Why Rain Chances Change During the Same Day
A rain percentage is a chance for an area over a period, not a promise that a cloud will sit on your street. It changes during the day for two different reasons. The atmosphere actually changes, and the forecast is updated as new observations come in. Both can move the number you saw at breakfast.
Showers are small. A line of storms, a sea breeze, or a pocket of moisture can shift by a short distance and change who gets wet. Morning can be dry while afternoon carries most of the chance, or the reverse can happen when a morning batch clears and the rest of the day dries out. The daily rain chance is only the summary. The timeline and the daypart rows are where the timing lives.
Read the day in bands
Under about 20 percent, rain is a side possibility for most plans. From about 20 to 40 percent, timing matters more than the single daily figure. Above about 40 percent in the hours you care about, have a real backup. A jump from 30 to 34 percent is not a new day. A jump from 15 percent in the morning block to 60 percent in the afternoon block is.
If the highest chance today is low, the page says rain is not a major part of the forecast. That sentence follows the returned chance. It is not a claim that rain is impossible, and it is not a warning. If a wetter stretch shows up in the hourly data, the rain section names the hours instead of inventing a story.
Chance and amount are different
A high chance of light rain is a different problem from a lower chance of a short heavy burst. The amount, when it is shown, is the forecast total for the day, not a gauge in your yard. Use the chance to decide whether rain belongs in the plan. Use the amount only as a rough sense of how much water is in the forecast.
The percent also does not, by itself, mean lightning. If the condition word says thunderstorm, that is the cue to get indoors when thunder is nearby. A plain rain chance is not a severe-weather notice, and this site does not issue warnings.
Why the morning number goes stale
Forecast runs update through the day. A storm that looked likely at dawn can weaken. A clear morning can grow clouds by lunch as the ground heats. If your plan is this afternoon, look again near midday when the chance was close to a cutoff you care about. If the chance was very low and the timeline stays flat, another check adds little.
Two nearby places can disagree because showers are narrow. A search for one side of a city and a search for the other can show different afternoon percents. Pick the place you will actually be, then read that timeline. The daily number is the headline. The hours are the decision.