CONTEST STATUS - Updated: WED ... 13-DEC-17 @ 8:30 PM EST

Winter '17 / '18 - Snowfall Forecast Contests
19th Annual 'Regular Season'
Snow Storm #1
Synoptiscope in VCP32

17th Annual 'Season-total'
Deadline for entries has passed
Forecasters' summary here

Winter '16 / '17 - Snowfall Forecast Contests
18th Annual 'Regular Season'
FINAL results here
16th Annual 'Season-total'
FINAL results here

Tuesday, December 20, 2011

Winter '11 / '12 - Arctic Oscillation - Day 20

The persistantly positive state of the Arctic Oscillation (AO) may be starting to lean toward a long awaited change of sign.

This three day Height-Latitude Cross Section of Zonally Averaged Zonal Wind loop shows deep-layer easterly winds blowing over the pole...a weakening polar vortex (PV)...and a strengthening sub-tropical jet (STJ)...all of which are favorable ingredients for the Arctic Oscillation to finally go negative.

As a result...the AO has ducked below zero for the first time in what seems like ages.


Whether this trend continues remains to be seen.
Recent daily AO data here.

Contours show zonal wind speed with an interval of 2.5 m/s.
Easterly winds are shaded in warm colors.
Graphics courtesy the Japanese Meteorological Agency (JMA).

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