The correct forecasting of the formation of a squall line is still an important issue. The solution of this problem need better understand both microphysical and dynamical processes occur in thunderstorms. The cold pools coexist with the squall lines are affected by the evaporation of water drops. The formation of water drops due to the melting of snow flakes and graupel particles is crucial for the correct simulation of latent heat cooling. In most of the models it is supposed that the melted water immediately sheds off the surface of the partly melted solid hydrometeors. Several laboratory studies have shown that the shedding of meltwater occur only when the solid precipitation particles larger than about 1 cm. Previous research showed that the vertical wind shear and the circulation around the developed cold pool is necessary to keep alive the storm.
The Convective Precipitation Experiment (hereafter COPE) was established to investigate the dynamical and microphysical properties of severe storms and squall lines through their entire life-cycle. During 3rd August 2013 two convergence lines developed parallel to the coastlines. Convective storms developed along the two lines and produced precipitation during the day. Such conditions are difficult to forecast and with one major uncertainty relating to role of ice processes, in particular ice multiplication, in the formation of precipitation.
Numerical simulations have been conducted using a bin microphysics scheme to reveal the role of the different microphysical processes on the formation of precipitation in both (idealized and real) cases coupled with Advanced Weather Research and Forecast (WRF) model.