TROPOSPHERE

• Adjacent to the earth’s surface
• Varies in height from an average of 55,000 feet over the equator to 28,000 feet over the poles
• Temperature decreases with increasing altitude
• Contains large amounts of moisture and condensation nuclei due to proximity to earth’s surface
• Upper boundary is the tropopause, marked by an abrupt change in the rate of the temperature decrease with increasing altitude

• Transition zone between the troposphere and the stratosphere
• Temperature is isothermal with altitude
• Winds normally increase in speed with altitude below the tropopause
• Contrails frequently form and persist near the tropopause since it is normally the coldest area in the lower atmosphere
• Water vapor and large scale vertical currents do not exist to any extent in the tropopause

• Increasing temperature with increasing altitude due to the presence of ozone gas
• Thin air offers little resistance to aircraft
• Lack of weather makes for outstanding flying
• Above the stratosphere are the mesosphere thermosphere

• Turbulence due to the increasing wind speed with increasing altitude
• Storms are present and can limit visibility

• Turbulence due to the increasing wind speed with increasing altitude
• Contrails are often present

• Excellent conditions with maximum visibility and very little resistance to the aircraft
• Lack of weather makes this the best flying level

- Temperature

- Atmospheric pressure

• Wind
• Humidity
• Clouds
• Precipitation

TURBULENCE

• Comes in many forms and can be dangerous to flight
• Pilot may not be able to control aircraft due to being violently "bounced" around the cockpit
• Structural damage may also occur to aircraft

• Contain all hazards in one package
• Extensive damage to aircraft
• Loss of communications due to damaged antennae
• Altered airfoils to the point of producing entirely different flight characteristics
• Low ceilings and low visibility accompany these storms
• Turbulence may be found with wind shear as well as outside the storm in close proximity and with microbursts
• Lighting can damage or explode the aircraft
• Icing should be expected

• Movement of air at different velocities in the same or opposite directions
• Causes changes in aircraft performance that can have disastrous results
• Microbursts, strong downdrafts, are most dangerous and are especially dangerous during low and slow flight such as take-off and landing

• Ice build-up adds to the weight of the aircraft and changes the shape of the airfoil
• Ice build-up on the pitot tube causes inaccurate air speeds
• Ice build-up on the static pressure ports can cause inaccurate altimeter, vertical velocity, and airspeed readings

• Make approaches to land hazardous or even impossible
• May cover areas so large that fuel becomes a consideration
• If a pilot flies below the ceiling he may crash into the ground or some other obstacle

• Often associated with low ceilings
• May be caused by smoke, haze, dust, and fog even with no low clouds present
• May make landings hazardous or impossible

• Specific heat is the amount of heat required to raise the temperature of one gram of a substance one degrees Celsius
• Specific heat of an object is constant
• A land surface will heat up and cool much faster and to a much greater extent than will a water surface
• Specific heat of water is four times that of most land surfaces

• Insolation is the primary source for all weather phenomena on earth
• Insolation is the total radiation reaching the earth’s surface
• Insolation ceases at night and is replaced by terrestrial radiation which cools the earth thus maintaining the heat balance

• Lapse rate is the change in atmospheric temperature with increasing altitude

• The average or standard lapse rate is 2 degrees Celsius per 1000 feet

STEEP LAPSE RATE

• Steep lapse rate is when the temperature decreases very rapidly with altitude, greater than 3 degrees per 1000 feet

• Shallow lapse rate is when the temperature decreases very gradually, between 1.5 and 3.0 degrees Celsius per 1000 feet

• Isothermal lapse rate is when there is no temperature change with altitude

• Inversion is when the temperature increases with increasing altitude
• Inversion is inverted lapse rate
• Restricted to small layers of the atmosphere

• Atmospheric pressure is the pressure exerted on a surface by the atmosphere due to the weight of a column of air directly above that surface
• Always decreases with altitude
• Decreases more rapidly at lower atmospheric levels due to the density decreasing as altitude increases

• The standard units of pressure measurement are inches of mercury (in-Hg) and millibars (mb)
• Inches of mercury is a measure of the height of a column of mercury that can be supported by atmospheric pressure
• A millibar is a direct representation of pressure, which is defined as force per unit area

SEA LEVEL PRESSURE

• Sea level pressure is the pressure at mean sea level (MSL), measured directly at sea level or calculated if the station is not at sea level

• Station pressure is the atmospheric pressure at an airfield or station

• The standard atmosphere is the standard day at sea level conditions of 29.92 in-Hg at 15 degrees Celsius.

ELO 2.14 List the major items found on the surface pressure/analysis chart.

