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

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

12/18-0.024
12/19-0.882
12/20-0.438

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

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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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