500 mb height anomalies
three states of the
Thirty days into the season...the Arctic Oscillation (AO) remains well above zero despite a weakening polar vortex (PV) and hi-latitude easterly winds.
The 500 mb height anomalies (below right) have looked more like the top chart which has kept arctic cold away from the mid-latitudes. The ECMWF continues to depict a weak anti-cyclone building over the Pole; however the on-set is always at least seven days away.
Today/s 500 mb height anomalies
The minor stratospheric warming event @10 mb has contributed to a weakened PV but is occurring well away from the pole INVOF northeast Asia and has not propagated below 30 mb.
Minor warmings do not cause the PV to break down or cause a wind reversal from west to east so it's debatable how much influence this event will have on establishing hi-latitude blocking. Best guess: very little.
Below is a time-series of the AO on 30-DEC throughout the 60+ year period of record (1950 - 2011). The blue line is a trace of the daily AO index on 30-DEC. The dark red line is a a trace of the same data after applying a nine-point binomial filter. The filter removes low frequency noise and highlights decadal trends.
Not sure what this says about the AO at the end of December other than there is a decernable cycle every seven years or so.
99/00 - spawned on USENET/s ne.wx newsgroup to discover which poster(s) made skillful forecasts for synoptic-scale snowfalls in the NE and Mid-Atlantic. No formal entry process. Forecasts gleaned from newsgroup posts. Five 'contest' storms.
00/01 - Permanent station list created. (RDU - CAR). Rules and scoring formalized. First Contest 12/30. 10 Contest storms.
01/02 - 'Season-total' forecasting contest launched. Twenty-five forecasters predicted each station/s 'total snowfall' for the winter. First Contest storm 12/9. Nine Contest storms.
02/03 - First Contest storm 11/27. Ten Contest storms.
03/04 - Web site launched. Forecasts submitted via online entry form. Forecast reporting and verification processes streamlined. Two forecast stations added (BGR, BGM). First Contest storm 12/14. Ten Contest storms.
04/05 - First Contest storm 12/20. Nine Contest storms.
05 /06 - First Contest storm 12/5. Four Contest storms.
06/07 - Regular season starts late with first Contest storm 2/14. Five Contest storms...last one in April.
07/08 - Record number of forecasters (36) enter 'Season-total' Contest. Regular season starts 12/3.