Among the different precipitating events that were observed during the MAP field experiment, the case of IOP2b (19/20 September 1999) was the most intense and produced in the Lago Maggiore target area local precipitation maxima reaching 300 mm in less than 48h. This case has been selected for an intercomparison exercise of different numerical models (MC2, MM5, MESO-NH, MOLOCH, WRF, ...) run with a 2 to 3 km horizontal resolution and starting from the same initial analysis , the ECMWF operational analysis from September 19, 12 UTC. All the models have been integrated over a 30 hour period.

The different results are compared with the available observations: hourly surface measurements, radar derived precipitation and radar reflectivities. The precipitation patterns obtained with the different models are quite similar. More discrepancies are found in the the precipitation intensities. Some very fine structures (North-South elongated narrow bands with a width of 6 to 8 km) present in the radar fields are nicely captured in the simulations, indicating probably the strong influence of some small scale feature of the topography.