Extreme Events

Temperature extremes have been pretty unusual across the United States so far in 2014. Looking back over this time period quickly reveals at least part of what was going on: the polar jet stream got into a serious rut.

Wednesday, January 1, 2014

  • The most populated state in the country is facing what may be its worst drought in a century of record-keeping. On January 20, the governor of California declared a state of emergency, urging everyone to begin conserving water.

  • The Arctic Oscillation describes simultaneous, geographically “choreographed” shifts in multiple features of the polar vortex: air pressure, temperature, and the location and strength of the jet stream. They all follow the hemisphere-wide oscillation of atmospheric mass back and forth between the Arctic and the middle latitudes, sort of like water sloshing in a bowl.

  • A few days of unusually cold weather in the U.S. and Canada aren't a sign that a century-or-more trend of rising global surface temperatures has reversed itself. In fact, the cold wasn't even all that widespread for the Northern Hemisphere.

  • Meteorologists have known for years that the pattern of the polar vortex determines how much cold air escapes from the Arctic and makes its way to the U.S. during the winter. Climate scientists are wondering if a warmer Arctic could explain its odd behavior in recent years.