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Which statement is correct for an absolutely unstable atmosphere?
  • A
    Visibility is good between showers
  • B
    Clouds are mainly of the stratiform type
  • C
    The environmental lapse rate is less than 1°C / 100 m
  • D
    The dry adiabatic lapse rate is more than 1°C / 100 m

Processes that increase atmosphere’s stability: Stability increases when lower layers are cooled, or upper layers warmed.
=> WARM AIR MASS (air warmer than surface below) - stable

Stable weather characteristics:

  • Clear skies or Clouds (layer type of clouds will form - STRATIFORM) - great horizontal extension, little vertical development: ST, SC,AS,NS,CI,CS.
  • Moderate to poor visibility (especially in an inversion)
  • Light turbulence (except in an inversion or mountain waves)
  • Possibly fog (especially in winter)
  • Continuous or intermittent light turbulence.

Processes that destabilize the atmosphere: Instability increases when lower layers are warmed, or upper layers cooled.
=> COLD AIR MASS (air colder than surface below) - UNSTABLE

Unstable weather characteristics:

  • Clouds (heap type of clouds - CUMULIFORM) - extensive vertical extension: CU, TCU, CB, AC, CC.
  • Moderate to heavy showers
  • Potential for moderate to heavy precipitation
  • Good visibility except in showers.
  • Gusty winds

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