Snow level forecasting methods and parameters; two practical examples on eastern italian Alps

In this work the methods to forecast the snow level in a precipitation event are investigated at first, considering the pertinent forecasting parameters and the necessary knowledge of the specific territory which will be interested by the precipitation event. Particularly the Freezing level altitude, the Wet Bulb Pseudo Potential Temperature at 850 and 1000 hPa, humidity fields, vertical motions, dew point temperatures at different pressure altitude, temperature's gradients, forecasted sounding (temperatures' identification in the boundary level) and forecasted precipitation maps are used to determine the snow level in a forecasted precipitation event.

Then two examples concerning two typical situations are shown:

a first case of different snow level in a restricted area (Val Belluna) of the venetian Pre-alps, depending on the different persistence of the low-level cold air mass. The effects on the snow level of the turbulent air motion in case of pre-existent cold air layer nearby to the ground are investigated, considering the influence of the low level flow in different orographic conditions. Different times of entering mild low level flow determines the change between snow and rain. In the closest part of the valley, no mild low level flow enters, so that the precipitation remains snow for all the event also if this part of the area is at slightly lower altitude.

A second case of snow level falling in Dolomites area, depending on intensity and persistence of precipitation; the case investigates a situation in which a non-turbulent air motion determines falling snow level due to air cooling by snow-melting. The influence of orography on the air cooling is also analyzed, considering also different intensity of precipitations depending on different orographic effects, as some possible micro-Foehn conditions or the presence of micro-turbulence induced by orography.