El Niño in; ridiculously resilient ridge out
acquired October 5, 1997 – October 4, 2015
El Nino: NASA Observatory October 13, 2015
The latest analyses from the National Oceanic and Atmospheric Administration and from NASA confirm that El Niño is strengthening and it looks a lot like the strong event that occurred in 1997–98. Observations of sea surface heights and temperatures, as well as wind patterns, show surface waters cooling off in the Western Pacific and warming significantly in the tropical Eastern Pacific. “Whether El Niño gets slightly stronger or a little weaker is not statistically significant now. This baby is too big to fail,” said Bill Patzert, a climatologist at NASA’s Jet Propulsion Laboratory. October sea level height anomalies show that 2015 is as big or bigger in heat content than 1997. “Over North America, this winter will definitely not be normal. However, the climatic events of the past decade make ‘normal’ difficult to define.” The maps above show a comparison of sea surface heights in the Pacific Ocean as observed at the beginning of October in 1997 and 2015. The measurements come from altimeters on the TOPEX/Poseidon mission (left) and Jason-2 (right); both show averaged sea surface height anomalies. Shades of red indicate where the ocean stood higher (in tens of millimeters) than the normal sea level because warmer water expands to fill more volume. Shades of blue show where sea level and temperatures were lower than average (contraction). Normal sea-level conditions appear in white. “The trade winds have been weakening again,” Patzert said. “This should strengthen this El Niño.” Weaker trade winds out of the eastern Pacific allow west wind bursts to push warm surface waters from the central and western Pacific toward the Americas. Click here to watch a video of Kelvin waves propagating across the ocean in the first seven months of 2015 In its October monthly update, scientists at NOAA’s Climate Prediction Center stated: “All multi-model averages predict a peak in late fall/early winter. The forecaster consensus unanimously favors a strong El Niño…Overall, there is an approximately 95 percent chance that El Niño will continue through Northern Hemisphere winter 2015–16.”
By Kurtis Alexander SF Chronicle Updated 10:49 am, Thursday, October 15, 2015
The areas that need strong El Niño storms the most are likely to get them, forecasters said Thursday. The U.S. Climate Prediction Center, in its monthly long-term weather outlook, boosted the odds of precipitation for California this winter and spring — including, crucially, the areas in the North State and Sierra that supply the bulk of the state’s water supply. Forecasters have long pegged Southern and Central California for rain in coming months, but with El Niño in the tropical Pacific gaining strength and warm pockets of ocean water expected to add moisture to the atmosphere, federal forecasters have broadened their bullishness. The updated outlook calls for at least 40 percent above-average chances of wet weather between January and March for nearly the entire state, including all of the Sierra Nevada. San Francisco stands a more than 40 percent above-average chance of seeing a rainy winter, according to the federal forecasters, while the South Bay has 50 percent greater odds. “Well north of the Bay Area, we do have a slight tilt toward above-average precipitation,” said Mike Halpert, deputy director of the Climate Prediction Center, a division of the National Atmospheric and Oceanic Administration. “Only in the very north do we have equal chances” of a dry or wet winter. This El Niño, defined by warm equatorial waters that drive moisture into the atmosphere, is one of the strongest that forecasters have observed. Temperatures in the tropics are much greater than normal, and trade winds that typically push warm currents away from the Americas have died. While El Niños have historically meant above-average rain in Southern California, only the strongest have correlated with wet weather farther north….
October 15, 2015
…Strong El Niño conditions are ongoing across the equatorial Pacific, with robust atmospheric coupling. The latest CPC ENSO advisory indicates a 95 percent chance that El Niño conditions will persist through the winter months. Therefore, climate anomalies associated with El Niño events, which become increasingly prominent over the U.S. during the Fall and Winter months, played a significant role in this outlook….For the Southwest, El Niño associated climate anomalies favor an enhancement of the early wet season. Therefore, drought improvement is favored across central and southern California. There is greater confidence for improvement across the coastal regions and valleys, whereas significant improvement across the Sierras relies on colder temperatures to support substantial snowfall. Further east, drought removal or improvement is forecast across the southern Great Basin and interior deserts.
El Niño is expected to bring a low-pressure system, which will replace the high-pressure system that’s exacerbated California’s drought. nasa.gov
The high pressure system that has shunted storms away from California for much of the past four years has dissipated, possibly for a long time. The Ridiculously Resilient Ridge — as meteorologists and forecasters have dubbed the system because of its unusual persistence — has been absent for more than a month, according to a forecaster with the National Oceanic and Atmospheric Administration. “It hasn’t been like that since August really, and instead we’ve had sort of more variable weather patterns,” said Nate Mantua, a research scientist with NOAA’s Southwest Fisheries Science Center in Santa Cruz. Mantua said the ridge will likely stay away, because it will have been replaced by a low-pressure trough. “The expectations are as we get into Fall and Winter seasons more deeply, we’re going to see a lot more low pressure there, and that will be the more sort of dominant story,” Mantua said. Eric Boldt, a meteorologist with the National Weather Service in Oxnard, said low-pressure systems typically accompany El Niño events. “Lower pressure in the Eastern Pacific is a classic pattern you’d see with an El Niño setting up with the jet stream a little more to the south, and that’s were we get into our storm track coming up from the southwest across California,” Boldt said. The high-pressure ridge has created a large swath of unusually warm water off the coast. Boldt said the warm water would take months to dissipate and that its interaction with El Niño isn’t well understood. However, he said storms from strong El Niño events, which can bring heavy rains to California, could be bolstered by the warm water. “That’s the part that is a little bit unprecedented. We don’t really have a good idea about how that might impact us, but warmer ocean temperatures typically lead to fueling the atmosphere and kind of energizing those storms. So I don’t think it’s going to be a negative for us,” Boldt said.
Mantua said the disappearance of the ridge and the presence of a strong El Niño is likely to produce a lot of rain in Southern California. “[The low-pressure system is] just another factor that sort of favors a more normal winter, although I don’t think it’s going to be normal. I think it’s going to be probably an exciting winter, especially for Southern California,” Mantua said.