Monday October 07 2013 Stability is determined by comparing temperature of rising parcel to that of its surroundings environment By comparing lapse rate curves 3 atmospheric conditions exist 1 Absolutely Stable Atmosphere 2 Absolutely Unstable Atmosphere 3 Conditionally Unstable Atmosphere Absolutely Stable Fig 6 3 exist when environmental lapse rate is less than moist adiabatic rate rising air parcel is always colder than air surrounding it Conditions necessary to bring about a stable atmosphere 1 Warm air moving over cold surface 2 Nighttime radiational cooling 3 Advection of cold surface air Absolutely Unstable Fig 6 8 occurs when environmental lapse rate is greater than dry adiabatic rate rising air is always warmer than air surrounding it Conditions necessary to bring about an unstable atmosphere 1 Cold air moving over warm surface 2 Daytime solar heating of the surface 3 Radiational cooling of clouds loss of heat energy to space from clouds Conditionally Unstable Fig 6 9 Occurs when environmental lapse rate is between the moist adiabatic lapse rate and the dry adiabatic lapse rate Atmosphere is stable if rising air is unsaturated but unstable if rising air is saturated Stable Atmosphere Clouds are widespread Precipitation if any is light to moderate Most associated with fair weather Unstable Atmosphere Clouds are towering Heavy precipitation Can be associated with severe weather