Aviation Weather
Dynamically Speaking
Written for the Notre Dame Pilot Initiative
By the Pilots of the University of Notre Dame
“Teaching the Science, Inspiring the Art, Producing Aviation Candidates!”
Quote
Just remember, if you crash because
of weather, your funeral will be
held on a sunny day. –Layton A.
Bennett
Lesson Plan
Will learn
 Atmosphere & Global Circulation
 Weather & Climate
 Clouds & Stability
 Weather Forecasting
Will be able to recite
 Air Mass Types
 Lapse Rates
 Stages of Thunderstorm Development
 Types of Fog & Clouds
Will be able to distinguish
 Pictures of different cloud types
The Atmosphere
&
Global Circulation
“Teaching the Science, Inspiring the Art, Producing Aviation Candidates!”
Atmospheric Composition
Oxygen
21%
Argon
1% Other
0%
Nitrogen
78%
Earth's atmosphere has a unique
composition of gases when compared to
that of the other planets in the solar
system.
 At greater
altitudes, the
same
volume of air
contains
fewer
molecules of
the gases
that make it
up. This
means that
the density
of air
decreases
with
increasing
altitude.
The earth's atmosphere thins rapidly with
increasing altitude and is much closer to the
earth than most people realize.
Thermal Model of the Atmosphere
Sunlight Angle
 On a global, yearly basis, the equatorial region of the earth
receives more direct incoming solar radiation than the
higher latitudes. As a result, average temperatures are
higher in the equatorial region and decrease with latitude
toward both poles. This sets the stage for worldwide
patterns of prevailing winds, high and low areas of
atmospheric pressure, and climatic patterns.
Global Wind Patterns
Hot air rises over the equator due to the
fact that it is less dense.
This is called the intertropical
convergence zone
This rising air cools as it rises resulting in
precipitation in the region of the ITCZ.
The air then travels north and south at
high altitude.
Global Circulation
 With Globe, Coriolis
 Seasons – Have kid
stand on table as sun
 Chris Columbus trades
 With Fan, demonstrate
orthographic lifting
Global Wind Patterns
Hot air rises over the equator due to
the fact that it is less dense.
The cooled air descends to reach the
surface at about 24 ON and 24 OS of
the equator.
This forms a high pressure area
The great deserts of the world are
located in this high pressure area
Coriolis Effect
An object in
motion in the
northern
hemisphere
appears to
turn to the
right.
An object in
motion in the
southern
hemisphere
appears to
turn to the
left.
Global Circ Pix
Part of the generalized global circulation pattern of
the earth's atmosphere. The scale of upward
movement of air above the intertropical
convergence zone is exaggerated for clarity. The
troposphere over the equator is thicker than
elsewhere, reaching a height of about 12 mi.
 Air sinks over a highpressure center that moves
away from the center on the
surface, veering to the right
in the Northern Hemisphere
to create a clockwise
circulation pattern.
 Air moves toward a lowpressure center on the
surface, rising over the
center. As air moves toward
the low-pressure center on
the surface, it veers to the
left in the Northern
Hemisphere to create a
counterclockwise circulation
pattern.
Pressure
Areas
Weather and Climate
“Teaching the Science, Inspiring the Art, Producing Aviation Candidates!”
Definition
 Weather is a description of the changeable aspects of
the atmosphere, the temperature, rainfall, pressure, and
so forth, at a particular time. These changes usually
affect your daily life one way or another, but some of
them seem more inconvenient than others.
Air Masses
Polar air mass
An air mass that moves from a cold
region
Tropical Air Mass
An air mass that moves from a warm
region
Continental Air Mass
Moves in from a land mass
Maritime Air Mass
Moves in from over an ocean
Air Mass Types
Temperature/ Hot
Moisture
Cold
Wet
Tropical
Maritime
Polar
Maritime
Dry
Tropical
Continental
Polar
Continental
Current Weather
Clouds and Stability
“Teaching the Science, Inspiring the Art, Producing Aviation Candidates!”
Types of Clouds
Cumulus (heaped)
Stratus (layered)
Cirrus (curled)
Nimbus (rain)
How a Cloud Forms
 Temperature and Dewpoint Converge
 Water Condenses on Particles (Dirt, Dust, Smoke)
 Fog is a cloud very near to the surface
Precipitation
 Precipitation is water in the liquid or solid form that
returns to the surface of the earth. The precipitation
you see here is liquid, and each raindrop is made from
billions of the tiny droplets that make up the clouds.
The tiny droplets of clouds become precipitation by
merging to form larger droplets or by the growth of ice
crystals that melt while falling.
Condensation Nucleus (0.2 microns)
Average Cloud Droplet (20 microns)
Large Cloud Droplet (100 microns)
Drizzle Droplet (300 microns)
Average Rain Drop (2000 microns)
This figure compares the size of the condensation
nuclei to the size of typical condensation droplets.
Note that 1 micron is 1/1,000 mm.
Stability
Air may be:
Unstable (vertically)
Cumulus clouds
Stable (vertically)
Stratus clouds
Cumulus
Fair weather
Lapse Rate
Altitude (ft.)
2000
1500
1000
In therm al
3 deg/1000 ft
500
Std. Conditions
2 deg/1000 ft
0
19
21
23
25
27
T(°C)
 The average lapse rate (rate of cooling) is 2° C
per 1,000 feet or 3.5° F per 1,000 feet
 In order to calculate the base of thermal driven
cumulus clouds, divide the temperature /
dewpoint spread by the lapse rate (4.4 ° F per
1,000 feet )
Altocumulus
Mackerel sky
Altocumulus at Sunrise
Temperature Inversion
Altitude (ft.)
