How to read the Singapore rain radar

What the radar actually shows

Singapore's public rain radar is a weather-radar product from Meteorological Service Singapore. It measures returned microwave energy from raindrops, then paints rainfall intensity on a map. It is an observation of rain that is already falling, not a forecast of rain that has not formed yet.

That distinction matters. A clear radar loop does not mean it will stay dry. Afternoon thunderstorms can grow from nothing in 20 to 30 minutes, especially in April, May, October and November. Pair the radar with the 2-hour nowcast if you are about to leave the house.

The three ranges

NEA publishes three radar ranges. Use the one that matches the question you are asking.

• 50 km: island-scale. Best for "will it rain on my estate in the next 15 minutes?" You can see individual cells over Tampines, Jurong or Woodlands.
• 240 km: Peninsular Malaysia, the Strait of Malacca and nearby Sumatra. Best for incoming Sumatra squalls and monsoon rain bands still offshore.
• 480 km: regional. Useful during a monsoon surge or when a tropical cyclone in the South China Sea is reshaping the flow.

How to read the colours

Public radar products use a stepped colour scale from light to heavy rain. Exact hex values vary by product, but the meaning is stable:

• Light blues and greens: light rain or drizzle. You may get wet but flooding is unlikely.
• Yellows and oranges: moderate to heavy rain. Roads spray, drains run hard, outdoor events get disrupted.
• Reds and magentas: intense cells. Flash-flood risk in low-lying spots if the cell sits over the same catchment for more than 15 to 30 minutes.

Watch motion, not just colour. A red blob moving at 40 km/h will soak a town for 10 minutes. The same blob that stalls over Bukit Timah or the city can flood underpasses.

Radar vs the 2-hour nowcast

The 2-hour nowcast is an area-by-area forecast issued roughly every 30 minutes for about 47 towns. It is the right tool for "will Jurong West see showers between 3pm and 5pm?" The radar is the right tool for "is that cell over Clementi going to reach Queenstown in 20 minutes?"

A good habit: open the 50 km loop, step back a few frames, then check your town on the nowcast. If both say rain, take the umbrella. If the nowcast says fair but a squall line is on the 240 km loop west of Tuas, trust the loop.

Common gotchas

• Ground clutter and anomalous propagation can paint fake light rain near the coast on rare days. If the loop does not move, be sceptical.
• Very light drizzle can sit below the radar's detection threshold. You can still get wet in a misty monsoon morning.
• Tall buildings do not hide rain from a meteorological radar the way they hide it from your window. Check the map, not just the sky outside the CBD.

Questions