Fundamentals of Weather

Question 1

At what rate does atmospheric pressure decrease with an increase in altitude?

Answer 1

Atmospheric pressure decreases approximately 1” Hg per 1,000 feet.

Question 2

What are the standard temperature and pressure values for sea level?

Answer 2

15°C and 29.92” Hg are standard at sea level.

Question 3

State the general characteristics in regard to the flow of air around high and low pressure systems in the northern hemisphere.

Answer 3

Low pressure—Air flows inward, upward, and counterclockwise. High pressure—Air flows outward, downward, and clockwise.

Question 4

If your route of flight takes you towards a low-pressure system, what kind of weather can you expect?

Answer 4

A low-pressure system is characterized by rising air, which is conducive to cloudiness, precipitation and bad weather.

Question 5

What kind of weather can you expect if flying towards a high-pressure system?

Answer 5

A high-pressure system is an area of descending air which tends to favor dissipation of cloudiness and good weather.

Question 6

Describe the different types of fronts.

Answer 6

Cold front—occurs when a mass of cold, dense, and stable air advances and replaces a body of warmer air. Occluded front—A frontal occlusion occurs when a fast-moving cold front catches up with a slow-moving warm front. Warm front—The boundary area formed when a warm air mass contacts and flows over a colder air mass. Stationary front—When the forces of two air masses are relatively equal, the boundary or front that separates them remains stationary.

Question 7

What are the general characteristics of the weather a pilot would encounter when operating near a cold front?

Answer 7

Towering Clouds: Cumulus or Cumulonimbus
Precipitation: Heavy rain, lightning, thunder, hail
Severe Weather: Tornadoes possible
Atmospheric Conditions: Poor visibility, variable and gusty winds
**Rapid Changes: **Temperature, dew point, and barometric pressure drop rapidly

Question 8

What are the general characteristics of the weather a pilot would encounter when operating near a warm front?

Answer 8

Warm Front—As the front passes, expected weather can include stratiform clouds, drizzle, low ceilings and poor visibility; variable winds; rise in temperature.

Question 9

What is a ‘trough’?

Answer 9

A trough (also called a trough line) is an elongated area of relatively low atmospheric pressure. It is an area of rising air, conducive to cloudiness and precipitation.

Question 10

What is a ‘ridge’?

Answer 10

A ridge (also called a ridge line) is an elongated area of relatively high atmospheric pressure. These are areas of descending air, favoring dissipation of cloudiness.

Question 11

What is a dryline and why is knowledge of its location important?

Answer 11

A dryline is a low-level boundary that separates moist and dry air masses. Severe thunderstorms often develop along a dryline, especially when it begins moving eastward.

Question 12

Why do surface winds generally flow across the isobars at an angle?

Answer 12

Surface friction causes winds to flow across isobars at an angle.

Question 13

When temperature and dew point are close together (within 5°), what type of weather is likely?

Answer 13

Visible moisture is likely, in the form of clouds, dew or fog.

Question 14

What factor primarily determines the type and vertical extent of clouds?

Answer 14

The stability of the atmosphere determines type and vertical extent of clouds.

Question 15

Explain the difference between a stable atmosphere and an unstable atmosphere.

Answer 15

A stable atmosphere makes vertical movement difficult, while in an unstable atmosphere, small vertical air movements tend to become larger, resulting in turbulent airflow and convective activity.

Question 16

How do you determine the stability of the atmosphere?

Changes in atmospheric stability are inversely related to ____________ changes with ____________. Several stability indexes exist to evaluate atmospheric stability.

Answer 16

Changes in atmospheric stability are inversely related to temperature changes with height. Several stability indexes exist to evaluate atmospheric stability.

Question 17

List the effects of stable and unstable air on clouds, turbulence, precipitation and visibility.

Answer 17

Stable Conditions:

Cloud Type: Stratiform
Turbulence: Smooth
Precipitation: Steady
Visibility: Fair to Poor

Unstable Conditions:

Cloud Type: Cumuliform
Turbulence: Rough
Precipitation: Showery
Visibility: Good

Question 18

What are the two main categories of aircraft icing?

Answer 18

Aircraft icing in flight is usually classified as either structural icing or induction icing.

Question 19

Name the three types of structural ice that may occur in flight.

Answer 19

Clear Icing, Rime Icing, Mixed Icing.

