One of the paradoxes of climate change is that reduction of sea ice on the European side of the Arctic basin leads to increased Siberian snowfall in the fall months and possibly colder than normal winter temperatures in central and eastern Siberia. There was an old (failed) hypothesis about glacial cycles that an ice free Arctic led to increased snowfall in Eurasia and north America which then led to a new glacial cycle. This hypothesis failed for multiple reasons, the most interesting being that open water in the European Arctic seas and greater than normal Siberian snow extent destabilizes the polar vortex. A strong polar vortex tends to keep cold air “locked up” in the Arctic. A sudden weakening of the vortex lets the cold air out of the Arctic. This winter, mainly because of the La Niña weather pattern caused by cold water in the equatorial western and central Pacific oceans, the sudden weakening of the polar vortex has driven the Arctic air out of Siberia and across the northwestern Pacific ocean behind an extreme cold front following a storm that “bombed” in the Aleutians.
Over the next month the west coast of North America will likely be hit by storm after storm as the intensified jet stream over the north Pacific brings on an extremely active weather pattern. California and Oregon will get much needed rains. Further north, unwelcome storm damage may happen because storms will likely be more intense than normal. Water temperatures in the north Pacific average well above normal. The enhanced outflow of Siberian air over the warmer than normal water will lead to stronger than normal storms.
The atmospheric wave patterns and weather patterns are coupled from the surface to the top of the stratosphere at this time as warm air has driven from the north Atlantic into the Arctic and cold air has been displaced from the Arctic to Siberia then out into the north Pacific. A massive breakdown of the polar vortex in the lower atmosphere is taking place concurrently with the major stratospheric warming.
The surface pressure map of the northern hemisphere taken at the time of this writing on New Year’s eve shows the bomb Aleutian low and the powerful outbreak of Siberian air into China and the western north Pacific. The polar vortex breakdown has caused this extreme weather pattern.
The good news for North Americans is that we are not yet getting cold blasts from this weak polar vortex event. I will discuss the potential impact of this on the weather for the rest of the winter in a future post but for the next week the Arctic air will be pouring out over the north Pacific.
There’s much imagery and discussion on twitter about this event. There are a number of excellent animations that show how this polar vortex break down is affecting the weather. For detailed technical discussion see Judah Cohen’s blog. Cohen’s twitter posts lead to his blog posts.
Here’s the environment Canada total ozone map that shows stratospheric ozone intruding into the lower atmosphere over the north Pacific.
New Year’s day update from the comments.
The bomb low in the Aleutian islands has set a new record for the lowest pressure, 924.8mb, recorded on land in Alaska.