Alpine lee cyclogenesis is the birth of a cyclone in the lee (downstream side) of the Alps. Überströmungs-type Alpine lee cyclones form in northwesterly large-scale flow as cold air is blocked and flows cyclonically to the west of the Alps, while the upper-level trough continues to move downstream, inciting cyclone development in the western Mediterranean region. Terrain impacts are especially pronounced in cyclones that form in this fashion.
The satellite and sea level pressure loop below shows the situation from 1200 UTC 11 November through 1200 UTC 13 November. The system begins as a surface trough that plunges southeastward across the British Isles, France, and Germany. The cold air plunges southward through the low elevation region between the Alps and Pyrenees (note faint rope cloud in the loop), and strong cyclogenesis occurs over northern Italy.
@severe-weather.EU is the feed to monitor this morning as they are tweeting out some wonderful images from across the region. Here are a few.
40-50 cm of fresh snow in the northern Apennines of Tuscany and Emilia Romagna, N Italy today! Photo: Robbe E Cri / Italia live meteo pic.twitter.com/IL7A3klNWb— severe-weather.EU (@severeweatherEU) November 13, 2017
Increasingly thick (>30 cm) fresh #snow in Piandelagotti, Emilia-Romagna, N #Italy (Apennines, 1220 m elevation) right now. #winteriscoming pic.twitter.com/UuAh4bScIq— severe-weather.EU (@severeweatherEU) November 13, 2017
Enjoy the look at the fresh snow. Let's hope we can join the party later this week.Problems in finding cars in Val Thorens, France this morning. Report: Meteo @MeteoExpress #snow #winter pic.twitter.com/0kLmguB6G6— severe-weather.EU (@severeweatherEU) November 13, 2017