Will El Nino bring rain?

While the predicted likelihood of an El Nino year is quite high, it's not necessarily clear that California will experience increased rainfall as a result.

El Nino Finally Arrives

El Nino climate events are associated with low atmospheric pressure, resulting in cooler, wetter weather in California. Last autumn, with climate scientists predicting an upcoming El Nino event, there was hope that it would coincide with California's winter, which is the rainy season, leading to healthy rainfall and mitigating the 4-year-old drought.

Unfortunately, El Nino never arrived during California's rainy season. It has very recently arrived, as we can verify at NOAA's website here. This El Nino event is still associated with cooler, wetter weather, relative to a typical California spring and summer. However, at this time of year, there aren't many major wet storms in the Northern Pacific to route to California. As such, we'll have a chilly, drizzly spring and summer, but no impact in the way of drought relief.

I lived in San Diego during one of the recent El Nino summers. It never really got warm. It was a chilly, unsatisfying summer. Perhaps this summer's weather will be similar.

El Nino, California Drought

NOAA performs a vital a national and international service in monitoring ocean and atmospheric conditions, recognizing patterns, and classifying and predicting significant climate events.

One of the somewhat-well-understood phenomena is the El Nino Southern Oscillation cycle. Characterized by warmer-than-average ocean temperatures across the Pacific Ocean, and a weakening or reversal of the prevailing Pacific Trade winds, El Nino years tend to bring unusual weather and some extreme weather events. In past El Nino years, we've seen unusual shifts in precipitation, including drought in some places, flooding and even snow in others.

All this is of interest to the drought-stricken American West and Southwest, because strong El Nino years tend to correlate with above-average rainfall in these regions. NOAA maintains a public communication, including monthly updates here. Currently, we are in an El Nino advisory state. A more detailed document, detailing various observations and methodologies is here.

Overall, NOAA predicts the probability of an El Nino by fall or winter at about 80%, but the El Nino is likely going to be "weak to moderate'.

I really enjoyed viewing the satellite imagery, and temperature time series in the .pdf document. I also enjoyed the numerous temperature prediction models, split into "Statistical" and "Dynamical" models. They also included an ensemble prediction. Good stuff.