Download weather forecasting to predict tornados

WEATHER FORECASTING TO PREDICT TORNADOS
Meteorologists collect data about current weather condition from a widespread system of
observing stations (global weather data are collected at more than 1000 observation points
around the world).
All forms of forecasting make use of numerical data such as temperature, atmospheric
pressure, and humidity.
The trend method is based on the knowledge that weather conditions are strongly influenced by
the movement of air masses and by the existence of similar maps in the past.
ISOBARS
Isobars are lines that connect points of equal pressure on weather maps. The word originates
from Greek, where isos means equal and baros means weight. The isobar lines are always
referred to sea level.
An important consequence of air pressure differences is wind, because wind blows from areas
of high pressure to areas of low pressure. The greater the pressure contrast and the shorter the
distance, the faster the wind will blow, so closer isobars mean faster wind.
Isobars are useful for weather analysis or forecast. We can expect the winds blow from high
pressure to low pressure, but because of the effect of the rotation of the earth, in the Northern
Hemisphere the winds tend to blow clockwise round an anticyclone (area of isobars surrounding
a high-pressure area) and anticlockwise round a cyclone (area of isobars surrounding a lowpressure region). South of the equator the situation is reversed.
AIR MASSES AND FRONTS
An air mass is an extensive body of air that has a relatively homogeneous temperature and
humidity content over a significant altitude.
A front is the boundary at which two air masses of different temperature and moisture content
meet.
Certain locations on the earth's surface possess the topographical characteristics that favour the
development of air masses. The two most important of these characteristics are topographic
regularity and atmospheric stability. Deserts, plains, and oceans typically cover very wide areas
with relatively few topographical irregularities. In such regions, large masses of air can
accumulate without being broken apart by mountains, land/water interfaces, and other features
that would break up the air mass. The absence of consistent wind movements also favours the
development of an air mass.
The movement of air masses across the earth's surface is an important component of the
weather, they can bring with them cold temperatures, strong winds, and heavy precipitation.
When a mass of cold air comes into contact with a warm air mass, the cold air mass may force
its way under the warm air mass, because the cold air is denser than the warm air. The boundary
formed between these two air masses is a cold front.
Cold fronts are usually accompanied by a falling pressure and the development of large
cumulonimbus clouds that bring rain showers and thunderstorms. Cold fronts are represented on
weather maps by lines that contain triangles at regular distances along them. The direction in
which the triangles point shows the direction in which the cold front is moving.
A situation opposite to the preceding is when a warm air mass approaches and slides up and
over a cold air mass. The boundary formed in this case is a warm front. As the warm air mass
meets the cold air mass, it is cooled and some of the moisture condenses to form clouds.
Warm fronts are designated on weather maps by lines with half circles. The direction in which
the half circles point shows the direction in which the warm front is moving.
In some instances, the collision of two air masses results in a stand-off. Neither mass is strong
enough to displace the other, and essentially no movement occurs. The boundary between the
air masses in this case is known as a stationary air mass and is designated on a weather map by
a solid line with triangles and half circles on opposite sides of the line. Stationary fronts are
often accompanied by fair, clear weather, although some light precipitation may occur.
THUNDERSTORMS
Thunderstorms happen quite often in summer, but in fact they can happen at any time of the
year.
The main things a thunderstorm needs are damp air near the ground and a layer of much
colder air above it. The Warmer air rises, taking water vapour with it. The water vapour
condenses into water droplets, making a cloud. The water vapour in this air condenses to form
more water droplets as it rises and cools. When water vapour condenses, it releases latent heat.
This warms the air and forces it to rise more vigorously, strengthening the storm. The cloud
grows and rises up to 10 km high. Even in summer the air at 3 km or so is so cold that water
freezes. The top of the cloud is made of ice crystals.
The streams of cold and warm air flowing past each other in different parts of the cloud produce
electrically charged particles (ions) due to friction. The top of the cloud becomes positively
charged, the bottom becomes negative and there is a huge voltage between the cloud and the
ground. A lighting flash starts with a fairly small current that jumps between different parts of
the cloud or between the base of the cloud and the ground. As it does so it makes more ions.
