How to read New Zealand's rain radar
Colours show rainfall intensity, the animated loop shows where rain is heading - but mountains cast radar shadows. Here's how to read it like a forecaster.
MetService's rain radar shows where rain is falling right now and how heavy it is, using colour to indicate intensity - light blues and greens for drizzle and light rain, through yellow and orange to red for heavy or torrential downpours. Play the animated loop and you can see which way the rain is moving and roughly when it will reach you. The main catch in New Zealand: the Southern Alps and other high country block the radar beam, leaving blind spots you need to allow for.
What is rain radar and how does it work?
Weather radar sends out pulses of microwave energy that bounce off raindrops, hail and snow. The stronger the returned signal - the "reflectivity" - the heavier the precipitation. The radar also measures how far away the echo is, building a live map of where rain is falling. Crucially, radar detects precipitation in the atmosphere, not necessarily rain reaching the ground; in dry conditions light rain can evaporate before it lands, and heavy echoes aloft may arrive weaker at the surface.
MetService operates a network of radar sites covering much of the country, stitched together into a national picture on its website and app.
What do the radar colours mean?
Colour is the quickest read on intensity. While the exact scale is labelled on the MetService radar key, the universal logic is cool-to-hot:
| Colour | Roughly means |
|---|---|
| Light blue / green | Light rain or drizzle |
| Yellow | Moderate rain |
| Orange | Heavy rain |
| Red / dark red | Very heavy to torrential rain - flash-flood potential |
Always check the on-screen legend, as scales differ between providers. A block of red sitting over a small catchment is a classic flash-flood signal, especially in summer thunderstorms.
Why is the animation loop the most useful tool?
A single radar frame tells you where rain is now; the loop tells you where it is going. By playing the last hour or two of frames you can see the direction of travel and the speed of the system, then extrapolate roughly when the rain will reach your location and whether it is intensifying or fading. This simple "nowcasting" is the single most valuable habit when reading radar - far more useful than a static snapshot. MetService also offers short-range rain forecasts that project the radar picture forward for the coming hours.
What are the limitations of New Zealand's radar?
Radar is powerful but not perfect, and New Zealand's terrain creates specific pitfalls worth understanding:
- Mountain blocking (radar shadow): the Southern Alps and other ranges physically block the beam, so rain falling behind them, relative to the radar site, may not show up. This is a significant limitation on the West Coast and in alpine valleys.
- Beam overshooting: the beam rises with distance, so far from a radar it may pass over the top of low-level rain and miss it entirely.
- Coverage gaps: some remote and mountainous areas sit beyond reliable radar range altogether.
- Ground clutter and false echoes: hills, buildings and occasionally the sea surface can return spurious echoes near the radar.
- Precipitation type: radar can struggle to distinguish rain, hail and snow, and the "bright band" where snow melts can exaggerate intensity.
The practical upshot: an empty patch on the radar over the mountains does not guarantee it is dry there - it may simply be hidden.
How should you combine radar with other tools?
Radar answers "what is happening now and in the next hour or two". It does not tell you what tomorrow holds. For that you need forecast models and official warnings. The best practice is to layer your sources: use satellite imagery to see the wider cloud picture, radar for the live nowcast, MetService warnings for official hazard guidance, and forecast models for the days ahead. When radar shows heavy rain training over the same area repeatedly, cross-check whether a MetService Heavy Rain or Severe Thunderstorm Warning is in force.
Where does model comparison fit in?
Radar is a record of the present; the value of a forecast is in the future, and that is where models - and their disagreements - come in. For New Zealand, checkweather.io compares the three global heavyweight models - ECMWF, NOAA's GFS and DWD's ICON - and converts how closely they agree into a plain-English forecast-confidence score, while linking through to MetService for the official radar and warnings. Radar tells you the rain has arrived; the confidence score tells you, before it does, how much to trust the forecast that it would. An accuracy scoreboard then grades each model against what actually fell - the "no black boxes" principle applied to the days ahead, with radar as the reality check for the here and now.
A quick checklist for reading the radar
- Check the colour key first - intensity scales vary.
- Play the loop to judge direction, speed and whether rain is growing or decaying.
- Remember mountains cast radar shadows - absence of echo is not proof of dry weather.
- Watch for slow-moving red cells over one catchment - a flash-flood flag.
- Cross-check against MetService warnings and, for the days ahead, the model picture.
The bottom line
MetService's rain radar is the best tool for the next hour or two: read the colours for intensity, play the loop for movement, and always allow for the blind spots the Southern Alps create. Then pair it with warnings and a model-confidence view for anything beyond the immediate nowcast.