Feb. 9 – Feb. 11, 1978 were three historic days for Los Angeles.
Following the record-breaking drought of 1976-77, Dr. Jerome Namias of the Scripps Institute at La Jolla, California had successfully pioneered long-range forecasting based on ocean temperature models.
Late in November, 1977, Namias had predicted an end to the two-year drought in California calling for what would become known as the El Nino phenomenon, bringing copious rains to the Golden State.
Late in December '77 this prediction began to materialize as the eastern Pacific polar jet stream took on a zonal (direct west to east) flow pattern, dropping far south and joining forces with the Pacific subtropical jet. This merging of forces was directed straight into California affecting the entire state. December, 1977 and January, 1978 saw rainfall nearly every day in Los Angeles, but February, 1978 would bring unprecedented storms to the region.
It had become one of the strongest El Nino event winters in Southern California history.
On February 9th a fast-moving short wave and surface low developed some 400 miles due west of Los Angeles and began tracking directly east. Predictions called for more rain, but no one was prepared for the onslaught that would occur in the early morning hours of Friday, Feb. 10th. Initially mild, the storm system intensified rapidly, deepening to a 994 millibar low by the time it blew onshore at 1 a.m just south of Santa Barbara.
Steady rainfall increased through the evening, and just around midnight, news reports of torrential rains, 80 to 90 mph winds, mudslides, widespread urban flooding and road closures began pouring in across Los Angeles and continued for several hours. The L.A. Times reported power outages to as many as 500,000 customers at the height of the storm, when news services were overwhelmed and couldn't keep up with the massive amount of information rapidly accumulating.
Along and off the coast, waves threw water 60 feet skyward. Elsewhere, at least 700 residents were forced out of their homes. Winds were clocked at 92 mph at Newport Beach and similar velocities wreaked havoc from the coast across inland areas. Downed trees and power lines were reported in nearly every Southland community.
The storm didn't set any records for 24-hour rainfall, but the sheer rapidity and suddenness with which it developed, grew and intensified, and it's direct path across southern California ranks it with the most powerful and destructive events in Los Angeles weather history. More storms would follow, and the 1977-78 season would be one of the wettest on record. Los Angeles would actually receive more precipitation than Seattle that year, and the period from 1978 through 1982 would be among the wettest in L.A. history.
High pressure usually blocks Pacific storms from directly striking southern California, but in the case during years of strong El Nino presence, this surface high is noticeably weakened, and displaced south or southwestward or sometimes far to the north towards Alaska. This opens the door for what has become popularly known as the "pineapple express," a massive sometimes 3,000 mile long plume of moisture which streams toward the west coast, sometimes following a trajectory straight towards Los Angeles.
Such was the case in January, 1969, early in 1980, and November, 1982, and on a number of occasions following in varying degrees. This pattern can develop at any time from about November through April, but is often short-lived except during years of marked El Nino presence.