Temperatures are dropping today in the south but Monday and Tuesday are the two cold days with Tuesday looking to be peak cold in the south.
Latest data suggests Tuesday will be bitterly cold in Otago and Southland. Dunedin’s current high is +3C on Tuesday with a ‘feels like’ temperature (or wind chill) of -6C during the middle of the day.
The automatic wind chill calculator at www.RuralWeather.co.nz still shows that Southland has 50 hours coming up with sub-zero wind chills starting Sunday night and not easing until Wednesday.
The strong complex low-pressure system has moved southeastward from the south Tasman Sea over the Southern Ocean near the lower South Island.
Fronts extending from this system are now crossing NZ from west to east. In addition, as the pressure gradients are larger due to the deeper system (and getting larger by the hour), the strong windy conditions start today across NZ and continue through Tuesday. Therefore, this system is likely to affect NZ on Sunday through Tuesday.
Upper level cold air mass of -34°C or less at 500 hPa is likely to pass over the southern South Island on Sunday through Monday. This upper level (very high up, not ground/sea level – around 5000 metres, so higher than Mt Cook) strong cold air mass is expected to pass over the South Island on Monday afternoon through Tuesday afternoon.
Heavy bursts of snow including blizzard conditions could be brought to the alpine areas and highlands of the South Island and the snowfall could be brought even to the low-level areas mainly to Southland, Otago and Fiordland on Sunday through Tuesday morning. Some flurries will likely make it to sea level for a time and may even settle.
In a nutshell, showers, localised heavy rain/sleet, gusty winds, isolated thunderstorms, hail, highland and alpine snow and rough seas including high swells are expected to be brought to NZ from Sunday to Tuesday.
High pressure is expected to approach NZ from the northwest on Wednesday and to dominate the South Island on Wednesday through Thursday and the North Island on Wednesday through Friday. This will bring milder weather back fast by Friday.
Snowfall totals could reach up to 75cm or more in several alpine areas of the South Island by Wednesday morning and could reach 10-20cm or more in the low-lying areas of Southland by Wednesday morning.
Max temperatures are likely to be much higher than normal by 4 degrees C or more, mainly in eastern Canterbury on Sunday due to the warmer westerly to northwesterly wind influx combining with Foehn winds. This changes by Monday and Tuesday is the main cold day.
The main cold pulse arrives later on Monday in the south and peaks on Tuesday.
Wind chills will be significant – www.RuralWeather.co.nz has an automatic windchill calculator for every hour across the next 10 days. Look for it in the TEMPS button/graphs at the top of the page.
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