Why La Nina Winter may veer off course

The Pacific Ocean exerts a great deal of influence on weather and climate. But it is not the only ocean that does, nor are the oceans the only factors that impact climate and weather.

La Nina is not everything, it’s not the be-all and end-all of seasonal forecasting. Other factors play a role and sometimes take control unexpectedly.

We know the past doesn’t always predict the future, but we can use it as a guide.

As I’ve stated so many times before, no two La Ninas or El Ninos are ever exactly alike, although many are similar. The two El and La are together known as ENSO. El Nino Southern Oscillation.

Many long-range forecasters who do seasonal (3 months or more) and sub-seasonal outlooks (2-6 weeks) have observed many of the old connections and correlations have weakened or vanished over the last decade, so in the warmer background state of the 21st Century the old connections of the 20th Century no longer hold up, and we are yet to have enough time to discern the new decadal signals and how they are altered, there may be a new regime paradigm for ENSO.

So as a result, when the models detect and forecast a LA NINA they all default largely to what the average of past La Nina’s have produced in winter. You can see that in the model output for this coming winter below:

8 models winter 500mb jet pattern forecast

The 8 model composite mean for winter temperatures and precipitation:

Multi-model winter temp forecast average

Multi-model forecast average winter precip

But observation tells us there has been greater variance in what El Nino and La Nina (ENSO) produce in the winter in the recent decade, and we are seeing in real time the past two years and this year weather patterns that are at odds with La Nina behavior in the past. So caution is advised in just blind acceptance that this winter will be like most La Nina winters of old.

Even the 6 model blend shows an interesting January snow anomaly forecast. I don’t put much weight in it this far out but if the signal remains in the months ahead it will get my attention.

6 model blend January snow anomaly forecast

And another thing... the extreme distortion of current global sea-surface temperatures is unlike anything we’ve seen before in history, making it a wild card for predicting the season ahead, because it has no past close match globally (yellow is warmer than normal, red shades are way above-normal):

Just to offer one example. CSU hurricane researcher noted that ...

Not your father's La Nina hurricane season

Maybe it doesn’t mean anything or maybe it does, but just for reference (not a forecast) here is the average winter temps from those years:

Winter since 1990 with similar major hurricane #

Not like most La Nina’s at all.

Also, research by WeatherBell and others have observed ocean warm pools in certain regions can telegraph winter temp means IF they continue in the months ahead, these are called teleconnections: