Winter '14 / '15 - Weakening Polar Vortex ==> Sudden Stratospheric Warming: UPDATE 3

Minor warming in progress INVOF Siberia.

 

10-hPa temperature change in a week in the Northern Hemisphere

The contour interval is 5 °C. The pink and light blue shadings indicate warming and cooling, respectively. The red shading denotes warming for values higher than 25 °C.

 

"A stratospheric warming is called 'minor' if a significant temperature increase is observed ([...] >= 25°C in a ... week or less) at any stratospheric level in any area of winter time hemisphere. The polar vortex is not broken down and the wind reversal from westerly to easterly is less extensive." (REF)

 

Imagery courtesy Tokyo Climate Center, Climate Prediction Division

Major warming appears imminent.

"Major SSWs occur when the westerly winds at 60N and 10 mb  reverse direction. A complete disruption of the polar vortex (PV) is observed.  The PV will either be split into daughter vortices ... or be displaced from its normal location over the pole." (WMO)