Why This Winter’s Forecast in the Pacific Northwest is More Uncertain Than Usual

Forecasting the weather for the whole winter is always difficult, but several factors may make this winter harder than most.

By Rich Marriott, King 5 News

Autumn’s arrival is announced by falling leaves, less daylight, and the ever-pressing question: what about winter?

NOAA’s Climate Prediction Center has put out its official winter forecast for the Pacific Northwest. Our region and much of the country for that matter is predicted to get above-normal temperatures this winter.

Here in the KING 5 Weather Center, I also think our winter will have above-normal temperatures, partly because of the “Blob” off the coast, and partly due to the recent trend of winters being warmer. Rainfall may end up being a little bit more than normal – but not by much. Finally, due to the changeability of a neutral winter, there will probably be a least one cold snap where we might see snow for lower elevations, but amounts are impossible to predict for a whole season. But after last February’s official 21″ of snowfall at Sea-Tac, having two heavy snow winters in a row seems less likely.

El Nino and La Nina are the best predictors of how our upcoming winter will trend. These systems are tied to the “sea surface temperatures” (SSTs) in a specific part of the Tropical Central Pacific Ocean.

When the SSTs are warmer than normal, we call it El Nino. And we tend to have warmer than normal winters with no clear-cut trend in rainfall.

When SSTs are below normal, it’s La Nina. And we tend to have winters that are cooler and wetter than normal. But “tend” is the critical word here.

The systems may push our winters in a certain direction, but other less predictable processes can affect the outcome for a winter. The best analogy is that they load the dice for one outcome or another, but don’t guarantee it on every roll of the dice.

And even when the forecast is correct for the winter, it may not feel correct. Last winter was a classic example of this.

It was an El Nino winter and the forecast was for “above-normal temperatures.” But what do people remember about last winter? How cold and snowy it was in February. However, last winter’s forecast was right overall.

Summer flower pots were still blooming when the snow hit in February because November, December, and January were in the top 10 warmest ever recorded for each of those months.

Forecasts for a whole season are tricky. And even trickier than usual this year.

Rather than having an El Nino or a La Nina, we are expected to have “neutral conditions,” which means the SSTs in the critical part of the Pacific are normal.

So this winter, the dice are not loaded for anything and that tends to give us changeable winters where we can be locked into one pattern for a while — just to have it change to another pattern for a while. But there doesn’t seem to be a significant push for one type of weather over another for the Pacific Northwest.

You may recall the “Blob” of unusually warm water off the Pacific coast of North America in 2013-2016. It is more technically called a marine heatwave.

The Blob was associated with the Pacific Northwest snow drought in the winter of 2014-2015, when the mountains received mostly rain rather than snow.

Well, it’s back again and has been described by Washington State Climatologist and UW Associate Professor Nick Bond as the “Daughter of Blob.”

This pool of warm water is still a wild card, as it appears weaker than the previous Blob and shallower, so it could be more easily broken up.

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