Recentscary pile-upson highways in California have been blamed on tule fog, a specific type of fog that's native to the state's Central Valley.
The recent huge, fog-related pileups in California include a 59-vehicle crash on Highway 99 in Tulare County on Jan. 31, which caused 10 injuries. Another major accident occurred nearby on Jan. 27, in which 43 vehicles crashed on Highway 58 near Bakersfield, leading to nine injuries. No one was killed in either wreck.
Named after the tule grass of the Central Valley, tule (TOO-lee) fog is a type of radiation fog. It forms on clear, calm nights when the ground loses heat rapidly. And forecasters warn that the danger will continue for several days.
"Tule fog is a major hazard to navigation and is the leading cause of weather-related accidents in California," according to a release from NASA.
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What is tule fog?
One of the most dangerous aspects of winter in California's Central Valley is tule fog, according to the National Oceanic and Atmospheric Administration's western region headquarters. It forms on clear nights when the ground is moist and the wind is nearly calm. On nights such as this, the ground cools rapidly.
In turn, the moist air above it cools and causes water vapor to condense, creating fog.
Once it has formed, the air must be heated enough to either evaporate the fog or lift it above the surface so that visibilities improve.
Visibility can drop to near zero
The visibility in tule fog is often less than 1/8th of a mile, about 600 feet, but can be less than 10 feet, NOAA said. Visibility can vary rapidly in any area, with sudden decreases to near zero in only a few feet. It is situations like these that often lead to multi-car accidents where one car follows another into a fog bank.
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Another area prone to fatal accidents is intersections across major roads or heavily traveled roads, where the cross traffic does not have to stop, according to NOAA.
What's the forecast?
According to a Feb. 4 forecast from theNational Weather Service in Hanford, California, "High to very high transportation risk will continue through the week. Visibility will be near zero at times. Dangerous fog can move in quickly, before you have time to react, drive carefully or make other plans."
"Highways impacted include, but are not limited to Interstate 5, State Routes 99, 41, 43, 46, 58, 59, 140, 152, 165, 180 and 198."
"Low visibility will make driving conditions hazardous," the weather service said.
Tule fog forming less often
Central California has seen long stretches of cold, socked-in days in the past, NASA said. In 1985, for example, Fresno experienced 16 consecutive days of dense fog, and Sacramento endured 17, according to news reports.
Researchers have found, however, that tule fog has been forming less often in California in recent decades.
How to drive in tule fog
Here are some tips from NOAA for driving in tule fog:
Drive with your lights on, even during daylight hours. But use the low beam only. High beam lights decrease your visibility by reflecting more fog back to you.
Reduce your speed. If you are late to your destination, then just be late. It is far better to be late a few minutes due to fog than to be late by several hours or days via a trip to the hospital because of an accident.
Listen for traffic you cannot see.
Avoid intersections where cross traffic does not stop.
Be patient. Do not pass lines of traffic.
Do not stop on a freeway or heavily traveled road unless absolutely necessary. If you must stop, get away from your vehicle to avoid personal injury.
If possible, postpone your trip until the fog lifts, usually by late morning.
Finally, be sure to heed instructions in those areas where the California Highway Patrol is providing escorts.
Always read and obey the overhead traffic and weather information on signs along California highways.
This article originally appeared on USA TODAY:Infamous 'tule fog' back in California forecast after huge crashes
