Weather is an important factor that influences aircraft performance and flying safety. It is the state of the atmosphere at a given time and place with respect to variables, such as temperature (heat or cold), moisture (wetness or dryness), wind velocity (calm or storm), visibility (clearness or cloudiness), and barometric pressure (high or low). The term “weather” can also apply to adverse or destructive atmospheric conditions, such as high winds.

This chapter explains basic weather theory and offers pilots background knowledge of weather principles. It is designed to help them gain a good understanding of how weather affects daily flying activities. Understanding the theories behind weather helps a pilot make sound weather decisions based on the reports and forecasts obtained from a Flight Service Station (FSS) weather specialist and other aviation weather services.

Be it a local flight or a long cross-country flight, decisions based on weather can dramatically affect the safety of the flight.

Objective

To determine that the applicant exhibits satisfactory knowledge, risk management, and skills associated with weather information for a flight under VFR.

Knowledge

The applicant demonstrates understanding of:

• Sources of weather data (e.g., National Weather Service, Flight Service) for flight planning purposes.

• Acceptable weather products and resources required for preflight planning, current and forecast weather for departure, en route, and arrival phases of flight.

• Meteorology applicable to the departure, en route, alternate, and destination under VFR in Visual Meteorological Conditions (VMC) to include expected climate and hazardous conditions such as:

  1. Atmospheric composition and stability

  2. Wind (e.g., crosswind, tailwind, windshear, mountain wave, etc.)

  3. Temperature

  4. Moisture/precipitation

  5. Weather system formation, including air masses and fronts

  6. Clouds

  7. Turbulence

  8. Thunderstorms and microbursts

  9. Icing and freezing level information

  10. Fog/mist

  11. Frost

  12. Obstructions to visibility (e.g., smoke, haze, volcanic ash, etc.)

• Flight deck displays of digital weather and aeronautical information.

Risk Management

The applicant demonstrates the ability to identify, assess and mitigate risks, encompassing:

• Factors involved in making the go/no-go and continue/divert decisions, to include:

  1. Circumstances that would make diversion prudent

  2. Personal weather minimums

  3. Hazardous weather conditions to include known or forecast icing or turbulence aloft

• Limitations of:

  1. Onboard weather equipment

  2. Aviation weather reports and forecasts

  3. Inflight weather resources

Skills

The applicant demonstrates the ability to:

• Use available aviation weather resources to obtain an adequate weather briefing.

• Analyze the implications of at least three of the conditions listed in K3a through K3l above, using actual weather or weather conditions in a scenario provided by the evaluator.

• Correlate weather information to make a competent go/no-go decision.

References

• 14 CFR part 91

• FAA-H-8083-25

• AC 00-6

• AC 00-45

• AC 00-54

• AIM

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