It is early morning. Just after the first golden rays of sunlight have broken through the dark curtain of night. As I drive into Beckley Creek Park my vision is obscured by something. Something eerie, something that seems older than the forest itself.
Fisherman on the William F. Miles Lakes move in and out of sight like silent ghosts. Joggers and bikers braving the early morning chill appear seemingly out of nowhere. I am surrounded, engulfed, consumed, lost, and then…it’s gone.
What was obscuring my vision you may ask? Fog.
Fog is a ground level cloud that forms when the air temperature lowers to the dew point or within 5° Fahrenheit. Fog generally forms overnight as the ground is cooled by the night sky. As the night in a valley becomes cool, clear, and calm the ground radiates (releases) energy gained from the sun during the day into space. As the earth’s surface continues to cool, provided a deep enough layer of moist air is present near the ground, the humidity will reach 100% and fog will form. This type of fog is called radiation fog.Photo from http://charliesweatherforecasts.blogspot.com/
After fog develops overnight, it usually persists until the sun rises. Afterwards it begins to dissipate. When the sun rises, the energy from the sun begins to warm the ground surrounding the fog, and the top layer of the fog. As the sun’s energy begins to warm the ground, the air molecules closest to the ground begin to warm by conduction from the ground. This causes the air molecules at the ground surrounding the fog to become relatively warm. This warming of the air causes the air around the perimeter of the fog to rise. Energy from the sun is able to warm the top layers of the fog which causes the air temperature in those layers to increase. The air temperature increases away from the dew point temperature, and causes the fog to start evaporating. As the sun continues to rise, more of the sun’s energy is able to reach deeper and further into the perimeter of the fog. Eventually the fog evaporates.
The picture above shows radiation fog on Angler Lake, evaporating as the sun rises.
Fog forms more often in the fall and winter. So come out to The Parklands on a cool, early fall morning and get lost in the fog!
Fun Fog Facts:
- The foggiest place on earth is Grand Banks near the Canadian island of Newfoundland. They have up to 200 foggy days per year!
- The foggiest place in the United States is Point Reyes, California.
- The only difference between mist and fog is density and its effect on visibility. A cloud that reduces visibility to less than 1 km (about 1,094 yards or 0.62 miles) is called fog, whereas it’s called mist if visibility range is between 1 and 2 km.
- Fog forms often near creeks, waterways, and river valleys as the water increases the humidity in the air.
About the Author
As Director of Education, Curtis Carman oversees The Parklands Outdoor Classroom, promoting STEAM-based education through engaging, hands-on learning both outdoors and inside the classroom. Each year, his team of Education Specialists, Interpretive Rangers and Camp Counselors guide nearly 20,000 participants of all ages through school field trips, camps, Parklands Explorer, Junior Explorer and Wednesday Wonders. Prior to his promotion to Education Director in May of 2018, Curtis first joined The Parklands team as an Interpretive Ranger and led the department as Education Coordinator for three years. A native of Louisville and a graduate of Ballard High School, Curtis returned to his hometown after having worked as an environmental educator in Maine and Colorado at Acadia and Rocky Mountain National Parks. Curtis also served as Membership Manager at the Rocky Mountain Conservancy. Curtis enjoys hiking, biking, camping and kayaking.