El Niño and the Polar Vortex Could Shape a Very Unusual Winter

The impacts of El Niño are seeping into nearly every weather pattern, with forecasters warning that its influence is going to be even more pronounced heading into the winter. One big question being pondered by climatologists is how the emergence of a Super El Niño will influence the behavior of the polar vortex. Here is what you need to know about what this means for the weather in November.

How the Behavior of the Polar Vortex Influences the Weather in the U.S.

The polar vortex is generally strong during the fall months, building up the cold air that will eventually break through and dive into Canada and the U.S. However, the latest forecast models are indicating that this traditional pattern might not be the story this year.

Forecasters are predicting that El Niño will continue to strengthen over the next few weeks. The end result will be a warmer-than-average winter for much of the U.S. How the polar vortex responds to this climate phase will significantly influence what type of winter is in store.

The polar vortex is the term used to describe the zone of fast-moving winds whipping around the Earth's poles. While this vortex always exists, it is primarily during the winter that it drives the weather across the U.S. The periodic outbreaks of Arctic air that spread over the U.S. during the winter are the result of an unstable polar vortex.

A sudden temperature increase in the stratosphere thousands of feet above the Earth's surface is known as a "Sudden Stratospheric Warming" event. These events unfold when the typically stable vortex is disrupted, allowing the bottled-up cold air to escape its normal resting place.

These Sudden Stratospheric Warming events work by stretching the polar vortex away from the pole. This movement drags the core of the coldest air to the south, sending it spilling into the northern U.S.

What the Latest Models Say About the Interaction Between El Niño and the Vortex

While the polar vortex is usually extremely stable in the fall, recent forecast models suggest that the disruptions may happen sooner than normal because of the strengthening El Niño. The latest models predict that the vortex will begin to weaken to record low levels through the first part of November. While that element is certain, what is less clear is how this disruption will influence the atmosphere below.

There is a chance that these changes could infiltrate the lower levels of the atmosphere in the weeks ahead. This development would support the threat of frigid temperatures being released into North America.

However, the Super El Niño could also offset some of this cold air. This is because this climate phase is marked by a stronger southern jet stream that ushers in warmer temperatures for a large portion of the northern U.S. As such, the forecast of high pressure anchored over Canada and mild air coming in from the Pacific could limit the duration and severity of any Arctic air invasions.  

The Arctic Oscillation (AO) is a measurement of the pressure contrast between the Arctic and the planet's middle latitudes. A negative AO means that it is more likely that cold air will dip down into the lower latitudes. Conversely, a positive AO generally means that the most frigid air will remain contained in the Arctic.

The long-range AO guidance demonstrates that the AO will remain positive through the first week of November, translating to milder air for the U.S. However, the models begin to differ beginning the second week of November. Although some models indicate that the AO will trend negative, others suggest it will stay positive.

The National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center (CPC) is calling for above-average temperature readings for most of the country through the third week of November. That could change if the polar vortex begins to show signs of movement. The good news is that any Arctic air that makes it into the U.S. this early in the season would not be nearly as bone-chilling as when the polar vortex unleashes during the middle of the winter.

We will continue to follow how this pattern unfolds in the next few weeks and update accordingly.

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