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Soaring Definitions

Convective Condensation Level (CCL) - is the height to which a parcel of air, if heated sufficiently from below, will rise adiabatically until it reaches saturation or condensation. It approximates the base height of cumulus clouds which are, or would be, produced by surface heating.

Equilibrium Level (EL) - is the height in the upper troposphere where a parcel of saturated air, rising because of its positive buoyancy, encounters negative buoyancy. It is as this point where the parcel becomes colder than the surrounding air.

K-index - is a measure of thunderstorm potential based on vertical temperature lapse rate and the moisture content in the lower atmosphere (700 mb and 850 mb). Numbers greater than 25 indicate good thunderstorm potential. Numbers greater than 35 indicate flash flood potential or thunderstorms accompanied by heavy rain. K= (850mb temp-500mb temp) + 850mb dew point-700 dew point depression.

Lifting Condensation Level (LCL) - is the height at which a parcel of air becomes saturated when lifted dry-adiabatically. The LCL for a surface parcel is always at or below the CCL.

Level of Free Convection (LFC) - is the height at which a parcel of air lifted dry-adiabatically until saturated (LCL) and moist adiabatically thereafter would first become warmer (less dense) than the surrounding air. At this point the buoyancy of the parcel would become positive and the parcel would accelerate upward without further need for forced lift.

Lifted Index (LI) - determined using the temperature and dew point in the lowest 100 mb from an averaged mixing ratio. The parcel is lifted dry-adiabatically to the LCL, then moist adiabatically to 500 mb. The algebraic difference (Deg C) between the parcel temperature and the actual sounding temperature at 500 mb is the index value. Positive values imply greater stability. Values less than zero imply instability or positive buoyancy.

Maximum Altitude - Altitude determined from forecast high surface temperature expected for the day, when raised up the dry-adiabatic lapse rate curve to where it intercepts the actual sounding temperature plot. Note: The max altitude reported here is limited to 18,000 feet by FAA regulations.

Showalter Index (SI) - determined by lifting a parcel of air using the 850 mb temperature and dewpoint dry-adiabatically to the LCL, then moist-adiabatically to 500 mb. The algebraic difference between the parcel temperature and actual sounding temperature is the index value. Positive values imply greater stability.

Soaring Index - A forecast of maximum lift rate in feet per minute (fpm) by thermals expected at the time of maximum temperature. This empirical formula is based on maximum altitude of thermals and the lapse rate from the trigger altitude 4000 feet above the surface.

Trigger Temperature - The surface temperature reached when the temperature from the morning upper air sounding at 4000 feet above the surface is lowered dry-adiabatically to the surface.

Trigger Time - The local time the trigger temperature is reached. A minimum lift rate of 260 fpm would be obtained at this time up to 4000 feet.

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