Most rainfall here occurs between October and May. Morning and evening fog in the summer keeps the temperature cool in the river basin. The fog usually burns off by noon. Snow is not common, but does occasionally fall in the higher elevations. In summer, it can be sunny and hot during the day and cool and foggy at night. Rain, even in summer, is not uncommon.
Winter weather can be unpredictable and sometimes very cold.
If you are visiting in winter, come prepared for rain, cold, or sun. Mosquitoes are plentiful in some areas of the park. Mosquito repellent and sunscreen are recommended for summer. Fog and rain make this a favorable climate for the coast redwood trees to grow in. Some larger trees can transpire up to 500 gallons of water a day.