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Transcript
Air Masses, Clouds,
and
Fronts
The “nuts and bolts” of day-to-day
weather analysis and forecasting
Frank Brody / Brian Hoeth
National Weather Service
Spaceflight Meteorology Group
Johnson Space Center
Houston, TX
Weather and the Space Shuttle

The Space Shuttle
cannot fly:
• Through thick low
clouds
• Through rain and
snow
• Near thunderstorms
• Near lightning
• In winds that are too
strong
• In strong turbulence
2
3
High and Low Pressure
Isobars: Lines of constant pressure
• aka “anticyclone”
• Sinking air
• Usually associated w/ fair
weather
• aka “cyclone”
• Rising air
• Usually associated w/ clouds4
and precipitation
Forces and Winds

Forces creating wind
• Pressure Gradient Force
• Coriolis Force
• Frictional Force
“Use the Force”
5
Pressure Gradient Force
The pressure gradient force
results in a net force that is
directed from high pressure to
low pressure
6
Coriolis Force
7
Geostrophic Wind
• Wind blows parallel to isobars (lines of constant pressure)
• Clockwise around High Pressure
• Counterclockwise around Low Pressure
8
Frictional Force
• Cause: Surface of earth is
rough
• Effect: Slows the wind
down  Coriolis force
weakens, pressure gradient
force becomes dominant
• Result: Converging winds
near lows and diverging
winds near highs.
9
Cyclonic Circulation
10
Cold Fronts
11
Warm Fronts
12
Stationary Fronts
13
“Classic” Frontal Pattern
14
Occluded Fronts
• Cold front and warm front merge
• Further lifts already rising warm air
• Typically associated w/ intense, mature cyclones 15
How to Read a Weather Map
Temperature
Pressure
Weather
Dew Point
Wind
16
17
18
And now …
It’s time for a pop quiz
…
A warm front exists when ___ air
is rising over ___ air




(a) cold, warm
(b) hot, moist
(c) warm, cold
(d) cold, stable
20
A warm front exists when ___ air
is rising over ___ air

(a) cold, warm
(b) hot, moist

(c) warm, cold

(d) cold, stable

21
At the surface, winds tend to
flow ___ and ___ towards a
center of a low pressure center




(a) clockwise, outward
(b) counterclockwise, outward
(c) clockwise, inward
(d) counterclockwise, inward
22
At the surface, winds tend to
flow ___ and ___ towards a
center of a low pressure center

(a) clockwise, outward
(b) counterclockwise, outward
(c) clockwise, inward

(d) counterclockwise, inward


23
The pressure gradient force
results in a net force that is
directed from ___ to ___




(a) high pressure, low pressure
(b) low pressure, high pressure
(c) left, right
(d) right, left
24
The pressure gradient force
results in a net force that is
directed from ___ to ___




(a) high pressure, low pressure
(b) low pressure, high pressure
(c) left, right
(d) right, left
25
Clouds



How clouds are formed?
Types of clouds
• Cumulus
• Stratus
• Cirrus
• Nimbus
Clouds by height
• High: Cirro
• Mid: Alto
• Low: Strato
26
Cloud Formation
• Clouds form when air is cooled to its
dewpoint or when the air reaches
saturation.
• Air rises  Lower pressure  requires
work  Air is cooled!
• Cooler air holds less water vapor  some
of the vapor condenses  CLOUDS!
27
Cloud Types
Latin Root
Translation
Example
Cumulus
Heap
Fair weather
cumulus
Stratus
Layer
Altostratus
Cirrus
Curl of hair
Cirrus
Nimbus
Rain
Cumulonimbus
28
Clouds by Height
Height in the
atmosphere
Prefix
Cloud Base
Height (ft)
High
Cirro
Above 20,000
Mid
Alto
Between
6,000 and
20,000
Low
Strato
Below 6,000
29
Cirrus –
“Curl of Hair”
Thin, wispy clouds
composed of ice crystals
30
Stratus ”Layer”
Layered low
clouds,
sometimes
patchy with
poorly defined
edges
31
Cirrostratus
Cirro prefix: High Cloud
Cirrus: “Curl of Hair”
Thin, wispy clouds
Stratus: “Layer”
Poorly defined
edges
32
“Halo around the sun”
Cumulus – “Heap”
Fair weather cumulus – small
heaps of scattered clouds w/
flat bottoms and round tops
Altocumulus – common
33
ahead of cold front
Altocumulus
Alto prefix: Mid Cloud
Cumulus: “Heap”
Flat bottoms, round
tops
34
Stratocumulus
Strato prefix: Low Cloud
Cumulus: “Heap”
Flat bottoms, round
tops
StratoCumulus –
• Dark fluffy clouds
• Relatively stable air
• Not as menacing as
it may appear
35
Nimbus –
“Rain”
Cumulonimbus Cumulo: “Heap”
Nimbus: “Rain”
Easier Translation:
“Thunderstorm cloud”
Nimbostratus -
Widespread thick layer
of cloud with poorly
defined edges
producing precipitation
36
Got any questions or have we
left you in a fog???
Thank you for
coming … buh bye
now!!
37
Contact Info/Websites







Frank Brody: [email protected]
Brian Hoeth: [email protected]
http://www.srh.noaa.gov/smg
http://ww2010.atmos.uiuc.edu
http://virtualskies.arc.nasa.gov/main/mweather.html
http://www.srh.weather.gov/jetstream/
http://www.windows.ucar.edu
38
Backup Slides
39
FRICTIONAL FORCE
40
FRICTIONAL FORCE
41