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Introduction to Weather
Chapter 1


A basic understanding of weather and the
atmosphere.
TV, radio, newspapers, the internet and
NOAA Weather Radio
High Pressure
1.
Also called an anticyclone
2.
Winds blow clockwise and away (diverge) from the center
3.
Associated with fair weather
4.
Symbol - H
Low Pressure
1.
Also called a cyclone
2.
Winds blow counterclockwise and into (converge) the center
3.
Associated with poor weather
4.
Symbol - L
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An air mass is a huge volume of air
covering hundreds of thousands of square
miles that is relatively uniform horizontally
in temperatures and moisture. The
temperature and humidity of an air mass
depend on the properties of its source
region AND the nature of the surface over
which it travels.
AIR MASSES – large volume of air that has a relatively
uniform temperature and humidity
1. Continental Polar – cP – cold and dry (Canada)
2. Maritime Polar – mP – cold and wet (Gulf of Alaska)
3. Continental Tropical – cT – hot and dry (Mexico)
4. Maritime Tropical – mT – hot and wet (Gulf of Mexico)
5. Arctic – A – very cold and dry (Northern Canada)
Notes on air masses
1. Tropical air masses show less variation throughout the
year compared with polar air masses because solar
intensity and duration is more constant in the tropics
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This means that cP air is much colder in the
winter than in the summer
2. An air mass changes as it moves from its source
-
The modifications in an air mass depend on the
surface that it is moving over – bare land, snow
covered land, water
Fronts – the boundary between air masses transition.
1. Cold Front
a.
Generally, a narrow band of
precipitation along or just ahead
of the surface front, where
precipitation is brief (couple of
minutes to a few hours)
b.
Precipitation can be severe
c.
Boundary between advancing cold
air and retreating warm air
d.
Plotted on a map as a blue line
with triangles pointed in the
direction of motion
a narrow zone of
2. Warm Front
a.
Generally, a wide band of precipitation
along or just ahead of the surface warm
front, where precipitation can be
persistent (12-24 hours)
b.
Precipitation is generally light to
moderate
c.
Boundary between advancing warm air
and retreating cold air
d.
Plotted on a map as a red line with
semi-circles pointed in the direction of
motion
Ways to locate a front on a surface weather map:
1. Precipitation/Clouds
2. Wind Shift
3. Temperature Difference
4. Dew Point Difference (change in relative humidity)
A cyclone with the
warm and cold fronts
extending outward
from the low pressure
center. Showers
generally form along
the warm front, while
more severe weather
can occur along the
cold front.
This shows how the
warm and cold
fronts act as
boundaries between
different air masses.
Notice how the
wind directions are
different on either
side of the fronts,
and that the flow is
counterclockwise
and convergent.
Other Fronts
1. Stationary – a nonmoving front where
winds on either side blow
in opposite directions
2. Occluded – when the air
behind the cold front
overtakes the air ahead of
the warm front
Other Interesting (Non-frontal) Surface Weather
1. Hurricanes and Tropical Storms
2. Lake Effect Snow
3. Land/Sea Breeze – in the summer, areas near large
bodies of water are generally cooler during the day and
warmer at night
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Sensors onboard weather satellites
remotely measure two types of radiation:
sunlight that is reflected or scattered by
and, and infrared radiation that is emitted
by earth. Weather satellites are either in
geostationary or polar orbits and generate
data that are processed into visible and
infrared images.
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Weather radar continually emits pulses of
microwave radiation that are reflected by
raindrops, snowflakes, or hailstones…
which appear as blotches on a TV-type
screen or image. Both intensity and area of
precip can be tracked. The new Doppler
radars can “see” air circulation inside the
storm.