Probability is not intensity or duration

A probability alone does not tell you how hard it will rain or for how many minutes. Read the chance alongside the forecast precipitation type, and consult official rainfall forecasts and alerts when needed.

Example: 30% at 09:00, 60% at 10:00, 30% at 11:00

Do not add these to get 120%. The maximum of 60% is not a calculated probability for the whole three-hour outing either. The useful starting point is that the forecast probability is higher at 10:00, and whether you will be outdoors then. These are illustrative values.

Match preparation to your journey

The outing tool highlights hours at or above 40%, or with a forecast precipitation type. This is WHENTHER’s display threshold, not a promise of dry weather below it. Consider whether your journey involves a long exposed walk or quick access to shelter. During dangerous weather, official safety instructions take priority over umbrella choices.

Missing data and updates

An absent probability does not mean 0%. The tool summarizes available values and does not join wet periods across missing hours. Recheck the forecast before leaving. The methodology explains how coverage is handled.

Sources and methods

WHENTHER · Content updated: 2026-09-21