LOCAL INITIATION OF DEEP CONVECTION ON THE CANADIAN PRAIRIE PROVINCES

摘要

Our study found that local mesoscale circulations associated with highland areas, and transient evapotranspiration discontinuities, are likely to influence the timing and location of the initiation of deep convection across the Canadian prairie provinces when synoptic-scale forcing is weak (e.g., weak low level winds and no frontal boundaries). The cumulus congestus and cumulonimbus clouds that formed over the highland areas were initiated by anabatic wind induced mesoscale circulations. These deep convective clouds generally formed relatively early in the day (about 1030 Central Standard Time (CST)). In the relatively flat cropped grassland region, transient evapotranspiration gradients influenced the location of deep convection initiation, and theaverage soil moisture in the root zone had a direct impact on their timing. As root zone soil moisture declined from greater than 70% to less than 30%. convection initiation was delayed from about 0930 to 1630 CST. Cumulus congestus and cumulonimbus clouds that formed over the ephemeral evapotranspiration gradients were initiated by land-land circulations. The study has improved the understanding of the influence of local surface forcing on the development of deep convective cloud on the Canadian prairie provinces. The identification of areas where deep convection is likely to be initiated with weak synoptic forcing will also aid in the forecasting of thunderstorms in this region.