ISOBARS

• Isobars are lines of equal barometric pressure depicting the horizontal distribution on the earth’s surface

• A high is an area of pressure where the center is at a higher pressure than the surrounding areas

• A low is an area of pressure where the center is at a lower pressure than the surrounding areas

• A ridge is an extension of the high pressure area

• A trough is an extension of the low pressure area

• Pressure gradient is the rate of pressure change in a direction perpendicular to the isobars (horizontal distance)
• Gradient is steep when isobars are close together and shallow when they are far apart

• Indicated altitude is the altitude read on an altimeter when the current local altimeter setting is displayed in the Kohlsmann window

• Calibrated altitude is the indicated altitude corrected for instrument error

• MSL altitude is the actual height above mean sea level (MSL)

• AGL altitude is the aircraft’s height above the terrain directly below the aircraft and is measured in feet above ground

• Pressure altitude is the height above the standard datum plane.
• Standard datum plane is the actual elevation at which the barometric pressure is 29.92 in-Hg

• Density altitude is the altitude in the standard atmosphere that had the same density as the local air
• It is found by correcting the pressure altitude for non-standard temperature deviations

• A change in pressure of 0.10 in-Hg will result in a change of 100 feet on the altimeter reading
• If your flight path takes you into an area of higher MSL pressure the aircraft will be higher than the altimeter indicates
• If your flight path takes you into an area of lower MSL pressure the aircraft will be lower than the altimeter indicates

• For every 11 degrees Celsius that the temperature deviates from the standard, the altimeter will be in error by 4%
• If the air is colder than the standard atmosphere, the aircraft will be lower than the altimeter indicates
• If the air is warmer than the standard atmosphere, the aircraft will be higher than the altimeter indicates

• All problems completed on legal pad

• The irregular distribution of oceans and continents
• The relative effectiveness of differing surfaces in transferring heat to the atmosphere
• Irregular terrain
• Daily variations in temperature
• Changes of seasons
• Other factors

• The shape of isobars determines wind direction
• Where a high pressure system displaces a low pressure system with small distances between them the air flow is direct
• As distances between systems increase, other forces come into play:
• Coriolis force
• Friction
• Gravity
• Pressure gradient force

• Coriolis force effects pockets of air migrating north or south and it causes the pocket to be pushed to the right regardless of which way it is headed
• Northward winds get pushed ahead (to the right) as the rotation of the earth slows towards the north pole
• Southward winds lag behind (to the right) as the rotation of the earth speeds towards the equator
• Coriolis force is strongest at poles and decreases to zero at the equator

• A low pressure area arises when the air over the equatorial region is heated, rises toward the tropopause, and results in an area of low pressure on the surface and extends from the equator to about 30 degrees north
• An area of high pressure arises when the air beneath the subtropical jet stream subsides to the surface, and creates a high pressure belt at about 30 degrees north

• Winds that travel from the northeast to southwest
• Winds travel between the equator and 30 degrees north

• Winds that flow from the west to the east
• Winds travel between 30 degrees north and 60 degrees north

• Winds that flow from the east to the west
• Winds travel between 60 degrees north and the north pole

• Gradient winds flow parallel to the isobars and above 2,000 feet AGL
• Winds flow counter-clockwise around low pressure areas and are called cyclones
• Winds flow clockwise around high pressure areas and are called anti-cyclones

• Winds flow counter-clockwise around low pressure areas and are called cyclones
• Winds flow clockwise around high pressure areas and are called anti-cyclones
• Surface winds are deflected across isobars toward lower pressure

• Winds flow counter-clockwise around low pressure areas and are called cyclones
• Winds flow clockwise around high pressure areas and are called anti-cyclones

• Buys Ballot’s Law states that if the wind is at your back, the area of lower pressure will be at your left
• Aircraft tend to drift flying towards a high or low pressure system and if the pilot knows the change of pressure along the path he can estimate his direction of drift

• The jet stream is a narrow band of strong winds found most often in the vicinity of the tropopause
• Winds average 100-150 knots but can exceed 250 knots
• Jet streams are three dimensional having a length, depth, and width
• Meander in wavelike patterns around the globe and have profound effects on weather patterns

LAND BREEZE

• A land breeze is the movement of air from land to sea
• Cooler air moves towards lower pressure over the water during the night
• Shallow in depth

• A sea breeze is the movement of air from sea to land
• Do not penetrate far inland
• Winds of up to 15-20 knots are not uncommon
• Cool air over the water moves inland from the water during the day

VALLEY WINDS

• Warm air moves up a mountain during the day, out of the valley

• Cool air moves down the mountain at night, into the valley

SATURATION

• Saturation occurs when the actual specific humidity is equal to the maximum specific humidity and the air contains the maximum amount of water vapor

• Dew point is the temperature at which moisture first starts to condense and form dew on exposed surfaces

• Dew point depression is the difference, in degrees, between the air temperature and the dew point temperature

• Percent of saturation

• Ratio of water vapor weight to the weight of a total sample of air

• The relationship between specific humidity and dew point temperature is that the dew point is an indication of, and is directly related to specific humidity
• Generally, the higher the specific humidity, the higher the dew point temperature and the more variable the weather

