Saturday, April 16, 2011

Severe Weather Awareness Week

The spring season is anxiously awaited by many. Snow begins to melt. The white landscape slowly matches the colors of your imagination. But possibly most welcome, conditions begin to warm. However, the weather begins to turn volatile during this stormy season. As the warm air from the south begins to interact with our cold, Wyoming air, the atmosphere begins to become more unstable. With instability comes thunderstorms...and with thunderstorms comes potential tornadoes. April is in fact the 4th most tornado-filled month climatologically (source) between 2003-2005. So we must become aware of the severe weather that begins to form during Spring.

Severe weather awareness week for Wyoming will last from April 18-22. As of April 15 of this year: 333 tornado reports & 5 deaths due to tornadoes (source). Combine this with the damage severe weather brings with hail & strong winds, it is imperative both forecasters and the public work together to keep society safe. Here a few topics to keep you more informed and prepared during this season:

1 - What is the difference between a watch and a warning?

Both watches and warnings are issued by the National Weather Service (NWS) to inform the public of impending severe weather weather. There is a substantial difference between the two that is generally determined by the timing of the storm's development. Here are the official definitions from the NWS: 
A WATCH is used when the risk of a hazardous weather or hydrologic event has increased significantly, but its occurrence, location, and/or timing is still uncertain. It is intended to provide enough lead time so that those who need to set their plans in motion can do so.
A WARNING is issued when a hazardous weather or hydrologic event is occurring, is imminent, or has a very high probability of occurring. A warning is used for conditions posing a threat to life or property.
2 - What does it take to form a thunderstorm?  

Thunderstorms take many different shapes and forms. There are multiple classifications. They will be studied for years and years and thousands form across the globe every single day. With all of this going for them, thunderstorms generally need only three things to form: (1) moisture, (2) instability & (3) something to force lifting.

The instability (2) will most often develop as a result of something we see and feel every single day: sunshine (also a suitable lifting mechanism). As solar radiation heats the ground beneath our feet during a spring/summer day, an unstable atmosphere forms. Air is able to lift freely if warm air is BELOW colder air. This simple relationship causes instability. If a suitable amount of moisture (1) is combined with the warm air at the surface, clouds begin to develop as the air is forced up. Finally, we need some strong force to really force the air upward (3), developing a thunderstorm in the process as the moisture begins to condense. A front will usually do. But a sunny day or a mountain-like barrier will do as well. 

You can visualize this by thinking of a simple teapot on a stove. The stove heats the water in the pot (making the moisture in the pot warmer that the air above it). Whoa, instability in your own home!!! After time passes, the hot, boiling water rises due to evaporation within the pot. The the gaseous form of water condenses into a "cloud" out of the teapot (when you hear that whistling noise telling you the water is ready). Essentially, this is the same prosses that forms a thunderstorm.

3 - When do you seek shelter and what to do to prepare?

Warning the public of severe weather has dramatically improved in recent decades. This has come with the inventions of radio, internet and TV. So having access to a weather radio will come in handy. Also viewing your local weather broadcaster early in the day will prepare you if thunderstorms could develop later that day. You will obviously want to take shelter when a strong cell is in the path of your home. The center-most room within the lowest floor of your house free of windows is the safest place to be. If you're in a pinch, a bathtub may do. But you will want to get yourself and others in the center of your basement or tornado shelter.

Your best judgment becomes more important if your notice a tornado while you're driving. If the tornado is far enough away from you, you will want to drive away from the tornado, PERPENDICULAR to its path towards clear skies. If the tornado forms close to you, the best option is to get out of the car and lay on your stomach within a ditch or some other surface that slopes downward.

Busting the myths:
   1 - Do not spend time opening all of your windows in your home
   2 - Possibly the WORST cover you could take from a tornado is under a bridge or highway underpass!!!
   3 - Second-worst is a mobile home. They do not physically attract tornadoes, but those mobile home parks are often called tornado-magnets.

4 - Lightning 101 

Generally, there are three types of lightning: Intracloud, cloud-to-cloud and cloud-to-ground. Obviously, the one most of us are concerned about is the lightning that reaches the ground. I will not go into lightning development (possibly a later blog). Rather, I will spend time here helping you stay safe. 

You can use lightning and thunder to your advantage when judging a thunderstorm's path. Since lightning travels at nearly the speed of light, it is faster than the speed of sound (thunder in this case). You can use a simple 5 second rule to judge if a thunderstorm is traveling towards or away from you. Right after you see a bolt of lightning, start counting. When you hear the thunder arrive after, stop. Thunder travels approximately 1 mile in 5 seconds. So if there is a 5 second difference between the lightning and thunder, you can approximate the storm is 1 mile away from you. If the time between a successive lightning-thunder combination decreases, then the storm is traveling towards you.

If you do see lightning or hear thunder, whether the storm is traveling towards or away from you, I strongly recommend you take shelter asap. This means a solid building. Places you do not want to be include: out in the open, under trees, near water, on a golf course (seriously), or anywhere that makes you the tallest object. If you are near a car, get in it! The lightning's electricity will pass through the car, keeping you safe. If you are caught outside, there is a last resort. You must crunch down to your knees, while still on your feet (don't lay on your stomach). Look strait to the ground and wrap your arms around your knees. You will need to do this quickly because you may have only a few to seconds to react. Once you feel static electricity pass through your body while caught outside, this is the only safe defense you have from the lightning. Another clue you will have before you know you will be struck is: you'll notice your hair on your arms and head standing up towards the sky.

One final note on lightning-safety, there is something called "bolt from the blue." This refers to lightning that travels through clear skies. Lightning is capable of traveling dozens, possibly hundreds of miles. Even after a thunderstorm passes, I strongly urge you from going back outside until 30 minutes from the last bolt has passed. Lightning kills nearly 60 people per year (source). Please be sure you don't become a statistic.

5 - Other Sources

A future blog will go in depth on the sources I use to forecast. However, I will direct you the National Weather Service's sources strictly on Severe Weather Awareness. Severe weather is upon us. Soon Wyoming may see severe thunderstorms and tornadoes develop. We must all stay safe. Do not overlook the power of weather. The moment we take it for granted may be the moment it affects you the worst.


Stay safe and have fun!

Joe Hansel
KCWY News13 meteorologist
Casper, WY