A weaker El Niño pattern than originally predicted could mean less rainfall for drought ridden California this winter according to a report issued by weather forecasters at the Climate Prediction Center and the International Research Institute for Climate and Society last week.
The lack of a coherent atmospheric El Niño pattern and a return to near-average sea surface temperatures in the central Pacific means the chance of a moderate El Niño has dropped dramatically according to the report released August 7. The chance of El Niño has decreased to about 65 percent for the coming fall and early winter, a downgrade from predictions of a moderate event in June.
According to Joe Dandrea, a weather forecaster with the San Diego Weather Forecast Office, it is impossible to predict rain and snowfall amounts with a weak to moderate El Niño.
“The only type of El Niño that has any good predictive capability is if we are predicting a strong El Niño,” Dandrea said. “The forecast never really was for that. It was for a weak to moderate El Niño. We were hoping that we would trend stronger but now it looks like its trending weaker. It’s still an El Niño, but unfortunately weak El Niños have little predictive capability so it’s basically up in the air what our winter will be like.”
Dandrea said it doesn’t necessarily mean the winter will be drier, but rather that there is just no predictive capability on what the weather will be over the next few months and how that could affect the drought.
“It can still go either way. The way I like to look at it is the ocean water temperatures are little above what they usually are which means there is more water vapor in the atmosphere so that storms that do come through have a little better chance of dumping more rain on us,” Dandrea said, adding that there really is no pattern to when strong El Niños will occur.
“Forecast is for the fall and winter and that is really when it has a more predictive capability,” Dandrea said, noting that recent rainfall is due to the summer monsoon rather than an El Niño pattern. “This time of the year we get the summer monsoon which is associated with the big subtropical systems that develop over the four corners and the desert southwest.”
“There is moisture there to produce thunderstorm but unfortunately it is not the soaking rains we really need,” he said. “They don’t make a difference in terms of the drought but they can make a difference in the wetness of the ground and really dampen the fire threat for awhile.”
Over the last month, model forecasts have slightly delayed the El Niño onset with most models now indicating the onset during August to October with the event continuing into early 2015. Most models are calling for a weak event rather than the moderate one that was predicted earlier this year. El Niño is expected to peak at a weak strength during the late fall and early winter.
It’s not just the El Niño that could bring relief to Californians though, said Dandrea. If other factors such as a stagnant upper level ridge of high pressure controlling the wind flow would shift, then storms would be able to move in more freely from the Pacific bringing more rain into drought stricken California.
“I don’t think anyone really can predict the position of that ridge … all we have to do is see a shift in the position of that ridge and we could be vulnerable to all kinds of storms coming across the Pacific, even without an El Niño,” he said.