Steady rain is unusual at Pebble Beach

When professional, amateur and celebrity golfers tee off Thursday at the annual AT&T Pebble Beach National Pro-Am, the topic most likely to be discussed besides bogeys and birdies will be the tournament's infamous weather.

The tournament may have changed its name to the AT&T some years back, but the climatic vagaries that can make the course so challenging are still known as ``Crosby weather.'' The tournament, which dates back to 1937, when Bing Crosby started his annual ``clambake,'' has seen rain, snow, sleet and winds play havoc with the course, the players and the spectators. However, a look at the weather statistics shows that it's not quite the constant deluge we often envision.

Probably the most memorable example of ``Crosby weather'' was back in 1962, when the final day of the tournament had to be delayed until Monday because of a half-inch of snow on Saturday night and sleet on Sunday. In the 64 years that the tournament has been played, it has been shortened several times and the final day has been postponed on occasion. But 1996 was the only time it has been canceled.

In 25 years there have actually been 10 when it has not rained any of the days during the tournament, while in the same period there have been two occasions when it rained all four days. In the other 13 years, it rained one day on six occasions, two days for another six years and only once did it rain three of the four days. But the time it rained three days was in 1998, when 2.74 inches were recorded and the tournament ended up being postponed for about six months.

Almost as critical are the conditions during the week before the players tee off. It's here that the rainy character of late January and early February shows up, with rain having occurred during 22 of the past 25 years. Historically, the chance of getting rain in Monterey on any single day from January through the first week of March is about 35 percent. This may dissuade some from the idea of moving the tournament to the end of February.

Q First, let me say that my family reads and appreciates the weather column. We would like to have your definitions of the often-heard weather expressions ``mostly cloudy,'' ``partly cloudy,'' ``mostly sunny'' and ``partly sunny.'' James Hermstad - Saratoga

A In some ways these definitions are an ``Is the glass half full or half empty?'' situation. To one person a day might be ``partly cloudy,'' while to another it's ``mostly sunny.'' But here are the definitions used by the National Weather Service that are based upon the amount of opaque cloud cover and the time of day. If the sky has between one-eighth and one-fourth opaque cloud cover, it is called ``mostly sunny'' at day and ``mostly clear'' at night. For three-eighths to one-half coverage it's ``partly sunny'' during the day and ``partly cloudy'' at night. If the opaque coverage is between three-fourths and seven-eighths, the weather service says it's ``mostly cloudy,'' and of course eight-eighths would be ``cloudy.''

Probably the most subjective term and the one that is the source of the most confusion is ``fair.'' The weather service defines it as ``less than four-tenths opaque clouds, no precipitation, no extremes of visibility, temperature or winds. Describes generally pleasant weather conditions.'' Hmmm, but what's ``pleasant''?

Q Thanks for a nice description of barometric pressure in a recent column. Now for a little harder one. How does one go about setting a hygrometer for home use? John Buckley - Milpitas

A For the uninitiated, a hygrometer is a device for measuring the amount of moisture in the air. This is usually expressed as a percentage of the amount of moisture needed to make the air totally saturated: the ``relative humidity.'' The simplest way to calibrate one is to get the bathroom nice and steamy, which would mean the air is totally saturated, or 100 percent relative humidity. You would then use the adjusting screw to set your hygrometer to 100 percent.

Electronic hygrometers use a tiny carbon plate that has a small electrical current moving through it. Changes in moisture affect the electrical resistance and require little calibration. Requiring more calibration but more interesting are the older dial-type hygrometers. These use a length of either human hair or horsehair that changes about 2.5 percent in length between 0 and 100 percent humidity. Hair gets shorter with lower humidities and longer as the air becomes more moist.

Q What is it about the Gulf of Alaska that spawns winter storms with very low atmospheric pressures? Carleton Wright - Los Gatos

A The Gulf of Alaska is just one of several regions around the globe that are conducive to the formation of storms. These regions are about 60 degrees latitude, where cold polar air masses meet warmer middle-latitude air, and cold polar fronts and areas of low pressure develop.

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 weathercorner@ggweather.com. Please indicate in your e-mail what city you live in.