The ongoing cold spell, which may bring down the mercury to as low as -50C (-60F), is caused by the expansion of the polar vortex.
The polar vortex primarily affects countries situated in the Northern Hemisphere's mid to high latitudes, where extreme cold weather events are common.
When the stratospheric polar vortex is in a weakened state, the chilly winds expand beyond its circular North Pole region, reaching as far south as Florida.
The upward movement of warm air triggers the weakening of the polar vortex, allowing frigid arctic air to spread widely across the regions.
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