Transcript (a) high pressure, low pressure

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
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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
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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
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Forces creating wind
• Pressure Gradient Force
• Coriolis Force
• Frictional Force
“Use the Force”
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Pressure Gradient Force
The pressure gradient force
results in a net force that is
directed from high pressure to
low pressure
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Coriolis Force
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Geostrophic Wind
• Wind blows parallel to isobars (lines of constant pressure)
• Clockwise around High Pressure
• Counterclockwise around Low Pressure
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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.
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Cyclonic Circulation
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Cold Fronts
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Warm Fronts
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Stationary Fronts
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“Classic” Frontal Pattern
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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
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And now …
It’s time for a pop quiz
…
A warm front exists when ___ air
is rising over ___ air
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(a) cold, warm
(b) hot, moist
(c) warm, cold
(d) cold, stable
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A warm front exists when ___ air
is rising over ___ air
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(a) cold, warm
(b) hot, moist
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(c) warm, cold
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(d) cold, stable
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At the surface, winds tend to
flow ___ and ___ towards a
center of a low pressure center
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(a) clockwise, outward
(b) counterclockwise, outward
(c) clockwise, inward
(d) counterclockwise, inward
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At the surface, winds tend to
flow ___ and ___ towards a
center of a low pressure center
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(a) clockwise, outward
(b) counterclockwise, outward
(c) clockwise, inward
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(d) counterclockwise, inward
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The pressure gradient force
results in a net force that is
directed from ___ to ___
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(a) high pressure, low pressure
(b) low pressure, high pressure
(c) left, right
(d) right, left
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The pressure gradient force
results in a net force that is
directed from ___ to ___
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(a) high pressure, low pressure
(b) low pressure, high pressure
(c) left, right
(d) right, left
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Clouds
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How clouds are formed?
Types of clouds
• Cumulus
• Stratus
• Cirrus
• Nimbus
Clouds by height
• High: Cirro
• Mid: Alto
• Low: Strato
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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!
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Cloud Types
Latin Root
Translation
Example
Cumulus
Heap
Fair weather
cumulus
Stratus
Layer
Altostratus
Cirrus
Curl of hair
Cirrus
Nimbus
Rain
Cumulonimbus
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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
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Cirrus –
“Curl of Hair”
Thin, wispy clouds
composed of ice crystals
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Stratus ”Layer”
Layered low
clouds,
sometimes
patchy with
poorly defined
edges
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Cirrostratus
Cirro prefix: High Cloud
Cirrus: “Curl of Hair”
Thin, wispy clouds
Stratus: “Layer”
Poorly defined
edges
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“Halo around the sun”
Cumulus – “Heap”
Fair weather cumulus – small
heaps of scattered clouds w/
flat bottoms and round tops
Altocumulus – common
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ahead of cold front
Altocumulus
Alto prefix: Mid Cloud
Cumulus: “Heap”
Flat bottoms, round
tops
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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
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Nimbus –
“Rain”
Cumulonimbus Cumulo: “Heap”
Nimbus: “Rain”
Easier Translation:
“Thunderstorm cloud”
Nimbostratus -
Widespread thick layer
of cloud with poorly
defined edges
producing precipitation
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Got any questions or have we
left you in a fog???
Thank you for
coming … buh bye
now!!
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Contact Info/Websites
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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
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Backup Slides
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FRICTIONAL FORCE
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FRICTIONAL FORCE
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