Note: This post talks about the impact of the El Niño-Southern Oscillation on historic weather in the Tri-Cities and is the first in a series on my thoughts for the upcoming winter. Other posts in this series can be found here after they are released.
INTRODUCTION
As we transition toward the cold season, arguably the most frequent question anyone involved in meteorology gets asked is some version of “how much snow will we get this winter?” Unfortunately, seasonal forecasting has not reached the point where bold statements like that can have any sort of accuracy. In fact, a recent study states that “a skillful forecast lead time of midlatitude instantaneous weather is around 10 days, which serves as the practical predictability limit” (Published in the Journal of Atmospheric Sciences, quoted in the Washington Post). Instead, seasonal forecasts are quite generalized, which is to say that they’re both regional in nature (a forecast might apply to the Pacific Northwest rather than the Tri-Cities) as well as generalized temporally (averaged month/seasonal conditions rather than daily weather).
Rather than attempting to make my own winter forecast for the Tri-Cities and Columbia Basin, I will instead be discussing past weather for seasons that could be similar to this one for various reasons. Looking into the past can help us get an idea of some of the scenarios that could be possible this winter. There’s a lot to cover, so instead of one single long post, I will do this as a series. Don’t worry, though – at the end of the series I’ll touch on the seasonal forecasts issued by the Climate Prediction Center (abbreviated CPC) and Environment Canada and take a swing at interpreting what these could imply for the Tri-Cities. I’ll also sprinkle some tidbits in from the Winter Weather Conference I attended in Portland in October.
For the purposes of this discussion, I’ll be using meteorological winter, which is December 1 to February 29.
EL NIÑO-SOUTHERN OSCILLATION
No proper winter weather discussion can start without the El Niño-Southern Oscillation (abbreviated ENSO). This climate pattern largely refers to sea surface temperatures (abbreviated SSTs) near the Equator in the central and eastern Pacific Ocean. When sea temperatures are significantly above average, this is called El Niño; significantly below-average sea temperatures are called La Niña. If sea temperatures are near average, this is considered ENSO Neutral.
Variations here can contribute to major year-to-year seasonal weather patterns for the Pacific Northwest. Last year, we experienced a weak El Niño, but this transitioned into ENSO Neutral and is expected to remain there through the course of the season. We started keeping regular records of ENSO patterns in 1950, giving us a 68-year dataset to run through when considering how this has an effect on the Tri-Cities.
The quick summary for the following sections is that ENSO Neutral years are highly variable. Previous neutral years have presented a lot of different winter weather patterns that make it hard to use this situation as a solid predictor of what to expect. Furthermore, as my good friend and fellow WeatherTogether blogger Karl Bonner notes – “the past two winters have largely defied the general ENSO theme.” You can read more about that in the blog post he published today.
TEMPERATURE
Interestingly, while the average temperature during ENSO Neutral is close to El Niño and La Niña years, neutral years seem to have more variability than the other two. This means that neutral years have a higher chance of being both unusually warm and unusually cold in our area (which would be why the average is about the same). That said, not every neutral year is unusually cold or warm.
This could lead to, but does not guarantee, extreme cold. Since 1980, the Tri-Cities has experienced 14 winters where temperatures got below zero with four of those winters being during neutral periods. On the other hand, the same period brought the Tri-Cities 17 winters with temperatures that got above 65º with seven of these occurring during neutral years. Historically, our neutral years lean slightly warmer, but those four extreme cold events mentioned above demonstrate that nothing is out of the picture.
When the seasonal temperature variability and small dataset are combined, there simply isn’t enough information to make a forecast based on this alone.
RAIN & WIND
Precipitation is a different story. While temperatures can vary greatly between different neutral years, precipitation values seem to have about the same variability as the other two ENSO options. This would mean that the amount of snowfall we receive during neutral years is heavily dependent on what the temperature decides to do that winter.
Neutral years tend to lean drier than El Niño and La Niño years for the Tri-Cities. This is not a statistically significant difference, though, and neutral years can come with higher than average precipitation. But, as Kelley Bayern at KOIN-TV (formerly KEPR-TV) noted in the conference, regional winter storms tend to occur more often during neutral years. These frequently bring a decent amount of rain to our area, but their biggest impact for us is usually the wind that they bring.
Not every neutral year comes with a major regional storm and not every regional storm happens during a neutral year. One significant, semi-recent regional storm that comes to mind is the 2006 Hanukkah Eve Storm, which knocked out power to 1.8 million customers in the Puget Sound Region. Another is the one in November 2015 that created strong winds that caused an 11-car pileup on I-84 near Hermiston. Both of these storms came during El Niño years.
The Columbus Day Storm of 1962, which is one of the strongest regional storms to strike the Pacific Northwest on record, did strike during a neutral year. Interestingly, the Columbus Day Storm wasn’t all that strong here in the Tri-Cities, with wind gusts probably only peaking to around 40 mph thanks to the track it took.
SNOW
Tyree Wilde at NWS Portland noted at the conference that out of the top ten snow years recorded in Portland since 1980, six of them occurred during neutral years. Since there is a large gap in snowfall data for the Tri-Cities, I’ll be relying on records from Pendleton and Yakima to see if this translates to heavy snow on our side of the mountains.
It seems that top-ten snowfalls in Portland don’t necessarily correlate to top-ten snowfalls in Pendleton, but there is a decent amount of overlap with Yakima. I would have to do several more hours of research to say this definitively, but this could imply that snow events during neutral winters may not have as strong of an impact on the Blue Mountains. Another possibility is that storms during neutral years do have a strong impact in Pendleton, but that storms during non-neutral years don’t bring as much snow to Portland. Lastly, it’s also possible that this difference is simply due to chance.
The higher frequency of significant snowstorms in Portland during neutral years can probably be at least partially attributed to the increased frequency of regional storms. Had the unusual cold snap that we experienced at the end of September come during December or January instead, Portland (and the Tri-Cities) may have seen some decent snowfall. That storm was already cold enough to bring snow to Ritzville, with a few inches falling in Spokane.
Finally for those into winter sports, Bayern also noted that Mount Hood Meadows has opened by Thanksgiving during most neutral years. As of writing (November 12), they’ve had 31″ of snow so far this season, but currently don’t have any on the ground at their base elevation of 5,366 feet.
