Determining the precipitation actually fallen in mountainous basins may turn out to be a nightmare, even before applying one single hydrological model. One way to illustrate this is to look at the water balance of catchments affected by snow. Indeed, they may present unrealistic physical behaviours: annual runoff could be (much) greater than annual estimated precipitation on the catchment, or at least, annual measured precipitation. We point out two main difficulties about our monster: on one hand, the underestimation at the gauge stations and, on the other hand, the altitudinal effect on precipitation. These two hydro-meteorological aspects are enhanced by the scarcer point measurements at high altitudes than in valleys. Besides, they are correlated: the higher the altitude, the more uncertain the altitudinal gradients (low stations density) and the more important the underestimation of the precipitation (higher quantity of snow). In order to improve our precipitation knowledge on mountainous catchments and to try to bring a solution about this monstrosity, we start our work by the determination of altitudinal gradients for air temperature. This meteorological data present the advantage to be more spatially homogeneous than the precipitation, and it will be very useful in the correction of solid precipitation losses. Then we work on the determination of altitudinal gradient for precipitation, despite the probable importance of very local influences. Finally, we look at the possible corrections of the solid precipitation underestimation. We present our results on three countries: Switzerland, Sweden and Canada(Québec).