Last week, Alex Tardy, meteorologist with the National Weather Service in San Diego provided the following YouTube video comments about the current drought and the possibility of relief if a fall or winter El Niño pattern develops. [These comments are paraphrased so are not in quotes.]:
An El Niño is the warming of the equatorial Pacific Ocean. This change in ocean conditions can alter the jet stream. The result is that the jet stream tends to move across Southern California bringing more storms.
The Pacific Ocean, in the region monitored for developing El Niños, has warmed significantly over the past couple months. Recently, it has leveled off.
Based on the forecasts from various computer models, we expect to go into a moderate El Niño between the fall and early winter.
Southern California would need about 150 percent of normal precipitation to end the drought or to call it a drought buster.
While wet and rainy weather are associated with El Niños, past El Niños have resulted in variable precipitation. For example, during the winters of 2004-05 and 2006-07, similar El Niño conditions occurred but dissimilar weather resulted.
The winter of 2004-05 is famous for significant floods in Southern California. It was a very wet year overall with numerous storms moving across that region. In contrast, in 2006-07, with a similar strength El Niño, very little precipitation fell. In fact, it was near record-breaking precipitation on the dry side across the state and a drought ensured.
The average rainfall in San Diego from October to April during an El Niño season is 11.8 inches. But it ranges from 3.8 to 22.5 inches The large variability in seasonal precipitation mainly occurs during weak to moderate El Niños. The strong El Niños have been more consistent with above-normal precipitation.
The Climate Prediction Center has just released its outlook for temperature and precipitation for the rest of the summer and early fall. While this forecast unfortunately projects continued warm weather, optimistically it expects above-normal precipitation in Southern California.
This winter, from December through February, the NWS is forecasting an above normal chance of precipitation.