Early snow cover patterns point to polar vortex disruption, signaling harsh winter ahead across North America and Europe
An unusual snow buildup from Siberia to North America in late October could destabilize the polar vortex, leading to colder and snowier conditions across the United States, Canada, and Europe this winter.
500 hPa geopotential height - October 15, 2024. Image credit: Climate Reanalyzer
A substantial increase in snow depth is forecast from Siberia to North America during the last two weeks of October, according to an analysis by Andrej Flis from Severe Weather Europe (SWE). This early buildup of snow cover could have significant implications for the upcoming winter across the northern hemisphere.
Snow accumulation in October can disrupt the stability of the polar vortex, a large-scale cyclone centered around the North Pole that influences weather patterns across the mid-latitudes. A destabilized polar vortex increases the likelihood of winter weather disruptions in regions such as the United States, Canada, and Europe. In particular, a larger snow cover in the northern hemisphere during autumn may lead to more erratic winter pressure systems, potentially resulting in harsher cold and increased snowfall.
Meteorologists are closely monitoring a broad low-pressure system forming over Siberia, which is expected to bring snow patches to the northwest, the Rockies, the Upper Midwest, and the far northern United States over the next two weeks, culminating in late October. This system plays a crucial role in laying the groundwork for winter conditions.
The polar vortex, which extends from the Arctic to the mid-latitudes, varies in strength and shape throughout the season. When this system weakens, it can cause significant shifts in weather patterns. Increased October snow cover could lead to the development of a stronger high-pressure system, which in turn could weaken the polar vortex later in the winter. A weaker vortex tends to create a more disrupted jet stream, enabling cold polar air to surge southward, affecting regions like the United States and Europe with potentially severe winter conditions.
Currently, snow cover over Eurasia exceeds 10 million km² (3.86 million square miles), marking the third-highest level in the past 20 years. This rapid rise in snow coverage, which is above normal for this time of year, is a critical indicator of potential shifts in winter weather dynamics.
Additionally, an unusual pressure pattern in the stratosphere, alongside a warming anomaly over the western half of the polar circle, hints at a weakened polar vortex heading into the winter months. Forecasts show that stratospheric wind speeds may decrease between December and January, further suggesting the possibility of a weaker polar vortex. This weakening could trigger a sudden stratospheric warming (SSW) event, a phenomenon known to lead to drastic weather changes.
If an SSW event occurs, it is often followed by the collapse of the polar vortex. Such a collapse could pave the way for above-average snowfall in Europe and the eastern United States, as the weakened vortex allows cold Arctic air to penetrate deeper into these regions.
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1 Polar Vortex is affected by October Snow extent in an unexpected way, with a large snow advance now being Forecast – SWE – October 14, 2024
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