Southern Californians in general, and San Diegans in particular, take their winter weather with a great dose of complacency. After all, with an average rainfall of only 9.32 inches a year, a warm average mean temperature of 64 degrees, and only two recorded snowfalls in modern history--the flakes melting after five minutes--San Diego's climate is correctly perceived as mild.
Even officials of the National Weather Service don't worry too much about the area. When they first established a national priority list for installing sophisticated new radar around the country to detect severe weather, San Diego ranked 114th out of 117 stations.
But San Diego's version of winter weather, usually in the form of rainstorms, does come with occasional dangers that can find residents unprepared. Such problems include high waves, extensive flooding in low-lying beach zones, strong winds and blowing snow in the Cuyamaca mountains, and even an occasional funnel cloud or two which can develop into small tornadoes. About 85% of area rainfall comes between December and March.
Phenomena such as the El Nino, where tropical eastern Pacific waters warm up and sometimes cause worldwide climatic dislocations, also may bring unusual weather aberrations here, including heavier-than-usual rainfall and greater coastal flooding.
The winters of 1979-80 and 1982-83 are remembered by those who suffered property damage from a barrage of storms. But many others, in particular the flood of new residents who have moved here recently, expect only morning low clouds and fog to obscure an otherwise steady succession of pleasant, sunny afternoons.
"The attitudes here mean that we can have more of a problem when severe weather does strike," Wilbur Shigehara, meteorologist in charge of the local National Weather Service office, told a county-sponsored seminar on winter weather last week.
"Here, if we put out a warning (of flooding or high winds), many people either don't take notice or they panic."
Shigehara explained that a weather watch, such as for flash flooding in the desert, or coastal flooding in beach areas, is issued when the potential for severe weather--based on radar, wind patterns and other data--develops.
Watch advisories for severe weather such as high winds or damaging thunderstorms are issued for all areas of the United States by the service's Severe Weather Center in Kansas City after consultation with the affected area's local office. Flood watches come from the Los Angeles regional forecasting office in a similar manner.
"I recall a couple of years ago when we got reports of a few mobile homes in Mission Valley being uprooted by funnel clouds, or small tornadoes," Shigehara said. "I called Kansas City to see about a watch being issued, but since pilot reports showed no thunderstorm activity, the center said just to issue special weather statements about the (tornado) possibility, which we did."
In terms of dealing with winter weather here, local meteorologists usually limit themselves to special weather statements, warning that predicted rains could bring flooding in Mission Valley, or that high winds along Interstate 8 through the mountains could make driving dangerous.
And they hope residents will take proper precautions, which in low-lying areas can include having a personal evacuation plan to follow.
Occasionally, after a weather watch comes down from Kansas City or Los Angeles, weather conditions worsen after several hours.
Shigehara's office has the responsibility then for issuing weather warnings, which say that the actual weather patterns forecast are taking place and that danger is imminent or actually occurring. Because the weather can change rapidly in such cases, the San Diego office depends on reports from the California Highway Patrol, county flood engineers and other people in the field.
In addition, the office participates in a multiagency effort that established an automated rainfall measuring network throughout the county last year. Rainfall measurements near reservoirs and river channels can be instantaneously monitored at any time through computer hookups, allowing the weather service to detect immediately and heavy downpour that might bring flash flooding.
As a consequence, warnings can now be issued with much greater accuracy and timeliness to allow residents of areas such as Lakeside or Mission Valley a better chance than in 1979-80 to organize an evacuation.
In the case of beach-area flooding, residents of coastal areas should be attuned to tide tables, Reinhard E. Flick, UC San Diego oceanographer at the Scripps Institution of Oceanography, told county officials.
"Tides are absolutely predictable," Flick said, defining tides as the up-and-down motion of waves due to gravitational interaction between the earth, moon and sun. "The tides are not the same as the sea level, which is also affected by wind, rain and other factors which are meteorological."