Quotes

“You must have been warned against letting the golden hours slip by; but some of them are golden only because we let them slip by.” James M. Barrie

“I saw the angel in the marble and carved until I set him free." Michael Angelo

Tuesday, February 7, 2012

The Ingredients

For endless reasons, weather has always been a major issue in the aviation industry. It's hard to predict, it's hard to understand, it's continuously underestimated, and it constantly poses a threat to anybody. Whether you are on the ground or in the air, weather will be there and it will affect you. According to the National Weather Service (NWS), weather has been responsible for an average 543 deaths in the United States each year for the past 10 years; about half are aviation related.

Normally, teachings in flight schools about weather, go only as far as the basics. Pilots learn how to interpret charts, read the undecoded, and understand the theory to some extent. What many pilots don’t learn is the details of how the weather phenomenon forms and comes to be as it is. Knowing what specific factors or “ingredients” are needed for the formation of an affecting weather phenomenon, will not only help pilots have a greater understanding of the theory, but also to have a better overall picture and know what to expect.

Thunderstorms often present some of the most hazardous conditions. They are responsible for damaging hail, heavy rain, icing, tornadoes, lightning, and turbulence in many forms, including downbursts. Normally, there a 2 categories of thunderstorms: Air-Mass Thunderstorms and Severe Thunderstorms.

Air-mass thunderstorms are isolated thunderstorm cells showing little organization that form in a maritime tropical air mass (warm and moist air mass). They are the most common type of thunderstorm and usually form as a result of daytime surface heating in areas of very little to no vertical wind shear. Vertical wind shear is the change in speed and direction of wind with increasing altitude.

Severe thunderstorms are the strongest type of thunderstorm and form in areas of strong vertical wind shear. These are most commonly found along or ahead of cold fronts and often show more organization. Unlike air-mass thunderstorms, severe thunderstorms are longer lasting, sometimes forming as a result of contrasting air masses, can spawn tornadoes under the right conditions, and present more hazardous conditions to both aircrafts and people on the ground.


Seven various ingredients are needed in creating a severe thunderstorm; these are:

1.   Wind shear
The foundation of a severe thunderstorm is dependent upon wind shear. With vertical wind shear, wind speed increases abruptly and changes direction with height; this gives a severe thunderstorm a tilt that helps to fuel the storm thus increasing its life span. The tilt creates updraft (rising air) on a section of the thunderstorm and downdrafts (sinking air) on sections where precipitation occurs. The updrafts and downdrafts side-by-side work together to increase the life span, generate hail and sometimes create tornadoes. Tornadoes occur when horizontal and vertical wind shears near the surface work together to spin and tilt columns of air.

Air-mass thunderstorms, on the other hand, form with little to no wind shear and therefore have a tower-like shape with no tilt and no chances of tornadoes. Without wind shear, a thunderstorms would be classified as air-mass thunderstorms.

2.   Contrasting air masses
Tornado Alley is an area of the United States known for its amount of tornadoes each year. Severe thunderstorms in that area are very common. One of the reasons why severe thunderstorms occur at this location is due to 2 contrasting air masses that interact in that very region causing strong fronts. Strong fronts are ideal lifting mechanisms for the formation of powerful long-lasting thunderstorms. Due to the differences in moisture levels, dry lines form causing the most hostile conditions.

3.   Low level moisture
In Tornado Alley, warm, moist air coming from the Gulf of Mexico to the south, lower in the atmosphere, brings the high levels of moisture. Moisture is needed for the formation of storm clouds since it is one of the things that fuels thunderstorms. The higher the moisture levels, the more powerful a thunderstorm will become.

4.   Cold, dry air above
Cold, dry air from the northwest also comes to Tornado Alley. Cold air is essential for strengthening a thunderstorm. The colder the air above than the air below, the more unstable the conditions become due to a higher decrease in temperature with altitude and strength of the cold front’s lifting mechanism.

5.   Low level jet
Low level jets are also needed for the formation of wind shear. A low level jet is a rapidly moving stream of air at lower levels in the atmosphere. In Tornado Alley the low level jet brings the warm, humid air from the gulf that helps fuel the storm.

6.   Upper level jet
An upper level jet bringing the cold, dry air from the west at high speeds is also necessary. The jet stream is a continuous rapidly moving stream of air. Pressure differentials at the surface sometimes accelerate a section of the jet stream, called jet streaks; as a result, jet streaks curve and speed up. This is a sign of strong upper level divergence and low level convergence in the area of low pressure at the surface. This means more unstable conditions and increase updraft strength to form severe thunderstorms.

7.   Upper level trough
A trough is an elongated area of low pressure. When there is an upper level trough, strong upper level divergence exists upstream (east side in the northern hemisphere) of the trough, a factor that contributes to strengthening the lifting mechanisms of the surface low pressure center and the updraft strength in a severe thunderstorms. Usually, one can expect stormy weather upstream of an upper level trough. 

Now that you know the basics of the ingredients, I encourage you to do a little more research. There are actually 3 ways in which severe thunderstorms organize themselves: Squall Lines, Multicell Thunderstorm Complexes, and Supercell Thunderstorms. The most common severe thunderstorm is the Squall Line and the rarest is the Supercell Thunderstorm (most powerful).




Quote:
"The more man meditates upon good thoughts, the better will be his world and the world at large." Confucious