The at our door Forecasters one day will be able to predict which rivers will be hit by a Pineapple Express. Will it be soon enough for Sacramento? By Stuart Leavenworth -- Bee Associate Editor Published 2:15 am PST Sunday, January 15, 2006 Story appeared in Sacramento Bee Forum section, Page E1

Somewhere out there is a monster storm that will swamp Sacramento.

It probably won't arrive this , but it's out there.

And when this Godzilla of a storm takes aim at Northern , there is a strong chance that Wayne Higgins will be among the first to take notice.

Higgins, a climatologist with the National Oceanic and Atmospheric Administration, is a leading authority on a quirky atmospheric oscillation that encircles the world's tropics. This wave, known as the Madden-Julian Oscillation, moves west to east in cycles of 30 to 60 days. It is weak in some years, strong in others. When it is strong, it can produce tremendous amounts of moisture in the western Pacific.

When this pool of moisture is blown just east of the island of Borneo, Higgins takes notice, particularly during the winter. "At that point, we know that seven to 10 days later, there is enhanced likelihood for a rainy period on the Pacific Northwest coast," says Higgins, lead specialist at NOAA's Climate Prediction Center in Camp Springs, Md.

Sacramento is a long way from Borneo, but our ability to prepare for is linked with seeing several thousands miles away. When conditions are just right, the dips down and picks up the accumulated atmospheric moisture of the western Pacific, then hurtles it toward California and Oregon in a narrow ribbon of wet mayhem.

This type of storm—popularly known as a Pineapple Express—walloped in 1986 and 1997, dumping two feet of in three days in some areas and flooding thousands of homes. Scientists now know much more about how these originate; how they shift intensities while approaching the coast; how they dump such enormous volumes of rain on the Sierra and other mountain ranges.

Yet even with advances in forecasting, meteorologists still have work to do in reliably predicting which river basins will take the brunt of these storms. Precise forecasts could save lives. With a few days of solid warning, emergency responders could evacuate the elderly and infirm. Operators of dams could release extra water and be assured they wouldn't be left with an empty reservoir when the skies clear.

"It is still a major challenge to figure out what watershed will be hit," says Marty Ralph, who works at NOAA's Environmental Technology Laboratory in Boulder, Colo. "Wind direction is critically important in determining intensity of rainfall and where that rainfall will go." "Can we do it? The answer is, absolutely yes," said Ralph, who has been experimenting with a variety of technologies to track incoming storms. "The only question is how long it will take."

The may not have much time to wait. During the 20th century, the 10 biggest floods on the American River have all come from "low-latitude" storms—the term meteorologists use for Pineapple Expresses. Eight of these storms have occurred since the 1950s, with the three largest in 1997, 1986 and 1964, according to a 2002 study by the U.S. Bureau of Reclamation.

All this suggests that, since the 1950s, the frequency and intensity of Pineapple Express storms has increased. On the other hand, 50 years is just a blink of the eye in geological time. It is hard to say if the storms of the last half century were unusual or just a warm-up for the big show.

Robert Kelley, author of "Battling the Inland Sea," made this point clearly in his 1989 book.

"The Sacramento Valley, after all, is millions of years old, storms have been coming up from far out in the Pacific for many millennia," Kelley wrote. Given the great age of the natural environment, the experience of Americans in comprehending floods "can only be described as shallow to the extreme."

Pineapple myths

Many weather experts dislike the term Pineapple Express, just as they frown on storms (many of them named by TV weathermen) that have monikers such as "Chattanooga Choo-Choo" and the "Alberta Clipper."

In attempting to lend personality to the weather, these names tend to misstate the science, says John Cox, author of "Weather for Dummies" and two other books on .

"There are a lot of myths about Pineapple Express storms," says Cox, a former reporter for The Sacramento Bee. "For one thing, they don't have anything to do with Hawaii, except that they cross over Hawaii on their way here."

Mike Ekern, a forecaster with the in Sacramento, agrees that people have misused the term. Some local residents now think that every warm is a Pineapple Express. In fact, he says, a unique series of conditions must be in place to get a truly juicy Pineapple.

Prior to such a storm, a high-pressure system forms in the Gulf of Alaska and pushes the jet stream to the south, says Ekern. Packing winds of 200 miles an hour, the upper-level winds in the jet stream can suck up the available moisture and carry it to the West Coast in a matter of three or four days.

This is much different from the typical weather pattern, in which the jet stream moves across the Northern Pacific, carrying storms with it. Since they are cold, these storms carry relatively little moisture. And since much of their falls in the form of instead of rain, it sticks to the mountain ranges, instead of cascading down the creeks and rivers. Some weather forecasters speak about Pineapple Expresses with the same urgency reserved for a tropical hurricane.

"It is a different kettle of fish," said Cox. "A Pineapple Express doesn't have self-generating capability. It doesn't live off of ocean temperatures like a hurricane does. And it doesn't carry the winds."

The only similarity is that both storms can carry enormous volumes of water—enough to drop several feet over a single area.

"A Pineapple Express is a hose," says Cox. Seen in satellite photographs, such a storm looks like a long water cannon, stretching hundreds of miles across the Pacific. When it hits, it often drops several days of near continuous rain over a region.

One ground zero for these storms, at least in recent decades, is Bucks Lake, a Sierra camping resort set at 5,200 feet in Plumas County. During the storm of February 1986, a range gauge at this lake measured more than four feet of rain in a mere 10 days.

During the January 1997 storm, the gauge at Bucks Lake measured 42 inches of rain in nine days. At the storm's peak, the storm dropped 27 inches in 72 hours.

An often-heard myth about Pineapple Express storms is they only cause major flooding during a year of big snowpacks. The warm rain melts all the accumulated snow, it gallops downstream and overwhelms levees and reservoirs.

