BAKERSFIELD, Calif. (KGET) -- In the San Joaquin Valley, we most often see what is called "Tule Fog," which is technically "radiation fog." After a rain event that has soaked our soil, this type of fog forms at night under clear skies with calm winds. The fog forms when heat is absorbed by the earth's surface during the day is radiated into space. Weather Wednesdays: Autumnal Equinox As air along ridgetops and the upper slopes of mountains begins to cool after sunset, the air becomes dense and heavy and begins to drain down into the valley floor. That air in the valley floor continues to cool due to radiational cooling, the air becomes so saturated, the humidity level reaches 100%, when fog forms. Radiation fog varies in depth from 3 feet to about 1,000 feet and usually remains stationary.This type of fog can reduce visibility to near zero at times and make driving very hazardous. It also tends dissipate very quickly once the sun comes up and starts to evaporate the fog layer. Fog driving tips: Slow down - allow extra time to reach your destination. Leave plenty of distance between you and the vehicle in front of you to account for sudden stops or changes in the traffic pattern. Use regular headlights - Use fog lights if you have them. Never use your high-beam lights since they causes glare, making it more difficult for you to see what's ahead of you on the road. Follow shoulder lines - To ensure you are staying in the proper lane, follow the painted lines on the shoulder with your eyes. Pull over & wait it out - When visibility is near zero, turn on your hazard lights, pull into a safe location and wait.