SHOWERS

• Characterized by a sudden beginning and ending and abruptly changing intensity and/or sky conditions
• Associated with cumuliform clouds

• Steady, intensity changes gradually, if at all
• Associated with stratiform clouds

• Stops and restarts at least once during the hour
• May be showers or continuous
• May be associated with cumuliform or stratiform clouds

DRIZZLE

• Very small droplets of water which appear to float in the atmosphere

• Drizzle which freezes on impact with objects

• Precipitation in the form of water droplets which are larger than drizzle and fall to the ground

• Rain which freezes on impact with objects

• Small balls or other pieces of ice falling separately or frozen together in irregular lumps
• Consists of alternate opaque and clear layers of ice in most cases

• Transparent or translucent pellets of ice that are spherical or irregular
• They usually bounce when hitting hard ground and make a noise on impact

• Very small white, opaque grains of ice
• Do not bounce or shatter upon impact
• Usually fall is small quantities from stratus type clouds, never as showers

• White or translucent ice crystals, usually of branched hexagonal or star-like form

• Light Rain
• Visibility is somewhat restricted
• Forward visibility is restricted as rain picks up
• Heavy Rain
• Heavy rain on runways may cause hydroplaning
• Loss of control may result
• Visibility is severely reduced
• Heavy rain ingested into the engines of a jet or turboprop aircraft in flight can cause power loss or actual power loss or even flameout
• Snow
• Can reduce vision and lead to a total lack of forward visibility
• Buildup on the runway can cause enough friction to prevent the aircraft from reaching enough speed for takeoff
• Hail
• Can cause serious damage to the aircraft, but so can rain at high speeds

• Dense, sharply outlined clouds, appearing singly or in groups throughout the sky
• Light to moderate shower activity

• Large, dense, towering clouds with cauliflower like top often flattened into an anvil shape or consists of a cirrus formation resulting from ice crystals
• Thunderstorms, strong winds, precipitation is heavy, lightning
• Well developed cumulonimbus may be the parent of the hailstorm and tornado

• Form in layers with smooth bases and tops
• Gray in appearance and cover the entire sky
• Generally produces a light steady rain or drizzle

• Dark massive cloud layers having a wet appearance
• Accompanied by heavy precipitation of rain or snow
• Only cloud that builds down in the atmosphere

• Form a uniform blue or gray fibrous sheet covering all or most of the sky
• Produce light to moderate precipitation
• In some cases the sun may be barely visible

• Composed of white, hair-like filaments, sometimes in an orderly pattern, that may cover all or part of the sky but do not obscure it
• Composed of ice crystals and are transparent to sunlight
• Contrails from high altitude aircraft are man-made cirrus clouds

ATMOSPHERIC STABILITY

• The atmosphere is said to be stable if it tends towards one single equilibrium point

• The atmosphere is said to be unstable if it tends towards a point far from the equilibrium point

• The atmosphere is said to be neutrally stable if it does not tend to move from its position either towards or away from the equilibrium point

• The adiabatic process occurs when the temperature of a body of air changes without heat being added or taken away

• Describes the temperature decrease that occurs when a quantity of air is lifted
• As air descends it is compressed and warmed adiabatically

• Decreases at a rate of 3 degrees Celsius per 1000 feet

• Decreases at a rate of 1.5 degrees Celsius per 1000 feet
• Moist air cools at a slower rate than dry air because heat is released during the condensation process as the air is lifted

• Refers to the vertical temperature distribution within the atmosphere at any given time
• Described as steep, shallow, isothermal, or as an inversion

CONVERGENCE

• Two winds converging at one point pushing the excess upward, consequently, areas of convergent winds are regions favorable to the occurrence of precipitation

• A front flows in and pushes the air upward, displacing it

• Wind pushes air upward by using a geographic feature such as a mountain, the air is pushed up the mountain into the sky

• The sun creates heat that carries the air upward into the sky

• Conditional instability exists when the environmental lapse rate falls between the moist and dry adiabatic lapse rates
• Only factor determining stability is moisture

• Convective instability exists when extensive lifting is applied to air which has a layer of extremely dry air overlying a layer of moist air
• Lifting must be applied to a large volume of air
• As the layers cool the top layer cools faster than the lower layer and this causes the more dense top layer to try to switch places with the lower layer resulting in a violent clash giving severe thunderstorms, tornadoes, and turbulent flight

• An air mass is a large body of air that has essentially uniform temperature and moisture conditions in a horizontal plane
• May vary in size from several hundred to thousand miles

• The air mass classification system is based on the location of the air masses source region and according to the surface (air or water) of their source region
• Polar is not air from the poles, arctic is air from the poles

• If the air mass is warmer than the surface, it is cooled by contact with the cold ground, becomes more stable, and is called a warm air mass.
• If the air mass is colder than the surface, it is heated from below, resulting in convective currents and instability, and is called a cold air mass

