Our September Weather Watch Special Report is sponsored by:
By Scott Borgioli, WeatherAg Chief Meteorologist
Data signals hint at higher odds of slightly above-average mean temps (overall) through December, with the highest probabilities of above-average/significantly above-average precipitation potential south of Sacramento. This is not a guarantee and is probabilistic odds based on current data and historic trends. Historically, the valley doesn’t experience significant Mean Temperature anomalies during a Strong or Very Strong El Niño episode. December-February Mean Temperatures have almost always remained within +/- 3°F of the seasonal average. Conversely, this doesn’t mean that temperature anomalies (including frost-freeze events) won’t occur during the Fall/Winter/Spring season.
The ongoing El Niño episode, currently in the “Strong” category, is expected to continue strengthening and is on track to reach the “Very Strong” category within the next 30-60 days. Updated data strongly indicate that this El Niño episode will remain in the Strong to Very Strong category through the January-February period and may extend at that strength into March, although a slight weakening trend is favored to develop at some point during December-January. Most models support this gradual (but steady) weakening trend continuing into Summer 2027, with “Neutral” conditions (neither El Niño nor La Niña) possibly returning by late Summer 2027.
Historically, a Very Strong El Niño influences California’s winter precipitation because:
- Other weather phenomena and specific phases of atmospheric oscillations typically interact with El Niño and enhance precipitation effects across parts, or all, of California.
- During a Strong-Very Strong El Niño, we often experience a storm track that’s more persistently directed into certain parts of California, see more frequent moisture-laden low-pressure systems that are associated with an Atmospheric River / Pineapple Express, which cause excessive precipitation events, and low-pressure systems that are “wetter” overall due to the ability to “tap into” abundant moisture that’s present in the tropics/subtropics.
- Since El Niño records began in 1950, all four Very Strong El Niño events have resulted in average to above-average rainfall across the valley. However, statewide results are mixed. As we’ve seen with previous El Niño events, the jet stream may favor NorCal, CenCal, or SoCal, which could result in a “Precipitation Dipole Pattern” occurring where precipitation is focused on one part of the state (causing above-normal precipitation) but the other part is anomalously dry: in one of the four (25%) Very Strong El Niño events, NorCal was anomalously dry and SoCal anomalously wet, but another one of four events was opposite – a wet NorCal, dry SoCal. Conversely, the entire state could experience above-average rainfall (the remaining two of four events had anomalously wet conditions statewide). Note that these four Very Strong events do not form a scientific conclusion.
- This far in advance, there is no way to predict precipitation anomalies for the 2026-27 water year, whether the jet stream will favor only certain parts of the state, or whether above-average precipitation will occur statewide. Please use caution with information obtained from sources on the internet, in social media, and news media sites. Many sites have one goal: generating revenue from ads, which they can only do through “clickbait” from hype and fearmongering (we don’t participate in this). Very Strong El Niño is the official meteorological term (“Super” El Niño is media hype).
Expect El Niño to influence our weather patterns through Spring 2027.
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