Phoenix, Arizona - The term El Niño refers to the large-scale ocean-atmosphere climate phenomenon linked to a periodic warming in sea-surface temperatures across the central and east-central equatorial Pacifi. El Niño represents the warm phase of the El Niño/Southern Oscillation (ENSO) cycle, and is sometimes referred to as a Pacific warm episode.
Currently, we're seeing a very good signal that the on-going El Niño is establishing itself very well in both the ocean waters (image below) and, importantly, in the atmosphere. As you may recall, we did have weak El Niño conditions this past winter in the ocean, but the atmosphere failed to respond. That is clearly not the case now as we are seeing numerous signs of all the pieces coming together.
The latest from the NOAA Climate Prediction Center is that there is a 90% chance the still strengthening El Niño will continue through the coming winter, and an 80% chance in persist into early Spring. If you're interested in the details, you can read their diagnostic discussion here. Most climate models indicate at least a moderate event, with an increasingly likely chance it will be a strong event.
So, what does that all mean? Historically, El Niño has usually, not always, resulted in above average rainfall for the Southwest U.S. While there are other factors that influence our winter precip, ENSO is a pretty big one. Therefore, the NOAA Climate Prediction Center is currently indicating a very good chance that this coming winter will see above average precipitation. Looking at the map above, we see that Phoenix has an approximately 63% chance of above average rainfall for Dec-Jan-Feb. Conversely, there is still a 37% chance that precipitation will be below average through those three months. In short, you can think of this as the dice are loaded for the winter to be wetter than usual, but it isn't a guarantee.