Quick Take
Although global climate patterns are neutral right now, signs point to a weak La Niña year forming by the late fall or early winter. However, due to its location, it’s difficult to predict whether Santa Cruz County will see a wetter, cooler winter or a drier, warmer winter.
Meteorologists say that it’s a toss-up whether Santa Cruz County will see a warm and dry winter, a wet and cold one, or an average winter this year.
As recently as July 10, the National Oceanic and Atmospheric Agency (NOAA) gave about a 50% chance that a weak La Niña could form between October and January.
While El Niño is a weather phenomenon associated with the warming of surface waters in the eastern equatorial Pacific Ocean, La Niña is the opposite. It blows warm water westward, making the eastern Pacific Ocean, which largely covers the west coasts of the Americas, colder and drier. La Niña often creates drier, warmer conditions in the southern United States, including Southern California, and wetter, colder conditions to the north, specifically the Pacific Northwest, whereas El Niño usually brings drier, warmer weather to the Pacific Northwest and colder, wetter weather to the southern United States.
Santa Cruz is essentially right in the middle of those two areas, which makes predicting the local effects of both a La Niña year and an El Niño year difficult, said National Weather Service (NWS) meteorologist Rachel Kennedy.
Last winter, the Golden Gate Bridge acted as the sort of dividing line between the drier Central Coast conditions and the wetter Northern California ones. “South of the Golden Gate Bridge, we started to see more sites running normal to below normal for the water year,” Kennedy said.
Santa Cruz County also saw a La Niña pattern this past winter, which resulted in a somewhat drier season. Kennedy said the county received about 80% to 90% of the normal amount of precipitation for the water year, which runs from Oct. 1 to Sept. 30.
Kennedy said that more often than not, that’s how it unfolds in the Central Coast. However, given how Santa Cruz County represents just about the northernmost part of the Central Coast, it often proves to be even less predictable than the other parts of the region. Despite overall drier conditions last winter, a site in Ben Lomond received about 13% more rain than in a normal year: “So we definitely have some localized areas that get more rainfall than others.”
It’s always challenging to accurately predict a forecast, but that’s especially true during La Niña and El Niño years. Kennedy said that if the La Niña conditions hold, the weather agency will subtly change its forecasting approach. Rather than attempting to predict weather conditions far into the future, meteorologists will focus on shorter periods of time, often two-week intervals. “Then it’s a lot of keeping track of consistency in the models,” she said.
Kennedy said that meteorologists will also pay attention to Arctic oscillation, which refers to a large region of cold, rotating air that forms during the fall when Arctic temperatures cool quickly. Typically, the winds associated with these remain in the Arctic regions, but they can dip down into more southerly regions, like the continental United States. If that happens, it can bring a colder winter than usual to the country, including Santa Cruz County.
“Rather than thinking, ‘OK, it’s a weak La Niña, and it could go either way,’ we really pay attention to those shorter-term patterns and changes,” Kennedy said.
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