Stratospheric warming events, and extremely cold weather in North America

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The current wave of extremely cold weather affecting North America, with surface atmospheric temperature below -20°C (right Figure) and perceived temperature as low as -50°C appears to be connected to an intense episode of stratospheric warming, bringing polar air down to lower latitudes in the North American quadrant (left Figure). These stratospheric warming events are known to be persistent and can last up to a few weeks. Therefore, this cold outbreak could continue for several days.

190201_img_extreme_cold_North America

Left, 200 – mb streamlines and isolines showing the wind velocity at the top of the troposphere.
Right, air temperature (coloured contours), atmospheric circulation (streamlines) and relative humidity (shading) at 850 millibar.Forecasts issued by the National Centers for Environmental Prediction (NCEP, 



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