PHAK 12: Weather Flashcards
How high does the Earth’s atmosphere extend vertically?
Almost 350 miles.
What is the composition of the atmosphere?
- 78% Nitrogen
- 21% Oxygen
- 1% Other gases (mostly Argon)
What are the layers of the atmosphere from Earth to space?
- Troposphere
- Tropopause
- Stratosphere
- Mesosphere
- Thermosphere
- Exosphere
Certain factors combine to set the atmosphere in motion, but a major factor is…
The uneven heating of the Earth’s surface.
What causes higher temperatures in equatorial areas?
Solar heating.
How much would a sealed column of air 350 miles high with a 1 square inch footprint weigh?
14.7 lbs
What is the Coriolis force?
A force caused by Earth’s rotation that deflects moving air and water.
Mercurial Barometer
A barometer that measures atmospheric pressure using a column of mercury.
Aneroid barometer
An instrument that measures the absolute pressure of the atmosphere by balancing the weight of the air above it against the spring action of the aneroid.
The Coriolis force deflects air to the ______ in the Northern Hemisphere.
Right
Standard Sea Level Pressure
- 59°F or 15°C
- 29.92” Hg or 1013.2 mb
What causes Convective Currents?
Plowed ground, rocks, sand, and barren land absorb solar energy quickly and can therefore give off a large amount of heat; whereas, water, trees, and other areas of vegetation tend to more slowly absorb heat and give off heat. The resulting uneven heating of the air creates small areas of local circulation called convective currents.
Effect of Obstructions on Wind
Obstructions on the ground affect the flow of wind and can be an unseen danger. Ground topography and large buildings can break up the flow of the wind and create wind gusts that change rapidly in direction and speed.
Depiction of winds on a surface weather chart.
Calm
Depiction of winds on a surface weather chart.
NW/5 kts
Depiction of winds on a surface weather chart.
SW/20 kts
Depiction of winds on a surface weather chart.
E/35 kts
Depiction of winds on a surface weather chart.
N/50 kts
Depiction of winds on a surface weather chart.
W/105 kts
Wind conditions
Each barb represents a speed of…
10 knots.
Wind conditions
Each half barb represents a speed of…
5 knots.
Wind conditions
Each pennant represents a speed of…
50 knots.
What are the characteristics of stable air?
Calm conditions and smooth airflow.
What type of clouds form in Stable Air?
Stratiform clouds
What is surface visibility typically like in Stable Air?
Poor surface visibility
What type of precipitation is found in Stable Air?
Steady or continuous precipitation.
What are the characteristics of unstable air?
Strong surface winds and turbulent airflow.
What type of clouds form in Unstable Air?
Cumulus clouds
What is surface visibility typically like in Unstable Air?
Good surface visibility.
What type of precipitation is found in Unstable Air?
Showery precipitation.
Trough
Elongated area of low pressure, rising air.
Ridge
Elongated area of high pressure, descending air.
Isobar
- Solid lines on a weather chart depicting lines of equal pressure.
- Lines closer together indicate steep pressure gradient and strong winds.
Wind Shear
- Sudden, drastic change in wind speed and/or direction over a very small area.
- Extremely dangerous at low altitudes.
Microburst
A small but intense downdraft causing extremely strong wind shear and hazardous winds.
3 Main Layers of Atmosphere that affect weather
- Troposphere
- Tropopause
- Stratosphere
Wind
Air movement caused by differences in atmospheric pressure.
Describe a High-Pressure Area
- Clockwise and dry.
- Descending air.
- Good weather.
- Clear skies.
Is a High-Pressure area typically moist or dry?
Dry
How does the air in a High-Pressure area move?
- Clockwise rotation
- Anticyclonic
- Descending
Describe a Low-Pressure Area
- Counterclockwise rotation.
- Cyclonic.
- Rising air.
- Poor visibility.
- Rain, fog, thunderstorms, cloudiness.
How does the air in a Low-Pressure area move?
- Counterclockwise rotation
- Cyclonic
- Rising
Dew Point
Temperature at which the air cannot hold any more moisture.
What happens when the air temperature reaches the Dew Point?
The air is completely saturated and moisture begins to condense out of the air in the form of fog, dew, frost, clouds, rain, or snow.
