| Published Tuesday, October 9, 2001 in the San Jose
Mercury News Weather Corner BY JAN NULL Winter rains won't be led by potential El Niņo storms
Most oceanic and atmospheric indicators currently reflect neutral conditions in the tropical Pacific, but there are indications that an El Niņo is trying to develop. After two years of cooler-than-normal water temperatures, the tropical Pacific is showing signs of warming. Exactly when this will happen and how strong of an event it will produce are unclear, but current forecasts point toward a weak El Niņo beginning late this year or in early 2002. What does that mean for California this winter? Since 1950, there have been nine weak to moderate El Niņos. The rainfall in the Bay Area was above normal during four of those years and below normal in five, telling us that there is no strong indicator during these weak El Niņo events. Thus, El Niņo is probably not going to be a controlling factor in winter rainfall. For a detailed analysis of the relationship between El Niņo, La Niņa and California rainfall, see http://ggweather.com/enso/calenso.htm. Q My subjective memories make me think that winter has been milder, later in coming and longer. The calendar spring, then, seems more like winter, and I have a heck of a time getting my tomato seedlings into the ground because the soil doesn't seem to warm up until late May or June. Do weather records corroborate this, or is this a senior moment? Victoria - Saratoga A I can't find any collaborative evidence in long-term records. However, the rainfall pattern of the past two seasons has included an extended dry period from mid-December to mid-January and significant rainfall from the latter part of January into April. This would account for the late planting of both our tomato seedlings. Q In a recent Mercury News article, you said, ``In the Northern Hemisphere, air flows clockwise and outward from an area of high pressure.'' Am I correct that in the Southern Hemisphere, air flows counterclockwise and also outward from an area of high pressure and vice versa from low-pressure areas? Your article caught my eye because I know physicists have never been able to explain why toilets flush counterclockwise in Australia. Carlos Houed - San Jose A Yes and no. You are correct that in the Southern Hemisphere, air flows outward from high pressure in a counterclockwise direction and toward an area of low pressure with a clockwise rotation. The reason the air curves is the rotation of Earth and something called the Coriolis force. These factors deflect winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. To visualize this, think of two people on opposite sides of a merry-go-round in motion, and one throws a ball toward the other. By the time the ball reaches the other side of the merry-go-round, the person catching the ball would have moved and it will appear that the path of the ball curved. These forces are noticeable only on a large scale and do not affect how water drains in a toilet or sink. This is an often-heard misconception that has taken on the proportions of an urban myth. The flow of air or water in small objects like sinks and toilets is determined by how they are engineered. Q I would like to know why the television news weather data differs so radically from what I observe. I have three thermometers that register outdoor temperatures, and they all seem to agree within a half-degree. I tune into the noon news and find out that the present San Jose temperature is 70 degrees, but my instruments show temperatures above this, sometimes 10 to 14 degrees. I live eight miles south of San Jose International Airport and can't believe that this distance makes that much difference. Robert Smith - San Jose A Because all of your thermometers have similar readings, let us assume that they are accurate and recording the proper temperature at their locations. But are those good locations? Is a thermometer near a wall that reflects heat and gives an artificially high reading? Temperatures should be measured in the shade, inside a well-ventilated shelter about five feet above a natural surface such as dirt or sod. Another factor is that the readings you hear on the noon news may have been the 11 a.m. reading from San Jose Airport. Taken on the hour, these readings are usually not available until about 10 minutes after the hour. This makes it generally impossible to use the noon readings, create the necessary graphics and have them ready in time for the weather news. 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. Please indicate in your e-mail where you live. |