This allows a much bigger current to flow, which usually goes from the ground up to the cloud.
This “return stroke” may carry a huge current, possible 10 000 amperes. It last less than a
thousandth of a second.
TORNADOS
Tornadoes are the most violent of all wind storms. A tornado occurs over land and is a
revolving cyclonic storm. It has a fairly small diameter, but has a high intensity. A tornado
appears as a funnel extending out from the cloud base (vortex). A tornado hangs from the
bottom of a single thunderstorm. In their early and mature stages, all thunderstorms are
characterized by rising air, called updrafts. These updrafts supply the warm, humid air that
fuels thunderstorms. Often, a tornado is located on the edge of the updraft, next to air that's
coming down from the thunderstorm with falling rain or hail. This is why a burst of heavy rain
or hail sometimes announces a tornado's arrival.
The centre of the tornado's vortex is a low-pressure area. As air rushes into the vortex, its
pressure lowers, which cools the air. Cooling condenses water vapour in the air into the
tornado's familiar funnel-shaped cloud. As the swirling winds pick up dust, dirt, and debris
from the ground, the funnel turns even darker. Twisters that pick up little dirt can retain their
white, cloud coloration. Some tornadoes have taken on a red hue by picking up red dirt.
Although the air is rising in a tornado, the funnel itself grows from the cloud toward the ground
as the tornado is forming. The term "funnel cloud" refers to a tornado-like vortex that doesn't
reach the ground. When a funnel cloud touches the ground, it becomes a tornado.
The ingredients are: a big thunderstorm; winds blowing from opposite directions; and a strong
updraft. Strong updrafts surge up through storm clouds, these clouds will become a severe storm
capable of producing tornadoes only under certain circumstances. Severe storms are often
associated with a very unstable atmosphere and moving low-pressure systems that bring cold air
into contact with warmer, more humid air masses. A tornado can form when the air in these
updrafts begins to rotate as opposing winds cause the storm to start spinning.
The exact mechanism of tornado formation inside severe thunderstorms is still a matter of
dispute, but it appears that tornadoes grow in a similar fashion to the small vortices that form in
draining bathtubs. Tornadoes appear to be upside down versions of this phenomenon. As
updrafts in a severe thunderstorm cloud get stronger, more air is pulled into the base of the
cloud to replace the rising air. Some of this air may be rotating slightly since the air around the
base of a thunderstorm usually contains some rotation, or vorticity. As the air converges into a
smaller area, it begins to rotate faster due to a law of physics known as the conservation of
angular momentum. This effect can be seen when an ice skater begins spinning with arms
outstretched. As the skater brings his or her arms inward, his or her rotational speed increases.
In the same way, air moving into a severe storm begins to move in a tighter column and
increases its rotational speed. The rapid air movement causes the surrounding air pressure to
drop, pulling more air into the growing vortex. The lowered pressure causes the incoming air to
cool quickly and form cloud droplets before they rise to the cloud base.
Tornadoes are also relatively small. An average tornado will be 400 to 500 feet wide and travel
four or five miles on the ground, lasting only a few minutes. A mile-wide tornado is an
extremely large one and tornadoes this big is rare. Many tornadoes are small, less than 100 feet
wide, and last only a few minutes. Winds rarely exceed 250 mph and most tornadoes have
winds of less than 112 mph. In a few cases, the vortex becomes a strong tornado with wind
whirling around at speeds close to 300 mph.
Although tornadoes occur in many parts of the world, these destructive forces of nature are
found most frequently in the United States east of the Rocky Mountains during the spring and
summer months. The United States is the tornado capital of the world with an average of 700
tornadoes per year. The U.S. has this many tornadoes because of west winds. Winds from the
west are forced to stream over the Rocky Mountains. On the other side these winds encounter
the low, warm, moist winds from the Gulf of Mexico. These two air masses collide over the
central U.S and provide the possibility for tornado development. That's why Kansas had more
than 1200 tornadoes from 1953 to 1980 while Alaska only had one.