Radiation Fog
Forms on clear nights with little or no wind and generally over land.
As the Earth’s surface radiates its stored heat into space, it cools down.
When the near-surface air temperature drops to the dew point, humidity reaches 100%, and fog forms.
What type of fog forms on clear nights with little or no wind and generally over land.
Radiation Fog
Where does Radiation Fog form?
Always found at ground level.
How does Radiation Fog affect pilots?
Reduces visibility near the ground.
When does Radiation Fog dissipate?
Burns off once the sun rises and temperature increases.
Advection Fog
Wind blows moist, warm air over colder land or water. The air mass is cooled from below and the temperature is reduce to the dew point.
What type of fog occurs when wind blows moist, warm air over colder land or water.
Advection Fog
Where does Advection Fog form?
Common in coastal areas where sea breezes can blow the air over cooler landmasses.
Upslope Fog
Light wind pushes moist, stable air up a slope, such as a mountain range, to the level where air becomes saturated and condensation occurs.
Covers a large area.
Can persist for days.
What type of fog forms when light wind pushes moist, stable air up a slope, such as a mountain range, to the level where air becomes saturated and condensation occurs.
Upslope Fog
Steam Fog
“Sea Smoke”.
Cold, dry air moves over warm water.
As the water evaporates, it cools to its dew point, and the fog forms resembling smoke.
What type of fog forms when cold, dry air moves over warm water.
Steam Fog
What is Sea Smoke
A nickname for Steam Fog.
How much does Hg increase with altitude?
Approximately 1 “Hg per 1,000 feet
ISA
International Standard Atmosphere
What happens to takeoff and landing distances with increased altitude?
They increase.
Are aircraft engines and propellers more or less efficient in higher density altitudes?
Less.
At what altitudes do people become impaired due to lack of oxygen?
The average person around 10,000 feet.
Some as low as 5,000 feet.
What is low-level wind shear commonly associated with?
- Passing frontal systems
- Thunderstorms
- Temperature inversions
- Strong upper level winds. (25+ knots)
What is a microburst typically associated with?
Convective precipitation into dry air at cloud base.
Generally the wind 2,000 feet AGL is what?
20° to 40° to the right of surface winds and greater in speed
Adiabatic heating
A process of heating dry air through compression. For example, as air moves down a slope it is compressed, which results in an increase in temperature.
Adiabatic cooling
A process of cooling the air through expansion. For example, as air moves up slope it expands with the reduction of atmospheric pressure and cools as it expands.
As a parcel of air rises…
Pressure decreases, volume increases, and temperature decreases.
As a parcel of air descends…
Pressure increases, volume decreases, temperature increases.
Lapse Rate
Change in temperature over altitude.
Average Lapse Rate
2 °C or 3.5 °F per 1,000 feet
up to 36,000’
Water vapor is ______ than air.
Lighter
Moisture ______ air density, causing it to ______.
Decreases, rise.
As moisture decreases, air becomes ______ and tends to ______.
Denser, sink
Moist air cools at a ______ rate and is generally ______ stable than dry air.
Slower, less.
Dry Adiabatic Lapse Rate
(unsaturated air)
3 °C or 5.4 °F
per 1,000 feet
Moist Adiabatic Lapse Rate
- Varies from 1.1 °C to 2.8 °C per 1,000 feet.
- Varies from 2 °F to 5 °F per 1,000 feet.
The combination of moisture and temperature determine the…
Stability of the air and the resulting weather.
Cool, dry air is very ______ and resists…
Stable, vertical movement.
Leads to good and generally clear weather.
The greatest instability occurs when the air is…
Moist and warm.
Inversions
The air temperature rises with altitude.
Every 20 °F increase in temperature…
Doubles the amount of moisture the air can hold.
How can you double the amount of moisture air can hold?
Increase the temperature by 20 °F.
Every 20 °F decrease in temperature…
Cuts the amount of moisture the air can hold in half.
How can you cut the amount of moisture the air can hold in half?
Decrease the temperature by 20 °F.
Water is present in the atmosphere in what three states?
- Liquid
- Solid
- Gaseous
Which processes add water to the atmosphere?
Evaporation and sublimation.
