This blog contains the latest on the wild weather heading our way this long weekend. Read on for details of the current severe weather outlook and watch, as well as the latest chilly temperature forecasts for Monday and Tuesday.

Severe weather

A weather front bringing some pretty nasty weather is edging closer to New Zealand from across the Tasman Sea. The cloud generated by this front can be seen to the west and south of the country in the visible satellite picture below (for a quick overview of satellite images see our blog http://blog.metservice.com/2015/04/a-satellite-image-for-every-occasion/ )

Visible satellite image at 4:00 pm NZST on 24 April 2015, courtesy of MTSAT. Visible satellite image at 4:00 pm NZST on 24 April 2015, courtesy of MTSAT.

As we get closer to a weather event occurring, our models become more accurate, and we start to issue severe weather watches and warnings. Fiordland, Westland and Southland will be the first to be hit by this front, and a severe weather watch has been issued for these areas. Rain is expected to become heavy about Fiordland late Saturday afternoon and then in Westland Saturday night. Rainfall amounts may exceed warning criteria (greater than 100mm over 24hr). Northerly gales may become severe at times in Fiordland and Southland during Saturday afternoon and early evening.

Other regions of the country are covered in our severe weather outlook, the latest of which is shown below. Many regions are expected to experience heavy rain and/or severe gales. As this is a developing situation, we advise people to stay up to date with the latest forecast for their region.

Severe Weather Outlook for Monday 27 and Tuesday 28 April 2015. Issued at 2:39pm Thursday 23 April 2015. Low confidence: a 20% likelihood (or 1 chance in 5) that the event will actually happen. Moderate confidence: a 40% likelihood (or 2 chances in 5) that the event will actually happen. High confidence: a 60% likelihood (or 3 chances in 5) that the event will actually happen. For the latest Severe Weather Outlook head to http://www.metservice.com/warnings/severe-weather-outlook Severe Weather Outlook for Sunday 26 to Wednesday 29 April 2015. Issued at 2:45pm Friday 24 April 2015. Low confidence: a 20% likelihood (or 1 chance in 5) that the event will actually happen. Moderate confidence: a 40% likelihood (or 2 chances in 5) that the event will actually happen. High confidence: a 60% likelihood (or 3 chances in 5) that the event will actually happen. For the latest Severe Weather Outlook head to http://www.metservice.com/warnings/severe-weather-outlook

Cold blast

Following on from the horizontal rain, we are expecting the temperatures to drop several degrees during the first half of next week as a cold front sweeps up the country. Snow is possible to 700 metres in the far south on Tuesday, but there is still considerable uncertainty regarding the snow level and the amount of snow.

The latest temperature forecasts for Monday 27th and Tuesday 28th April are shown in the figure below from the European Centre for Medium range Weather Forecasting (ECMWF). You can see the cold air gradually pushing the warm air away to the northeast. On the map for Tuesday, you will notice the slightly warmer areas in the Canterbury Plains, Hawkes Bay and Gisborne regions. These higher temperatures are caused by the Foehn winds that occur when a northwesterly airstream flows from the Tasman Sea across the hills and mountains running up the spine of New Zealand. The intricacies of the Foehn effect are described in the following blog: http://blog.metservice.com/2010/10/the-foehn-wind/

Surface temperatures (degrees C) for midday on Monday 27th (left) and Tuesday 28th (right) April 2015 from the ECMWF model. Surface temperatures (degrees C) for midday on Monday 27th (left) and Tuesday 28th (right) April 2015 from the ECMWF model.