The strength of the current El Niño in the Pacific has made headlines and could very well become the strongest El Niño since records began in 1950. Despite its impressive status, there remains some questions regarding how it will impact the weather pattern over North America, particularly over the Western US where a historic drought has developed the past few years. Let's dive into the facts and explore what’s been happening and what it could mean for the upcoming winter.
First, let’s investigate what’s currently going on in the Pacific. Recent observations show a strong El Niño brewing with sea surface temperature anomalies as of November 30th reaching 3.0°C above normal. While it’s only one measure, this is the highest departure on record! However, the long-standing measure of El Niño, the Oceanic Niño Index (or ONI), is at 1.7°C… which isn’t a record, but sure is coming close (previous record is 2.1°C).
Okay, so we know that the ongoing El Niño is record breaking but has it had any affect on the weather along the West Coast? The answer to that question is not so clear-cut. Multiple factors influence the weather pattern and El Niño is but only one. We can say that the persistent ridge in the Western U.S. that was a dominant feature for the past few winters and one of the main reasons for the record drought has flipped. In fact, a series of troughs replaced the semi-permanent ridge over the West in recent weeks, leading to much needed wet weather. The typical pattern of a strong El Niño during the winter is detailed below, clearing showing support for above average precipitation over the West and Southwest US.
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Again, while El Niño is not solely responsible for this pattern change, it has been a major influence. Some of the effects of this pattern flip are already leaving a mark on the West including beneficial snowfall replenishment across the Sierra Nevada, which reached dangerously low levels last winter shown in the graph below. This pattern change has also brought good news to the Southwest US where precipitation levels are at or above normal for this time of year.
Although it will take quite some time to completely alleviate the drought in the West, the recent train of storms is certainly a solid start, slowly eroding away some of it over the past few weeks, especially across the Pacific Northwest shown below. Going forward into the winter, Westerns should observe an even greater depletion thanks in part to the record El Niño.
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