What are the 6 types of water changes?
- Evaporation
- Sublimation
- Condensation
- Deposition
- Melting
- Freezing
Sublimation
The changing of ice directly to water vapor.
Evaporation
The changing of liquid water to water vapor.
Latent Heat of Evaporation
As water vapor forms, it absorbs heat from the nearest available source.
Relative Humidity
The actual amount of moisture in the air compared to the total amount of moisture the air could hold at that temperature.
How to determine the cloud base using temperature and dew point.
Temperature (T)
Dew Point (DP)
Convergence Rate (CR)
T - DP = Temperature Dew Point Spread (TDS)
TDS / CR = X
X * 1,000 feet = height of cloud base AGL
What is the temperature and dew point convergence rate as altitude increases?
4.4°F per 1,000 feet.
This is because unsaturated air cools at a rate of 5.4°F per 1,000 feet, while the dew point decreases at a rate of 1°F per 1,000 feet.
OAT
Outside Air Temperature
What are the 4 methods by which air can reach the saturation point?
- When warm air moves over a cold surface. Air temperature drops.
- When warm air and cold air mix.
- When air cools at night through contact with the cooler ground.
- When air is lifted or forced upward in the atmosphere.
If radiation fog is less than 20 feet thick it is known as?
Ground Fog
What is associated with steam fog?
Low-level turbulence and icing.
When and where is Steam Fog common?
Over bodies of water in the coldest times of the year.
Ice Fog
Water vapor turns directly into ice crystals. Same conditions as radiation fog except for temperature of -25 F or colder.
Saturation Point
When air temperature matches the dew point.
Cloud type is determined by
- Height
- Shape
- Characteristics
Clouds are classified by
The height of their bases.
* Low
* Medium
* High
* Clouds with vertical development.
Low Clouds form…
Near the Earth’s surface and extend up to about 6,500 feet AGL.
Typical Low Cloud types
- Stratus
- Stratocumulus
- Nimbostratus
- Cumulus
- Fog
Stratus clouds form in what level?
Low
Stratocumulus clouds form in what level?
Low
Nimbostratus clouds form in what level?
Low
Cumulus clouds form in what level?
Low
Fog forms in what level?
Low
Middle clouds form…
Around 6,500 feet AGL and extend up to 20,000 feet AGL.
Middle clouds are composed of…
- Water
- Ice crystals
- Supercooled water droplets
Typical Middle cloud types
- Altostratus
- Altocumulus
Altostratus clouds form in what level?
Middle
Altocumulus clouds form in what level?
Middle
Altostratus clouds can produce…
Turbulence and moderate icing.
Altocumulus clouds usually form when…
Altostratus clouds break apart.
Altocumulus clouds may contain…
Light turbulence and icing.
High clouds form…
Above 20,000 feet AGL and usually only in stable air.
Typical High cloud types
- Cirrus
- Cirrostratus
- Cirrocumulus
Cirrus clouds form in what level?
High
Cirrostratus clouds form in what level?
High
Cirrocumulus clouds typically form in what level?
High
High clouds are made up of…
Ice Crystals
Clouds with extensive vertical development are…
Towering cumulus or cumulonimbus clouds.
What type of storm is formed due to lifting of air by a mountain or hillside.
Orographic thunderstorm
Orographic thunderstorm
Formed due to lifting of air by a mountain or hillside.
Cumulus cloud bases form…
In the low to middle cloud base region but can extend into high altitude cloud levels.
Towering cumulus clouds indicate…
Areas of instability in the atmosphere, and the air around and inside them is turbulent.
Towering cumulus clouds often develop into…
Cumulonimbus clouds/thunderstorms.
Cumulonimbus clouds contain…
Large amounts of moisture and unstable air and usually produce hazardous weather phenomena, such as lightning, hail, tornadoes, gusty winds, and wind shear.
Inside a thunderstorm, aircraft could experience updrafts and downdrafts that exceed…
3,000 fpm
Cloud Type Descriptions
Cumulus
Heaped or piled clouds
Cloud Type Descriptions
Stratus
Formed in layers.
