What does a 20% chance of rain mean?

A 20% chance of rain means the forecast indicates a relatively low probability of measurable precipitation occurring during the specified forecast period at the location. It does not mean that rain will last for 20% of the period, cover 20% of the city, or be exactly 20% intense. Weather forecasts contain uncertainty, so even a low probability can occasionally result in rain. Conversely, a higher probability does not necessarily mean continuous rainfall. When WeatherPerch shows precipitation probabilities, consider them together with the hourly forecast, expected precipitation amount when available, radar, and current alerts. If an outdoor activity is important, a low rain probability may still justify checking the forecast shortly before you leave.