Can we expect same La Niña outcome with new climate norms?

Eye on Climate

PORTLAND, Ore. (KOIN) – You may recall that we have shifted the climate normals from 1981-2010 to 1991-2020. This is the 30-year time frame that we will use to base the average temperature or rain for a specific location. You can find an article about the impact of that on our Portland averages here.

However, what does this new period of time mean for the El Niño-Southern Oscillation (ENSO) phases and will that impact our emerging La Niña advisory? Before we discuss that, you should check out the first part of the La Niña climate outlook. You will find information about the previous five La Niña winters, which happened in the last decade. If you’re curious about the amount of snow or rain we have had during those La Niña winters, that article will help you out.

Courtesy of NOAA

At present, we are under a La Niña advisory. This means the conditions are currently observed and expected to stick around. This means the sea surface temperatures are below average and we should expect a winter that is going to be influenced by the conditions of La Niña. Again, if you’re not familiar with those conditions, you can read the first part, which you can find in the link above.

Below is a graphic that will give you an idea of the current sea surface temperature anomaly. It’s noticeably cooler around the central equatorial Pacific, with a few spells of warmer water in expected locations. You may be asking, what is the gauge? Of course it is that 30-year period of time that this anomaly is built from.

Well, one would suspect that it has changed from 1981-2010 or the previous 30-year periods. There is no doubt about that. Does this change the results?

Below is a graph that shows the average sea surface temperature across 12 months over a 30 year base period. According to the Climate Prediction Center, there has been a significant warming trend in the Nino-3.4 (specific region of the central equatorial Pacific) region since 1950. You can find the most recent 1991-2020 period of time in the chart below, represented by the lime green dotted line. If you focus your attention on the months of August through December (right side of the graphic), you can see the sea surface temperature is much warmer than the early to mid 1990s. Yet, we still expect the same type of pattern here in the Pacific Northwest (PNW) for the winter season (more rain and more mountain snow). Should our expectations change?

Courtesy of NOAA

Although the sea surface temperature is warmer, that is not the full story of what occurs during an El Niño or La Niña phase. The wind and pressure patterns that set up during each phase (Walker Circulation) has an impression on our predicted arrangement in the United States. We have come to expect wetter conditions in our region during the winter because the blocking high pressure and the path of the polar jet. This seems to be consistent.

I want to leave you with a visual graphic from the Climate Prediction Center below. It is the yearly surface temperatures by each decade since 1950. It shows the warmest and coolest year by decade and the corresponding ENSO phase. Most decades tend to see the coldest year on record during a La Niña year, with the warmest surface temperature during an El Niño year. There are a few outliers, but that has been the general trend (climate article).

Courtesy of NOAA

Until there is more research and evidence that the global pattern is shifting due to the warming sea surface temperatures, the winter pattern is still expected to follow the same rule here in the PNW, wetter.

Climate.gov of NOAA helped contribute to this article

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