- High potential temperature and water vapor content increase buoyancy while cloud water and precipitation decrease buoyancy.
- Precipitation loading significantly decreases positive buoyancy.
- Entrainment of dry air and evaporation of rain both act to decrease buoyancy in thunderstorm updrafts.
- WMax is a formula for estimating maximum updraft speed.
- Wmax is the square root of (2 x CAPE) in meters / second.
- Practically, the above calculation is divided in half to arrive at a realistic updraft speed.
- Soundings with moist mid levels would produce a stronger updraft while dry mid-levels produce a stronger downdraft due the entrainment of dry air (cooling).
- Downdraft Strength:
- Precipitation loading: adds weight -- dependent on the amount of moisture and updraft strength
- Evaporation: the amount of precipitation, dryness of air and precipitation type.
- Downdrafts typically originate near the level of the minimum wet-bulb temperature (3-5 km AGL)
- Downdraft path on sounding: Determine the wet bulb temperature at the origin of the downdraft and follow the moist adiabat to the surface.
- DCAPE: the are between the downdraft moist adiabat and the environmental temperature trace.
- Mid-level moisture tends to increase wet bulb temperature, thereby reducing downdraft strength.
- Cold Pool Strength:
- Depth of the cold pool
- Temperature difference between cold pool and environment.
- Wet Microburst: moist, nearly saturated conditions at low levels and drier conditions aloft.
- Dry Microburst: low levels are relatively dry with moist conditions at mid levels (inverted V sounding).
- When vertical wind shear is weak, buoyancy processes are the dominant control on convective updrafts and downdrafts.
- Updrafts dominant during the early port of an ordinary cell's life cycle, downdrafts in the later stages.
- CAPE provides a quantitative estimate of buoyant energy.
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