New Zealand: Severe weather forecast to continue across parts of South Island through at least July 31 /update 1

Severe weather is forecast to continue across parts of South Island through at least July 31. A low-pressure system in the Tasman Sea is expected to continue to bring heavy rainfall, strong winds, and snowfall in higher elevations over the coming hours. Additional snowfall accumulations of 15-35 cm (6-14 inches) are possible in elevated areas of Canterbury, and winds gusting up to 130 kph (81 mph) are possible in southwestern and western parts of South Island. Snowfall will likely lead to hazardous travel conditions in mountainous areas due to slippery roads and reduced visibility caused by blowing snow.

As of July 30, the New Zealand National Meteorological Service (MetService) has issued the following weather warnings across the affected area:

• Orange Heavy Snow Warning (the middle level on a three-tier scale): North Canterbury High Country and the foothills north of the Rangitata River and South Canterbury High Country and the foothills about and south of the Rangitata River.

• Orange Storng Wind Warning: Fiordland, mainly about the Fiords and Westland and Grey districts.

• Yellow Heavy Rain Watch:  Canterbury Plains from Christchurch northwards and eastern Marlborough.

• Road Snowfall Warning: Lewis Pass (SH7), Arthur's Pass (SH73), Porters Pass (SH73), Lindis Pass (SH8), Crown Range Road, and Dunedin to Waitati Highway (SH1).

Authorities will likely issue new alerts or update/rescind existing advisories as weather conditions change over the coming days.

Where precipitation falls as rain, flash and areal flooding is possible. This may occur in low-lying communities near watercourses and other large bodies of water and in urban areas with easily overwhelmed stormwater drainage systems. Sites downstream of large reservoirs 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 are possible 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. Power outages are likely throughout the affected area.

Floodwaters and related debris will likely render some bridges, rail networks, or roadways impassable, impacting overland travel in and around the affected area. Flooding in urban areas will probably cause significant traffic congestion. Heavy snow will make driving hazardous in some areas; authorities will likely 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.

The disruptive weather will likely cause delays and cancellations at airports across the affected region. Authorities will probably suspend port operations temporarily if strong winds trigger hazardous sea conditions, impacting freight and passenger maritime traffic. Flooding/snow will likely block regional rail lines, causing freight and passenger train delays and cancellations.

Disruptions triggered by inclement weather and resultant hazards, such as flooding or avalanches, will likely persist well after conditions have improved - it could take days before any floodwaters recede and/or officials clear debris. Repair or reconstruction efforts may result in residual disruptions if there is severe damage to infrastructure.