NUMERICAL PREDICTION OF THE 10-11 JUNE 1985 SQUALL LINE WITH THE CANADIAN REGIONAL FINITE-ELEMENT MODEL

In an effort to improve operational forecasts of mesoscale convective systems (MCSs), a mesoscale version of the operational Canadian Region al Finite-Element (RFE) Model with a grid size of 25 km is used to pre dict an intense MCS that occurred during 10-11 June 1985. The mesoscal e version of the RFE model contains the Fritsch-Chappell scheme for th e treatment of subgrid-scale convective processes and an explicit sche me for the treatment of grid-scale cloud water (ice) and rainwater (sn ow). With higher resolution and improved condensation physics, the RFE model reproduces many detailed structures of the MCS, as compared wit h all available observations. In particular, the model predicts well t he timing and location of the leading convective line followed by stra tiform precipitation; the distribution of surface temperature and pres sure perturbations (e.g., cold outflow boundaries, mesolows, mesohighs , and wake lows); and the circulation of front-to-rear flows at both u pper and lower levels separated by a rear-to-front flow at midlevels. Several sensitivity experiments are performed to examine the effects o f varying initial conditions and model physics on the prediction of th e squall system. It is found that both the moist convective adjustment and the Kuo schemes can reproduce the line structure of convective pr ecipitation. However, these two schemes are unable to reproduce the in ternal flow structure of the squall system and the pertinent surface p ressure and thermal perturbations. It is emphasized that as the grid r esolution increases, reasonable treatments of both parameterized and g rid-scale condensation processes are essential in obtaining realistic predictions of MCSs and associated quantitative precipitation.