In fact, surveys by the California Department of Water Resources have found that just 10 percent to 15 percent of runoff from these storms comes from snow melt, says Maury Roos, a veteran DWR hydrologist. The bulk of the runoff comes from precipitation, falling in the form of rain instead of snow.

Roos and others note that an extra 10 percent can be significant, causing levees to be overtopped. But a warm storm alone can be enough to cause serious destruction.

"Snowmelt is definitely a factor in flooding," said Roos. "But not the predominant one." No sign of Pineapple

Over the New Year's Eve weekend this year, a set of warm storms hammered California's wine region and much of the north state. For hundreds of residents, the flooding was destructive, but it wasn't a Pineapple Express.

For reasons that aren't entirely clear, the western Pacific hasn't produced a big pool of moisture for the dipping jet stream to capture this year. Despite earlier predictions, the Madden-Julian winds near Indonesia haven't been very active. So the fuel for a big storm is not of Pineapple proportions.

There's also no sign of an El Niño, the seasonal pattern of warm water that can stretch across the Pacific for months, delivering soaking storms to .

What triggers these natural cyclical events? What mechanisms set them in motion? Slowly, scientists are unraveling the mysteries of the tropical Pacific, making connections among episodes of weather and climate.

The MJO was first identified by two U.S. scientists, Roland Madden and Paul Julian, in the early 1970s. Interest in the MJO died off for a while, but recently climatologists have started to study the connections between MJO wind bursts and major storm systems of the world.

Along with scientists from the University of Washington, Higgins has linked the MJO to the formation of hurricanes in the Atlantic during the . Scientists also believe the MJOs, Pineapple Expresses and El Niños all have a connection, since flooding storms tend to occur a year before an El Niño hits. (The most recent example was in 1997, when a warm winter storm was followed by the 1998 El Niño.)

Stormy detective work

To get better data on these weather patterns, Higgins would like to see more investment in rain gauges and instrumentation in the western Pacific. Not all MJOs lead to Pineapple Express storms, he says, and he would like to understand why.

Closer to home, Marty Ralph and other NOAA scientists are studying the ribbons of moisture that feed into the West Coast. These include not just Pineapple Express storms but others that have a slightly different fingerprint.

Last January, for example, a flare-up in the MJO caused a funnel of moisture to take aim at Southern California, producing more than 40 inches of rain in just four days. That storm helped relieve drought conditions in the region, but it also led to the mudslide in La Conchita, which killed 10 people.

Ralph, along with a few other researchers, believes the trajectory of West Coast's big storms can be reliably predicted, with more lead time, given enough effort. He has popularized the theory of atmospheric rivers—thin ribbons of moisture that carry the bulk of the precipitation to the West Coast.

Ralph says these ribbons are relatively narrow, roughly 150 to 300 miles wide, and travel in the lowest 10,000 feet of the atmosphere. Most originate in the mid-latitudes, above the tropics, but occasionally they can tap into tropical moisture and wreak havoc in either Northern or Southern California.

Since the late 1990s, Ralph and other NOAA scientists have used airplanes to fly into these storms. There they drop little weather reconnaissance devices, known as "dropsondes," that transmit information back. Ralph uses wind profilers—a type of vertical pointing radar—to relay key information about the profile of the storm. He also is experimenting with unmanned aircraft to get real-time, "inside-the-storm" data. Knowing the vertical formation of a storm is essential for accurate forecasts, says Ralph. If most of a storm's moisture is carried in a low-level jet, it will fall on the mountains of the California coastal range and never reach the Sierra.

Trajectory is also crucial. If a Godzilla storm were to come up the Carquinez Straits and totally miss the coastal range, it would create a monumental —depending on which watershed had the misfortune to be in its path.

Dam rules and regulations

To maximize the Valley's flood protection, some engineers are urging federal authorities to formally change their rules on how they operate reservoirs, including Folsom above Sacramento.

Currently, the U.S. Army Corps of Engineers requires operators of dams to make flood releases only when observed inflows into the reservoir reach a certain volume. That system works fine for moderate storms, but if a reservoir is limited in how fast it can release water—Folsom is an example—the operating rules may not be protective enough.

Joe Countryman, a former corps official who heads MBK Engineering, is one of those seeking changes. Countryman says water agencies already fudge the rules and release water in advance of storms. He wants to formalize the process.

Many operators of dams, however, are skeptical of weather predictions, especially they sit on liquid gold - water supply—that could be needlessly lost with a bad forecast. Some recall what happened in January of 1997 when, following a big flood that year, forecasters predicted another large storm. It never materialized, but extra releases left water agencies with less water than they might have had coming into a dry .

Supporters of "forecast-based operations" say that occasional false alarms must be balanced with the larger flood threat.

Plus, says Countryman, operators can be flexible after a storm appears on the horizon.

"Once you get to about 24 to 48 hours in advance, you will have a reliable idea whether this storm is a monster or not. You can adjust," said Countryman. "You don't have to release water for six or seven days just because of a single forecast."

The debate here centers on a wonky term—adaptive management. As California learns more about the flood threat it faces, it is adapting by investing millions in better levees and modifications of dams.

Along with those investments, why not spend more in understanding the weather? And why not use that knowledge to adjust how we operate our dams?

California Extreme Precipitation Symposium

Much of the information in this article was gleaned from annual weather symposiums organized by Auburn resident Gary Estes. The next all-day symposium is scheduled for June 23, 2006, at UC Davis. The draft theme is "Forecasting advances since the February 1986 flood."

For more information, go to www.arwi.us and click on California Extreme Precipitation Symposium. About the writer:

Reach Associate Editor Stuart Leavenworth at (916) 321-1185 or [email protected].