Wet Week May Mark Return of Normal Rains

More rain is expected throughout Southern California this week, signaling what forecasters say may be a significant shift in weather patterns that could result in normal rainfall for the first time in several years.

“It looks like it’s going to stay cool and showery for the next four to five days. And, while we can’t say for sure at this point, it looks like that’s going to continue,” said Rick Dittmann, a meteorologist with WeatherData Inc., which provides forecasts for The Times. “There’s still time for Southern California to have a normal rainfall season.”

Don Yoeman, a spokesman for the Drought Center at the state Department of Water Resources office in Sacramento, said that although his staff had yet to complete its measurements, the cool, moderate storm that swept the entire state over the weekend appeared to be a good first step toward ending the prolonged drought that has parched much of California.

“It’ll take a lot more precipitation to get us back to normal,” Yoeman said. “But it’s a start. And hopefully, it will continue.”

Dittmann said the cloudiness that mottled Southland skies on Monday should congeal into a solid gray overcast by this afternoon, with light rain beginning “about the time most people begin the commute home. . . .”

“The showers should continue into Wednesday, and after that, things look unsettled, with more showers at times through Friday,” Dittmann said. “There should be about half an inch of rain at the Los Angeles Civic Center through Wednesday, with more--not a ton, but more--through Friday. It could put a dent in this drought--maybe a good dent.”

The forecaster said the snow level in Southern California’s mountains should drop as low as 3,500 feet by Wednesday morning, with “definitely cool temperatures”--highs in the 50s and 60s, following nighttime lows in the mid-40s to low 50s--in the Los Angeles area for the next few days.

Dittmann said the cool, damp weather that began last weekend and promises to continue at least through this week marks the return of the normal winter storm patterns “that have been rare during the last year or two.”

For much of that time, he said, the high-altitude jet stream winds that steer Pacific storm systems toward the West Coast have stayed well to the north, with a lot of the precipitation falling in the mountains of British Columbia. While meteorologists know that this abnormal shift to the north results from such factors as variations in ocean temperatures, the phenomenon is still not fully understood.

Now, in a return to more normal patterns, those jet stream winds have split in two, with one branch still crossing the coast near the Canadian border, but the other swinging south to hit the coast about halfway down Mexico’s Baja California peninsula.

“The southern portion is quite vigorous,” Dittmann said. “It’s directing the storm systems into the western United States. . . . The storms it’s bringing are high-latitude storms, originating in the north.”

These high-latitude storms tend to be cold, which means widespread shower activity with snow in the mountains, he said. Precipitation from such storms tends to run off gradually into collection basins and reservoirs. Rarer, low-latitude storms from the warmer areas of the mid-Pacific tend to bring the concentrated, sudden deluges that can lead to uncollected runoff and widespread flooding.

Yoeman said that while the state’s reservoirs in the northern Sierra are already pretty well filled, “there are still (drought) problems in the southern Sierra.

“We got three to five feet of snow (from last weekend’s storm) up here in the north,” he said. “While we’re not sure what we have down there yet, we do know that that storm did get down there. . . .

“The ground is saturated now, so any more rainfall will start running off to fill the reservoirs,” Yoeman said. “So if he (Dittmann) is right, it looks good. It’s not the end to anything yet. But it’s a start.”

Statistics for Southern California mirror the drought that has affected much of the state since 1986.

In the 112 years the National Weather Service has been tabulating rainfall in Los Angeles, totals for the seasonal years--which run from July 1 through June 30--have averaged 14.93 inches.

However, during the last three years, the average has been considerably lower than that--9.51 inches. Only 7.96 inches fell in 1986-87, 12.48 inches in 1987-88 and 8.08 inches in 1988-89. Even so, each of these was considerably more than the lowest seasonal total ever recorded here--4.85 inches in 1960-61.

The storm over the weekend brought this season’s total at the Civic Center to 1.91 inches, still well below normal for the date of 6.07 inches.

The high temperature downtown on Monday reached 60 degrees, following an overnight low of 50. Relative humidity ranged between 84% and 58%.