Atmospheric circulation conditions and snowy weather in the Southern Alps: Case of the Isola 2000 weather station

This paper focuses on the relationship between atmospheric circulation and solid precipitation (SP) happening in the weather station of Isola 2000. Located in the French department of the Alpes-Maritimes at an altitude of 1912 m, it has the oldest series of daily SP and snow depth (SD) observations from the department. Study has two objectives, analyzed past orientations concerning air temperature, SP and SD, then, characterizes and explains the atmospheric circulation condition producing SP. Results show a warming of air temperature since the early 2000s, counterintuitive accompanied by an increase in the frequency of SP and a larger thickness of SD. In addition, by crossing SP observations with ERA-INTERIM reanalysis (EI-R), seven covariations have been measured: vertical velocity 700 hPa; specific humidity 850 hPa; sea level pressure; air temperature 850 hPa; geopotential height 700 hPa; U-component of wind 700 hPa, V-component of wind 700 hPa. The mapping of these variables shows two types of atmospheric circulation implicated in SP: westerly cyclonic circulation, producing SP in the range of 1–5 cm and 6–20 cm; southern circulation with a depression focused on Iceland and a trough on Western Europe, causing SP in the range of 21–40 cm and 41–93 cm.