El Nino Not the Fix-All California Hopes For

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Across the board, the forecast for this summer is oceanic warming west of South America. Colloquially, this is known as “El Nino”, an oft talked about phenomenon that affects the global weather pattern for as long as it is in place. Nowhere does El Nino affect the weather pattern more than in the Americas.

Generally speaking, the pattern leads to a more persistent jet stream running through the southern United States, which acts as a conveyor of Pacific moisture through California into the Southern Rockies. With the redirection of moisture this leads to a dryer, warmer pattern to the north and a moist pattern in the southern US.

This summer, El Nino is expected to emerge across the eastern Pacific again. This seems like good news for a drought stricken California. As the statistical gurus at 538 report, however, the data doesn’t necessarily suggest that this is going to be the cure-all that the region needs. Statistically, summertime El Nino patterns don’t usually bring additional rainfall to California until they are strong El Nino’s, and even then, that hasn’t happened frequently enough to be statistically relevant.

There is a meteorological reason for this to be the case. The reason for a jet to be strong and persistent is because of dueling air masses. In the winter, Arctic air plunges into lower latitudes, but hangs further north in the summer. With a warmer flow over the tropics than is normal, and cooler air to the north, the jet, and subsequently the weather pattern, will be stronger and more persistent.

In the summer, the Arctic air hangs back to the north, and the conflicting air masses aren’t as dramatically opposed. In fact, there is more typically a split flow aloft, which diverts energy and doesn’t allow for the same persistence across the west coast.
If El Nino holds on into the autumn, when the Californian rainy season really takes hold, good news is on its way, but for the time being, it’s way too soon to be optimistic.

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