Preflight - Fundamentals of Weather

Question 1

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

Answer 1

Atmospheric pressure decreases 1”Hg per 1,000’

Question 2

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

Answer 2

15°C and 29.92” 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 you route of flight takes you towards a low-pressure system, what kind of weather in general can you expect? What if you were flying towards a high-pressure system?

Answer 4

Low-pressure system is characterized by rising air: cloudiness, precipitation, and bad Wx
High-pressure system is characterized by descending air: dissipation of cloudiness and good Wx

Question 5

Describe the different types of fronts?

Answer 5

Cold: Cold, dense, stable air advances and replaces warmer air
Occluded: fast cold front catches up with slow warm front, (Cold front and warm front occlusion)
Warm: Warm mass contacts and flows over colder mass
Stationary: 2 ≈ air masses remain stationary and last for days (typically mix of warm/cold fronts)

Question 6

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

Answer 6

Cold Front:
-As front passes: Expect towering cumulus or cumulonimbus, heavy rain, lighting, thunder, hail, or tornadoes
-During passage: Poor visibility, variable/gusty winds, temp/d.p and pressure falling rapidly
Warm Front:
-As front passes: stratiform , drizzle, low ceilings, poor visibility, variable winds, rise in temp

Question 7

What is a “trough”?

Answer 7

Is an elongated area relatively low pressure, conducive to cloudiness and precipitation

Question 8

What is a “ridge”?

Answer 8

Is an elongated area relatively high pressure, conducive to good weather

Question 9

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

Answer 9

Coriolis force causes winds aloft to flow parallel to isobars

Question 10

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

Answer 10

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

Question 11

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

Answer 11

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

Question 12

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

Answer 12

Stability of the atmosphere

Question 13

Explain the difference between a stable atmosphere and unstable atmosphere. Why is the stability of the atmosphere important?

Answer 13

Stability depends on its ability to resist vertical motion.

Question 14

How do you determine the stability of the atmosphere?

Answer 14

When temperature decreases uniformly and rapidly as you climb (3°C per 1,000’). If temperature remains unchanged or decreases slightly with altitude air is stable. When surface air is warm/moist suspect instability

Question 15

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

Answer 15

Stable air: Stratiform, smooth, steady precip., and fair/poor visibility
Unstable air: Cumuliform, rough, showery precip., and good visibility

Question 16

What are the main types of icing an aircraft may encounter?

Answer 16

Structural, induction system, and instrument icing

Question 17

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

Answer 17

Clear icing:Clear or translucent ice from large supercooled droplets. Freezes as it flows over aircraft surface
Rime icing:Rough or opaque ice from supercooled droplets freezing on impact
Mixed icing:Form from a combination of clear/rime ice forming

Question 18

Describe the types of icing found in stratiform clouds; also in cumuliform clouds.

Answer 18

Stratified clouds: Rime and clear icing
-Icing in Middle/low level usually confined between 3-4,000’ layer
Cumuliform clouds: Clear/mixed and rime in upper levels
-Icing is variable in cumuliform because of the various stages of developement

Question 19

What is necessary for structural icing to occur?

Answer 19

Aircraft must fly into visible water (rain/cloud droplets) temperature must be at point that strikes the aircraft colder then 0°C

Question 20

What are the intensity categories of aircraft structural icing?

Answer 20

Trace: ice is perceptible at 1 hour with no deicing equipment
Light: Accumulation could cause a problem after 1 hour without deicing but the deicing will prevent issues
Moderate: Accumulation requires the use of deicing equipment
Severe: Accumulation is too high for deicing

Question 21

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

Answer 21

Location of fronts:location, type, speed, direction
Cloud layers: bases/tops to know how to get out of icing
Freezing levels: to determine how to avoid icing
Air temperature and pressure: icings tends to be in low pressure areas at or around freezing
Precipitation: Know type/location to be able to avoid

Question 22

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

Answer 22

Lowest altitude of 0°C, multiple layer can occur with temperature inversion
Can find freezing level in: area forecasts, PIREPS, AIRMETs, SIGMETs, convective SIGMETs, low-level sig. Wx charts, surface analysis, wind/temp aloft
Graphical sources: Current icing product (CIP)/ forecast icing product (FIP)

Question 23

What are the factors necessary for a thunderstorm to form and what are the three stages of thunderstorm development?

Answer 23

Moisture/unstable lapse rate/lifting force
Cumulus- strong updrafts
Mature- precipitation and downdrafts
Dissipating- downdrafts

Question 24

What are “squall line” thunderstorms?

Answer 24

Non-frontal narrow band of active thunderstorms

Often develop in front of a cold front

Question 25

State two basic ways that fog may form?

Answer 25

Cooling air to the dew point

Adding moisture to the air near the ground

Question 26

Name several types of fog.

Answer 26

Radiation
Advection
Upslope
Frontal/precipitation induced 
Steam

Question 27

What causes radiation fog to form?

Answer 27

Clear sky with little wind and small temp/dew-point spread

Almost exclusively at night

Question 28

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

Answer 28

Moist air moving over colder ground or water

Requires ≈15 knot winds

Question 29

Define upslope fog.

Answer 29

Moist stable air, being cooled adiabatically as it moves up terrain

Question 30

How does steam fog form?

Answer 30

Very cold air moving across warm water

Water vapor rises and condenses to form

Question 31

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

Answer 31

Warm moist air is lifted over front, clouds, and precipitation may form. If cold air below is near dew-point precipitation may evaporate and form fog

Question 32

Other than fog, what are several other examples of IFR weather producers?

Answer 32

Low clouds, haze, smoke, blowing obstructions, and precipitation