Standard and special observations collected during the field experiment are assimilated into the ARPS at hourly intervals in a six-hour pre-forecast period in the control experiment. This experiment captured the initiation of 4 groups of convective cells rather well, with timing errors ranging between 10 minutes and 100 minutes and location errors ranging between 5 km and 60 km. The general processes of convective initiation are carefully analyzed. Interestingly, a secondary initiation of cells due to the collision between the main outflow boundary and the gust fronts developing out of model-predicted convection earlier is also captured accurately about seven hours into the prediction. The organization of cells into a squall line after seven hours is reproduced less well.
A set of sensitivity experiments are performed in which the impact of assimilating non-standard data gathered by IHOP_2002, and the length and interval of the data assimilation are examined. The lateral boundary location is also found to have a significant impact on the initiation and subsequent evolution of convection. The impact of the vertical correlation scale in the analysis scheme is also examined.