Will spring deliver big rains?
Although there are still a few months left in the rainy season, this year’s El Niño hasn’t exactly been the drought buster California was hoping for. Thus far, plentiful precipitation in the northern part of state will go a long way toward replenishing reservoirs, but central and southern California have remained relatively dry.
The “exceptional drought” footprint is now spread across about 38 percent of the state, as compared to 45 percent three months ago, and precipitation in the key snowpack areas of the Sierra Nevada has been about average. Farther south, especially in the L.A. Basin, precipitation is still well below average for the rainy season to date.
That may be due to the fact that the distribution of warm water across the Pacific Ocean is quite different than during past El Niños that brought more widespread heavy precipitation to California.
Local forecasters, like Mammoth Lake’s Howard Scheckter, have commented on the subtle differences in the El Niño pattern. In a Feb. 22 post, Scheckter asked, “What happened to El Niño?” and then answered his own question:
“Looking at the distribution of the anomalous warmth over the central and eastern pacific, and comparing the Winter of 98 with this winter, one can see that the warmest water is well west of where it was in 1998. The main axis of the warmth along the Equator For the El Nino winter of 1998 was on a west-east axis at about 105 west, or due south of Puerto Vallarta vs. this winter, where the axis is west-east, south of the Hawaiian islands. That is a displacement if several 1,000 miles west of the winter of 1998.”
Federal meteorologists also weighed in.
“The start of an El Niño is important,” said Robin Kovach, a research scientist with the Global Modeling and Assimilation Office at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “The ’97 El Niño was much stronger in the Eastern Pacific, with much warmer water up to the coast of South America,” Kovach said. In 2015, the warmest waters are instead in the Central Pacific and extend west of the International Date Line, Kovach added.
The water temperature variations typical of El Niño are not only at the surface of the equatorial Pacific, but below the surface as well. And these variations were also different in 2015, compared to 1997. At the height of the El Niño in November, colder-than-average temperatures in the Western Pacific and warmer-than-average temperatures in the Eastern Pacific were stronger and extended deeper in 1997 than in 2015.
Goddard’s computer models, with input from ocean buoys, atmospheric models, satellite data and other sources, can also simulate what ocean water temperatures could do in the coming months. The GMAO seasonal forecast, which takes 18 hours to complete, and creates more than 9 Terabytes of data, shows that this 2015 El Niño could be different until the end.
“In the past, very strong El Niño events typically transition to neutral conditions and then a La Niña event,” said Kovach. February computer model runs forecast a return to normal sea surface temperatures by June.
The latest Feb 5, 2016 forecast does not yet predict below normal sea surface temperatures that would result in a large La Niña. As of Feb. 14, 2016, the latest ocean computer model shows colder-than-average water temperatures off the South American coast from Ecuador to Panama. “This current El Niño has been different so it will be interesting to see what happens in the next forecast and the coming months,” Kovac said.