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Outdoor activity weather in Singapore

Check five things before you keep a group outside: lightning, heat stress, UV, air quality, and whether rain is a cell or a surge.

The five-point check

Lightning: thunder audible, or thunderstorm on the nowcast? Shelter. Wait 30 minutes after the last thunder.
Heat: WBGT in the high or extreme band? Shorten the session, add shade and water, or move to morning.
UV: 10am-3pm is Extreme on clear days. Hats and sleeves for long events, not only sunscreen.
Air: 1-hour PM2.5 spiking or PSI Unhealthy? Cut endurance work. Sensitive students sit out.
Rain type: a 15-minute cell is a delay. A monsoon surge is a cancellation. Look at the radar loop, not one frame.

Best and worst windows

Best long-effort window most days: 7am to 9am. Worst lightning window: 2pm to 5pm in the inter-monsoon. Worst haze window: dry Southwest Monsoon afternoons when winds are southwesterly and hotspots are up. Worst heat: still May afternoons.

Questions

Should we cancel if the nowcast says "fair"?

Fair means no significant rain expected, not "no lightning possible later". Recheck at lunch. Cells can still grow.

Is a drizzle a reason to cancel?

Usually no, unless lightning is present, the field is unsafe, or a flood warning is up for the venue.

Independent guide based on publicly described NEA and Meteorological Service Singapore products. Not affiliated with NEA.