What does winter hold in store for Sisters?

It shouldn't be much of a stretch to suppose that wildfire-weary residents of Central Oregon - and much of the entire western U.S. - will welcome the onset of the fall and winter seasons. Since early August, smoke-filled skies haven't just been an annoyance to outdoor enthusiasts, but have posed health risks in many areas.

The key to returning to some semblance of normalcy is, of course, the weather.

At this writing, cooler and wetter weather from the Gulf of Alaska has moved into the Northwest, helping to slow the spread of these fires. But what lies ahead for the remainder of fall into the winter? Does a low-elevation September snowfall portend an early or harsh winter?

The short answer is - no.

It's no secret that seasonal weather forecasts over the past couple of years have not verified well. The El Niño monster of 2015-16 was supposed to menace Southern California with torrential rains and numerous mudslides. None of that materialized, as rainfall amounts were barely normal. Here in our neck of the woods a warm and dry winter was expected by most. Instead it was cooler and wetter than normal, except for February 2016. Most of the rest of the U.S. received the El Niño-like conditions that were anticipated, but not here in the West.

And we all know what happened last winter.

A neutral El Niño Southern Oscillation (ENSO) signal was in play, causing most forecasters to lean toward an "average" to slightly warmer winter, mainly because of a warm blob of water in the eastern Pacific last fall. Spurts of extreme weather tend to favor neutral ENSOs - but that's not what happened.

After a warm and dry November, winter roared into Sisters Country early in December and stuck around for quite some time. Temperatures in December 2016 and January 2017 were far below normal, with copious amounts of precipitation that translated into an accumulated snow depth in January of about four feet, which was record-setting in some areas.

It was still cold in February but slightly drier than usual. Temperatures returned to normal by March, allowing Central Oregon residents to begin digging out.

On September 14, 2017, the Climate Prediction Center and the International Research Institute for Climate and Society issued a La Niña watch. They say there is an increasing chance (55-60 percent) of a La Niña to develop during the Northern Hemisphere fall and winter 2017-18. Over the last month, equatorial sea surface temperatures have been near-to-below average across the central and eastern Pacific Ocean. The Oceanic Nino Index (ONI) is currently at 0.2, making the ENSO signal neutral. It needs to fall below negative 0.5 to usher in a La Niña.

And even if La Niña does arrive, it will probably be a weak one. Of course, figuring out what this means for our weather this winter is the tricky part. Wintertime La Niñas generally result in cooler and wetter conditions in the Pacific Northwest.

For the three-month period December through February, the Climate Prediction Center is calling for an equal chance of temperatures to be below normal, normal, or above normal. Precipitation is expected to be slightly above normal.

To attribute last winter's extreme weather to a single climatic index is way too simplistic. On the broadest scale, every ONI ENSO signal is based just on the temperature of the water in the tropical Pacific Ocean. Upon this, however, ride a number of other weather cycles of various durations, such as the Arctic Oscillation, the Madden-Julian Oscillation and the Pacific Decadal Oscillation.

It's much more likely that the kind of weather experienced over a season is determined by how these climatic entities interact.

There is no evidence to support the notion that our weather this winter will approach the severity of last year's.

Note: Those interested in further exploration may want to read an article that appeared in the October 2016 edition of Scientific American entitled "On the Trail of El Niño" by Emily Becker.