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Winter '15 / '16 - Snowfall Forecast Contests

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Sunday, January 15, 2012

Winter '11 / '12 - Arctic Oscillation - On the Cusp

NYC - East 46th St. near 2nd Ave.
The Arctic Oscillation (AO) at winter's mid-point remains pegged in a persistently positive mode.  Save for a few brief flirtations with its alter ego...the AO has been above zero for 41 days since the start of meteorological winter (01-DEC) 46 days ago.

The polar vortex (PV) has been wicked strong until recently when it weaken slightly during the on-going minor stratospheric warming.  Minor warmings are not known for their association with there's little expectation this event will be reflected at the surface in the form of a negative AO.

What a difference a year makes.  Last December/s monthly AO was the second lowest (-2.631) during the period of record which began in 1950.  JAN-11 didn't stand out in the historical record (ranked 14th) but it was strongly negative.  This winter...December was the polar opposite at +2.221.  January is on-track to finish...not unexpectedly positive...around +1.

Below is a time-series of the AO on winter's cusp throughout the 60+ year period of record (1950 - 2011).  The blue line is a trace of the daily AO index on 15-JAN.  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 on 15-JAN other than there is a discernible cycle every nine years or so.  It does have an interesting comparison to the cycles found in the 30-DEC data.


Anonymous said...

If I am reading the chart correctly then 1967, 1978 and 1993 all have positive values (on Jan 15). That's a faint sign of hope anyway. I expect February to be a much better winter month for the northeast U.S., not a prolonged snow drought. Feb 21-22 new moon MECS if we're lucky. -- Roger Smith

TQ said...

I hope you're right about FEB...esp. the periods around Preznits Day. It is climatologically the best month for mid-Atlantic snowfall.

If JAN/s AO turns out positive...which it most likely works against a flip in FEB b/c the historical monthly index data shows DEC/s AO begets JAN/s AO and JAN/s AO begets FEB/s AO.

The data peaks you note are a result of applying a '9-point binomial filter' which smooths out the yearly 'noise' to show decadal-scale signals / cycles...not the value of any one year.

The AO cycles...on average...every nine years (max = 11; min = 8). It's six years for the PNA.

I should overlay the two indexes to see where they amplify or cancel.

Anonymous said...

Thanks for that, I was looking at the actual data (blue) to get those values for the years in question. -- RS

TQ said...

Roger that...Roger.

So far your Winter '11/'12 Mild- Mild-Cold is following the script quite nicely.

Anonymous said...

Broken clock syndrome. -- RS