Download Wind-speed maps - Red Lodge Public Schools

Wind-speed maps
MAP:
http://www.weather.com/maps/maptype/currentweatherusnational/uscurrentwi
ndsgusts_large.html
QUESTIONS





Explain the main cause of winds.
Why are some winds stronger than others?
What is the Coriolis Effect?
How does wind effect the weather?
How are winds named?
The air in the atmosphere is made up of a number of gases. These gases press down
on the Earth’s surface, exerting a force that we call atmospheric pressure or air
pressure. Yes, air has weight, and probably more than you think. In fact, the weight
of the air on your desk at school weighs about 11,000 pounds. That’s about the
same weight as a school bus! Since air pressure pushes in all directions, the air
pressure pushing up from under your desk balances out the air pushing down on it,
so the desk doesn’t collapse under the weight.
What causes Air Pressure?
Air pressure depends on the density of the air, or how close together its molecules
are. You know that a hard rubber ball is more dense than a Styrofoam ball and that
ice cream is more dense that whipped cream. Air lower in the atmosphere is more
dense than air above, so air pressure down low is greater than air pressure higher
up. Temperature also makes changes in air pressure. In cold air, the molecules are
more closely packed together than in warm air, so cold air is more dense than warm
air.
Each layer of air presses down on the layers below, and so the greatest pressure is
at ground level where we have the maximum amount of air above. In the
stratosphere air pressure decreases until it reaches about zero.
Changes in air pressure are caused by the difference in air temperature above the
earth. Land masses and areas of water change the temperature of the air above
them. These changes create wind and cause pressure patterns to develop. The wind
moves these pressure patterns and change as they pass over mountains, oceans, and
other areas.
Areas of high pressure can be caused when cool air is sinking and pressing on the
ground. When warm air rises, however, it causes a region of low pressure.
Regions of sinking air are called highs, high pressure regions, or anticyclones. Clear
skies and fair, dry weather usually occur in these regions.
Regions of rising air are called lows, low pressure regions, depressions, or cyclones.
Clouds, rain, and strong winds often occur in these regions.
Changes in air pressure bring changes in the weather and make winds blow. Air
usually moves from areas of high pressure to areas of low pressure, and this
produces winds. This can be easily remembered with the phrase: “Winds blow
from high to low!”
The greater the difference in pressure, the stronger the force of the wind. Also, if the
high pressure area is very close to the low pressure area, or if the pressure
difference is very great, the wind can blow very fast. Wind also blows faster if
there’s nothing in its way, so winds are usually stronger over oceans or flat ground.
Meteorologists can forecast the speed and direction of wind by measuring air
pressure with a barometer.
Wind Direction
Although wind blows from areas of high pressure to areas of low pressure, it doesn’t
blow in a straight line. That’s because the earth is rotating. In the northern
hemisphere, the spin of the earth causes winds to curve to the right (to the left in the
southern hemisphere). This is called the Coriolis Effect. So in the northern
hemisphere, winds blow clockwise around an area of high pressure and counterclockwise around low pressure.
How Cold Do You Feel?
Wind makes you feel cooler, because it causes your body to lose heat faster. The
stronger the wind, the more heat is lost, and the colder you feel. Below is a table so
that you can figure out what temperature your body feels, called the Wind Chill
temperature.
How Does Wind Affect the Weather?
Wind direction will have an important influence on the expected weather. You can
often be given a wind direction and you will have a pretty good idea of how the
weather will change and what weather can be expected with that wind direction.
The typical wind direction that a location has for a certain time of the year is called
the prevailing wind. When the wind is from the prevailing direction then the
weather is generally typical. When the wind shifts away from the prevailing
direction, then it often indicates atypical or changing weather.
Wind shifting from the south often means warmer air is approaching and a wind
from the north often means cooler air is approaching. When the wind changes
abruptly it could be a frontal passage.
How are Winds Named?
In meteorology, winds are often referred to according to their strength, and the
direction from which the wind is blowing. Short bursts of high speed wind are
termed gusts. Strong winds of intermediate duration (around one minute) are
termed squalls. Long-duration winds have various names associated with their
average strength, such as breeze, gale, storm, and hurricane.
Many winds are named for the direction from which they are coming. For
instance, the Santa Ana winds are strong, extremely dry winds that blow inland
from southern California (where the city Santa Ana is located). The Prevailing
Westerlies are winds that blow from the west towards the poles. The Polar
Easterlies are dry, cold prevailing winds that blow from the poles towards the
equator. A Northeaster (or noreaster) blows from the northeast.