Prediction of Convective Initiation and Storm Evolution on 12 June 2002 during IHOP_2002

The 12-13 June 2002 convective initiation case from the International H2O Project (IHOP_2002) field experiment over the Central Great Plains of the United States is simulated numerically with the Advanced Regional Prediction System (ARPS) at 3 and 1 km horizontal resolutions. The case involves a mesoscale cyclone, a dryline, a cold front and an MCS outflow boundary. Convective initiation occurred in the afternoon at several locations along and near the dryline or near the outflow boundary but was not captured by the most intensive deployment of observation instruments during the field experiment.

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.