Weather Theory

Question 1

What are the general characteristics in regard to flow of air around a high pressure system?

Answer 1

Outward, Downward, and Clockwise.

Question 2

What are the general characteristics in regard to flow of air around a low pressure system?

Answer 2

Inward, Upward, and Counterclockwise.

Question 3

Describe the different types of fronts.

Answer 3

Cold Front - Occurs when a mass of cold, dense, and stable air advances and replaces a body of warmer air.
Warm Front - The boundary area formed when a warm air mass contacts and flows over a colder air mass.
Occluded Front - A frontal occlusion occurs when a fast-moving cold front catches up to a slow moving warm front.
Stationary Front - When the forces of two air masses are relatively equal, the boundary or front that separates them remains stationary and influences the local weather for days. The weather is typically a mixture of both warm and cold fronts.

Question 4

What are the general weather characteristics associated with a cold front?

Answer 4

The expected weather can include towering cumulus or cumulonimbus clouds, heavy rain, lightning, tornadoes, poor visibility, winds variable and gusting, sudden drop in temperature and dew point as well as barometric pressure. In other words, really shitty weather.

Question 5

What are the general weather characteristics associated with a warm front?

Answer 5

The expected weather can include stratiform clouds, drizzle, low ceilings and poor visibility; variable winds; rise in temperature. Not as shitty as a cold front.

Question 6

What is a trough?

Answer 6

An elongated area of relatively low atmospheric pressure. The air tends to rise in a trough resulting in cloudiness and poor VFR weather.

Question 7

What is a ridge?

Answer 7

An elongated area of relatively high atmospheric pressure. The air tends to descend in a ridge resulting in dissipation of cloudiness, making good visibility and VFR weather.

Question 8

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

Answer 8

15 degrees Celsius and 29.92 inches of Mercury.

Question 9

What are isobars?

Answer 9

Isobars are lines on a weather chart which connects areas of constant or equal barometric pressure.

Question 10

What do the spacing of the isobars indicate?

Answer 10

If they isobars are closer together, it means there is a steeper pressure gradient which results in higher wind velocity. If the isobars are further apart, it means there is a shallower pressure gradient resulting in less high wind velocities.

Question 11

What causes the winds aloft to flow parallel to the isobars?

Answer 11

The Coriolis Force

Question 12

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

Answer 12

Surface Friction

Question 13

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

Answer 13

1” Hg per 1,000’

Question 14

What does “dew point” mean?

Answer 14

Dew point is the temperature to which a sample of air must be cooled to attain a state of saturation.

Question 15

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

Answer 15

Visible moisture in the form of clouds, dew, or fog. These are also ideal conditions for carburetor icing.

Question 16

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

Answer 16

The stability of the atmosphere.

Question 17

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

Answer 17

The stability of the atmosphere depends on its ability to resist vertical motion. A stable atmosphere makes vertical movement difficult, and small vertical disturbances dampen out and disappear. In an unstable atmosphere, small vertical movements tend to become larger, resulting in turbulent airflow and convective activity. Instability can lead to significant turbulence, extensive vertical clouds, and severe weather.

Question 18

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

Answer 18

Stable:
- Clouds : Stratiform
- Turbulence : Smooth
- Precipitation : Steady
- Visibility : Poor
Unstable
- Clouds : Cumuliform
- Turbulence : Rough
- Precipitation : Showery
- Visibility : Good

Question 19

When significant precipitation is occurring at the surface, how thick can you expect the clouds to be?

Answer 19

Significant precipitation usually requires clouds to be at least 4,000 feet thick. The heavier the precipitation, the thicker the clouds are likely to be.

Question 20

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

Answer 20

Location of Fronts : A front’s location, type, speed, and direction of movement.
Cloud Layers : The location of cloud bases and tops, which is valuable when determining if you will be able to climb above icing layers or descend beneath those layers into warmer air; reference PIREPs and Area Forecasts.
Freezing Levels : Important when determining how to avoid icing and how to exit icing conditions if accidentally encountered.
Air Temperature and Pressure : Icing tends to be found in low-pressure areas and at temperatures at or around freezing.

Question 21

What is the definition of the term freezing level and how can you determine where that level is?

