Even though a strong El Niño is in progress and likely to last for many months, the prospect of drought-busting rainfall is not a guarantee for California this winter. The Climate Prediction Center of the National Weather Service suggests that a “Godzilla El Niño” may be on the way this winter.
However, how much rain and snow California as well as other areas along the West coast receive will be dependent on the interaction between El Niño and other conditions in the northern Pacific Ocean. El Niño is the warm part of a warm/cool cycle of ocean water temperatures in the tropical Pacific that spans several years.
All other conditions being average, a strong El Niño tends to fortify the winter storm track over the northern Pacific and can allow strong storms, loaded with moisture to blast onshore over the West Coast of the United States. In order for there to be a strong storm track, there needs to be a large temperature contrast from north to south. Here lies the potential problem for forecasting once-in-a-lifetime storms in California this winter.
What may happen in California this winter is that more modest storms could deliver episodes of soaking rain, rather than many storms with torrential rain, yards of snow in the mountains, damaging winds and major flooding. While moderate storms with less flooding rain and damaging winds would be good news for property owners and commuters, it would take several blockbuster storms to build snow levels significantly and fill reservoirs in order for more lasting drought-relief.
For example, in Los Angeles the total rainfall for the year in 1958 was 15.43 inches, compared to 27.06 inches in 1998 and the normal of 12.82 inches. Since rainfall deficits are currently extremely large in California, the tradeoff may be that near- or slightly above-average rainfall occurs and the drought is still intact by the end of the winter, but perhaps just not as extreme.
In many locations of California, the rainfall deficit ranges from 1-2 feet below average since July 1, 2013. People will still need to keep conserving water and be prepared for significant and disruptive storms this winter.