Kinematic structure of the 10-11 June 1985 long-track straight-line windstorm

Abstract

The long-track, straight-line windstorm observed during PRE-STORM (Preliminary Regional Experiment for Stormscale Operational and Research Meteorology) on 10-1 I June 1985 emanated from the central, bowed-out portion of the convective line. The system was found to have developed in and propagated through an environment with characteristics and scale similar to those associated with derechos. Severe winds are believed to have initially been produced by intense convective downdrafts. However, with the rapid development of a large mesoscale cold pool and an associated mesohigh near the central portion of the convective line, the windstorm became part of the mesoscale circulation associated with the rapidly propagating gust front. In addition, a rear-to-front flow which descended to the surface in the vicinity of the central portion of the squall line likely added mass and forward-directed momentum to the cold pool, thus enhancing the gust front circulation. Environmental characteristics ahead of the long-track windstorm were conducive to the enhancement of convective downdrafts and to the development and maintenance of a deep cold pool. However, the environment ahead of the northern section of the squall line did not exhibit such characteristics until late in the life of the system, when a short-track windstorm did develop. The windstorm is believed to have resulted from and to have been maintained by a combination of convective and mesoscale downdrafts. The variability within the pre-squall environment is believed to have played a role in the development of severe winds in the central portion of the convective line.