Answer 21

The freezing level is the lowest altitude in the atmosphere over a given location at which the air temperature reaches 0 degrees celsius. A pilot can use current icing products (CIP) and forecast icing products (FIP), as well as the freezing level graphics chart to determine the approximate freezing level. Other potential sources of icing information are : area forecasts, PIREPs, AIRMETs, SIGMETs, surface analysis charts, low-level significant weather charts, and winds a temperatures aloft.

Question 22

What conditions are necessary for structural icing to occur?

Answer 22

Visible moisture and below freezing temperatures at the point moisture strikes the aircraft.

Question 23

Name the main types of icing an aircraft may encounter in-flight.

Answer 23

1. Structural
2. Induction System
3. Instrument

Question 24

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

Answer 24

Clear Ice - Forms after initial impact when the remaining liquid portion of the drop flows out over the aircraft surface, gradually freezing as a smooth sheet of solid ice.
Rime Ice - Forms when drops are small, such as those in stratified clouds or light drizzle. The liquid portion remaining after initial impact freezes rapidly before the drop has time to spread out over aircraft surface. The air gets trapped in the ice creating a white hue.
Mixed Ice - A mixture of clear and rime.

Question 25

What action is recommended if you inadvertently encounter icing conditions?

Answer 25

Leave the area of visible moisture. Either descend, climb or turn to a different course.

Question 26

Is frost hazardous to flight?

Answer 26

Yes, because it spoils the smooth airflow, thus causing a slower airflow and less lift.

Question 27

What factors must be present for a thunderstorm to form?

Answer 27

1. Sufficient water vapor
2. An unstable lapse rate
3. An initial upward lifting force to start the storm process in motion.

Question 28

What are the three stages of a thunderstorm?

Answer 28

1. Cumulus Stage : Updrafts cause raindrops to increase in size.
2. Mature Stage : Rain at earth’s surface; it falls through or immediately beside the updrafts; lightning; perhaps roll clouds.
3. Dissipating Stage : Downdrafts and rain begin to dissipate.

Question 29

What is a “temperature inversion”?

Answer 29

An inversion is an increase in temperature with height. An inversion aloft permits warm rain to fall through cold air below. A ground-based inversion favors poor visibility by trapping fog, smoke, and other restrictions into low levels of the atmosphere. The air is stable, with little or no turbulence.

Question 30

State two basic ways that fog can form.

Answer 30

1. Cooling the air to the dew point.

2. Adding moisture to the air near the ground.

Question 31

Name several types of fog.

Answer 31

1. Radiation Fog
2. Advection Fog
3. Upslope Fog
4. Frontal Fog or Precipitation-Induced Fog
5. Steam Fog

Question 32

What causes radiation fog to form?

Answer 32

The ground cools the adjacent air to the dew point on calm, clear nights.

Question 33

What is advection fog, and where is it most likely to form?

Answer 33

Advection fog results from the transport of warm humid air over a cold surface. It forms primarily along coastal areas during the winter. Usually occurs by wind blowing air inland.

Question 34

What is upslope fog?

Answer 34

Upslope fog forms as a result of moist, stable air being cooled as it moves up sloping terrain. Upslope fog is quite often dense and extends to high altitudes.

Question 35

Define the term wind shear and state the areas in which it is likely to occur.

Answer 35

Wind shear is defined as the rate of change of wind velocity per unit distance. The three types of special concern are

1. Wind shear with a low-level temperature inversion.
2. Wind shear in a frontal zone or thunderstorm.
3. Clear air turbulence (CAT) at high levels associated with a jet stream or strong circulation.

Question 36

Why is wind shear an operational concern to pilots?

Answer 36

Wind shear is an operational concern to pilots because unexpected changes in wind speed and direction can be potentially dangerous to aircraft operations at low altitudes on approach to and departing from airports.

Question 37

What types of weather information will you examine to determine if wind shear conditions might affect your flight?

Answer 37

1. Terminal Forecasts : Reported as LLWS
2. METARs - Inspect for any indication of thunderstorms, rain showers, or blowing dust. Additional signs of warming trends, gusty winds, cumulonimbus clouds etc.
3. SIGMETs & Convective SIGMETs
4. PIREPs