All Weather News

Tule Take-Over: More Rain, More Fog

1 Feb 2017, 3:09 am

Earlier this week, a fifty car pile up caused a four mile back up near Hanford, California. The culprit: Tule Fog. The National Weather Service said that during the time of the crash, visibility was down to 50 feet. Dozens of schools were delayed Tuesday morning in hopes of keeping people of the roads and safe.

Tule fog is another name for radiation fog that forms in the Central Valley of California. It happens in the late fall and winter months following the first significant rainfall. Tule fog is a leading cause of weather related casualties in California. It forms on clear nights in the San Joaquin and Sacramento Valleys when the ground is moist and the wind is near calm. On nights like this, the ground cools rapidly. In turn, the moist air above it cools and causes water vapor to condense. 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.

The visibility in Tule fog is often less than 1/8th of a mile, about 600 feet, but can be less than 10 feet. 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.

Another area prone to fatal accidents is intersections across major roads or heavily traveled roads, where the cross traffic does not have to stop.

Some tips for driving in Tule fog include:

  • 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 CHP is providing escorts.
  • Always read and obey the overhead traffic and weather information on signs along California highways.

It wasn’t just the Valleys that saw dense fog this week, check out this incredible video from San Diego!

Cover Photo: Scott Rowe

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