• Maritime Polar
• Consists of the open unfrozen polar sea areas
• These areas are moist, but the moisture is sharply limited by the cold temperatures
• Considerable precipitation results in these areas
• Turbulence is considerable along mountain ranges due to the instability of the air and high velocities associated with movements over irregular terrain
• Icing conditions over mountains may also be severe
• After crossing the mountains the air begins to descend and warm adiabatically and the Maritime Polar Mass is reclassified as a Continental Polar Mass

• Continental Polar
• Consists of land areas dominated by the Canadian and Siberian high pressure cells
• Air is very dry
• Stability decreases as the air warms causing the lapse rate to become steeper
• Turbulence and snow flurries will form over rough terrain
• Air flowing over warm water experiences rapid heating resulting in rapid instability resulting in fog
• As air approaches mountains it is subject to orographic lifting causing instability resulting in cumulus clouds that may develop into cumulonimbus

• Maritime Tropical
• Air is warm and can hold considerable moisture
• Due to the moisture level, condensation may result in fog, low stratus, steady precipitation, or any combination of these
• As air approaches mountains, the conditional instability will be released resulting in possible thunderstorms or at least large and troublesome cumuliform clouds
• As air approaches flat land, the lift is not sufficient to release the instability and fog, or low stratus, will form, especially in the morning hours and may last for many hours covering thousands of square miles
• In the summer air moving north undergoes strong thermal heating resulting in towering cumulus and cumulonimbus clouds that give scattered rain storms and thunderstorms which should be avoided but usually die out by the evening

• Continental Tropical
• Consists of very warm and dry air, often called superior
• Due to low humidity cloud cover is sparse, yet when present they are of the cumuliform type and found mainly over mountains
• Flying is usually rough during the middle and low levels, especially during the day when surface heating increases instability

• A front is an area of discontinuity that forms between two contrasting air masses when they come together
• These air masses must have sufficiently different temperature and moisture properties

• Frontogenesis means the formation of a new front or the regeneration of a decaying front

• Temperature and pressure change
• Winds usually shift 90 degrees from one side to another
• Ahead of the front the, the wind blows parallel to the front and toward the lower pressure
• Behind the front, the wind blows perpendicular to the front and pushes the front along
• The speed of movement is often different
• Frontal cloud and precipitation patters of most fronts are not recognizable above 15,000 to 20,000 feet
• The most significant frontal weather occurs in the lower layers of the atmospheres
• Temperature contrast between the air masses can extend up to the tropopause

• The polar front is the zone separating the warm tropical air masses and the cold polar air masses in the middle latitudes
• The polar front is not stationary

• Differences in the various properties of adjacent air masses, such as temperature, moisture (indicated by the dew point), wind, and pressure are used to locate and classify fronts

• A front’s slope is determined largely by surface friction acting on an air mass below 2,000 feet and by the varying velocities of the air masses involved
• Shallow frontal slopes produce extensive cloudiness
• Steep frontal slopes produce narrow bands of cloudiness
• The speed of a frontal movement affects the weather associated with it
• Faster moving fronts are accompanied by poor weather
• Slower moving fronts have less severe weather
• The degree of stability of the air s lifted determines whether the cloudiness will be predominantly stratiform or cumuliform
• Stratiform gives mostly steady precipitation and little or no turbulence
• Cumuliform gives showers and turbulence
• Moisture is necessary for the formation of clouds and weather hazards
• With no water vapor present in the air, flight conditions would be perfect and there would be no worries about weather or clouds

• The upward motion often produces violent unstable conditions including cumulonimbus clouds, strong thunderstorms, and severe turbulence
• Rain showers or snow showers are present
• Barometric pressure decreases
• Cold frontal slopes range from 1/50 to 1/150 and average about 1/80

• A squall is a nonfrontal line of violent thunderstorms, or cumulonimbus clouds
• Most occur in the warm air mass
• Develop 50 to 300 miles in ahead of the front and parallel to it
• Contain severe weather conditions including turbulence, hail, icing, lightning, heavy rain, and/or tornadoes

• Slower moving than a cold front
• Not as defined as cold fronts
• Warm frontal slopes range between 1/50 and 1/200 with an average of 1/100
• Showery precipitation accompanies warm fronts

• Neither air mass replaces the other
• Surface winds tend to blow parallel on both sides of the front rather than against and/or away from it
• Similar weather as warm fronts, just less intense
• May persist in one area for days

• Form when a warm and cold front meet
• Three air masses are present
• Cold (most dense) air mass
• Cool (less dense) air mass
• Warm (least dense) air mass
• Warm is located in between the other two
• Forms when the cold front gradually overtakes the warm front
• Type of occlusion depends on which front is in contact with the ground
• Generally align themselves in a north south direction
• Exhibits weather characteristics from both warm and cold fronts
• Will move northeast at the speed of the front maintaining contact with the ground
• Cold front occlusion
• Cold front remains in contact with the ground
• Occurs when the air mass behind the cold front is colder and more dense than the cool air mass in advance of the warm front
• Situation resembles a typical cold front
• Warm front occlusion
• Warm front remains in contact with the ground
• Occurs when the air mass ahead of the warm front is colder and more dense than both the cold air mass behind the cold front and the warm air mass
• Situation resembles a typical warm front

