A powerhouse El Niño has been brewing in the tropical Pacific, already showing signs of influencing global weather patterns. A forecast for a strong El Niño — which has the chance to spread copious tropical moisture up the West Coast — is exactly what California needs. But there’s another meteorological powerhouse already in place that could put a pin in California’s stormy ambitions.
NOAA says there’s about an 80 percent chance that this El Niño will last through early spring of next year. Many forecast models are predicting a very strong event — something that’s only happened twice in the six decades we’ve been watching the tropical Pacific. The Capital Weather Gang’s Jason Samenow says this winter’s El Niño could rival the strongest on record, an intensity that would “have ripple effects on weather patterns all over the world.”
Most significantly, a very strong El Niño could be a rainy windfall for California, which is locked in historic drought. As of Thursday 95 percent of the state was in severe drought, and 46 percent — a vast swath through the northern Sierra, Central Valley and the central and south coasts — were in exceptional drought, the worst category on the U.S. Drought Monitor scale.
In general, El Niño’s tend to have a wet influence on the southern tier of the United States, including Southern California. But when it really gets cranking, like in the record-setting El Niño years of 1982-1983 and 1997-1998, the abnormally wet conditions can spread far north through much of the state. Both of these years amplified record-breaking rainfall in the northern Central Valley and Sacramento — an area currently entrenched in the worst of the drought.
In other words, a very strong El Niño is exactly what California has been hoping for.
But El Niño isn’t the only weather game in town, and there’s one major difference between this year and the strongest El Niño on record — a vast pool of much warmer than average water in the northeast Pacific Ocean, which some have dubbed “the blob.”
That pool of incredibly warm ocean water was a major player in the weather over western North America this past winter. A strong ridge of high pressure was parked over the region, keeping things warm and dry from California to Alaska. It was a tangled feedback process between hot, dry soil, the strong ridge, and the blob — all working together to enhance the ridge itself, leading to more hot, dry weather. The wintertime pattern has been so domineering that West Coast meteorologists dubbed it the “ridiculously resilient ridge.”
Under the seemingly unbreakable ridge, January to March of this year were the warmest such months on record for the entire western United States. Washington, Oregon, California, Nevada, Arizona, Utah and Wyoming all broke the record for the warmest period from January to March. California surpassed the previous record-warmest January-March period — set just one year earlier — by an astonishing 1.8 degrees. It was also the fourth driest such period on record for the Southwest.
We don’t know exactly how this El Niño will play out this winter — whether it will in fact become the strongest on record, or whether it will be a drought-buster for California. But in terms of outlooks, forecaster Michelle L’Heureux says you can expect NOAA to focus more on the effects of El Niño, rather than the North Pacific warm pool. Quite often, she says, the changes in the El Niño region drive weather patterns in the western states. In other words, expect a rainy California rather than the ridiculously resilient ridge.
But the Capital Weather Gang’s Matt Rogers says the North Pacific warm pool is a powerhouse right now and could prove hard to overcome, especially if El Niño turns out to be weaker than predicted.
“The positive SST feedback from that warm pool would likely get outweighed by tropical forcing from an El Niño if we see a strong or super El Niño hold through the winter just based on past performance,” Rogers said — and a few atmospheric indicators have him worried about the forecast for a super strong El Niño.
Looking back through previous events, he has found that global weather patterns — in particular, the North Atlantic Oscillation and Indian Ocean temperatures — are not quite matching up with previous strong events like the ones in 1997-1998, which throws a lot more uncertainty into the forecasts that are calling for a very strong El Niño.
Rogers says if El Niño ends up being weaker than predicted, “then the warm pool could influence bigger Alaska ridges like the last two winters,” which would mean another painfully dry rainy season for California.