A huge air current that circulates above the North Pole has suddenly reversed course, spinning in the exact opposite direction in a way that could change weather forecasts.
The ominously named polar vortex might sound like the title of a summer blockbuster movie but is actually a well-charted meteorological phenomenon that has a huge part to play in weather in the Northern Hemisphere.
Don't worry, though - while the situation might sound drastic, and like the sort of major weather event that could bring cyclones and temperature drops, it's actually a somewhat regular occurrence.
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In summer, those circulating winds slow down and blow in an easterly direction, changing over from westerly, and that's the movement that was recorded recently.
However, where there is a lot of variability is in how strong that reversal is - how quickly it happens and what windspeeds it results in.
The one that took place in March 2024, as it turns out, was one of the top six strongest reversals we've ever recorded, apparently.
Amy Butler from the National Oceanic and Atmospheric Administration (NOAA), told Spaceweather.com that this "was a substantial reversal, reaching -20.5 m/s a few days ago, which puts it in the top 6 strongest such events since 1979".
Those speeds are dramatically fast, after all, and could mean that we see some interesting weather patterns this season.
It's worth understanding that the polar vortex isn't just a constant wind pattern in our weather - it sits higher than most winds, in the stratosphere itself instead of the lower troposphere.
That means it's more like a sort of background factor, rather than being the direct source of a cold wind in your face as you try to get through a run on a rainy day.
Still, though, as has happened in the last couple of weeks, there are times when the polar vortex becomes more or less volatile, depending on the winds further below it and other factors in our atmosphere, which can indeed result in cold snaps at ground level.
Remarkably, though, with almost exactly a month on the clock since the polar vortex reversed its course, we don't seem to have recorded any major weather events as a result, so it might be that this remarkably strong reversal has had an equally remarkable lack of effects.
Still, it's all a useful reminder of how complex the forces that determine our weather really are - that there are multiple layers of atmosphere each with their own weather patterns that can affect each other or not.
All of that is before you start to consider the potential impact of events like geomagnetic storms caused by solar flares - which can throw things completely out of whack and even result in radio disruption.