• Occurs primarily in the winter
• Cold front moves over an even colder air mass lying in the lower layers of the atmosphere

• Clouds and precipitation do not accompany inactive fronts
• Warm air mass may be too dry for clouds to form even after the air mass has lifted
• Often referred to as dry fronts

• The requirements for thunderstorm (cumulonimbus cloud) formation are as follows:
• Lifting Action
• Necessary to bring warm air near a point where it will rise continuously
• Normally provided by orographic effects, fronts, thermals, or convergence
• Unstable Air
• Created when lifted air becomes high enough that it is warmer than the surrounding air (e.g. steep lapse rate)
• Also provided by convective instability
• Moisture
• Formed when air is lifted to the point where water vapor condenses
• Dew point temperatures of 80 degrees or higher are excellent indicators of thunderstorms activity
• Building Through The Freezing Level
• Causes cloud droplets to freeze
• Collisions cause a separation of charge released in the form of lightning

• Thunderstorms progress through three stages during their life cycle; the cumulus stage, the mature stage, and the dissipating stage
• Cumulus Stage
• Initial stage of a thunderstorm is always a cumulus cloud
• Main feature of this stage is the updraft which may extend from near the earth’s surface to several thousand feet above the visible cloud top
• Strongest updrafts occur at higher altitudes late in the stage and they may be greater than 3,000 feet per minute
• Stage has no precipitation due to moisture being carried upward in the updrafts but severe turbulence exists
• As the cloud forms, water vapor changes to liquid and/or ice particles providing a source of energy for the developing cloud
• Mature Stage
• Reached when rain and ice become too heavy to be supported by the cloud and begin to fall
• Average cell grows to a height of 25,000 feet during this stage
• Updrafts continue to increase in speed and may exceed up to 6,000 feet per minute
• Cold air accelerates creating downdrafts that may reach a velocity of up to 2,500 feet per minute
• Produces a sharp temperature drop, and strong, gusty surface winds
• Leading edge of this is called the gust front
• Updrafts and downdrafts result in wind shear that produces severe turbulence
• Thunderstorms reach their most intense time in this stage and are located in the upper 2/3 of the cell
• Dissipating Stage
• Downdrafts continue to develop while updrafts continue to weaken
• Eventually the entire thunderstorm becomes an area of downdrafts with precipitation in the dissipating stage
• The thunderstorm dissipates when there are no updrafts present
• Storms can dissipate without the entire loss of updrafts
• Pressure Changes
• A rapid fall in pressure as the storm approaches
• An abrupt rise in pressure with the onset of the first gust and arrival of rain showers
• A gradual return to normal pressure as the storm passes and the rain ceases

FRONTAL THUNDERSTORMS

• Caused by the lifting of warm, moist, unstable air over a frontal surface
• Normally form in lines
• Warm-frontal thunderstorms
• Least intense
• Not a strong lifting action
• Cold-frontal thunderstorms
• Most intense
• Form in a continuous line and typically in the afternoon
• Stationary-frontal thunderstorms
• Normally widely scattered
• Occluded-frontal thunderstorms
• Dangerous because they can be embedded in stratiform clouds and therefore difficult to see

• The hazards associated with thunderstorms are extreme turbulence, hail, microburst, icing, lightning, and tornadoes

• A microburst is an intense highly localized downward atmospheric flow with velocities of 2,000 to over 6,000 feet per minute

• May emanate from any convective cloud
• Dangerous during takeoff, approach, and go-around phases of flight
• May develop in families of two or more
• Visual indicators include virga, localized dust blowing, rain shafts with rain diverging away from the core of the cell, roll clouds, and an indication of vivid lightning or tornado-like activity
• Likely with gusty winds, heavy rain, or thunderstorms

• Form out of the top of a cumulonimbus cloud
• Winds range from 10-300 mph
• Land speed is 25-40 mph
• High winds are the primary destructive force
• Flying debris is the second force
• Third force is falling buildings
• The fourth is the explosive force associated with the rapid drop in outside pressure in relation to the higher pressure inside of buildings and houses
• Requirements for formation are:
• Warm and moist air near the earth’s surface
• Cold and dry air in the middle atmosphere
• Strong upper level winds
• Presence of cumulonimbus clouds
• Conditions indicating tornado activity
• Pronounced horizontal wind shear
• Rapidly moving cold front or squall
• Strong convergence
• Marked convective instability
• Dry air mass superimposed on a moist air mass, abrupt change in moisture content, usually below 10,000 feet
• Marked convection to the –10 degrees Celsius isotherm

