On early winter mornings, a thick grey wall holds back time, traffic and school. This is called fog, more specifically tule fog.
Tule fog consists of condensed water droplets that have been cooled to the dewpoint and cannot hold all the water vapor. In the Valley, the recent rain has moistened the air on the surface, making it viable for fog to form.
A humid air mass at night combined with the recent rain and cool weather makes thick, sometimes dangerous fog.
In the Central Valley, the foggy season takes place between mid-November and continues until late February.
Meteorologist Kevin Durfee, from the National Weather Service, explains that during fog, humidity is at 100 percent.
During the winter season, heavy rainfall and high moisture content establish a foundation for fog to develop, he says.
“The best way to explain why fog is so common in this valley is to to think of this valley as a giant bathtub,” Durfee said. “Water collects in this ‘bathtub’ during the rain season, and the long, clear nights of radiational cooling lead to fog formation.”
Safety in the fog
This year, multiple deaths have occurred in auto accidents caused by the fog. The highway patrol officers caution drivers to use lower headlights in the fog, avoiding the reflection of bright light that creates an even more dangerous situation.
California Highway Patrol officer Rob Avila urges drivers to take precautions to avoid dangers. He encourages them to roll down windows in order to hear oncoming traffic and to drive at speeds appropriate for conditions.
“The simple danger of fog is that it makes it harder to see what is ahead of you while driving a car,” Avila said. “Headlights are important during fog because they make the vehicle you are driving more visible to other drivers. This becomes very important when crossing intersections. But always use low beams, because high beams can reflect off the fog, thus making it harder to see.”
Some places are known as “death zones” during the foggy season. Places like Selma and Highway 99 are known to be especially dense. For officers, anywhere can be a death zone when the visibility is under 500 feet, Avila said.
“The death zone for fog is the distance you need to safely stop your car, but you cannot see it due to fog,” Avila said. “For example, the average driver traveling at 60 mph needs approximately 300 feet of distance to stop his or her vehicle safely. So if an accident was stopped in the road ahead of you, you could not stop your car in time, and [you would] crash. Be careful, because what you can’t see can kill you.”
Officers have established a policy to escort/pace traffic in order to avoid crashes in the “death zone” fog. At less than 500 feet of visibility, the CHP officers turn on their emergency lights and drive at a safe speed for current fog conditions. Most likely, the pace speed will be under the posted speed limit.
Students cope with conditions
High school students and teachers on campus live in many areas in the Valley, including Easton, Sanger and Caruthers.
Senior Tim DeGroot lives in Easton, where the foggy season impacts his drives to school every day.
“With a commute of 26 miles a day, fog slows me down quite a bit,” DeGroot said. “Driving in the country, I have to stay alert at all times. Stop signs are the worst. Having to roll down the windows and taking risks by pulling out onto blind roads becomes essential for making my way into town.”
High school students are encouraged to follow the safety guidelines during this season. They are the newest drivers and need to learn sooner rather than later, Avila says.
“High schoolers are our community’s newest drivers,” Avila said. “For some high schoolers, this is their first time driving in the fog. So that puts high schoolers at a greater risk for being involved in an accident; but with a little knowledge, that risk can be reduced.”
For more information, check out the CHP’s winter safety tips. For more coverage of local phenomena, read the Dec. 7, 2010 article, Honeybees critical to Valley agriculture.