South Island Met Agency (SIMA)

Significant Weather Outlook

The Significant Weather Outlook is a daily, forecaster-written product covering the next five days for the South Island of New Zealand. Each day has its own map highlighting the regions where notable weather is most likely, a risk category, and a short narrative explaining the reasoning behind it.

How the outlook is produced

Each outlook is written by a SIMA forecaster after reviewing global and regional numerical weather prediction model guidance alongside current observations, satellite and radar imagery. The forecaster identifies the synoptic features likely to affect the South Island over the coming five days, such as fronts, lows, troughs or northwest airstreams, and judges where significant weather is most likely to result.

The outlook is updated daily by 10:30pm NZT, or every two days during quiet, settled weather. The "Last Updated" chip at the top of the page shows when the current set of maps was issued.

Understanding the risk categories

Each highlighted sector on an outlook map carries one of three risk categories. The category reflects both the probability of significant weather occurring within that sector and the forecaster's confidence.

  • Slight Risk (10% to 30%): low probability of significant weather. Isolated or weak activity is possible, but confidence remains low.
  • Enhanced Risk (30% to 50%): moderate probability of significant weather. Localised impacts may occur across parts of the highlighted region.
  • High Risk (over 50%): high probability of significant weather with potential for widespread or noticeable impacts. A Regional Weather Notice may also be issued.

What counts as significant weather

Significant weather includes heavy rain capable of causing surface flooding or river rises, severe gales and damaging gusts, heavy snow to low levels, thunderstorms with hail or intense downpours, and unusually extreme temperatures. Ordinary showers, light winds or routine frost are not highlighted.

How to use the outlook

The outlook is intended as an early heads-up for planning: travel over alpine passes, outdoor events, farm work and marine activity. As an event gets closer, more detail is published through SnowCast, StormCast and Regional Weather Notices. For official New Zealand severe weather watches and warnings, always refer to MetService and follow instructions from local Civil Defence authorities.

South Island Met Agency is an independent private forecaster and does not issue official government severe weather warnings. For official New Zealand watches and warnings, visit MetService. Read our About Us & Terms and Privacy Policy.