Each zone starts at 100 and points are deducted for bad conditions:
| Forecast | Thundery −60, heavy rain −55, showers −45, light rain −45, drizzle −25, cloudy −3 |
| Rainfall | >5mm −45, >1mm −35, >0.2mm −20 (nearest 5 stations) |
| Temperature | >34°C −10, >32°C −5 |
| Humidity | >90% −10, >80% −5 |
| Wind | >20kn effective −10, >15kn −5, <5kn +3 (adjusted by zone exposure) |
| UV Index | ≥11 −5, ≥8 −3 |
| Shelter | Tree-covered/hilly zones get +5 during rain |
Wind is scaled by zone exposure: high ×1.3, medium ×1.0, low ×0.7. Readings use the nearest weather station to each zone.
80+ Excellent · 60–79 Good · 40–59 Fair · 20–39 Poor · <20 Avoid