16000
14000
12000
10000
8000
6000
4000
2000
0
0
2
4
6
T (°C)
8
10
Fog is a cloud very near to the surface
Types of Fog
Radiation (ground) fog
Advection fog
Requires wind
Warm air over cold land or water
Upslope (orographic) fog
Requires wind
Steam fog
Lake or ocean source of water
Cold air over warm water
Precipitation fog (rain fog)
Radiation Fog
From the Air
Advection Fog
Upslope Fog
Upslope Fog
Steam Fog
Most types of fog form in stable atmospheric conditions. The exception is steam fog,
shown in this picture of Maligne Lake, Alberta, Canada, just after sunrise in late
summer. The land cools off overnight while the water retains heat from the summer. As
the cooled air slips over the lake, heat and moisture are added from below, resulting in a
fog that twists and writhes-- hence the term "steam fog".
Orchard
Fans like this one are used to mix the warmer,
upper layers of air with the cooling air in the
orchard on nights when frost is likely to form.
Stratocumulus
Ice possible in the tops
Stratocumulus from above
Stratocumulus
Red sky in the morning, sailors take warning
Red sky at night, sailors’ delight—only applies in the tropics
Types of Clouds
Cumulus (piled up)
Stratus (layered)
Cirrus (curled)
Nimbus (rain)
Cirrus
Overrunning moisture
Cirrostratus
Moisture increasing
Cirrostratus
Hazy circle round the moon
Means that rain is coming soon!
Cirrostratus
Condensation Trails (Contrails)
Cirrocumulus
Thunderstorms
Thunderstorms require
 Unstable air
 Moisture
 Lifting mechanism
T-storms always have lightning
 Thunder is the sound of lightning
 T-storms are reported when thunder is heard
Only true for manned observation posts
Automatic Reporting (AWOS) detects lightning
discharge
Three stages in the life of a thunderstorm cell.
(A) The cumulus stage begins as warm, moist
air is lifted in an unstable atmosphere. All the
air movement is upward in this stage.
(B) The mature stage begins when precipitation
reaches the ground. This stage has updrafts and
downdrafts side by side, which create violent
turbulence.
 (C) The final stage begins when all the updrafts have
been cut off, and only downdrafts exist. This cuts off
the supply of moisture, and the rain decreases as the
thunderstorm dissipates. The anvil-shaped top is a
characteristic sign of this stage.
Lightning
Different parts of a thunderstorm cloud
develop centers of electric charge. Lightning is
a giant electric spark that discharges the
accumulated charges.
Thunderstorms
Types of thunderstorms
Air mass
Frontal
Upslope (orographic)
Hail
These hailstones fell from a thunderstorm
in Iowa, damaging automobiles,
structures, and crops.
Cumulonimbus
Distance to a
Storm
Thunderstorm
Bad Idea
Cumulonimbus
From Space
Boundaries between air
masses = fronts
Types of Fronts
Cold
Warm
Stationary
Occluded
Weather Fronts
Front
A boundary between two different air
masses
Cold Front
When a cold air mass moves into a
warmer area, displacing the warm air
mass
Provides lift to adiabatically cool the
warm air, resulting in towering cumulus
and thunderclouds.
A cold air mass is
similar to a huge,
flattened bubble of
cold air that moves
across the land. The
front is the boundary
between two air
masses, a narrow
transition zone of
mixing.
A front is
represented by a line
on a weather map,
which shows the
location of the front
at ground level.
Cold Front Pix
Warm Front
When a warm air mass moves into an
area, displacing the cold air mass
A gently sloping front as the Warm air
moves over top of the cooler air.
Stationary Front
When the edge of a front ceases to
advance
Warm Front Pix
An idealized warm front, showing a warm
air mass overriding and pushing cold air in
front of it. Notice that the overriding warm
air produces a predictable sequence of
clouds far in advance of the moving front.
Occluded Front
One that has been lifted completely
off the ground
Has a low pressure center and
cyclonic activity
Cyclones
Cyclone
A low pressure area with winds
moving into the low pressure
area and being forced upward.
Friction and the Coriolis effect
cause the air to move to the
right of the direction of
movement.
Anticyclone
A high pressure center
L
H
Hurricane John
This is a satellite photo of hurricane John,
showing the eye and counterclockwise
motion
Storm Tracks
Cyclonic storms usually follow principal
storm tracks across the continental United
States in a generally easterly direction.
This makes it possible to predict where the
low-pressure storm might move next.
Weather Forecasting
“Teaching the Science, Inspiring the Art, Producing Aviation Candidates!”
Computer Models
Weather Predictions
Weather predictions are based on
information about air masses, fronts, and
associated pressure systems in an area.
This information is used to produce a
model of behavior for weather using a
computer.
 Many models are used and then summarized
when the different models agree fairly closely
to a model of the weather.
Surface Pressure/Precipitation Plot
Predicted
Actual
Forecast for today
Supercomputers
 Supercomputers make routine weather forecasts
possible by solving mathematical equations that
describe changes in a mathematical model of the
atmosphere. This "fish-eye" view was necessary to
show all of this Cray supercomputer at CERN, the
European Center of Particle Physics.
Example of Atmospheric
Refraction
Where’s the pot of gold?