Transcript Lesson 2-2 Slides Part 2 of 2 Weather Elements

Lesson 2-2
Weather Elements
Part 2 of 2
Lesson Overview
 Types
of air masses and fronts
 Factors that impact air masses
 Fronts
 Wind and Atmospheric Motion
 High- and low-pressure systems
 Terrain factors that affect weather
 Normal weather patterns
Chapter 2, Lesson 2
Current Weather Map
Fronts – Quick Review

What color indicates a cold front? Warm front?
Stationary front? Occluded Front?
 Blue (triangle); Red (semicircle); Blue and Red (both
triangle and semicircle); purple
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How is a warm front defined?
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The air is warmer than the air it is displacing
Which front has more potential violent weather? Why?
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Cold Front. It moves faster, lifting warmer air and
causing updrafts and condensation of moisture
Fronts – Quick Review

What three types of high clouds might you see hundreds
of miles prior to the passing of a warm or cold front?
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Why does the air near the surface of a warm front
remain foggy or hazy with low cloud buildup?
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Cirrus, cirrostratus, cirrocumulus
Because dust, pollution and other particulates are not lifted
higher up as the warm air moves over the colder air
What do squall lines in a cold front represent?

Low pressure air cells in the warm air that meet with the
higher pressure cells of the cold front, causing increased
turbulence and cloud formation
Fronts – Quick Review

What direction do cold fronts normally take in the
Northern Hemisphere?
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What causes winds to shift right in the Northern
Hemisphere? Why does it shift right?
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The Coriolis Force. As the earth rotates, the surfaces nearer
the equator move faster than surfaces nearer the poles.
What causes wind?
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Northwest to Southeast
A low-pressure area next to as high pressure area
What is the difference between air currents and wind?

Currents go up and down; wind is horizontal
Key Factors in Wind and
Atmospheric Motion
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Sun’s heat is main driver causing
air to warm, become less dense
and lift upwards
Other atmospheric factors:
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Air pressure gradients
Temp changes of terrain
Earth’s rotation about axis
Coriolis Effect
The result is wind currents that
can and do change weather
Chapter 2, Lesson 2
Reproduced from NASA
Wind Patterns

Anticyclonic circulation


Flow of air from high to
low pressure, produces
clockwise circulation
Cyclonic circulation

Flow of air around a lowpressure area, produces
counterclockwise
circulation
Chapter 2, Lesson 2
Reproduced from US Department of
Transportation/Federal Aviation Administration
High- and Low-Pressure Systems
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High-pressure systems generally produce good weather
Low-pressure systems often bring in bad weather
Pilots who understand
high- and low-pressure
wind patterns can take
advantage of tailwinds
Chapter 2, Lesson 2
Courtesy of NASA
The Pressure Gradient
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The atmosphere is a constantly changing “airscape” of
high pressure and low pressure pockets of air
Air moves from the high pressure pockets to lower
pressure pockets….the result is wind
The Pressure Gradient is the difference in pressure
between high and low pressure pockets
Chapter 2, Lesson 2
Courtesy of NASA
The Pressure Gradient
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On weather maps lines called isobars show the
magnitude of the pressure gradient
Isobars are drawn through points of equal sea-level
atmospheric pressure
 Similar to topographic lines on an orienteering map
indicating the altitude of the terrain
Isobaric lines close together indicate a higher Pressure
Gradient and usually higher wind speeds
Chapter 2, Lesson 2
Courtesy of NASA
Chapter 2, Lesson 2
Courtesy of NASA
Local and Surface Air Movement
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The general circulation of air is complicated by
the irregular distribution of land and water areas
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Different types of surfaces differ in the rate at
which they absorb heat from the Sun and transfer
heat to the atmosphere
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In some regions local low-pressure areas form
over hot land surfaces and over warmer water
surfaces in the winter
Local and Surface Air Movement

Some surfaces give off or reflect a great amount
of heat
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Sand
Rocks
Plowed areas
Barren land
Other surfaces tend to absord and retain heat
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Meadows
Planted fields
Water
Local and Surface Air Movement
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Rising air currents are encountered by aircraft
flying over sand, rock, and other surfaces that
give off considerable heat
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Descending air currents are encountered over
surfaces that retain heat
Terrain and Mountains
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The presence of mountain ranges
change the characteristics of a
front
As air masses enter the United
States the mountains cause them
to rise
Upward slope pushes air up, water
vapor cools, condenses into clouds,
can rain or snow making air mass
dryer
After reaching the peak, air
descends on the leeward side,
warms up; little rain/snow
Terrain and Mountains
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Think of the air reaching the peak and then
descending on the leeward side
This air tends to break into eddies
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These eddies are descending and turbulent air
The stronger the wind rising up and over the peak, the
greater the turbulence
As a pilot, if you are coming towards the leeward side of
a mountain, say from Denver heading west, make sure
you have enough altitude between your plane and the
mountain so you’ll fly above the strong dangerous
descending air
Terrain and Bodies of Water
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Along many seacoasts there is a breeze from the sea
during the day (sea breeze)
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The land heats up more than water, warming the air and
lowering the pressure
As the cooler moist air from the water comes onto land, it
heats up, rises and causes water vapor to condense
Afternoon showers are quite common
Later in the day, as the land cools, the pressure over
land increases causing the wind to shift back from
land to sea (land breeze)

The clouds disappear as they turn back into water vapor
Terrain and Lake Effect Snow
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Lake Effect Snow is the result of a cold air mass
passing over a warmer body of large water like
Lake Erie
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Explain the process creating so much snow
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Why is it only the southern or eastern sides of
Lake Erie that get the lake effect snow and not
the Canadian side?
Climatic Provinces
Normal Weather Patterns
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Superhumid Province
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Lies along the north Pacific coast
Precipitation from 30 to 150 inches per year
Temperatures are mild and summers dry
Cloudiest part of the country.
Normal Weather Patterns
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Humid Province
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Area east of a line from Texas Gulf Coast to
Lake Superior
30 to 50 inches of rain annually
Average temperature from 40o F in north, 70o F
along the Gulf of Mexico, 75o F in Florida
Cold waves in winter, heat waves in summer
Hurricanes are common
Normal Weather Patterns
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Subhumid Province
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Belt 300-500 miles wide just west of humid province
Average rainfall 18 to 30 inches
Cold in winter, hot in summer
Quick and severe temperature changes
Tornadoes in most of southern part of this area
Normal Weather Patterns
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Semiarid Province
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300-500 mile wide area west of subhumid
province from Canada to Mexico
Precipitation ranges from 12 to 25 inches
Warm, dry air masses common in winter
Hail frequent in spring and early summer
The Great Valley of California is geographically
separated from rest of province
Normal Weather Patterns
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Arid Province
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Includes parts of California, Texas, Arizona,
New Mexico, Nevada and Utah
Less than 10 inches of rain annually
Hot and dry summers, winters above freezing
Clear dry air and plenty of sunshine
Normal Weather Patterns
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Hawaii
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Two major factors determine weather
Dramatic heights and contours of land areas
 Prevailing northeast trade winds
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Pleasant temperatures
Little distinctions between summer and winter
Normal Weather Patterns
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Alaska
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Has several different kinds of weather
No great extremes in southern part of state
Arctic slope lies in northern part of state
Broad valley and low mountain ranges
Continental weather
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 Temperatures from -70 F in winter to 90 F in summer
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Next….
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Done – weather elements

Next – aviation weather
Chapter 2, Lesson 2
Courtesy of NOAA/National Weather
Service