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I decided to use LIDAR data to look at the NWRP location to answer that question. NWPR lies in a bend of the Northwest River the surrounding areas of which are wetlands and moist bottoms. You can see the berm that exists in the north end of the parking lot. The equestrian area is surrounded on three sides by tall trees.

Notice that the surrounding area, around the parking, is lower and saturated on three sides by the river bottom. The park equestrian area is on a raised low platform somewhat like a peninsula surrounded by this moist ground.?

When the ambient temperature drops in the evening, the park area will see a greater drop in temperature than the wetlands due to the ability of dry land to change temperature faster than the surrounding saturated areas bordering the parking lot. Water and wetland's greater specific heat capacity retards temperature change in comparison with the dry elevated land (parking lot). The parking lot, in effect, gets cooler quickly and condenses the moist air from the surrounding low saturated terrain. The trees tend to block surface winds that would otherwise mix the air between the two areas. A moist, stratified, layer of cooler air sets up the condensation situation in the parking lot. If you were at yesterday's session you noted that the smoke from the Boy Scouts camp formed a stratified layer about 10 feet above the ground surface. The denser, moist, cool air extended from ground surface to the start of the less dense smoky layer. No air mixing was present at the start of the evening. Good for seeing, bad for dew as many observers without heaters have discovered. That is why it is so commonly cold at night and wet during observing sessions.

Attached is a LIDAR elevation map illustrating what I suspect. LIDAR (Light detection and ranging)