Bomb cyclone after bomb cyclone have exploded for the past two weeks in the far north Atlantic with the most intense weather over the Labrador and Greenland seas but extreme conditions also slammed northern Europe. Those storms sent heat upwards in winter version of a heat dome over northern Europe. Meanwhile, over the far north Pacific an intense storms that formed offshore of Japan and swung up into the Aleutian Islands formed the winter version of a heat dome over Alaska and the Alaskan side of the Arctic ocean. These two atmospheric domes caused an intense planetary wave number 2 to form sending an intense pulse of heat upwards into the stratosphere, disrupting the polar vortex. Extremely high levels of ocean heat in the north Atlantic off of the east coast of north America have provided extraordinary amounts of energy to intensify the bomb cyclones and build the ridge of warm air over Europe that has triggered the polar vortex splitting.
This is the polar vortex event I have been anticipating since last fall. www.dailykos.com/… This is the second year of La Niña, a situation where tropical convection is intensifies over Indonesia and Brazil while the welling up of cool water is intensified over the equatorial eastern Pacific ocean. This intensified equatorial convection pushes the jet stream polewards. However, it can also cause the polar vortex to become unstable. About half of all La Niña years have a significant disruption of the polar vortex. This fact combined with forecasts by the American CFS model that showed increasing instability of the polar vortex in midwinter, plus several other factors including extreme levels of ocean heat in the central temperate north Pacific and north Atlantic oceans (climate change) led me to think that the polar vortex would destabilize in mid to late winter. It is finally happening.
Severe Weather Europe has an outstanding discussion of the polar vortex split and the bomb cyclones that will be roiling the North Atlantic and the subarctic seas over the coming month. In particular, it answers all the questions that you were afraid to ask about what is the polar vortex and why does it do what it does. It’s a substantial piece that breaks down the science into comprehensible parts. What’s most interesting to me about this situation is that this vortex splitting event coupled with a surge in deep overturning of the water in the north Atlantic as the frigid polar air blasts off of the ice edge in the Labrador sea chilling the warm salty Atlantic water that originated in the Gulf Stream and wrapped around Iceland and the southern coast of Greenland. La Niña and the tight polar vortex directed the polar air towards the Labrador sea and away from the southeast coast of the U.S. This event has coupled the highest parts of the stratosphere with the depths of the north Atlantic ocean and has helped rejuvenate the flow of the Gulf Stream. Maps and cross sections showing the overturning are at: bulletin.mercator-ocean.fr/… But that’s not all.
The polar vortex split will lead to an atmospheric circulation pattern that will drive cold air from Alaska and northern Canada into the western U.S. at the same time as a dome of warm humid air builds over the southeastern states. Strong southerly winds will blow off of the Gulf of Mexico into the mid-continent as storms form and move along the boundary between the warm Gulf air and the Arctic air driving down on northwest winds from western Canada. The forecast below from the American model for this Sunday evening central time shows a zone of unstable air destabilizing ahead of a cold front. This is a set up for very severe weather because the winds aloft are very intense, the cold front is strong and the warm air is exceptionally warm and humid for early March. This forecast map is premature for determining whether severe weather will happen. It is useful for showing that a pattern is developing, starting this weekend, that may produce severe weather beginning on Saturday going into next week. This will be the first of a number of events where severe weather may be triggered by the combination of the intense mid-America storm track and extremely warm sea surface temperatures in the Gulf of Mexico and the western Atlantic ocean.
This is the time to get ready for the possibility of severe storms across a wide region of the American mid-continent. NOAA’s Storm Prediction Center has posted its first warnings of the possibility of severe storms beginning this weekend. Listen to these experts, and your trusted local forecasters for the details of the potentially dangerous weather in the week ahead.
On the forth of February I warned that the atmospheric circulation patterns associated with La Niña, the extreme north Atlantic heat and the colder than normal waters in the Gulf of Alaska were likely to be similar to the devastating spring tornado seasons of 1974 and 2011. The polar vortex split increases the potential above what was evident then and the extreme weather may begin as soon as this weekend. Be prepared for a very stormy spring in mid-America.