La Nina 2021
Quick Fall Outlook
September to November:
Forecast shows very little rain and the drought conditions continue. In the fall, we usually have cooler temperatures in the Central Valley and therefore less marine layer coming into the Bay Area. So... BEST weather for paddling with less wind and warmer temperatures!
Forecast shows potentially more rain in Northern California. Could it impact the Bay Area? It's not for sure, the San Francisco Bay Area is situated right at the border of what NOAA calls Northern and Southern California. Sometimes we are affected by the deluge up north and sometimes not. Be prepared for colder weather but be glad for those 70 degrees and sunny days!
We all know that California and much of the west coast has been under drought conditions for the last two years. It's been hard on areas surrounding the Bay Area but fortunately, other than the occasional smoke issues, we have been largely spared by the disasters. In the summer time, to much of the paddlers' dismay, the persistent marine layer covers the Bay Area with fog and wind in the afternoon, keeping the temperature down. However, in the fall we have awesome weather: very little wind, calm waters, and still super warm! For those of you looking forward to the winter, similar to last winter where we had very mild weather, not much rain and flat waters, what's gonna happen this year? NOAA is predicting a La Nina event for 2021, so let's look at what that means for the Bay Area.
What's La Niña or El Niño anyway?
El Niño is a term for the warming phase of the El Niño Southern Oscillation (ENSO), a cyclical weather pattern that influences temperature and rainfall across the global. It is a warming of the central to eastern tropical Pacific Ocean. During an El Niño event, sea surface temperatures across the Pacific can warm by 1–3°F or more for anything between a few months to two years. El Niño impacts weather systems around the globe, triggering predictable disruptions in temperature, rainfall, and winds.
La Niña is a cooling phase of ENSO that tends to have global climate impacts opposite to those of El Niño. Though ENSO is a single climate phenomenon, it has three states, or phases, it can be in “El Niño”, “La Niña” (the two opposite phases) or “neutral” (neither El Niño nor La Niña). To qualify as an El Niño event, according to the US National Oceanic and Atmospheric Administration (NOAA), sea surface temperatures (SSTs) must remain at or above 0.5°C (about 1°F) for at least three months. For La Niña, the SSTs are below average rather than above.
How does it affect the Bay Area?
Generally, the NOAA defines their forecast areas as Northern California and Southern California. The boundaries are usually right around the Bay Area, so we can get affected by the forecasts from both areas which gets confusing. Winter forecasts are varied for NorCal and SoCal, so it becomes very difficult to forecast long term what the rain fall will be like for the Bay Area. For La Niña NorCal/Northwest (Oregon/Washington), we generally have dry winters. For La Niña SoCal, we have these atmospheric river events (or what we call Pineapple Expresses) that brings a massive amount of warm rain. Unfortunately, those warm rain events don't really help with our water situation because they tend to melt the snowpack and overwhelm the dams.
Above graph shows moderate La Niña conditions have been present for over four separate winters in the past 70 years: 1955-56, 1970-71, 1995-96 and 2011-12. In two of those season, the Bay Area saw above average rainfall, and below average rainfall in the other two seasons.
Yup, we don't know!
To quote Jan Null from the Golden Gate Weather Services: "If La Niña was the only thing going on in the atmosphere, it would be much easier to predict," he said. "But you have all these other things going on and they mitigate what La Niña can do. This is a lot of words to say, 'I don’t know."
Well, I'm sorry you read all of this just to get the answer that you weren't looking for but that's the business of long term weather forecasting. You can read all you want, but there are so many factors such as global warming, major weather patterns from the Pacific (North, South, and Equatorial), local weather patterns, and just plain bad luck, it is so hard to predict 4-6 months ahead. Just be prepared and thankful for those sunny beautiful days we have in our mild Mediterranean winter weather.