Please Note: Even though the sprinkler system is always turned off before evening events in the park, "rain or shine, there's always a chance of a wet lawn in the mornings and evenings if the weather conditions are just right. Those tiny droplets you see clinging to the blades of grass are called "dew." Dew is liquid water droplets that form on grass and other things in the early morning or late evening. Dew only forms under certain conditions. If a warm, clear day is followed by a cool, clear evening, dew will likely form. On a normal warm day, water evaporates from the warm ground into the air. That means it turns from a liquid into a gas called "water vapor." When evening comes, the warm ground continues to radiate heat into the air. As the ground begins to cool, the air will not be able to hold all the moisture. At a certain point — a temperature called the "dew point" — water vapor in the air will begin to condense (turn back to liquid water) faster than water is evaporating. When this happens, dew forms on surfaces that aren't warmed by the heat radiated from the ground. That's why you mainly see dew on grass." Source:
wonderopolis.org