El Niño is creeping into “strong” territory, the National Weather Service’s latest advisory said Thursday, and the phenomenon is expected to remain at least at that intensity through the winter months. There is even a 35 percent chance that the situation will become historically intense.

The El Niño weather phenomenon, which begins with warming water temperatures in the eastern tropical Pacific, is a large-scale driver of atmospheric conditions that disrupts major weather systems around the world. But there’s a big problem right now: The atmosphere hasn’t really responded to the formation of El Niño the way it usually does.

Meteorologists often rely on El Niño to provide insight into major trends that could affect winter in the United States and other parts of the world. But El Niño’s hazy reflection in the atmosphere so far raises questions about what next winter could hold for the Lower 48 states.

Typically, during winters marked by El Niño, warmer air forms in Alaska, western Canada, and the northern United States. The Pacific jet stream, meanwhile, passes through the southern states, bringing moisture to the coasts and leading to cooler, wetter conditions.

While it may only be a matter of time before these typical El Niño weather patterns appear, let’s take a look at why they haven’t yet.

Why is this El Niño different from others?

In assessing the strength of an El Niño, meteorologists refer to differences in sea surface temperature from normal within an imaginary box that encompasses much of the eastern equatorial Pacific. This “Niño-3.4 region” experiences a temperature about 2.7 degrees (1.5 Celsius) above average, which is the threshold for what the weather service unofficially considers a strong El Niño .

But the atmosphere doesn’t do it as has historically occurred during other strong El Niño events. Here’s why:

  • There is an unusual heat blob in the western Pacific. Paul Roundy, a professor of atmospheric sciences at the University at Albany, says this alleviates some of the more classic symptoms of El Niño.
    • “The west-central Pacific, near and west of the (international) data line, remained warmer,” he said in an email. “(This) encourages more tropical rain to fall there, which in turn reduces precipitation intensity further east, as air rising in western Pacific thunderstorms falls toward the surface further east. is, drying out the atmosphere.” He further explained that the same mechanism triggers a “wave” that reduces precipitation in the eastern Pacific.
    • Todd Crawford, a consulting meteorologist at Atmospheric G2, echoed Roundy, saying in an email that experts are “monitoring” a weather pattern called the Madden-Julian Oscillation “to see if a strong, more conventional upward motion signal emerges.” establishes well east of the data line. .” The MJO is an overturning circulation that propagates across the Pacific, promoting upward motion with thunderstorms on one side and sinking, drying air on the other side. Crawford explained that “each successive MJO ‘pulse’ caused air to rise near the data line.
  • There is not much rising air over the Eastern Pacific. Usually, during El Niño, warmer waters from the eastern Pacific warm the air above, causing upward motion. This creates an area of ​​low atmospheric pressure, showers and thunderstorms. The air, in turn, calms down above the Atlantic. But at present, the area of ​​ascent over the eastern Pacific is meager and diffuse. It is likely that the out-of-place western Pacific warm blob is causing warming and upward motion. there and, as what goes up must come down, some of the air sinks into the eastern Pacific.

It’s possible that the bizarre nature of the El Niño phenomenon is also linked to a hangover resulting from three consecutive winters of La Niña conditions. Crawford said there could “still be a lagged response to La Niña that hasn’t completely gone away.” Rising ocean temperatures due to human-caused climate change could also contribute to warming in the western Pacific.

The question now is to what extent the warmth of the western Pacific will interfere with the evolving El Niño and shape its character. Roundy believes that the influence of the Western Pacific is declining.

“This interference from the western Pacific heat appears to be waning,” he said, “and there is now enough warm water east of the date line to allow heavier rains to enter there. to fall.”

Roundy also pointed to a burst of westerly winds that are expected to push warm surface seawater into the eastern Pacific, exposing and uplifting colder waters below in the western Pacific. “This will likely encourage the emergence of strong and more normal El Niño signals this winter,” he said.

But how will this shape our winter in North America? Roundy and Crawford estimated that, assuming a more classic El Niño signal emerges as expected, winter could be interesting in parts of the South.

“It is likely that this winter central and southern California will be wet, extending eastward across the southern part of the country,” Roundy said. “There is also an increased risk of wet conditions on the East Coast, particularly in December. » A recent simulation of the European forecast model supports this idea.

As for temperatures, Crawford thinks the U.S. will be “super hot” to “potentially record (warm) temperatures” early in the season, before punctuated cold blasts spread across the South and L. is from the United States later in the season. He compared what’s coming, in some ways, to the winter of 2009-2010, which brought record snow to the mid-Atlantic region.

“It was a very cold winter with a strong El Niño (sea surface temperatures),” he said, while noting that “there were probably other factors causing the cold that winter.

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