Weather theory - PowerPoint PPT Presentation

Weather theory l.jpg
1 / 77

  • Updated On :
  • Presentation posted in: General

Weather theory. Kyle BlackCarol Cushman. Environment and Flying. As pilots, do you need to have a basic understanding of weather? Do you need to know how different types of weather can affect you, be it rain, snow, sleet, or ice?. The Atmosphere.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

Download Presentation

Weather theory

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

Weather theory l.jpg

Weather theory

Kyle BlackCarol Cushman

Environment and flying l.jpg

Environment and Flying

  • As pilots, do you need to have a basic understanding of weather?

  • Do you need to know how different types of weather can affect you, be it rain, snow, sleet, or ice?

The atmosphere l.jpg

The Atmosphere

  • 99% located within 100,000 feet of the earth’s surface

Levels of the atmosphere l.jpg

Levels of the Atmosphere

  • What are the different layers of the atmosphere?

    • Troposphere (Surface to ~36,000’)

      • Tropopause (Layer just above Troposphere which helps to hold in water vapor and weather)

    • Stratosphere (to 100,000’)

    • Mesosphere

    • Thermosphere

Atmosphere composition l.jpg

Atmosphere Composition

  • How are the gases of the atmosphere proportioned? What percentage?

    • Nitrogen?

      • 78%

    • Oxygen?

      • 21%

    • Other Gases

      • 1%

Atmospheric circulation l.jpg

Atmospheric Circulation

  • Temperature

    • Circulation due to temperature variations created by unequal heating of the earth’s surface.

  • Convection

  • Three-Cell Circulation Pattern

    • 0-30 degrees latitude – Hadley Cell (Rises from equator, sinks by 30 degrees lat. etc)

    • 30-60 degrees latitude – Ferrel Cell

    • 60 degrees to poles – Polar Cell

  • Atmospheric Pressure (Pressure Gradient Force)

    • Air generally flows from cool, dense air associated with highs to less dense air of lows.

Atmospheric circulation9 l.jpg

Atmospheric Circulation

  • Coriolis Force

    • Earth’s rotation

    • Effects objects such as air (or aircraft) travelling large distances

  • Frictional Force

    • Wind is result of Pressure and Coriolis Force

    • Friction causes wind to shift directions when near the surface of the earth (within 2000’ of ground)

    • Lessens effects of Coriolis Force

Atmospheric circulation10 l.jpg

Atmospheric Circulation

  • Global Wind Patterns

  • Local Wind Patterns

    • Terrain Variations

      • Mountains

      • Valleys

      • Water

Atmospheric circulation11 l.jpg

Atmospheric Circulation

  • Sea Breeze

    • Heating differential between land and water surfaces…

    • Cool air moves to warm air (cool air over water to warm air over land)

  • Land Breeze

    • Land cools faster than water in evening

    • Cool air moves to warm air (cool air over land to warm air over water)

Atmospheric circulation12 l.jpg

Atmospheric Circulation

  • Valley Breeze

    • Air flows up valley and up the slopes during the day

  • Mountain Breeze

    • As ground cools air flows down slope and away from higher terrain

Atmospheric circulation katabatic winds l.jpg

Atmospheric Circulation – Katabatic Winds

  • Generally , any downslope wind

  • Usually refers to downwind flows which are stronger than mountain breezes

    • Usually given special names

Katabatic winds l.jpg

Katabatic Winds

  • Cold Downslope Winds

    • Large ice and snow fields accumulate in mountainous terrain

    • Overlying air becomes extremely cold and high pressure forms

    • Pressure gradient pushes air through gaps in mountains

    • What happens when constriction is reached? (Canyon, Valley, etc.)

  • Examples?

    • Bora in Croatia

    • Mistral in Rhone Valley of France

    • Columbia Gorge wind in northwestern U.S.

Katabatic winds15 l.jpg

Katabatic Winds

  • Warm Downslope Winds

    • Warm airmass moves across mountain range at high levels

    • Forms a trough of low pressure on downwind (lee) side – downslope wind develops

    • As air descends it is compressed – resulting in temp increase

    • Warmer wind can raise temperatures over 20 degrees in an hour

    • 20-50 knot winds, extreme cases can reach 100 knots

  • Examples?

    • Chinook winds along eastern slopes of the Rocky Mountains

    • Foehnin the Alps

    • Santa Ana in Southern California

Weather patterns l.jpg

Weather patterns

Atmospheric stability l.jpg

Atmospheric Stability

  • How is the stability of an airmass decreased?

    • Warming from below

  • What happens to temperature as pressure changes?

