Published Tuesday, May 23, 2004 in the San Jose Mercury News

Recent heat a reminder that climate is quite mild

By Jan Null
Special to the Mercury News

"Climate is what you expect, Weather is what you get.''  -- R. Heinlein

The recent spate of warm weather, the mention of record temperatures and a bit too much whining got me thinking about how mild our Bay Area climate really is. Like real estate, climate is a matter of location, location, location. In our case, the temperate climate results from our proximity to the relatively mild waters of the nearby Pacific Ocean.

For example, the all-time record hot day in San Jose was 109 degrees on June 14, 2000, but this is far short of the California record of 134 degrees in Death Valley or the world record 136 degrees in Libya. San Francisco is even milder, with a record of ``only'' 103, also on June 14, 2000, and has only had a dozen days since 1875 when the mercury reached triple digits.

Bay Area cold weather is also extremely temperate compared with other parts of the state and world, again because of the moderating influence of the Pacific. The coldest day in San Jose weather records is 17 degrees on two consecutive days; Jan. 9 and 10, 1920. San Francisco's all-time low is an almost balmy 27 degrees. Statewide, the mercury has fallen as low as 45 below zero at Boca Reservoir northeast of Truckee, while the world record is an almost unbelievable 129 degrees below in Antarctica.

The most rainfall in one hour was 12 inches in Holt, Mo., back in 1947. During a 24-hour period, San Francisco has had 6.19 inches, and the record is 3.60 inches for San Jose. The California record is just over 2 feet -- 26.12 inches -- of rain at Hoegee's Camp near Mount Wilson in Southern California. But that is barely respectable when compared to the more than 6 feet -- 73 inches -- on La Reunion Island in the Indian Ocean off the coast of Madagascar.

The annual rainfall in the Bay Area is quite variable, with averages ranging from about 15 inches in San Jose to 60 inches in the wettest spots of the Santa Cruz Mountains. In the record 1861-62 rainfall season, San Francisco had a phenomenal 49.27 inches of rain. The biggest seasonal total for San Jose was 30.25 inches in 1982-83.

To see more records, visit http://ggweather.com/sf/extremes.html on the Web.

Q Why does Eureka have such cool summers? The average high is 63 in September, the warmest month. Is the marine layer particularly strong in Eureka? Places up on the Oregon coast have warmer summers than Eureka. Scott Thistle - New York City

A The location of the Pacific high to the northwest of California results in the persistent northwest winds along the coast during the summer. This causes a phenomenon called upwelling along the coast where surface water is transported away from the coast and cooler subsurface waters come to the surface. The coldest upwelling along the West Coast is near Eureka and is reflected in the air temperatures.

Q Why is it that when you flush the toilet in the Northern Hemisphere, the water turns in one direction, but if you visit Australia in the Southern Hemisphere, the water in the toilet turns in the opposite direction? Mike Johnstone - Nampa, Idaho

A This is one of the great meteorological myths. Toilets and sinks do not drain in opposite directions in the Northern and Southern hemispheres! The flow is the result of how they are engineered or slight imperfections in their design, not the Coriolis Force, whose influence is too small to affect the rotation of water within them.

Q You have said that San Francisco has a higher humidity than Miami. However, when I was in Florida one summer, the heat was unbearable and the humidity was so high that your clothes stuck to your body. No matter how hot it gets in San Francisco, in my 27 years of living here, I have never experienced humidity like in Florida, so why is that? Olga Hadeed - San Francisco

A Yes, the average humidity is higher in San Francisco than Miami. San Francisco's average morning humidity is 84 percent, and the afternoon average is 62 percent, compared with 82 and 61 percent for the morning and afternoon in Miami. The discomfort that people feel is the combination of heat and humidity.

Jan Null, founder of Golden Gate Weather Services, is a retired lead forecaster with the National Weather Service. Send questions to him c/o Weather Corner, 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 or fill out a form online at http://ggweather.com/questions.htm