Polar vortex weakening, leading to repeated cold air outbreaks and storms of extreme intensity are one of the possible consequences of climate change. A stratospheric warming and polar vortex weakening event has been developing for the past week and weather models are now forecasting it will have major impacts across north America as cold air will be driven out of the Arctic towards the western states of the U.S. and provinces of Canada. Intense storms will develop in the midcontinent region as an intensified jet stream amplifies the “battles” between frigid Arctic air and warm air pulled in from the Gulf of Mexico.
As of the first of January the snow extent across north America was very low and ice on the Great Lakes was at record lows. That is about to change. The estimated snowfall amounts by the American model over the next ten days across the continental U.S. are very high.
One of the signatures of sudden stratospheric warming events is the subsequent development of sinking air over the Pacific side of the Arctic. In El Niño years, like this one, when the Pacific jet stream is strengthened by much warmer water than normal in the central and eastern tropical Pacific, the combination of El Niño and the blocking high over Alaska can bring on extreme rain events for California. The map below shows a southwesterly airflow from Hawaii to California that would be exceptionally wet if it develops. Forecast maps longer than a week out are not reliable for details but the polar and subpolar high pressure areas called blocking highs tend to move slowly from east to west counter to the flow of the jet stream and the waves in the jet stream. Therefore, a transition from intense storms for the next tens days in the midcontinent to intense west coast storms in the ten days plus period is a very realistic development following a polar vortex disruption event like we are going through right now.
Multiple research reports have shown that winter has become shorter, but more intense, with human caused climate change. One of the factors in these intense winters is sudden stratospheric warmings that disrupt the polar vortex and give a surge of momentum to the jet stream. The combination of El Niño, a polar vortex disruption, and a blocking high over Alaska is a classic severe weather set up for much of the United States, especially coastal California, in January and February.