    • As an airmass moves downward it is compressed – raising the temperature

    • As an airmass moves upward it expands – lowering the temperature

    • Known as adiabatic heating or adiabatic cooling (change of temperature in dry air)

Stability l.jpg


  • Rate at which temperature decreases with an increase in altitude is referred to as what?

    • Lapse rate

  • What is the average lapse rate?

    • 2°C per 1000’

Stability19 l.jpg


  • Dry Adiabatic Lapse Rate

    • 3°C per 1000’

  • Moist Adiabatic Lapse Rate

    • 1.1°C to 2.8°C

  • What is the average lapse rate?

    • 2°C per 1000’

Stability20 l.jpg


  • Temperature Inversions

    • Temperature increase with altitude

    • Below the inversion visibility is restricted by pollutants and weather – fog, haze, smoke, low clouds

Stability21 l.jpg


  • Moisture

    • Change of State

    • Humidity

      • Amount of moisture air can hold depends on air temperature

    • Dewpoint

      • Air contains 100% of moisture possible at that temperature

    • Dew and Frost

      • Objects cooling below dewpoint of surrounding air

      • Water vapor to ice on surface below freezing

Stability clouds l.jpg

Stability - Clouds

  • At saturation point, invisible water vapor changes to a visible state:

    • Fog

    • Clouds

  • Small temperature/dewpoint spread indicates favorable conditions for formation of fog

Stability clouds24 l.jpg

Stability - Clouds

  • Types of Clouds

    • Low Clouds (Surface to 6500’ AGL)

    • Middle Clouds (6500’ to 20,000’ AGL)

    • High Clouds (Above 20,000’ AGL)

Stability clouds25 l.jpg

Stability - Clouds

  • Low Clouds

    • Stratus

    • Nimbostratus

    • Stratocumulus

Low clouds l.jpg

Low Clouds

Stability clouds27 l.jpg

Stability - Clouds

  • Low Clouds (Surface to 6500’ AGL)

    • Fog

      • Ground

        • Fog less than 20 feet deep

      • Radiation

        • Forms over low-lying flat surfaces

        • Clear, calm, humid nights

      • Advection

        • Warm moist air moves over cooler surfaces

        • Up to 15 knots intensifies development of fog

      • Upslope

        • Moist stable air forced up a sloping land mass

      • Steam

        • Cold, dry air moves over warmer water

Stability clouds28 l.jpg

Stability - Clouds

  • Middle Clouds (6500’ to 20,000’ AGL)

    • Altostratus

    • Altocumulus

Stability clouds29 l.jpg

Stability - Clouds

  • High Clouds (Above 20,000’ AGL)

    • Cirrus

    • Cirrostratus

    • Cirrocumulus

Stability clouds30 l.jpg

Stability - Clouds

  • Vertical Development

    • Cumulus

    • Towering Cumulus

    • Cumulonimbus

Precipitation l.jpg


  • Water / ice particles must grow in size until no longer supportable by atmosphere

  • Types?

    • Drizzle and Rain

      • Virga – Evaporating Precipitation

      • Precipitation-induced fog – warm rain/drizzle falls through cooler air near surface – evaporation may saturate cool air

    • Ice Pellets and Hail

      • Rain freezes passing through colder air

      • Water droplets freeze in clouds before becoming to heavy to fall

Precipitation32 l.jpg


  • Types?

    • Snow

      • Precipitation composed of ice crystals

      • Snow grains are the solid equivalent of drizzle

      • Ice crystals that descend from cirrus clouds are called “fallstreaks”, or mare’s tails.

Airmasses l.jpg


  • What is an airmass?

    • A large body of air with fairly uniform temperature and moisture content.

    • May be several hundreds miles across and usually forms where air is stationary, or nearly so, for several days.

    • Source Region:

      • The area where an airmass acquires the properties of temperature and moisture that determine its stability.

Airmasses34 l.jpg


  • Classifications

    • Airmasses are classified according the the regions where they originate.

Modification l.jpg


  • As an airmass moves out of it’s source region, it is modified by the temperature and moisture of the area over which it moves.

  • The degree to which an airmass is changes depends on several factors:

    • Speed

    • The nature of the region it moves over

    • Depth of the airmass

    • Temperature difference of surface and new airmass

Modification36 l.jpg


  • Warming From Below

    • As an airmass moves over a warmer surface, its lower layers are heated and vertical movement of the air develops.

    • Depending on temperature and moisture levels, this can result in extreme instability.

Modification37 l.jpg


  • Cooling From Below

    • When an airmass moves over a cooler surface, its lower layers are cooled and vertical movement is inhibited.

    • Stability of the airmass is increased.

    • If the air is cooled to its dewpoint, low clouds or fog may form.

