lecture recording on 27 February 2025 at 15.13.13 PM

Overview of Weather Concepts

• The upcoming exam will cover chapters on cloud types and precipitation processes, but thunderstorms may not be included.

• It’s suggested to study previous notes and feel free to ask questions during the next class.

Cloud Types

General Classification

• Cloud names are based on altitude, vertical motion, and appearance.

• Three layers of clouds: high, middle, and low clouds.

High Clouds (Cirrus)

• Cirrus Clouds

  • Wispy appearance, resembling a horse's tail.

  • Composed of ice crystals; conditions lead to streaks forming due to wind currents.

Low Clouds (Stratus, Nimbostratus, Cumulus)

• Stratus Clouds

  • Layered, uniform gray clouds that can bring rain (nimbostratus).

  • Form from slow lift over large areas, common with cold fronts.

• Cumulus Clouds (Fair Weather Clouds)

  • Tall and puffy, associated with buoyant air parcels.

  • Growth occurs when latent heat is released once condensation level is reached.

  • Can become Cumulonimbus Clouds, which are associated with thunderstorms and precipitation.

Middle Clouds (Altostratus, Altocumulus)

• Altostratus Clouds

  • Found halfway through the troposphere and often have a layered appearance.

• Altocumulus Clouds

  • Puffy but larger than typical cumulus; can be mistaken for high or low clouds.

Other Cloud Types

• Cirrostratus

  • Thin, covering a large area, often causing glare through sunlight.

• Cirrocumulus

  • High, small, and puffy clouds indicative of instability.

• Stratocumulus

  • Low, broken layer of clouds that can appear puffy.

Cloud Coverage Conditions

Coverage Classification

• Clear: 0-5% coverage, no clouds.

• Few Clouds: 5-25% visibility of clouds.

• Scattered Clouds: 25-50% coverage, often termed partly cloudy.

• Mostly Cloudy (Broken): 50-87% coverage.

• Overcast: 87-100% coverage, completely clouded sky.

• Obscured: Visibility is limited due to conditions like fog or dust storms.

Weather Reporting Codes (METAR)

• Sky conditions are reported in a coded format (METAR) which gives pilots and meteorologists a concise weather report.

• Example: Lubbock METAR describes cloud coverage and other weather conditions in a standardized three-letter code system.

Precipitation Processes

Hydrometeors

• Definition: Any water particle (liquid or ice) that has condensed from vapor in the atmosphere, including clouds and rain.

• Growth Stages

  • Cloud condensation nuclei (CCN) grows into droplet sizes ranging from 10-50 micrometers before turning into raindrops (>100 micrometers).

  • Larger droplets eventually develop into precipitation.

Collision-Coalescence Process

• Grow larger droplets by colliding with and coalescing smaller droplets in clouds.

• The rate of coalescence is directly influenced by the size; larger drops fall faster and 'collect' smaller droplets.

• This mechanism occurs in clouds with significant depth such as cumulonimbus clouds, which are capable of producing rainfall.

Raindrop Characteristics

• As raindrops fall, they undergo deformation due to air drag; smaller droplets remain round while larger ones can become hamburger-shaped before breaking apart.

Summary and Next Steps

• Focus on distinguishing types of clouds, understanding conditions for precipitation, and recognizing cloud coverage conditions.

• Utilize visual resources to analyze cloud types in real scenarios.