Probability is not rainfall amount
Rain probability answers ‘how likely is measurable precipitation?’ Rainfall amount answers ‘how much precipitation may fall?’ A high probability can come with light rain, while a lower probability can still produce a heavy shower in one area.
How to think about 30%, 50%, and 90%
Thirty percent suggests rain is possible but not the most likely outcome. Fifty percent means the forecast is meaningfully uncertain. Ninety percent means precipitation is highly likely during the forecast period. None of these percentages says how long rain will last.
Why the number changes
New observations, radar trends, and updated forecast models can shift the timing or coverage of rain. Short-range forecasts often become more useful as the event gets closer.
What this means for your day
Use precipitation probability with the timing and expected amount. If an outdoor plan matters, check the hourly forecast and alerts again near departure.
Frequently asked questions
Why does rain probability change?
Weather information updates as new observations and forecast model runs become available. Small changes are normal, especially farther into the future.
Where can I see this information?
Use Weather Chase's current conditions, hourly forecast, daily forecast, and map tools to compare the latest information for a location.