Aviation Weather Theory Flashcards

A Comprehensive collection of vocabulary terms covering atmospheric layers, pressure systems, stability, humidity, cloud formations, and hazardous weather phenomena relevant to pilot flight training.

Troposphere

The first layer of the atmosphere extending to approximately $20,000$ feet where most weather occurs.

Stratosphere

The atmospheric layer extending up to $160,000$ feet where commercial jets fly to avoid weather and gain performance from faster winds.

Lapse Rate

The average decrease in temperature within the troposphere, occurring at a rate of $2^\text{o} \text{C}$ for every $1,000$ feet of climb.

Coriolis force

The force caused by the Earth's rotation that deflects air masses to the right in the Northern Hemisphere, with zero deflection at the equator and maximum at the poles.

Standard Day

A reference point for aviation calculations defined by sea level elevation, a temperature of $15^\text{o} \text{C}$, and an atmospheric pressure of $29.92$ inches of mercury.

Pressure Altitude

The altitude corrected for non-standard atmospheric pressure.

Density Altitude

The pressure altitude corrected for non-standard temperature, representing the altitude at which the aircraft perceivedly performs.

Wind

The lateral movement of air parallel to the Earth's surface.

Convective current

The vertical movement of air, characterized as either updrafts (rising) or downdrafts (sinking).

Isobars

Lines on a weather map that connect areas of equal atmospheric pressure, usually reported in millibars.

Pressure gradient

The difference between two pressures; closely spaced isobars indicate a steep gradient and result in stronger winds.

High pressure system

An area of high pressure characterized by a clockwise motion of air that pushes wind outward in the Northern Hemisphere.

Low pressure system

An area of low pressure characterized by a counterclockwise motion that sucks air inward and upward, typically associated with bad weather.

Stability

The ability of an air mass to resist vertical motion.

Adiabatic

The process by which an air mass cools as it is raised in the atmosphere.

Sublimation

The transition of a substance from a solid to a gas without passing through the liquid phase.

Evaporation

The process where liquid water transforms into vapor, adding moisture to the air.

Condensation

The transition from vapor to liquid, which removes moisture from the air.

Dry adiabatic lapse rate

The rate at which an unsaturated air mass cools: $3^\text{o} \text{C}$ per $1,000$ feet for temperature and $0.5^\text{o} \text{C}$ per $1,000$ feet for the dew point.

Moist adiabatic lapse rate

The cooling rate of a saturated air mass, which is slower than the dry rate, averaging between $1.2^\text{o} \text{C}$ and $3^\text{o} \text{C}$ per $1,000$ feet.

Low level wind shear

A sudden and drastic change in wind speed and direction, which is extremely dangerous when occurring close to the ground.

Microburst

A severe form of low level wind shear associated with thunderstorms that can create downdrafts up to $6,000$ feet per minute and lasts five to fifteen minutes.

Cumulus stage

The first phase of a thunderstorm, characterized by initial lifting action and predominant updrafts.

Mature stage

The second phase of a thunderstorm where water hits the ground, an anvil forms, and both updrafts and downdrafts are present.

Dissipating stage

The final phase of a thunderstorm where the cloud disappears and downdrafts dominate.

Front

The boundary or limit where two air masses of different characteristics collide.

Squall line

A narrow band of active thunderstorms that often develops ahead of a cold front.

Temperature inversion

An atmospheric condition occurring in stable air where temperature increases with altitude, rather than decreasing.

Relative humidity

The amount of water vapor contained in an air mass in relation to the total amount it can hold at its current temperature.

Dew point

The temperature at which an air mass must be cooled to become fully saturated.

Frost

Ice crystals that form on a surface when the dew point and the surface temperature are both at or below freezing.

Altocumulus clouds

Mid-level clouds that can indicate the presence of very strong turbulence.

Nimbostratus

Dark, puffy low-level clouds that typically bring rain.

Lenticular cloud

An almond or lens-shaped cloud, technically called autocumulus standing lenticularis, which indicates heavy turbulence near mountain peaks.

Radiation fog

Fog that forms in valleys or over land when the ground cools rapidly at night under calm winds, saturating the air mass.

Advection fog

Fog created when a warm, moist air mass moves over a colder surface, requiring wind to form; commonly found in coastal areas.

Upslope fog

Fog formed as moist air is forced uphill by wind and cools as it reaches higher altitudes.

Steam fog

Fog created when a cold, dry air mass moves over warm water, causing evaporating water to rise and reach saturation within the cold air.

Ceiling

The height of the lowest cloud layer reported as broken ($5/8$ to $7/8$ coverage) or overcast ($8/8$ coverage).

Virga

Precipitation, such as rain, that evaporates before it touches the ground.

Jet stream

A localized band of wind moving at speeds greater than $50$ knots, reaching up to $240$ knots, typically found at high altitudes.

Clear air turbulence (CAT)

Sudden, severe turbulence occurring in cloudless areas above $15,000$ feet AGL, often associated with the jet stream and cirrus clouds.