Download 2007 - Public Information

BOATING SKILLS AND
SEAMANSHIP
Lesson 12
Weather & Boating
Approved by DC-E USCG AuxA, Inc
Lesson Objective
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What Causes Weather
Wind, Waves, And Weather
Recognizing Signs Of Change
Weather And Clouds
The Signs Of Bad Weather & What To Avoid
Where To Get Weather Info
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Weather & Heat
• Sun Heats Earth & Air
• Warm Air Rises
– Creates Low Pressure
• Cooler Upper Air Falls
– Creates High Pressure
• Air Flows From Highs Toward Lows
– Creates Wind
• Greater The Pressure Difference
– Stronger The Wind
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Heat & Humidity
• Warm Air Can Hold More Moisture Than
Cold Air
• Relative Humidity
– The Amount Of Moisture In Air, Compared To
The Maximum Amount It Could Hold At That
Temperature
• Cooling Air To Its Dew Point Creates
100% Relative Humidity And Moisture
Condenses Out
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Land & Water
• Water Gains Heat Slower Than Land
• Water Loses Heat Slower Than Land
• Daytime
– Land Warmer Than Water
• Air Warms, Rises Over Land And Air Flows In From Sea –
Sea Breeze
• Nighttime
– Water Warmer Than Land
• Air Warms, Rises Over Water And Air Flows From Land to
Sea – Land Breeze
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Wind Patterns
North Pole
Equator
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Buys-Ballot’s Law
Present Surface Wind
Stand with back to surface
wind Turn Right 45o
Low Pressure is on left
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Coriolis Force
• Northern Hemisphere
– Earth’s Rotation Causes Any Air Motion To
Bend To The Right
– Air Moving Down & Out Of A High
Pressure Area
• Bends To The Right Causing A Clockwise
Motion
– Air Rushing Into A Low Pressure Area
• Rises, Bends To The Left
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Circulation of Air
Circulation Of Air
Down, Out & Clockwise
around High
Toward & Up Counterclockwise
around lows
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Wind & Waves
• Swells
– Dying Waves A Long Way From
Source
• Breakers
– Waves Nearing Shore
– Caused By:
• Shallow Water Slowing Bottom Of
Wave, Top Then Spills Over & Breaks
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Wind & Waves
• Wave Height Depends On
– Wind Strength
– Wind Duration
– Fetch (Long & Short)
Buffalo
Lake Erie
Toledo
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Wave Height
• Seas 3 to 5 Feet Means
– 15% Of Waves Over 5’
– 15% Of Waves Under 3’
– 70% Of Waves 3’ to 5’
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Fronts
• Defined As Zone Between Two Different Air
Masses
• Differences In:
– Temperature
– Humidity
– Wind – Direction & Speed
– Air Pressure
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Cold Fronts
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Air Cooler Behind Than Ahead
Fast Moving
Can Create Violent Weather
When Passes
– Pressure Rises Abruptly
– Temperature Falls
– Relative Humidity Decreases
– Wind Shifts Direction
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Cold Fronts
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Warm Fronts
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Air Warmer Behind Than Ahead
Slow Moving
Non-Violent Weather
Nighttime Fog Frequent
Can Have Long Periods Of Rain
When Passes
• Little Pressure Change
• Little Temperature Change
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Warm Front
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Cloud Identification
• Cumulus
– Fluffy, White, Fair Weather Clouds
– May Grow To Cumulonimbus
• Stratus
– Layered
• Nimbo/Nimbus
– Rain Clouds
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Cloud Families
• High - Cirriform
– Cirrus, Cirrocumulus, Cirrostratus
• Mostly Ice – No Precipitation
• Middle - Alto
– Altostratus, Altocumulus, Nimbostratus
• Mostly Water
• Low
– Stratus, Stratocumulus, Cumulus
• Mostly Water
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High Clouds
• Cirrus
– Mares’ Tails
• Cirrocumulus
– Mackerel Scales
• Cirrostratus
– Like A Sheet Or Veil
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Cirrus (Ci)
“Mare’s tails “
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Cirrocumulus (Cc)
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Middle Clouds
• Altostratus
– Mid-level, Layered
• Altocumulus
– Cumulus Clouds Gathered In Layers
• Cumulonimbus
– Rain Clouds
– May Develop Into Thunderheads (Towering
Cumulus)
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Cumulus Family
• Cumulus
– Summer Afternoon Cotton Balls
– Generally No Precipitation Unless Building
• Towering Cumulus
– Building Cumulus
– Deep Layer Of Unstable Air
– Thundershowers Can Result
• Cumulonimbus
– Thunderhead/Thunderstorm Cloud
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Cumulus
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Towering Cumulus (Tcu)
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Cumulonimbus (Cb)
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Altocumulus (Ac)
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Low Clouds
• Stratus
– Low Layers Of Solid Cloud Cover
• Nimbostratus
– Rain Clouds
– Intermittent Or Steady Rain
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Stratocumulus (Sc)
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Stratus (St)
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Turbulence In
Cumulonimbus Cloud
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Stages Of A
Thunderstorm
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Thunderstorms In
A Squall Line
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Lightning
• Cause
– Friction Of Raindrops & Ice Particles In
Thunderstorms Creates Electrical Charge
• Distant Lightning
– Heard As Static In AM Radios
– More Frequent The Static, The More Severe
The Storm
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Tornado
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Funnel Clouds
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Waterspout
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Fog
• Radiation
– Clear Sky
– Little Or No Wind
– Small Temp – Dew Point Spread
– Burns Off In Morning
• Advection
– Sea Fog
– Needs Light Winds – Up To 15 MPH
– Warm Moist Air Moving Over A Colder Body
– Long Lasting
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Fog
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Weather Information
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Radio
Television
Newspapers
Telephone
NOAA Weather Radio Stations
Pennants, Flags, Lights
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Tropical Weather
• Classifications
– Tropical Depression
• Wind Up To 34 Knots
– Tropical Storm
• Wind 35 - 64 Knots
– Hurricane
• Wind 65 Knots Or More
• Other Names For Hurricanes
– Typhoon
– Cyclone
– Willy-Willy
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Hurricane Tracks
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SUMMARY (1)
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Heat & Weather
Global Air Circulation
Wind & Boating
Highs & Lows
Frontal Weather
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SUMMARY (2)
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Clouds & Weather
Thunderstorms
Fog
Tropical Weather
Sources Of Weather
Information
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