• Let pilot know where thunderstorm is as it usually contains turbulence
• Pilot can circumnavigate the storms
• Most helpful when there are several thunderstorms present which are obscured by multiple cloud layers
• Airborne weather radar should be used as an avoidance rather than a penetration tool

• If at all possible avoid thunderstorms
• Do not venture closer than 20 miles to any mature visible storm cloud with overhanging anvils because of the possibility of encountering hail
• Do not attempt to fly under orographic thunderstorms even if the area on the other side of the mountain can be seen
• Avoid flying under thunderstorms because updrafts and downdrafts can exceed the performance of the aircraft
• If circumnavigation is impossible, the next best thing is to fly over the top

• The intensities used to describe turbulence are light, moderate, severe, and extreme

• Occasional Less than 1/3 of the time
• Intermittent 1/3 to 2/3 of the time
• Continuous More than 2/3 of the time

• Thermal turbulence occurs when cold air moves over warmer ground and is heated, or by localized convective currents due to surface heating

• Cumulus clouds form when the air is moist and are convective-type clouds

• Mechanical turbulence occurs from wind flowing over or around irregular terrain or other obstructions

• Lenticular Clouds
• Smooth in contour but may be quite ragged
• May occur singularly or in layers at heights usually above 20,000 feet
• Stationary in position
• Rotor Clouds
• Forms at a lower level and is generally found at about the same height as the mountain ridge
• Cap Cloud
• Usually obscures both sides of the mountain peak
• Must be avoided due to turbulence and obscuring the mountain peak
• Turbulence
• Severe turbulence can frequently be found from the surface to the tropopause and 150 miles downwind when the winds are greater than 50 knots at the mountaintop
• Extreme turbulence can often be found at low levels on the leeward side of the mountain in or near the rotor and cap clouds when the winds are 50 knots or greater at the mountaintop
• Moderate turbulence often can be experienced out to 300 miles under the previously stated conditions

• The following rules should be applied when mountain wave turbulence has been forecast:
• 1) Avoid turbulence if possible by flying around the areas, if it is impossible to avoid fly at a level that is at least 50% higher than the height of the nearest mountain range along your flight path
• 2) Avoid the rotor, lenticular, and the cap clouds since they contain intense turbulence and strong updrafts and downdrafts
• 3) Approach the mountain range at a 45 degree angle so that a quick turn can be made to avoid the ridge in the event of a downdraft
• 4) Do not place too much confidence in your pressure altimeter reading near mountain peaks, they may include altitudes that are more than 2,500 feet higher than your true altitude
• 5) Penetrate turbulent areas at air speeds recommended for your aircraft

• The lifting of warm air by a frontal surface leading to the instability and/or wind shear between the warm and cold air masses causes frontal turbulence
• The most severe cases of frontal turbulence are generally associated with fast moving cold fronts

• Frequently found around jet streams where large shears in both the horizontal and vertical planes are found as well as in association with land and sea breezes, fronts, inversions and thunderstorms
• A narrow zone of wind shear, with its accompanying turbulence, will sometimes be encountered in flight by aircrews as they climb or descent through a temperature inversion

• Always avoid turbulence whenever possible and avoid areas of changing winds and wind shear
• If it cannot be avoided follow the following techniques for turbulence avoidance:
• Trim the aircraft for level flight at the recommended turbulence air penetration airspeed
• Severe turbulence may cause changes in indicated airspeed, do not chase airspeed
• The key to flying through turbulence is proper attitude control, both pitch and bank should be controlled by reference to attitude indicator
• Establish and maintain thrust settings consistent with turbulent air penetration airspeed and aircraft attitude
• Severe vertical gusts may cause appreciable altitude deviations, allow altitude to vary
• Sacrifice altitude to maintain desired attitude, do not chase altimeter

• The presence of ice on an aircraft increases weight and drag and decreases lift and thrust, thereby decreasing performance
• Icing disrupts the smooth flow of air over airfoils, thereby decreasing lift and thrust, increasing drag, and increasing stall speed
• Icing can cause vibration that can cause damage to the aircraft
• Engines, fuel, and other instruments can also malfunction due to icing

• Supercool water is liquid found at air temperatures below freezing
• Supercool water droplets are numerous in clouds at temperatures between 0 and –15 degrees Celsius
• As supercooled water strikes a wing it forms ice resulting in icing

• Wet snow in its true state forms as the result of deposition in the upper limits of clouds
• Occurs at temperatures just below freezing
• The pilot can climb to increasing altitudes where moisture is not present and snow flakes will not cause flaking or he can drop to altitudes well above freezing if terrain and lapse rate permit

• The three requirements for structural freezing are outside air temperature below freezing, aircraft skin temperature below freezing, and visible moisture

• The most severe icing is encountered between 0 and –10 degrees Celsius
• Dangerous conditions can be encountered below –10 degrees Celsius