Question 20

What is necessary for structural icing to occur?

Answer 20

The aircraft must be flying through visible water such as rain or cloud droplets; temperature must be at or below 0°C.

Question 21

What are the intensity categories of aircraft structural icing?

Answer 21

Trace, Light, Moderate, Severe.

Question 22

During preflight planning, what type of meteorological information should you be aware of with respect to icing?

L
F
C
A
P
P

Answer 22

L - Location of fronts

F - Fronts

C - Cloud layers

A - Air temperature

P - Pressure

P - Precipitation

Question 23

What is the definition of the term ‘freezing level’?

Answer 23

The freezing level is the lowest altitude in the atmosphere at which the air temperature reaches 0°C.

Question 24

During preflight planning, how can you mitigate the total risk encountered en route when the possibility of operating in or around icing conditions exists?

Consider ____________ performance, determine ____________ exit strategies, account for extra ____________, and choose ____________ ____________ wisely.

Answer 24

Consider climb performance, determine icing exit strategies, account for extra fuel, and choose alternate airports wisely.

Question 25

What are the factors necessary for a thunderstorm to form?

Answer 25

Sufficient water vapor, an unstable lapse rate, and an initial upward boost (lifting).

Question 26

What are the three stages of thunderstorm development?

Answer 26

Cumulus, Mature, Dissipating.

Question 27

What are ‘squall line’ thunderstorms?

Answer 27

A squall line is a non-frontal, narrow band of active thunderstorms that often develops ahead of a cold front.

Question 28

How does fog form?

Answer 28

Fog forms when the temperature and dew point of the air become identical (or nearly so).

Question 29

What is the primary weather hazard to aircraft?

Answer 29

The line often contains severe steady-state thunderstorms and presents the single most intense weather hazard to aircraft.

Question 30

When does the line usually reach maximum intensity?

Answer 30

It usually forms rapidly, reaching a maximum intensity during the late afternoon and the first few hours of darkness.

Question 31

How does fog form?

Answer 31

Fog forms when the temperature and dew point of the air become identical (or nearly so). This may occur through cooling of the air or by adding moisture to elevate the dew point.

Question 32

Name several types of fog.

Answer 32

a. Radiation fog
b. Advection fog
c. Upslope fog
d. Frontal fog or precipitation-induced fog
e. Steam fog

Question 33

What conditions favor the formation of radiation fog?

Answer 33

Conditions favorable for radiation fog are a clear sky, little or no wind, and small temperature-dew point spread (high relative humidity).

Question 34

When does radiation fog typically form?

Answer 34

The fog forms almost exclusively at night or near daybreak.

Question 35

What is advection fog?

Answer 35

Advection fog forms when moist air moves over colder ground or water. It is most common along coastal areas but can develop deep in continental areas.

Question 36

How does wind affect advection fog?

Answer 36

It deepens as wind speed increases up to about 15 knots; wind much stronger than 15 knots lifts the fog into a layer of low stratus or stratocumulus.

Question 37

Define upslope fog.

Answer 37

Upslope fog forms as a result of moist, stable air being cooled adiabatically as it moves up sloping terrain.

Question 38

Where is upslope fog commonly found?

Answer 38

It is common along the eastern slopes of the Rockies and somewhat less frequent east of the Appalachians.

Question 39

How does steam fog form?

Answer 39

When very cold air moves across relatively warm water, enough moisture may evaporate from the water surface to produce saturation, leading to the formation of steam fog.

Question 40

When is steam fog commonly observed?

Answer 40

It is commonly observed over lakes and streams on cold autumn mornings, and over the ocean during winter when cold air masses move off the continents.

Question 41

Explain how frontal (or precipitation-induced) fog forms.

Answer 41

When warm, moist air is lifted over a front, evaporation from precipitation may saturate the cold air and form fog.

Question 42

What are the characteristics of frontal fog?

Answer 42

Frontal fog can become quite dense and continue for an extended period of time, often extending over large areas.

Question 43

What are several other examples of IFR weather producers?

Answer 43

Other examples of common IFR producers are low clouds (stratus), haze, smoke, blowing obstructions to vision, and precipitation.

Question 44

Which weather phenomena restrict navigation by visual reference more often than others?

Answer 44

Fog and low stratus restrict navigation by visual reference more often than all other weather phenomena.