Weather Theory and Hazards#
Atmosphere, patterns ,Coriolis force#
Air masses & fronts#
Temperature/pressure/humidity#
Moisture: clouds, fog & precipitation#
Stability, convection & inversions#
Turbulence, wind shear & microburst#
Clouds & ceilings#
For clouds to form, their must be adequate water vapor and condesation nuclei, as well as a method by which the air can be cooled. When the air cools and reaches its saturation point, invisible water vapor changes into a visible state.
Clouds are classified according to height:
Low: form near the Earth’s surface and extend up to about 6,500 ft AGL. Composed of water droplets, but can include supercooled water droplets that induce hazardous aircraft icing. Creates low ceilings, hamper visibility, and can change rapidly. They can make VFR flight impossible. Fog is classified as a type of low cloud formation.
Middle: form around 6,500 ft and extend up to 20,000 ft AGL. Composed of water, ice crystals, and supercooled water droplets.
High: form above 20,000 ft AGL. Composed of ice crystals and pose no real threat of turbulence or aircraft icing. Usually only form in stable air.
Clouds with extensive vertical development: cumulus clouds that build vertically into towering cumuls or cumulonimbus clouds. Bases form in the low to middle cloud base region butbut can extend into high altitude cloud levels. Indicates areas of instability in the atmosphere, and the air around and inside them is turbulent. Often develop into thunderstorms. When hidden within other cloud formations, they are called “embedded thunderstorms.”
Cloud classifications:
Cumulus: heaped or piled clouds
Stratus: formed in layers
Cirrus: wispy, fibrous, feathery clouds, also high level clouds above 20,000 ft.
Castellanus: common base with separate vertical development, castle-like
Lenticularus: lens-shaped, formed over mountains in strong winds
Nimbus: rain-bearing clouds
Fracto: ragged or broken
Alto: middle level clouds existing at 5,000-20,000 ft
- ceiling
The lowest layer of clouds reported as being broken or overcast, or the vertical visibility into an obscuration like fog or haze.
Clouds are reported as broken when five-eights to seven-eights of the sky is covered with clouds. Overcast means the entire sky is covered with clouds.
Low visibility, precipitation & fog#
- visibility
The greatest horizontal distance at which prominent objects can be viewed with the naked eye.
- precipitation
Any type of water particles that form in the atmosphere and fall to the ground.
Precipitation can reduce visibility, create icing situations, and affect landing and takeoff performance of an aircraft.
It occurs in several forms as it falls towards the Earth, including:
drizzle (very small water droplets, smaller than 0.02 in. in diameter)
rain (water droplets larger than drizzle)
ice pellets
hail
snow
ice
- virga
Rain that falls through the atmosphere but evaporates prior to striking the ground
Frrezing rain and freezing drizzle occur when the temperature of the surface is below freezing; the rain freezes on contact with the cooler surface.
Structural & induction icing#
Thunderstorms, hail & lightning#
These are extremely turbulent and pose a significant hazard to flight safety. An aircraft could experience updrafts and downdrafts that exceed 3,000 fpm. Thunderstorms can also produce hail, lightning, tornadoes, and large quantities of water—–all potentially hazardous to aircraft.