SUDDEN STRATOSPHERIC WARMING EVENT: A major disruption of the polar vortex appears to be underway as the Arctic stratosphere suddenly warms. Researchers call this a "sudden stratospheric warming event." It's caused by planetary atmospheric waves crashing into the vortex and breaking it up. Cold air spilling out of the weakened vortex could plunge the USA, Canada, and parts of Europe into bitter cold little more than a week before the arrival of Spring. This also marks the end of polar stratospheric cloud season for Arctic observers.