Europe: Adverse weather forecast across the region through at least Dec. 21

Severe weather is forecast across parts of southern Europe through at least Dec. 21. A storm system moving eastwards over the Mediterranean Sea is expected to bring strong winds, heavy rainfall, and snowfall in mountainous areas across parts of Albania, Bosnia and Herzegovina, Croatia, Greece, Italy, Montenegro, and Slovenia over the coming days. Winds are likely to be the hazard of greatest concern during the passing of the storm, with gusts of over 100 kph (62 mph) possible in places. Heavy downpours could trigger flooding in low-lying areas, and strong winds may cause property damage and power outages. Hazardous travel conditions are likely in mountainous areas due to slippery roads and reduced visibility caused by blowing snow.

The respective meteorological services have issued the following weather warnings across the affected area Dec. 20:

• Red strong wind warnings (the highest level on a three-tier scale): Most coastal waters in Croatia and Sardinia Region in Italy.

• Orange heavy rainfall warnings: Ionian Islands, West Peloponnese, and West Sterea regions in Greece, and Adriatic Coast and Central regions in Montenegro.

• Orange heavy snowfall warnings: Abruzzo and Marche regions in Italy.

• Orange thunderstorm warnings: Epirus, Ionian Islands, West Peloponnese, and West Sterea regions in Greece.

• Orange strong wind warnings: Bihac, Foca, Livno, Mostar, and Trebinje regions in Bosnia and Herzegovina; Knin, Rijeka, and Split regions and southern coastal waters in Croatia; Abruzzo, Aosta Valley, Basilicata, Calabria, Campania, Emilia-Romagna, Friuli Venezia Giulia, Lazio, Liguria, Lombardy, Marche, Molise, Piedmont, Sicily, Tuscany, Trentino Alto Adige, Umbria, and Veneto regions in Italy; and Northwest and Southwest regions in Slovenia.

• Yellow heavy rainfall warnings: Banja Luka, Bihac, Livno, Mostar, Prijedor, Sarajevo, and Trebinje regions in Bosnia and Herzegovina; Dubrovnik, Knin, Rijeka, and Split regions in Croatia; Epirus Region in Greece; Abruzzo, Basilicata, Calabria, Campania, Emilia-Romagna, Friuli Venezia Giulia, Marche, Molise, Sicily, Tuscany, Umbria, and Veneto regions in Italy; Continental and Mountains Region in Montenegro; and Southwest Region in Slovenia.

• Yellow heavy snowfall/ice warnings: Banja Luka, Foca, and Visegrad regions in Bosnia and Herzegovina; Gospic and Karlovac regions in Croatia; Emilia-Romagna, Friuli Venezia Giulia, Molise, and Tuscany regions in Italy; and Southeast and Southwest regions in Slovenia.

• Yellow thunderstorm warnings: Basilicata, Calabria, Campania, Lazio, Puglia, Sicily, and Tuscany regions in Italy.

• Yellow strong wind warnings: Banja Luka, Prijedor, Sarajevo, Tuzla, and Visegrad regions in Bosnia and Herzegovina; Dubrovnik, Gospic, Osijek, and Zagreb regions in Croatia; Puglia Region in Italy; across Montenegro; and Northeast Region in Slovenia.

• Yellow coastal warnings: Adriatic Coast Region in Montenegro.

Officials will likely update and possibly extend the coverage of weather alerts over the coming days.

Sustained heavy rainfall could trigger flooding in low-lying communities near rivers, streams, and creeks. Urban flooding is also possible in developed areas with easily overwhelmed or a lack of stormwater drainage systems. Sites located downstream from large reservoirs or rivers may be subject to flash flooding after relatively short periods of intense rainfall.

Precipitation could fall as snow in the higher elevations over the coming days. Wind gusts could cause blowing and drifting snow; decreased visibility is likely in mountainous areas. Rain-induced landslides cannot be discounted in areas of elevated terrain; there is also the possibility of avalanches in mountainous areas where the snowpack has become unstable due to heavy snowfall. Disruptions to electricity and telecommunications services are possible where significant winds, flooding, or landslides impact utility networks.

Floodwaters and debris flows may render some bridges, rail networks, or roadways impassable, impacting overland travel in and around affected areas. Ponding on road surfaces could cause hazardous driving conditions on regional highways. Authorities could temporarily close some low-lying routes that become inundated by floodwaters. Heavy snow will likely make driving hazardous in some areas; authorities could implement temporary road closures or detours in such locations. Mountain passes and tunnels could be closed as a precautionary measure during periods of intense snowfall.

Severe weather could also trigger flight delays and cancellations at regional airports. Flooding or snow could block regional rail lines; freight and passenger train delays and cancellations are likely in areas that see heavy rainfall and potential track inundation.