PRECIPITATION TYPE TRANSITION REGIONS IN WINTER STORMS OVER SOUTHERN ONTARIO

Two winter storms passed through the Toronto area during November and December 1987. Information from radar, rawinsonde, and surface observations was analyzed in order to determine the kinematic flow fields and thermodynamic environment in the vicinity of the transition at the surface between snow and rain. The region was also linked to heavy precipitation and thunder. Updrafts preferentially occurred over the snow region, and deep near-0-degrees-C layers occurred in the transition region. Observations are consistent with a mesoscale circulation initiated by melting snow and possibly with the occurrence of symmetric instability. It is further suggested that large, possibly wet, snowflakes being formed within such deep near-0-degrees-C layers would contribute to the radar detection of precipitation bands near the precipitation transition region.