Cloud Type Descriptions
Cirrus
- Ringlets
- Fibrous
- Also high level +20,000 ft
Cloud Type Descriptions
Castellanus
Common base with separate vertical development, castle-like
Cloud Type Descriptions
Lenticularus
Lens-shaped, formed over mountains in strong winds
Cloud Type Descriptions
Nimbus
Rain bearing clouds
Cloud Type Descriptions
Fracto
Ragged or broken
Cloud Type Descriptions
Alto
Middle level clouds existing at 5,000 to 20,000 feet
Ceiling
Lowest layer of broken or overcast clouds.
Visibility
The greatest horizontal distance at which prominent objects can be viewed with the naked eye.
Precipitation
Refers to any type of water particles that form in the atmosphere and fall to the ground.
Some types of precipitation
- Drizzle
- Rain
- Ice Pellets
- Hail
- Snow
- Ice
Drizzle
Very small water droplets, smaller than 0.02 inches in diameter.
Rain
Water droplets of larger size.
Virga
Rain that falls through the atmosphere but evaporates prior to striking the ground.
Freezing Rain/Freezing Drizzle
Rain/Drizzle that freezes on contact with the Earth’s surface or in a temperature inversion.
If rain falls through a temperature inversion it may…
Fall to the ground as ice pellets.
How is hail created?
Freezing water droplets are carried up and down by drafts inside cumulonimbus clouds, growing larger in size as they come in contact with more moisture. Once the updrafts can no longer support them, it falls as hail.
Snow
Precipitation in the form of ice crystals that fall at a steady rate or in snow showers that begin, change in intensity, and end rapidly.
Air mass
A large body of air with similar temperature and moisture properties throughout, large flat areas of stagnant air.
An air mass passing over a warmer surface…
Is warmed from below, and convective currents form, causing the air to rise. This creates unstable air with good surface visibility.
An air mass passing over a colder surface…
- Creates a stable air mass with poor surface visibility.
- Smoke, dust, and other particles cannot rise.
- Can produce low stratus clouds and fog.
Front
The transition zone between two types of air masses.
What are the 4 types of fronts?
- Cold Front
- Warm Front
- Stationary Front
- Occluded
Cold Front
Mass of cold, dense, and stable air advances under and replaces a body of warmer air.
What type of weather does a Cold Front produce?
- Severe weather possible.
- Rapid development of heavy rain showers.
- Lightning, hail and/or tornadoes.
How is the visibility after a Cold Front passes?
Eventually, good visibility prevails once the cold air dominates the area.
What type of clouds are formed ahead of a Cold Front?
- Cirriform.
- Towering cumulus clouds
- Cumulonimbus clouds
What two metrics indicate an imminent Cold Front?
- Rising dew point.
- Falling barometric pressure.
Is a Cold Front stable or unstable air?
Stable air.
How are Cold Fronts shown on the map?
Row of blue triangles.
Cold fronts typically move at a speed of…
- 25 to 30 mph
- Extreme Cold Fronts have hit 60 mph
Stationary Front
When the forces of two fronts are relatively equal and the masses remain stationary.
What type of weather does a Stationary Front produce?
Mix of cold and warm front conditions.
How are Stationary Fronts shown on the map?
Row of alternating and opposing red half circles and blue triangles along a line.
Occluded Front
Fast-moving cold front catches up to a slow-moving warm front.
What type of weather does an Occluded Front produce?
Mix of cold and warm front conditions.
How are Occluded Fronts shown on the map?
Row of purple alternating triangles and half circles.
Warm Front
Warm mass advances over and replaces a body of colder air, producing steady rain, sleet or snow.
What type of weather does a Warm Front produce?
Light to moderate precipitation in the form of rain, sleet, snow, or drizzle, poor visibility.
Which direction does the wind blow from in a Warm Front?
South-Southeast
Is a Warm Front stable or unstable air?
Unstable air.
Warm fronts typically move at a speed of…
10 to 25 mph
What forms along the frontal boundary of a warm front?
- Cirriform/Stratiform clouds
- Fog
- Cumulonimbus Clouds in summer
How are Warm Fronts shown on the map?
Row of red half circles.
What is the rule of thumb distance for circumnavigating thunderstorms?
20 nm
Hail may fall for miles outside of the clouds.
If flying around is not an option, stay on the ground.