    • Cooling from below creates a temperature inversion and may result in low ceilings and visibility for long periods of time.

Modification38 l.jpg


  • Cooling From Below

Fronts l.jpg


  • What is a Front?

    • The boundary between airmasses is called a front.

    • Weather along fronts often presents a serious hazard to flying, it is important to have a thorough understanding of the associated weather.

  • What are some types of Fronts?

    • Cold Front

    • Warm Front

    • Stationary Front

    • Occluded Front

Frontal discontinuities l.jpg

Frontal Discontinuities

  • Temperature

    • One of the most easily recognized discontinuity across a front.

    • Can be observed in the cockpit by looking at the OAT gauge.

  • Wind

    • The most reliable indication that you are crossing a front are changing wind directions and velocities.

    • In the northern hemisphere, the wind always shifts to the right when crossing a front.

  • Pressure

    • Pressure changes across fronts as well.

    • Must update altimeter settings to maintain the proper altitude.

Frontal weather l.jpg

Frontal Weather

  • Cold Front

    • Separates an advancing mass of cold, dense, and stable air from an area of warm, lighter, and unstable air.

    • Because of it’s greater density, the cold front moves along the surface and forces the less dense, warm air upward

Cold front l.jpg

Cold Front

Frontal weather43 l.jpg

Frontal Weather

  • Fast-Moving Cold Front

    • Cold fronts that are pushed along by an intense high pressure systems located will behind the front.

    • Surface friction acts to slow down the movement of the front, causing the leading edge of the front to bulge out and steepen the front’s slope.

    • Hazardous because of the wide differences in moisture and temperature between fronts.

  • Slow-Moving Cold Fronts

    • Produces clouds that move far behind the leading edge of the front. Broad area of stratus clouds.

Frontal weather44 l.jpg

Frontal Weather

  • Warm Fronts

    • Occur when warm air overtakes and replaces cooler air.

    • Usually move much slower than cold fronts.

    • The slope of a warm front is very gradual, and the warm air may extend over the cooler air for hundreds of miles.

Warm front l.jpg

Warm Front

Frontal weather46 l.jpg

Frontal Weather

  • Stationary Fronts

    • When the opposing forces of two airmasses are relatively balanced, the front that separates them may remain stationary and influence local flying conditions for several days.

    • The weather is typically a mixture of weather found in both warm and cold fronts.

Frontal weather47 l.jpg

Frontal Weather

  • Occluded Fronts

    • Occurs when a fast-moving cold front catches up to a slow-moving warm front.

    • The difference in temperature within each frontal system is a major factor that influences which type of front and weather are created.

Frontal weather48 l.jpg

Frontal Weather

  • Occluded Fronts

    • Cold Front Occlusion

      • Develops when the fast-moving cold front is colder than the air ahead of the slow-moving warm front.

      • The cold air replaces the cool air at the surface and forces the warm front aloft.

    • Warm Front Occlusion

      • Takes place when the air ahead of the slow-moving warm front is colder than the air within the fast-moving cold front.

Occlusions l.jpg


Weather hazards l.jpg

Weather Hazards

  • What types of hazards do we as pilots have to worry about?

    • Thunderstorms

    • Turbulence

    • Lightning

    • Hail

    • Tornadoes

    • Windshear

    • Icing

    • And even Volcanic Ash

Thunderstorms l.jpg


  • Thunderstorms are arguably the single greatest threat to aircraft operations.

  • Contain strong wind gusts, icing, hail, driving rain, lightning, and sometime tornadoes.

  • In order for thunderstorms to form, three conditions must be met:

    1. Air that has a tendency toward instability

    2. Some lifting action

    3. Relatively high moisture content

Thunderstorms52 l.jpg


  • Types of Thunderstorms

    • Airmass Thunderstorms

      • Scattered thunderstorms which are common during summer afternoons, or coastal areas at night. Short lived.

    • Severe Thunderstorms

      • Violent t-storms with wind gust +50 kt., hail ¾” diameter, and/or tornadoes.

    • Single-Cell

      • Thunderstorm that last less than one hour

    • Super-Cell

      • Thunderstorm that lasts up to two hours or more

    • Multicell

      • Compact cluster of thunderstorms

Thunderstorms53 l.jpg


  • Types of Thunderstorms

    • Squall Line

      • Thunderstorms that form a line

      • Often forms 50 to 300 miles ahead of a front, but the existence of a front is not necessary.

      • Can be a mixture of single-cell, multicell, super-cell

      • Very dangerous storms

    • Frontal Thunderstorms

      • Thunderstorms that are associated with frontal activity

      • Often obscured by stratiform clouds

      • Can form with Warm or Cold Fronts

Thunderstorms54 l.jpg


Thunderstorm life cycle l.jpg

Thunderstorm Life Cycle

  • 50 years ago it was dicovered that thunderstorms go through three definite stages.

