The Convention & Visitors Bureau advertises San Diego as the “only area in the United States with perfect weather." Those days may be ending, according to recent theories, but whether they’re the rule or the exception, our blue skies and fair temperatures can be deceiving.
Over our heads, the jet stream rages, with winds howling at up to 150 miles an hour when tropical and arctic air masses collide. “The jet stream dictates where the storms will go,” says meteorologist Wilbur Shigehara. Roaming 30,000 to 50,000 feet up. these “high-level winds are like freeways in the sky. Knowing that the jet stream was coming this way would tell me that a storm would be coming this way.”
At the National Weather Service office on Pacific Highway, a chest-high row of computers the color of a paradise sky forms an arc around Shigehara. the service’s chief meteorologist. With these computers, he or any of the eight forecasters-technicians in the office can track the jet stream and begin formulating a local forecast. Six a day are prepared by the weather service for the San Diego area.
Jacket off. Shigehara sits down at the keyboard at the left of the arc and. with two fingers, types a code. Numbers and letters appear on the 15-inch screen in front of him. On a screen at his right, a map of curving lines takes shape, superimposed on a portion of earth he has specified, for an altitude he has specified. The forecaster now has a picture of the upper atmosphere. If he wants, he can use yet another screen to magnify a portion of the map or to compare the current picture with that of yesterday or a future day.
Having this three-dimensional structure is important in weather forecasting. Shigehara says, "because you have to study the winds at 30,000 feet to determine what’s going to be on your toes." Still, even the best weather chart captures only one moment of a constantly changing pattern.
The atmosphere is a restless mass of air, more turbulent than the ocean. It’s 260,000 feel deep, and we, bystanders to its power and whims, live at the bottom. Continuous winds scream above us, unheard. Some, bundled together in tubular ribbons, blast through the atmosphere at speeds of up to 250 miles an hour. The number and paths of these jet streams vary from day to day, season to season.
A computer-generated map gives Shigehara a portrait of wind circulation around the Earth by charting isobars, lines that connect points of equal atmospheric pressure. In places, these isobars seem to meander, but eventually they circle around areas of high and low pressure. "Mother Nature says that winds will go from high to low pressure," Shigehara says. And "wind causes weather.”
The wind picture changes depending on altitude. Forecasters here like to study the 500-millibar map. which, though only about 1000 feet up, marks the halfway point of the atmosphere in terms of air pressure, which is billions of times greater at the Earth’s surface than at the edge of the atmosphere. Meteorologists can look at any atmospheric altitude in any part of the world because twice a day, at exactly the same time, about 800 people around the world send balloons into the sky
At 2330 Greenwich (or Universal) Mean Time, which is 3:30 p.m. Pacific Daylight Time in San Diego, a technician begins balloon preparation for a 0000 launch. Surrounded by computer equipment in a weather office on Kearny Villa Road, he checks out and loads the battery-powered radiosonde that will send back weather information. He lays out an eight-foot-long balloon and attaches its tip to a gas jet, which is hooked in turn to one of many canisters of hydrogen.
To determine visibility, he peers beyond the airport toward Point Loma, the arm of land that juts into the Pacific Ocean. If he can see the end clearly, it's seven miles. Today he can't. )He calls it six, and hazy.
The flesh-covered balloon is made out of neoprene, a type of latex, and dusted with talc. It feels silky. Inflated to a diameter of 7 feet at ground level, the balloon will expand in the thin air of the upper atmosphere to almost 100 feet before bursting.
Inflation is slow, but gradually the balloon rises and bobs straight up. The balloon is connected to the radiosonde and an orange paper parachute that will carry the device to earth after the balloon bursts. The radio unit, no bigger than a shoebox, weighs less than a pound. Styrofoam protects the delicate instruments that constantly measure temperature, wind, and humidity on both the ascent and descent. A cardboard sheath holds everything tight.
The radiosonde will climb and fall at 15 miles an hour, taking two and a half to three hours to complete its round trip of roughly 200,000 feet. A tracking disk at the weather station will receive its transmissions, once the technician accurately trains the disk on the balloon — a tricky task on cloudy days. The operator has only a minute to find it if it’s lost. After that, it’s gone, and there’s nothing left to do but assemble another.
The National Weather Service office on Pacific Highway occupies several rooms on the second floor of a nondescript building owned by the Port District. Behind it, jet planes blast down the runway at Lindbergh Field. Though muffled, their roar finds its way inside the office. Bookcases cover some walls, and the shelves are lined with binders and manuals full of rules handed down by the National Oceanic and Atmospheric Administration and NOAA’s superior, the U.S. Department of Commerce. Otherwise, the decor includes a couple of large, framed satellite maps, including one of Hurricane Katrina, a perfect spiral cloud formation, off the southern tip of Baja in 1975.
Outside, an American flag flies 24 hours a day because inside, a day never ends. Except for Shigehara, who mostly works a standard 8:30 a.m. to 4:30 p.m., weekday schedule, the forecasters-technicians rotate among three shifts, beginning at 8:00 a.m., 4:00 p.m., and midnight.