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Meteorology
I. Air Masses
Air Mass: a large body of air
with uniform temperature
and moisture content.
A. Types of Air Masses
Air masses are classified according
to their source regions:
1.
2.
3.
4.
Polar = P = cold
Tropical = T = warm
Maritime (ocean) = m = moist
Continental (land) = c = dry
B. North American Air Masses
1. Polar

cP Canadian:
Northern US

mP Pacific: cool
water off Alaska

mP Atlantic:
Greenland and
Iceland
2. Tropical

cT: Mexico, summer
only

mT: Gulf Coast
and Atlantic

mT Pacific: heavy
rain in the winter

Air Mass Characteristics
II. Fronts
Front: boundary between air
masses of different densities.

Types of Fronts
A. Types of Fronts
1. Cold Front: when a cold air mass
overtakes a warm air mass.
Cold front storms are fastmoving, short-lived and often
violent.
What cloud type do you get
with a cold front?
Squall Line: long line of
thunderstorms ahead of a cold
front
Thunderstorm .... Ocracoke NC – Summer 2013
2. Warm Front: warm air mass
overtakes a cold air mass
Warm fronts usually produce
nimbostratus clouds

What will the weather be like?

Precipitation over a very large area.
3. Stationary Front: two air
masses meet and the front
moves parallel
Neither air mass is displaced
 Little movement
 Precipitation continues for long
period of time

4. Occluded Front: fast-moving
cold front lifts warm air
completely off the ground.

Occluded Front:
B. Hurricanes
severe storms that form over WARM
tropical oceans
 tropical cyclones
 LOW pressure centers
 winds spiral rapidly inward
 counterclockwise rotation
 winds over 120 km/hr (75 mi/hr)

warm, moist air rises rapidly
 as it condenses it releases latent heat
 this increases the rate of evaporation
and sustains the storm

Anatomy of a Hurricane

Eye:
– calm (little or no rain)
– warmest part of the storm

Eyewall:
– surrounds eye
– wall of thunderclouds
– most rain
– stongest winds

Spiral rainbands:
– spiral inward to eyewall
Saffir-Simpson Hurricane Scale
 used
to classify hurricanes
 divides hurricanes into five
categories based on
intensities of sustained winds
Storm surge is the most
dangerous aspect of a
hurricane.

Typical beach along the coast

Sea walls are built to minimize
damage

Category 1: Minimal storm
Winds: 74 to 95 mph
Storm surge: Up to 5 feet

Category 2: Moderate storm
Winds: 96 to 110 mph
Storm surge: 6 to 8 feet


Category 3: Extensive storm
Winds: 111 to 130 mph
Storm surge: 9 to 12 feet

Category 4: Extreme storm
Winds: 131 to 155 mph
Storm surge: 13 to 18 feet

Category 5: Catastrophic storm
Winds: More than 155 mph
Storm surge: More than 18 feet
2005 Hurricane Season
First year with 28 named storms
 First year with 15 Hurricanes
 First year with four category 5
hurricanes
 First year with four major hurricanes
hitting the U.S.

C. Tornadoes
 Smallest
most
violent shortlived storms
 Form when
thunderstorms
meet high
altitude winds

Narrow, violent funnel-shaped cyclone; a
column of spiral winds that extends
downward from a cloud base toward
Earth
Joplin, Missouri May 2011
Joplin – Then & Now
Fujita Scale of Tornado
Intensity
Before thunderstorms develop, a change in wind
direction and an increase in wind speed with
increasing height creates an invisible, horizontal
spinning effect in the lower atmosphere.
Rising air within the thunderstorm updraft
tilts the rotating air from horizontal to
vertical.
An area of rotation, 2-6 miles wide, now extends
through much of the storm; Most strong and violent
tornadoes form within this area of strong rotation.
III. Weather Instruments
A.
Measuring Air
Temperature:
 thermometer
B. Measuring Wind Speed and
Direction:
anemometer:
measures wind
speed.
wind vane: shows wind direction
– The arrow always points into the wind!
C. Radar: can detect weather
conditions by sending and receiving
radio waves.
IV. Forecasting the Weather
 Station
Model: cluster of weather
symbols plotted around a
reporting station showing the
current conditions.
Wind patterns around areas of HIGH
and LOW pressure: