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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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