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
