Sunday, November 3, 2013

Analysis of October Snow Cover and its Impacts on This Winter

There has been an emerging idea that the amount of change of Eurasian snow cover below 60N in October can give excellent clues on the prediction of the Arctic Oscillation for the following winter. Judah Cohen, who made the Snow Advance Index (or the SAI), says that if snow cover ends up higher at the end of October than at the beginning of the month, the chances of a negative Arctic Oscillation greatly rise. On the other hand, a negative change anomaly from October 1 to November 1 then influences the potential for a positive Arctic Oscillation, and thus warmer weather for the US in winter.

Now that October has passed, let's take a look at the graph of October snow cover for the 35N-55N latitude region.

Taking a look at this graph, we see a definitive above normal snow cover trend for the month of October. The graph suggests snow cover began around normal, and ended well above normal. This tells me that the Arctic Oscillation may very well be negative this winter, as Cohen's SAI would deduce.

I'm not fully sold on the idea of a sustained negative Arctic Oscillation for this winter. For one, the Quasi-Biennial Oscillation (a wind-related oscillation that affects the stratospheric and tropospheric weather patterns, particularly in the Arctic) is in a weakening positive state. The positive QBO state means that the polar vortex is more likely to be seen as stronger in the winter, and a stronger polar vortex fits the definition of a positive Arctic Oscillation. If you've seen my Final 2013-2014 Winter Forecast, you also know that Michael Ventrice was able to fit the QBO into eight phases, each of which has different effects on the northern hemisphere. We are currently entering Phase 6 of the QBO, which enhances the strength of the polar vortex, per the QBO phase composite included in that forecast. A ridging pattern in the Southeast also appears possible based on this QBO composite, but the point is that the negative AO that may be induced by this snow cover anomaly may need some time to deal with the unfavorable QBO. I expect we see some down right cold weather in the end half of winter, and this could very well be when the AO is at its lowest points.



Anonymous said...

I think you just made a confusion. QBO can't get into phase no.6, you have mistaken it with MJO.

Best regards,

Andrew said...

The QBO has been made into phases, as i showed in my final winter forecast, and it is currently entering Phase 6.

Anonymous said...

Its not any snowcover increase in Oct supports negative AO, its the rate of increase. Snow cover will always increase in Eurasia in October!

Anonymous said...

A few posts back, someone mentioned about weather police, what is that? Sorry for asking such a dumb question.

WxJAK said...

Hi Andrew,

I think you might be in error with respect to SAI. Cohen, in his 2011 GRL paper [Cohen, J., and J. Jones (2011), A new index for more accurate winter predictions, Geophys. Res. Lett., 38, L21701, doi:10.1029/2011GL049626] where he introduced SAI, said: "The snow advance index (SAI) is the regression coefficient of the least square fit of the daily Eurasian SCE equatorward of 60°N calculated for the month of October. The units of the SAI index are million km2/day." I calculated SAI using the available complete data 1999 through 2013, (days 274-304 between 25N-60N and 0E-180E), and from it produced each years standardized anomaly, using 1999-2012 as my climo.

I get the following:
YEAR, SAI (StdAnom)
1999, -0.57
2000, 0.40
2001, -0.38
2002, 0.50
2003, -0.18
2004, -0.69
2005, -0.43
2006, -0.58
2007, -1.47
2008, -0.31
2009, 2.14
2010, -0.44
2011, -0.25
2012, 1.99
2013, -0.98

Taking the std anom allows one to make more direct comparison to DJF AO. The reason for this is illustrated in supplemental figure S2.

All of this I say to note that 2013's SAI is, as far as I understand, *not* suggestive of a negative AO winter, rather just the opposite.

I hope that makes some sense.


Christopher said...

Interesting. Thank you for the article.

R.J. said...

How fast do you think it'll get into phase 7? Is it possible it could happen before Christmas?