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Rainfall in Orange County is not evenly distributed.

Although yearly precipitation totals are the same, seasonal distribution has changed over time. Because many plants have distinct seasonal water needs, the uncertain persistence and /or direction of these trends makes it difficult to predict which plants will thrive here in the future.

monthly precipitation

• Summer rainfall occurs mostly in connection with showers and thunderstorms that are highly local.
• Autumn is historically the driest season, with November historically the driest month. Any significant rain is usually due to hurricanes (the hurricane season is June–November).
• Precipitation during winter and spring occurs mostly in connection with migratory low pressure storms. Historically, these occur more frequently and are distributed more evenly than in the summer.

Garden-effective rain

The graph below shows the likelihood of 0.5 inches of rainfall in Chapel Hill over any 7-day period, based on all available historic data (119 years). Note that Orange County does not receive reliable, garden-effective rain at any time of year.

• Reliable rain is defined as having at least an 80% likelihood of occurring.
• Garden-effective rain is defined as totaling at least 0.5 inches over 7 days.
• Plant selection and siting should consider ease of irrigation.