Weather Warning Criteria

This page lists the criteria for the MetService weather warnings. Please read the definitions below, and then consult the Severe Weather Criteria Chart at the bottom of the page.

Severe Weather Warning

MetService will issue a Severe Weather Warning whenever there is an expectation that any of the following weather conditions will occur within the next 24 hours:

  • Widespread* rainfall greater than 50 mm within 6 hours or 100 mm within 24 hours;
  • Widespread* snowfall below 1000 metres on the North Island, South Canterbury or Otago - or below 500 metres elsewhere on the South Island with a snow depth of 10 centimetres within 6 hours or 25 centimetres within 24 hours;
  • Widespread* severe gales with a minimum mean speed of 90 km/hr or frequent gusts exceeding 110 km/hr.

* "Widespread" means over an area of 1000 square kilometres or more.

Severe Weather Watch

MetService will issue a Severe Weather Watch whenever there is an expectation that conditions may deteriorate to the thresholds specified for the issue of a Severe Weather Warning:

  • After the next 24 hours but within 48-72 hours, or
  • If there is a high level of uncertainty within the next 24 hours.

Road Snowfall Warning

MetService will issue a Road Snowfall Warning for Napier-Taupo Road (SH5), Desert Road (SH1), Remutaka Hill Road (SH2), Lewis Pass (SH7), Arthur's Pass (SH73), Porters Pass (SH73), Haast Pass (SH6), Lindis Pass (SH8), Crown Range Road, Milford Road (SH94) or Dunedin to Waitati Highway (SH1) whenever there is a likelihood of snow settling on one or more of those roads within the next 24 hours.

Severe Weather Criteria Chart

Definitions:

One Day [High]
Within the next 24 hours, with a high level of certainty
One Day [Low]
Within the next 24 hours, but with a low level of certainty
One-Two/Three Days
Between 24 hours and 48-72 hours from now
Weather Event One Day
[High]
One Day
[Low]
One-Two/Three
Days
1. Heavy rain
over an area of 1000 square kilometres or more:

* 50 mm or more in a 6-hour period
* 100 mm or more in a 24-hour period
Severe Weather Warning Severe Weather Watch Severe Weather Watch
2. Strong winds
over an area of 1000 square kilometres or more with:

* Minimum mean speed of 90 km/h, or
* Frequent gusts exceeding 110 km/h
Severe Weather Warning Severe Weather Watch Severe Weather Watch
3. Heavy snow - North Island
over an area of 1000 square kilometres or more below an altitude of 1000 metres:

* 10 cm or more in a 6-hour period
* 25 cm or more in a 24-hour period
Severe Weather Warning Severe Weather Watch Severe Weather Watch
4. Heavy snow - South Island
over an area of 1000 square kilometres or more either below an altitude of 1000 metres in South Canterbury and Otago or below 500 metres elsewhere:

* 10 cm or more in a 6-hour period
* 25 cm or more in a 24-hour period
Severe Weather Warning Severe Weather Watch Severe Weather Watch
5. Snow on key roads
settling on any of the following roads: Napier-Taupo Road (SH5), Desert Road (SH1), Remutaka Hill Road (SH2), Lewis Pass (SH7), Arthur's Pass (SH73), Porters Pass (SH73), Haast Pass (SH6), Lindis Pass (SH8), Crown Range Road, Milford Road (SH94) or Dunedin to Waitati Highway (SH1)
Road Snowfall Warning