to experience on a golf course.

Perhaps just a little word of caution here. It's very easy to get carried away with weather watching, particularly when major weather events are developing with great rapidity. Unfortunately severe weather comes with its own risks to life and property, and a contingency plan for protection of your family, your property and yourself is a great idea. Before you get too involved in watching a particular severe weather event develop, spend a few moments taking care of everything valuable to you. And keep in mind that the time may come for you to head for cover, so put your weather station receiver onto battery power, and wait out the storm safely, knowing that there will always be another opportunity.

OK, enough of this preambling.

Severe weather can be divided into several categories, related to the driving force behind the events. So in order of decreasing destructive potential, here we go. Most of the links in the following section will take you to more detailed articles on the weather types.

Now anyone who's searched the net looking for severe weather related topics will know that the amount of material is huge, particularly when hugely destructive phenomena like tornadoes and hurricanes are included. I can't hope to cover all the information available, but I can suggest the better sites where you can find out what you want to know.

In general, the first places to look are the official weather sites, which do an excellent job in providing educational and background information. In the USA visit NOAA and its weather sites such as the National Weather Service and the Storm Prediction Center. My aim in these pages is suggest ways in which you can make the most of the capabilities your weather station gives you when severe weather events come your way. Although I am sure you already have a good weather knowledge, by focussing on understanding the progress of extreme weather through an area I hope to be able to add a little more to your experience than just facts, figures and news reports.

Major Weather Systems

Included here are large weather systems that can last for days as they develop, approach and pass over an particular place. They are typified by a central zone of intense low pressure, usually form over oceans or large seas, and make themselves felt in strong destructive winds, often flooding rain, and abnormally high tides in coastal areas.

When they form in tropical areas they are known as Hurricanes, Typhoons or Cyclones, depending on which part of the world you are in. Most of them remain at sea until they degenerate, acting as a hazard to shipping, aircraft, and the odd island. But when they come ashore their full power is apparent to all. They are so significant that they each have their own name.

Almost as destructive, but with less of a publicity team behind them, are the intense lows that form in more temperate areas ("The Perfect Storm"). Because they form in cooler seas, the energy going into them is less, and they are overall less destructive than hurricanes and their relatives. But it's only a matter of degree, and their effects on coastal areas can be just as dramatic.

Many of these occur during or on either side of winter, and information on them is included in the Winter Weather pages.

Tornadoes and Thunderstorms

Truly severe weather, thunderstorm related events are smaller than the large intense lows discussed above, form much more quickly, are far more common, and frequently more destructive.

The large and spectacular Thunderstorms usually form on the boundaries of large airmasses when warm humid air rises over an approaching mass of colder or drier air. When large storms rotate, they are called supercells and it is these that are most likely to produce the most severe weather conditions, including;

• Tornadoes. Tornadoes, although they occur world wide, are just as typical of America as apple pie. Their formation is controlled by an unusual combination of climatic conditions which often develop in mid continent North America, particularly in Spring.

• Downbursts and Microbursts. These local thunderstorm phenomena, are outward, often invisible bursts of cool air and can result in tornado like destruction. Microbursts are less than 2.5 miles (4km) in diameter, and have been responsible for several aircraft landing disasters.

• Derechos. Another almost exclusively North American thunderstorm feature, a Derecho is a straight line wind with severe gusts associated with rapidly moving lines of thunderstorms and extending over a large area. Although not as spectacular as tornadoes, derechos give little warning and can be just as deadly.

• Waterspouts. Similar in appearance to tornadoes, waterspouts are often less destructive. They form over water, and their appearance may be due to water vapour forming around the central very low pressure zone rather than to water being lifted from the surface. Best not to take too many chances though.

• Hail. Hail is frequently associated with larger thunderstorms, particularly supercells, and becomes very dangerous and destructive when hailstones reach golf ball size and larger.

• Flash Floods Thunderstorms can deliver a lot of rain to a small area in a very short time. Local flash flooding is often the result. Slow moving supercells may result in more regional flooding. Longer lasting river system Floods are the subject of another article.

• Lightning Unlike the examples of severe thunderstorm weather listed above, which may or may not occur in any particular thunderstorm, lightning is always present - no lightning, no thunder, no thunderstorm

Other events

Also associated with the summer storm and hurricane seasons are long term heat related events, including droughts, heat waves and fire weather. More information on these can be found in the Hot Weather Pages.

Other occasional severe weather examples are strong winds, dust storms and volcanic ash clouds. Neither of the latter two are strongly related to weather conditions, but the effect and area of incidence of both can be monitored and predicted by forecasters.

Dust storms are usually associated with bare soil caused by drought, and can be reduced in frequency and intensity by careful land management.

Volcanic ash clouds are rare, but of more than passing importance to those downwind of the volcano, as residents in the vicinity of Mount St Helens will clearly remember. Ash clouds are also critical to long distance aviation - high concentrations of very fine suspended dust will stop jet engines, at least until the plane loses enough altitude to regain clear air.

Not much of a problem to you and me, perhaps, but I'm sure it would concentrate the mind of an unfortunate passenger.

In conclusion, severe weather events can be costly in lives, property, and disruption to normal activity. And while forecasting of both extreme and normal events has improved markedly over the last 20 years, rapidly developing weather can still keep forecasters on their toes.

And observation of severe weather provides periods of high interest to those with their own weather stations, particularly when the recorded data can be tied into visual observations as the event builds, peaks, and passes.

Just a brief word about the photos you will see in the articles connected to the links scattered throughout this page. I have selected illustrations from NOAA's huge Photo gallery to show both the type of weather and something of the history of research and observation contained in these collections. As much as possible they include historic material, such as the first image of a hurricane acquired from a satellite. I hope you like them, and there are plenty more at the NOAA Photo Library site.

If you have records of a severe weather event from your area, particularly if backed up by your own observations, I would love to hear from you. Just use the Contact Us button.

This link will get you to some reviews about the better Home Weather Stations available at the moment.

And as an aside, for some tips about preventing or minimizing severe weather damage to your home, visit this Home Protection page.

This link will take you back to the Top, or, when you're ready, here's how to return to the Home page.

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