• The rate of ice accumulation on an aircraft is affected by the following items:
• The size and number of water drops in a given volume of air
• Small drops follow the airflow, large drops resist the airflow and strike the airfoil more readily than small drops
• Airfoil thickness
• Thick airfoils have a larger deflective force so they collect ice more slowly than thinner air foils which have a smaller deflective force
• Airspeed
• As airspeed is increased more water is encountered and thus buildup is increased

DEICING EQUIPMENT

• Eliminates or removes ice that has already accumulated on the aircraft
• Rubber boots on leading edges of lift producing surfaces inflate and deflate to crack ice and allow the air stream to peal it off
• Heat, fluid, and mechanical techniques are also used to de-ice

• Anti-icing fluids are freezing point depressants and are pumped through small holes in the wing’s leading edge
• Critical areas can be heated electrically in newer aircraft

CLEAR ICE

• Clear ice forms at temperatures between 0 and –10 degrees Celsius, but my occur at up to –25 degrees Celsius
• Occurs in cumuliform clouds with appropriate temperatures where vertical currents can large drops

• Rime ice is a milky white, opaque and granular deposit of ice formed through the rapid freezing of small supercooled water droplets
• Most likely to occur at temperatures from –10 to –20 degrees Celsius
• Rime ice can be expected in stratiform clouds since vertical currents are not strong enough to support large droplets

• Mixed ice is a combination of clear ice and rime ice
• Most frequent type encountered

• Frost is a thin layer of crystalline ice that forms on exposed surfaces when the temperature of the exposed surface is below freezing and the dew point of the air is below freezing
• Also occur when both the temperature and the dew point are below freezing and they are within 5 degrees of each other, the night skies are clear, and the winds are calm
• May form when the free air temperature is slightly above freezing

• The most hazardous aspect of structural icing is its aerodynamic effects
• Ice can alter the shape of an airfoil
• Ice thickness, along with location, roughness, and shape all determine the effect of icing
• Roll upset is an uncommanded and uncontrolled roll phenomenon resulting from airflow separation that causes self deflection of the ailerons
• A tailplane (empennage) stall occurs when, as with the wing, the critical angle of attack is exceeded
• Application of flaps can aggravate or initiate the stall in two situations, when the flaps are approaching the fully extended position or during flight through wind gusts

INDUCTION ICING

• Occurs at the air intake duct
• Similar to wing icing when below freezing
• When above freezing, induction icing can occur when the reduced pressure that exists at the intake lowers the temperature to the point that condensation and/or deposition take place, resulting in the formation of ice

• Occurs on compressor inlet screens and compressor inlet guide vanes
• Restricts the flow of inlet air
• Causes thrust and a rapid rise in exhaust gas temperature
• Ice build-up on inlet screens sufficient enough to cause turbine failure can occur in less than one minute in severe conditions

• As an aircraft is refueled in the rain or in high humidity, the fuel absorbs water and can cause frozen fuel lines under cold outside air conditions
• Results in an engine flameout

• Water or slush that is blown onto the aircraft can form an ice cover on the under side of flaps, control surfaces, and the landing gear mechanism
• Ice and snow on runways can cause problems breaking

AIR MASS ICING

• Stable air masses often produce stratus-type clouds with extensive areas of rime icing conditions
• Unstable air masses generally produce cumulous clouds with limited horizontal extent of icing conditions
• Pilots can tend to expect more icing while flying over mountainous terrain under icing conditions, than over other types of terrain with the same atmospheric conditions

• Cold fronts and squall lines generally have a narrow weather and icing band
• Associated clouds will be cumuliform
• Icing will be predominantly clear
• Warm fronts and stationary fronts generally have a wide weather and icing band with stratiform clouds
• Icing will be predominantly rime
• Rain or drizzle falling from warm air above to cold air below causes severe clear icing and evasive action is to climb to an altitude where the temperature is above freezing
• Occluded fronts often produce a wide weather and icing band with both stratiform and cumuliform-type clouds
• Icing will be clear, mixed, and rime

• Worst conditions encountered at or above the freezing level
• Cumulus cloud
• Icing is clear from 0 to –5 degrees Celsius
• Icing is mixed from –5 to –10 degrees Celsius
• Icing is rime from –10 degrees Celsius and below
• Mature cloud
• Icing temperatures same as for cumulus cloud
• No icing in downdrafts, only in updrafts
• Dissipating
• Icing is clear and mixed from 0 to –5 degrees Celsius
• No icing below –5 degrees Celsius due to downdrafts

• Do not fly parallel to a front while encountering icing conditions
• Avoid the area below 4,000 or 5,000 feet above ridges when flying on instruments through clouds at indicated air temperatures less than 0 degrees Celsius
• Do not make steep turns with ice on the airplane due to increased stall speeds
• Do not land with reduced power, use higher airspeeds when the potential for ice on the wings or other exposed surfaces exists
• Avoid high angles of attack when ice has formed on the aircraft since stalling speeds are increased
• Do not forget when flying under icing conditions, that fuel consumption is greater, due to increased drag and the additional power required
• Avoid icing conditions as much as possible in the terminal phase of flight due to reduced airspeeds
• Always remove ice or frost from airfoils before attempting to take off
• In stratiform clouds, you can likely alleviate icing by changing to a flight level with above-freezing temperatures or to one colder than –10 degrees Celsius; an altitude change may also take you out of the clouds

