Climate scientists are being less bullish this week about the possibility of winter bringing a severe El Niño rainy season, though it remains a possibility. Federal forecasts are now calling for a weak to moderate El Niño, with a 2-in-3 chance that an El Niño pattern will form, but recent cooling in surface temperatures in the central-Eastern Pacific mean that the big, 80-percent chance of an El Niño that had been predicted as of last month had to be downgraded, as the Washington Post and others report.

As National Weather Service climate analyst Michelle L’Heureux said to Climate Central, all hope of a drought-curing El Niño has not been lost. The cooling pattern they're seeing has occurred in previous, non-severe El Nino years, which is quickly followed by more warming ocean temps in the fall.

And while she is loathe to compare any one El Niño to another since the record of well-observed El Niños is short, L’Heureux said that other El Niños saw similar dips in sea surface temperatures around this time in the season before finally forming. Of the seven El Niños that have formed since 1990 (as far back as weekly sea surface temperature records go), three — 1994, 2004 and 2006 — saw similar drops, all of which happened in late June and July.

“So there is precedent for this, I guess, sort of summertime lull,” L’Heureux said. And summer is actually a tricky time to get the atmosphere and ocean to act in sync, she added, so it could simply be seasonal effects keeping the El Niño from moving forward.

A switch from the weak El Niño back to a strong one, however, would be unprecedented, if not impossible. That means that while we may be in for rain, it probably won't be the deluge that would be needed to start the recovery from the three-year drought we're in.

Back in May we were talking about how this was looking like it could be as severe and wet of a winter as we had back in '97-'98, which is the last severe El Niño cycle that California experienced. Since then, we've had repeated cycles of El Niño and La Niña, but all in the weak to moderate range and none bringing as much rain as that winter 15 years ago. In fact, the "negative" phase of the longer ocean cycle known as the Pacific Decadal Oscillation (PDO), which kicked in after that severe winter can be partly blamed for the drought we're in now, and we're overdue for a winter that shifts us back to a warmer, "positive" phase of the PDO.

Let the rain dances continue, please.

[Washington Post]
[Climate Central]

Previously: Chances Now Higher That This Will Be A Severe El Niño Year