|Published Tuesday, December 4, 2001 in the San Jose
Tule Fog Clouds the Valleys
Now that the region has seen its first significant rains of
the season, we have to watch out for dense night and morning valley fog.
Locally the areas with the highest incidence of tule fog are
in the southern Santa Clara Valley and the Livermore Valley. In these areas
the fog will usually clear by mid-morning, but it may last all
Dense fog can reduce the horizontal visibility to only a few feet, making driving extremely hazardous. Each year there are numerous traffic accidents when fog limits visibility and vehicles can't stop in time. Many are chain reaction pileups involving many cars that drive into the fog and encounter stopped vehicles. In December 1997, five people died and 28 were injured when 25 cars and 12 big rig trucks collided inside a fog bank on Interstate 5 near Elk Grove south of Sacramento.
The National Weather Service issues ""dense fog advisories'' when visibilities are expected to be an eighth of a mile or less. Under those conditions, someone driving 65 miles per hour has only 7.5 seconds to see a hazard and stop.
The California Highway Patrol's first recommendation when driving in fog is to slow down. The CHP also suggests driving with headlights on, but use only the low beam because high beams would be reflected by the fog to reduce visibility further. The CHP also recommend drivers delay trips through especially foggy areas until midday when visibilities usually improve.
And if you are stuck at home waiting for the fog to clear, check out an entire web site of haiku poetry about tule fog at http://wdsroot.ucdavis.edu/clients/pcbr/what/haiku.html.
Weather gifts for the holidays
In response to several requests about holiday gifts for
weather enthusiasts, I have put together a webpage at
http://ggweather.com/gifts.htm that has
links to several online catalogs with everything from weather stations to
A Historically, an aurora is visible in the Bay Area about once every five to ten years. Because of light pollution from the metropolitan area, it takes a fairly strong aurora event to be visible.
To predict a strong aurora requires monitoring the weather
on the sun, in particular the eruption of solar flares. These are related to
sunspot activity, which now is just passing its peak in an 11-year
Jan Null, founder of Golden Gate Weather Services, is a retired lead forecaster with the National Weather Service. Send questions to him c/o WeatherCorner, San Jose Mercury News, 750 Ridder Park Drive, San Jose, Calif. 95190. You also can telephone questions at (510) 657-2246, fax them to (510) 315-3015 or e-mail them to firstname.lastname@example.org. Please indicate in your e-mail what city you live in.