Radar Based Case Study of a Northeast Colorado Winter Storm

摘要

Radar and conventional meteorological data collected during the 19-20 January1991 winter storm over Northeast Colorado as part of WISP-91 (Winter Icing and Storm Project) were analyzed to describe observations of snow bands and possible band formation mechanisms. A review of the synoptic situation led to classification of this storm as an anticyclonic type of upslope storm. Single and dual-Doppler radar analyses showed well organized mesoscale snow bands oriented west-southwest to east-northeast, parallel to the 800-400 mb thermal wind, formed during upslope conditions several hours after passage of an arctic cold front over the research area. Embedded within the bands were precipitation cores that propagated along the band with the upper level winds and nearly stationary (band relative) trapped mountain waves. The evolution and structure of snowband kinematic properties were studied by analysis of horizontal and vertical velocity profiles and reflectivity distributions using PPI scans and Extended Velocity Azimuth Display (EVAD) techniques. Various mechanisms were examined for their potential role in formation and maintenance of snow bands. These mechanisms included: conditional instability, Conditional Symmetric Instability (CSI), ducted and internal gravity waves, jet streak circulations, seeder-feeder cloud structures, and terrain induced phenomena such as trapped mountain waves, low level barrier jets, and cold air damming.