Stormy weather and snow for the Mediterranean

  • Heavy snowfall in Venarotta, Italy. Photo: Riccardo Martini

    Heavy snowfall in Venarotta, Italy. Photo: Riccardo Martini

    ECMWF snow depth for the Apennines at 00:00 UTC on January 21. Photo: MG Midas

  • Stormy weather and snow for the Mediterranean
    22.01.2017 19:13

    Italy has borne the brunt of severe weather in Europe recently, with hurricane-force winds, excessive snowfall for the Apennines and flooding rains elsewhere. On top of this, a series of earthquakes resulted in a deadly avalanche. So what has been the cause of this severe weather?

    High pressure has remained in control of the weather over the past week for central and western Europe, and this has resulted in a southerly displaced jet stream over the Mediterranean. As a result, it has been unsettled for surrounding countries, with strong winds and heavy snow for Italy, and heavy rain more recently for Spain.

    While the Polar Jet Stream has remained rather weak, the Subtropical Jet Stream over North Africa and the Mediterranean is particularly strong. This has provided the dynamic support for some intense Mediterranean Lows to develop over the past week.

    Between January 16-18, a low developed to the south-west of Italy, and a tight pressure gradient on its northern flank brought very strong Bora winds to parts of the eastern Balkans and Italy. The Bora is a katabatic wind which flows off the cold, snow-covered landmass of the Balkans towards the Adriatic Sea. Aided by the strong pressure gradient from the cyclone, and funnelled through narrow gaps between mountains, gusts in excess of 120 mph were recorded.

    With the waters of the Adriatic between 12 – 14C at this time of the year, an extremely unstable environment was generated, with convective “lake-effect” snow bands developing and depositing extremely heavy snowfall over the Apennines of central Italy. This combination of convective snowfall banding and orographic ascent over the mountains resulted in excessive snow accumulations of over 2.5 metres in just three days, with snowfall reaching as low as 100 metres in elevation.

    More than 300,000 people were left without power in the Abruzzo region of Italy, which has badly affected those living in temporary accommodation following the 2009 earthquake there, with many people forced to move into hotels. In addition, buildings made fragile by this ’quake have been put under renewed pressure from the weight of the snow.

    Four major earthquakes struck the snow-affected region of Italy on January 18. It is thought that these caused an avalanche that devastated the Rigopiano Hotel in the Gran Sasso Mountain, and left several people dead.

    At the time of writing, a second depression has developed in the western Mediterranean, resulting in heavy rain and thunderstorms for the Balearics and eastern Spain, with up to 100 mm of rain recorded in eastern Spain on Sunday.  This has also brought several centimetres of snow for the mountains of eastern Spain, and strong winds to the Balearic Sea, with further strong winds and heavy rain expected on Monday. 

    By: Richard Martin-Barton