The storm enters its final dissipating stage when the inflow and updrafts finally stop and the storm is only downdrafts. While this may seem a less-violent stage than the vertical windshear of updrafts and downdrafts, it should not be confused with a diminution of the storm's violence.
In the post-maturity dissipation stage, when downdrafts dominate, the storm's footprint on the ground beneath can expand in the form of an outwash far beyond the edge of the storm.
Dry air in the mid-levels increases evaporation in downdrafts, increasing the risk of microbursts and downbursts.
This produces the downdraft, the other important part of the storm.
Markowski, "Surface in situ observations within the outflow of forward-flank downdrafts of supercell thunderstorms," Monthly Weather Review, vol.
Rasmussen, "Direct surface thermodynamic observations within the rear-flank downdrafts of nontornadic and tornadic supercells," Monthly Weather Review, vol.
The intensity of the downdraft
can reach 100 feet per second.
in even moderate mountain waves exceed 1000 fpm.
The other half of the storm is the downdraft
. Massive condensation in the updraft produces cloud droplets and precipitation particles--rain, ice crystals, graupel, even hail.
In its investigation of Fossett's accident, the NTSB found "moderate turbulence and downdrafts
of at least 400 feet per minute probably occurred at the time and in the area of the accident.
Soon after turning back down the canyon, the aircraft entered another strong downdraft
, and once again it sank toward the terrain, its main rotor rpm decreasing significantly.
The modeling program indicated cloud bases at 9200 feet, tops at 13,000 feet and mountain wave activity with downdrafts
exceeding 5000 fpm.