WEATHER CORNER

Weather Underground Uncovered

BY JAN NULL
Special to the Mercury News

MY RECENT tongue-in-cheek comment about the Weather Underground being a strange name for a weather company resulted in several comments from readers. These included:

From Walter Bremer: ``Weather Underground is not a strange name to those of us who remember the '60s. Of, course if you remember the '60s, you probably weren't there :-).''

From Chris Carrigan: ``I can only assume that the name derives from an inept anti-Vietnam War terrorist group which was originally called the Weathermen and then changed to the Weather Underground. That is, they were the Weathermen who were part of an underground (clandestine) organization. It had nothing to do with actual weather occurring underground.''

From John R. Grout: ``The Weather Underground got its name for a combination of reasons . . . a key (but obscure) reason was that users were connected to the original, non-commercial, non-graphic site running on a Unix server at the University of Michigan in Ann Arbor.

`` For various reasons, certain port numbers gain a sort of unofficial status . . . and the one WU chose (3000) is known as the ``underground'' port because it is used on many different systems for secondary (or unauthorized, or even unlawful) applications. They needed to use a port number
people would remember -- such as the '60s radical group's name -- so their name (Weather Underground) was a natural choice.''

Q. In addition to reporting weather conditions in the larger cities of the Bay Area, local news stations routinely report the current, high, low and forecast temperatures for smaller cities or communities. For instance, KNTV (Ch. 11) reports readings from and forecasts for the Evergreen, Blossom Valley and Almaden Valley districts of San Jose, in addition to the ``official'' readings from downtown San Jose. I assume that most reports on smaller communities aren't from ``official'' National Weather Service stations.

Therefore, I'm curious as to who reports these conditions -- city officials, schools, or private citizens? Also, is there an Internet site where real-time and/or historical data are available for these smaller, unofficial weather stations?  S. Nolan - San Jose

A. Good questions. I am often asked about the source of weather data, and there is no single or simple answer. As you surmised, the observations come from a variety of sources, including public agencies, schools and private individuals. The only ``official'' National Weather Service reports are for downtown San Jose, airports around the region and selected NWS sites in Fremont, Gilroy, Hollister and Redwood City. These sites are quality-controlled, unlike those of unofficial sites. However, the television forecasters are usually familiar enough with their local sites to monitor quality on a day-to-day basis.

There are several online networks of real-time weather reports from these smaller sites, most of which are associated with educational activities. The Weather Network, for instance, has about two dozen sites in the Bay Area and can be found at http://instaweather.com/kpix/sitelist.asp. The MASTEP program has 17 locations and can be found at www.kntv.com/mastep/default2.asp.

Q.  We were wondering if past tsunamis have had an effect on the San Francisco Bay. I know that there were some very bad coastal problems in 1956 from a tsunami. I don't know if there are more current ones. When I asked people if tsunamis have ever come under the Golden Gate, and how far, or what effect they had on shipping and the marinas in the bay, no one seems to remember or know.  Where would I find out about this, or do you know? Lois Masin - Sunnyvale

A. According to the tsunami experts I talked to, the mouth of the Golden Gate is too constricted to permit a significant wave to form inside the San Francisco Bay from a tsunami. (Tsunamis are waves generated by an earthquakes and are often referred to, incorrectly, as ``tidal waves.'')

Even the major 1906 and 1989 earthquakes created water level changes of less than 4 inches in the San Francisco Bay. On the coast, of course, tsunamis are a different matter and can be extremely dangerous. The Good Friday Alaskan Earthquake in 1964 was responsible for a dozen deaths and $10 million in damage along the Northern California coast -- 2,500 miles away. Because these great waves were bent by the coast, the areas that sustained the most damage were those that were directly in line with the Gulf of Alaska. This spared the San Francisco and San Mateo County coastlines -- which was fortunate, as an estimated 10,000 persons flocked to the beach to watch the wave!

Q.  I have a handblown ``Weather Glass'' and am having a problem in that the change in temperature (daytime vs. nighttime) seems to cause as much rise and fall in the spout as the change in local pressure. The glass is not in the sunlight or near any source of heat. The only thing I can think
of is reading it at the same time each day, but this is too restrictive. How did those on the ``clipper ships'' ever make sense out of the readings? Was it someone's job to observe it continuously? I enjoy your column. Bert Martel - Saratoga

A.  What you are noting is called the diurnal pressure change, the phenomenon responsible for our daily sea breeze.

When there are no external weather factors like an approaching low pressure front, the temperature causes the air pressure to rise and fall as it heats and cools. Because inland areas become much warmer than those along the coast, their pressure will decrease much more in the afternoon hours.
This creates a thermal low pressure area toward which cooler air rushes. Reading a barometer at the same time every day can be useful during a static weather pattern, but would not be especially useful when the weather pattern is changing.

Q.  I flew recently from San Francisco to Boston and watched the sun set behind us. We were over a dense cloud cover for much of the trip.

I noticed two things: as the sun was disappearing, in the last two or so seconds there was a distinct green flash just before it vanished. I had heard of this phenomenon, but have never seen it, nor do I have any idea why it happens.

The other interesting thing was la ge circular swirls in the clouds, some very regular. They appeared to be about three to five miles in diameter. Was I seeing something real, and if so, what causes it? John Ehrman - Sunnyvale

A.  What you saw is the ``Green Flash,'' the result of looking at the sun through the great thickness of atmosphere. Water vapor in the atmosphere absorbs the yellow and orange-colored light from the sun and scatters the violet light. That leaves red and blue-green light to travel directly toward
the observer. Near the horizon, the sun's light is so highly bent or refracted that it seems to create two suns -- a red one and a blue-green one, each partly covering each other. The red one is always closer to the horizon. So after it sets or before it rises, you see only the fleeting edge of the blue-green disk.

The second phenomena you mention may be eddies in the low clouds caused by the wind blowing around an obstruction like a hill or mountain. These are similar in nature to the swirls in a river or behind a large truck. These are frequently seen along the California coast in the lee
of the headlands or islands. The following Web site at the University of Wisconsin has a dramatic example of what are called ``Von Karmen Vortices'': http://cimss.ssec.wisc.edu/goes/misc/von_karman.gif

~As the Atlantic hurricane season gets into full swing, I have put together a list of weather Web sites with the latest information. See http://ggweather.com/hurricane.htm

~I have also created a Web site with detailed climatological information and links to forecasts for 39 Bay Area locations. See http://ggweather.com/climate/

Jan Null, founder of Golden Gate Weather Services and Adjunct Professor at San Francisco State University, 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 weathercorner@ggweather.com.