SEVERE DOWNSLOPE WINDSTORM AND AIRCRAFT TURBULENCE EVENT INDUCED BY A MOUNTAIN WAVE.

Abstract

A detailed analysis is presented of the large-scale, mesoscale and turbulent-scale features of a major downslope windstorm event in central Colorado on 11 January 1972. The storm is found to be associated with a moderate amplitude baroclinic disturbance moving across the northwestern United States within an intense zonal current. Optimal conditions for strong mountain wave generation are detectable from sounding data 12-24 hr in advance and about 1000 km upstream. The mesoscale structure is dominated by a single quasi-hydrostatic wave of extreme amplitude and variable location, with corresponding variations in the windstorm structure. Hazards to aircraft from this kind of event are illustrated and discussed. Avoidance by vertical path deviation is found to be impractical.