What circumstances are required for a thunderstorm to form?
- Sufficient water vapor.
- Unstable lapse rate.
- Initial lifting action.
All thunderstorms have conditions that are…
A hazard to aviation.
Squall Line
Narrow band of active thunderstorms, often forming on or ahead of a cold front.
What causes Turbulence?
Caused by
* Convective currents or small areas of local circulation
* Obstructions to wind flow
* Wind shear
What does structural icing do?
Structural icing increases weight and drag, thus decreasing lift and thrust, and reducing performance.
What is clear icing?
Smooth, hard, glossy, transparent ice forms after the impact of large raindrops spread and freeze sheet-like over an airfoil.
What is rime icing?
Brittle, frost-like ice created by small drops that freeze rapidly before a raindrop has time to spread across the airfoil.
What is mixed icing?
A mixture or clear ice and rime ice.
Embedded Thunderstorm
A thunderstorm “hidden” in the clouds.
When vertical clouds can be obscured by other cloud formations and are not always visible from the ground or while in flight.
3 Ingredients or stages of a Thunderstorm
- Cumulus - Initial updraft.
- Mature - Falling precipitation.
- Dissipating - Large downdraft as storm rains itself out.
Altocumulus clouds
Several patchy white or gray layers, and seem to be made up of many small rows of fluffy ripples. They are lower than cirrus clouds, but still quite high. They are made of liquid water, but they don’t often produce rain.
Weather prediction: Fair
Altostratus clouds
Gray or blue-gray mid-level clouds composed of ice crystals and water droplets. The clouds usually cover the entire sky.
Weather prediction: Be prepared for continuous rain or snow!
Cirrocumulus clouds
Thin, sometimes patchy, sheet-like clouds. They sometimes look like they’re full of ripples or are made of small grains.
Weather prediction: Fair, but cold. However, if you live in a tropical region, these clouds could be a sign of an approaching hurricane!
Cirrostratus clouds
Thin, white clouds that cover the whole sky like a veil. These clouds are most commonly seen in the winter, and can cause the appearance of a halo around the sun or the moon.
Weather prediction: Rain or snow will arrive within 24 hours!
Cirrus clouds
Delicate, feathery clouds that are made mostly of ice crystals. Their wispy shape comes from wind currents which twist and spread the ice crystals into strands.
Weather prediction: A change is on its way!
Contrails
Made by high-flying jet airplanes. They are still clouds, though, because they are made of water droplets condensed from the water vapor in the exhaust of the jet engines.
Weather prediction: Contrails can provide information about the layers of moisture in the sky.
Cumulonimbus clouds
Grow on hot days when warm, wet air rises very high into the sky. From far away, they look like huge mountains or towers.
Weather prediction: Look out for rain, hail, and tornadoes!
Cumulus clouds
Fluffy, white cotton balls in the sky. They are beautiful in sunsets, and their varying sizes and shapes can make them fun to observe!
Weather prediction: Fair
Lenticular clouds
Shaped like lenses or almonds or…flying saucers! They may get their shape from hilly terrain or just the way the air is rising over flat terrain.
Weather prediction: None!
Mammatus clouds
Actually altocumulus, cirrus, cumulonimbus, or other types of clouds that have these pouch-like shapes hanging out of the bottom. The pouches are created when cold air within the cloud sinks down toward the Earth.
Weather prediction: Severe weather might be on its way!
Nimbostratus clouds
Dark, gray clouds that seem to fade into falling rain or snow. They are so thick that they often blot out the sunlight.
Weather prediction: Gloomy with continuous rain or snow
Orographic clouds
Get their shape from mountains or hills that force the air to move over or around them. They can also be formed by sea breezes and often appear as lines where two air masses meet.
Weather prediction: An early sign that the conditions might be right to form afternoon thunderstorms!
Stratocumulus clouds
Patchy gray or white clouds that often have a dark honeycomb-like appearance.
Weather prediction: Fair weather for now, but a storm might be on its way.
Stratus clouds
Often look like thin, white sheets covering the whole sky. Since they are so thin, they seldom produce much rain or snow. Sometimes, in the mountains or hills, these clouds appear to be fog.
Weather prediction: Fair, but gloomy
