NOAA Raises Very Strong El Niño Odds to 90% for U.S. This Year

Q: With a historic El Niño nearly certain, why might Southern California still face a devastatingly dry winter this year?

Southern California could still have a very dry winter even with a historic El Niño because El Niño does not directly produce rain there. It describes unusually warm tropical Pacific waters and shifts the odds of weather patterns, but local rainfall depends far more on whether enough strong atmospheric rivers and winter storms actually reach the region. That is why forecasters stress that a “very strong” El Niño is a measure of ocean temperature anomalies, not a promise of local wet weather. NOAA’s categories describe how far Pacific sea-surface temperatures depart from normal, not how much rain Los Angeles will get. A powerful El Niño can tilt the odds toward wetter conditions in the southern U.S. and California, but those odds are not guarantees. Recent history shows the risk clearly. The last very strong El Niño, in 2015-2016, was among the strongest on record but still coincided with one of Los Angeles’ driest years. Another California drought year, 1976-1977, also occurred during an El Niño. Experts repeatedly note that no two El Niños are alike because each interacts differently with the jet stream, storm track, and other climate patterns. So the key question is not just how strong El Niño becomes, but whether it sets up the right track, timing, and intensity of storms over Southern California. If atmospheric rivers stay weak, infrequent, or aimed elsewhere, the region could still end up with a damagingly dry winter despite near-certain very strong El Niño conditions.

Q: If ocean temperatures guarantee a massive El Niño, what hidden atmospheric factor truly decides whether coastal cities flood or dry up?

The deciding factor is the storm track — especially the number, strength and timing of atmospheric rivers aimed at the coast. A very strong El Niño tells forecasters that tropical Pacific waters are unusually warm and that global weather odds are shifting. But it does not determine local rainfall totals by itself. NOAA’s categories measure sea-surface temperature anomalies, not whether Los Angeles, San Diego or other coastal cities will flood or stay dry. For Southern California and much of the West Coast, flood risk rises when repeated atmospheric rivers line up with low-pressure systems and a persistent jet-stream path into the state. If those moisture plumes hit one after another, soils saturate, runoff accelerates and flooding becomes more likely. If they are fewer, weaker, or steered elsewhere, even a powerful El Niño can leave coastal California relatively dry. That is why the 2015-2016 very strong El Niño, despite being one of the strongest on record, still coincided with one of Los Angeles’ driest years. The ocean signal was strong, but the seasonal storm pattern did not deliver the expected rain in the right place. Experts also note that a warmer climate can amplify impacts by making storms moister and reducing snowpack’s ability to store water, which can increase runoff. But the immediate atmospheric trigger remains the same: where the jet stream sets up and whether atmospheric rivers repeatedly target the coast.

3 articles · Updated · NBC Los Angeles · Aug 17

NOAA now sees a 90% chance of a very strong El Niño affecting the U.S. this year, up from 81% a month ago, while keeping its intensity outlook unchanged.
The agency said the event could rank among the strongest since records began in 1950, but warned that a powerful El Niño does not guarantee typical impacts in every region.
El Niño is a warming of Pacific waters off South America that usually peaks in winter and can shift atmospheric patterns, often boosting Pacific hurricanes while reducing Atlantic activity.
Southern California's winter outlook remains uncertain because rainfall depends more on the number and strength of atmospheric rivers than on El Niño alone.
Recent history underscores that variability: the last very strong El Niño in 2015-16 coincided with one of Los Angeles' driest years, while another in the late 1970s brought more than double average rainfall.