"Tule Fog"

TULE FOG

Here is what the NOAA web site has to say about "Tule Fog";

One of the most dangerous aspects of the rainy season throughout the San Joaquin Valley is the Tule fog. It forms on clear nights 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.

TULE FOG from the drivers view

When driving in the fog one should us low beams on headlights as the high beam will reflect back on the drive from the fog and reduced visibilty even more. You should drive at safe speeds which are usually below the speed limit.

Early today there was a major accident on Hwy 99 North just south of Fresno, Ca due in part to the fog. Visibilty was only about 500 feet in places in the early morning hours of Saturday.

Over 100 vehicles were part of the massive pile-up which killed two people and injured another 40+ people. Over a two mile stretch of Hwy 99. All three North bound lanes were closed for over 12 hours. A total of 108 vehicles, including 18 big rigs, were involved in the collisions.

The combination of fog and excessive speed by many vehicles was suspected to be the primary cause of the pileup, an official said. Officials considered it one of the worst accidents on California 99 in at least 10 years. Many people had to be extricated from their vehicles, including at least one person whose car slid under a big rig at the northern end of the crash scene.