  • What are these three stages??

    1. Cumulus Stage

    2. Mature Stage

    3. Dissipating Stage

Thunderstorm life cycle56 l.jpg

Thunderstorm Life Cycle

Cumulus stage l.jpg

Cumulus Stage

  • Lifting Action Required

  • Air rises and cools to dewpoint

  • Condensing air releases heat, causing further vertical development

  • Strong updrafts preventing precipitation from falling

  • Particle impact each other and grow in size

  • Becomes a Towering Cumulus Cloud (TCU)

  • Cloud can reach the Mature Stage in as little as 15 minutes.

Cumulus stage58 l.jpg

Cumulus Stage

Mature stage l.jpg

Mature Stage

  • Drops in the cloud become too large to be supported by the updrafts

  • Precipitation begins to fall

  • This creates a downward motion in the surrounding air and signals the beginning of the mature stage

  • This circulation of the thunderstorm cell is organized in this, the storm’s most violent stage

  • Warm updrafts and cool downdrafts exist side-by-side creating severe turbulence

  • At the surface, the air rushes downward and spreads outward rapidly

    • This cause a sharp drop in temperature, a rise in pressure, and strong, gusty winds

  • Gust Front/Roll Cloud

Mature stage60 l.jpg

Mature Stage

  • The top of the mature cell can reach higher than 40,000 ft.

  • Because of the drop in temperature, the moisture at the top of the cloud freezes giving the cloud a fuzzy appearance.

  • The vertical lift decreases towards the top and the moisture particle spread out horizontally, creating the well known anvil shape

  • The anvil is an indicator of the upper-level winds and the storm’s direction of movement.

Mature stage61 l.jpg

Mature Stage

Dissipating stage l.jpg

Dissipating Stage

  • Occurs 15 to 30 minutes after the storm reaches the mature stage

  • As the storm develops, more and more air aloft is disturbed by the falling drops

  • Downdrafts begin to spread out within the cell

  • The thunderstorm beginnings to weaken, predominated filled with downdrafts, it takes on a stratiform appearance, gradually dissipating.

Dissipating stage64 l.jpg

Dissipating Stage

Thunderstorm hazards l.jpg

Thunderstorm Hazards

  • What are some hazards associated with Thunderstorms?

    • Turbulence

    • Lightning

      • In cloud, Cloud-to-cloud, cloud-to-ground, cloud-to-clear air

      • 300,000 Volts per foot, heats air to more than 50,000 deg. F

    • Hail

      • Can occur at any altitude, inside or outside a cloud

      • Large hailstones have been encountered in clear air miles downwind from a thunderstorm

    • Tornadoes

      • Violent spinning columns of air which descend from the base of a cloud.

      • Winds may exceed 200 kt.

Lightning l.jpg


Slide67 l.jpg


Tornadoes l.jpg


Turbulence l.jpg


  • Low Level Turbulence (LLT)

    • Turbulence below 15,000 ft.

    • Most originates due to surface heating or friction within a few thousand feet of the ground.

    • LLT includes:

      • Mechanical Turbulence

      • Convective Turbulence

      • Frontal Turbulence

      • Wake Turbulence

Turbulence70 l.jpg


  • Mechanical Turbulence

Turbulence71 l.jpg


  • Mechanical Turbulence

Turbulence72 l.jpg


  • Convective Turbulence

Turbulence73 l.jpg


  • Frontal Turbulence

    • Occurs in the narrow zone just ahead of a fat-moving cold front where updrafts can reach 1,000 f.p.m.

    • When combine with convection and strong winds across the front, these updrafts can produce significant turbulence.

    • Over flat ground, any front moving at a speed of 30 knots or more will generate at least moderate turbulence.

    • A front moving over rough terrain will produce moderate or greater turbulence, regardless of its speed.

Turbulence74 l.jpg


  • Wake Turbulence

    • Whenever an airplane generates lift, air spills over the wingtips from the high pressure areas below the wings to the low pressure areas above the wings.

    • This flow causes rapidly rotating whirlpools of air called wingtip vortices, or Wake Turbulence.

    • Greatest vortex strength occurs when the aircraft is heavy, slow, and in a clean configuration.

    • Tend to sink below the flight path of the aircraft and spread out horizontally.

Wake turbulence l.jpg

Wake Turbulence

Wake turbulence avoidance l.jpg

Wake Turbulence Avoidance

The end l.jpg

The End

  • Any questions??

  • Next week we will be covering Weather Products!

    • Make sure you review this material before Monday…

  • Login