• Clear Ice
• Clear ice forms at temperatures between 0 and –10 degrees Celsius, but my occur at up to –25 degrees Celsius
• Occurs in cumuliform clouds with appropriate temperatures where vertical currents can large drops

• Rime ice is a milky white, opaque and granular deposit of ice formed through the rapid freezing of small supercooled water droplets
• Most likely to occur at temperatures from –10 to –20 degrees Celsius
• Rime ice can be expected in stratiform clouds since vertical currents are not strong enough to support large droplets

• Mixed ice is a combination of clear ice and rime ice
• Most frequent type encountered

• Trace
• Ice becomes perceptible
• Rate of accumulation slightly greater than that of sublimation
• Not hazardous
• Light
• Over one hour in this environment can create a problem
• Occasional use of anti-icing/deicing equipment needed to maintain no hazards
• Moderate
• Rate of accumulation is such that even short encounters are dangerous
• Use of anti-icing/deicing equipment is necessary
• Heavy
• Rate of accumulation is such that anti-icing/deicing equipment fails to reduce or control the hazard
• Immediate diversion is necessary

• PIREPS are the only form of knowledge the pilots have in regards to the icing conditions ahead.
• Accurate reports from other pilots can be vital to the safety of another aircraft

VISIBILITY

• Visibility is the ability to see and identify prominent unlighted objects by day and prominent lighted objects by night, and is expressed in statute miles, hundreds of feet, or meters

• Flight visibility is the average forward horizontal distance, measured in statute miles from the cockpit of an aircraft in flight, at which prominent unlighted objects may be seen and identified by day and prominent lighted objects may be seen and identified by night

• Prevailing visibility is the greatest horizontal visibility, measured in statute miles, equaled or exceeded throughout at least half the horizon circle, which need to be continuous

• Slant visibility is the distance on final approach when you can see the runway

• Runway visual range is the horizontal distance, expressed in hundreds of feet or meters, a pilot will see by looking down the runway from the approach end

• Obscuring phenomena are any collection of particles, such as haze, fog, smoke, volcanic ash and blowing spray to name a few which reduce horizontal visibility to less than seven miles
• They may be either surface based or aloft

CEILING

• A ceiling is the height above the ground (AGL) ascribed to the lowest broken or overcast layer; or the vertical visibility into an obscuring phenomena

• Vertical visibility is the distance that can be seen directly upward into an obscuring phenomena
• If the celestial dome is totally hidden from view (8/8’s) by some upward as seen from the ground

• The obscuring phenomenon reduces the slant range visibility in the case of vertical visibility
• Due to this, the pilot will have difficulty seeing the runway or approach lights clearly even after descending below the level of the reported vertical stability

• Fog is a visible aggregate of minute water particles (droplets) which are based at or within 50 feet of the surface, greater than 20 feet in depth, and reduces the prevailing visibility to less than 5/8 of a statute mile
• Reduces horizontal and vertical visibility and may extend over a large area

• The four conditions are as follows:
• The air must have a high water content
• The temperature and dew point temperature must be equal (or nearly so)
• Condensation nuclei must be present in the air
• Light surface winds must be present, calm winds (zero knots) will not produce fog

• Winds of 1 to 5 knots will produce eddy currents and a layer of fog with bases between 2 and 10 feet
• Winds of 5 to 10 knots will produce eddy currents and a layer of fog with bases up to 50 feet
• Higher wind speeds normally will cause the fog to lift and become a stratus type cloud or dissipate altogether

• Fogs are classified as either air mass or frontal and the specific types of fog are: radiation, advection, upslope, and frontal, steam and ice

• Radiation fog occurs because of a reduction in air temperature as a result of nocturnal cooling
• Nocturnal cooling of air is defined as the night-time radiational cooling that occurs over land areas
• An increase in the surface air temperature increases the ability of the air to hold more water vapor, and the fog particles tendevaporate

• Advection fog occurs when warm, moist air moves over a cold surface and the air cools to below its dew point
• Common in coastal areas, often referred to as sea fog
• Dissipation is caused by a "wind shift"

• Upslope fog forms when orographic lifting causes enough adiabatic cooling to reduce the air temperature to the dew point temperature
• Dissipation generally occurs when a wind shift pushes the air down the slope and causes adiabatic warming

• Steam fog is an evaporation fog forming when cold air moves over warmer water
• Occurs frequently in the winter over open bodies of water in polar regions
• Steam fog rises from the surface like smoke
• Steam fog dissipates by heating the air through conduction

• Ice fog is a form of radiation fog that forms in moist air during extremely cold, calm conditions
• Occurs mostly in the arctic