Aviation Weather and Pilot Operations

Stable and Unstable Air

  • Stable Air:

    • Cool, dry air.

    • Colder than its surroundings, causing it to sink and condense.

    • Spins clockwise.

  • Unstable Air:

    • Warm, moist air.

    • Warmer than its surroundings, causing it to rise and expand.

    • Spins counter-clockwise.

Ground Weather: Standard Conditions & Lapse Rates

  • Standard Pressure:

    • Is 29.92′′extHg29.92'' ext{ Hg} at Sea Level.

    • In Millibars, it is 1013.2extMb1013.2 ext{ Mb}.

    • Measured in inches of Mercury.

    • Unequal heating of the earth's surface causes changes in pressure.

  • Standard Temperature:

    • 15extoextC15^ ext{o} ext{C}.

  • Standard Pressure Lapse Rate:

    • 1extHg1 ext{ Hg} per 1,000′1,000' of altitude.

  • Lapse Rate/Pressure Change:

    • The rate at which temperature decreases with altitude.

  • Standard Lapse Rate:

    • 2extoextC2^ ext{o} ext{C} per 1,000′1,000' of altitude.

  • Dry Adiabatic Lapse Rate:

    • 3extoextCext(3^ ext{o} ext{C} ext{ (} 5.4extoextF5.4^ ext{o} ext{F}$ ext{)} per 1,000′1,000'

    • Dry air changes temperature faster than moist air due to the slower heating and cooling properties of water.

High and Low Pressure Systems

  • High Pressure System:

    • Surrounded on all sides by lower pressure.

    • Ridge: An elongated area of high pressure.

    • Air flows clockwise, down, and out.

    • Associated Weather:

      • Visibility: Poor

      • Clouds: Stratus

      • Turbulence: None

      • Ice: Rime

      • Precipitation: Steady

      • Pressure: High

  • Low Pressure System:

    • Surrounded by higher pressure.

    • Trough: An elongated area of low pressure.

    • Air flows counter-clockwise, up, and in.

    • Associated Weather:

      • Visibility: Good

      • Clouds: Cumulus

      • Turbulence: More Severe

      • Ice: Clear Ice

      • Precipitation: Showery

      • Pressure: Low

Temperature Inversions

  • Definition: A layer in the atmosphere where temperature increases with altitude instead of decreasing.

  • Occurrence: Usually occurs on calm, clear nights due to radiational cooling or under high pressure systems.

  • Significance for Pilots:

    • Can trap haze, smoke, or fog near the surface, reducing visibility.

    • Can create low-level wind shear if winds above the inversion are strong.

    • The air within the inversion is very stable, so turbulence is minimal.

    • Climb performance may be affected in hot conditions.

  • Characteristics:

    • Temperature increases with altitude.

    • Smooth, stable layer of air.

    • Restricted visibility below the inversion.

    • Turbulence may occur above the inversion.

  • Types:

    1. Surface-based temperature inversion: Forms on cool, clear, calm nights when the ground cools and lowers the temperature of the air directly above it.

    2. Frontal temperature inversions: Occur when cool air is forced under warm air, and the warm air spreads over the cooler air.

Types of Clouds

  • Cloud Formation: All clouds form when air is cooled to its dew point (or becomes saturated) and water vapor condenses into visible droplets or ice crystals.

    • Cooling usually happens when air rises and expands (adiabatic cooling).

    • Can also result from contact cooling, mixing, or adding moisture.

  • Classification: Clouds are classified by their appearance and height.

  • **High Clouds (Aboveext 20,000extftAGLAbove ext{ ~}20,000 ext{ ft AGL}): Made of ice crystals.

    • Cirrus (Ci): Wispy, hairlike clouds. Form from sublimation of ice crystals in very cold, stable air.

    • Cirrostratus (Cs): Thin, sheet-like clouds covering the sky, often produce halos around the sun/moon.

    • Cirrocumulus (Cc): Small, white patches or ripples, often described as