Powerful October Block

[donsutherland1]

The Arctic Oscillation (AO) fell to -3.130 today, marking only the 33rd case in which the AO fell to -3 or below in October. In addition, October 2012 became only the 9th case in which October had a block with an AO of -3 or below. The prior cases are below:

1979: Lowest: -3.471 10/8

1981: Lowest: -3.076 10/3

1984: Lowest: -3.087 10/5

1991: Lowest: -3.044 10/29

2002: Lowest: -5.098 10/18

2003: Lowest: -3.297 10/15

2006: Lowest: -3.192 10/17

2009: Lowest: -3.415 10/22

2002 had 8 days on which the AO fell to -3 or below. 2003 had 3 such days. 1979, 1981, 1984, and 2009 had 2 such days. 1991 and 2006 had 1 such day.

It should also be noted that the extreme October block of 1991 coincided with the "Perfect Storm" that raged during the October 28-November 4 timeframe.

Finally, 6/8 (75%) of the prior cases saw the winter AO average < 0. 1991 and 2006 were the exceptions. In short, the current extreme block may also be an indication that the coming winter will likely see more blocking than the previous one (a theme consistent with the summer blockiness).

[Ground Scouring]

The Arctic Oscillation (AO) fell to -3.130 today, marking only the 33rd case in which the AO fell to -3 or below in October. In addition, October 2012 became only the 9th case in which October had a block with an AO of -3 or below. The prior cases are below:

1979: Lowest: -3.471 10/8

1981: Lowest: -3.076 10/3

1984: Lowest: -3.087 10/5

1991: Lowest: -3.044 10/29

2002: Lowest: -5.098 10/18

2003: Lowest: -3.297 10/15

2006: Lowest: -3.192 10/17

2009: Lowest: -3.415 10/22

2002 had 8 days on which the AO fell to -3 or below. 2003 had 3 such days. 1979, 1981, 1984, and 2009 had 2 such days. 1991 and 2006 had 1 such day.

It should also be noted that the extreme October block of 1991 coincided with the "Perfect Storm" that raged during the October 28-November 4 timeframe.

Finally, 6/8 (75%) of the prior cases saw the winter AO average < 0. 1991 and 2006 were the exceptions. In short, the current extreme block may also be an indication that the coming winter will likely see more blocking than the previous one (a theme consistent with the summer blockiness).

The bolded portion could have interesting ramifications re: Sandy and perhaps lends support to the ECMWF and other ensembles showing a full phase. As always, you provide great and timely data, Don.

[uncle W]

The Arctic Oscillation (AO) fell to -3.130 today, marking only the 33rd case in which the AO fell to -3 or below in October. In addition, October 2012 became only the 9th case in which October had a block with an AO of -3 or below. The prior cases are below:

1979: Lowest: -3.471 10/8

1981: Lowest: -3.076 10/3

1984: Lowest: -3.087 10/5

1991: Lowest: -3.044 10/29

2002: Lowest: -5.098 10/18

2003: Lowest: -3.297 10/15

2006: Lowest: -3.192 10/17

2009: Lowest: -3.415 10/22

2002 had 8 days on which the AO fell to -3 or below. 2003 had 3 such days. 1979, 1981, 1984, and 2009 had 2 such days. 1991 and 2006 had 1 such day.

It should also be noted that the extreme October block of 1991 coincided with the "Perfect Storm" that raged during the October 28-November 4 timeframe.

Finally, 6/8 (75%) of the prior cases saw the winter AO average < 0. 1991 and 2006 were the exceptions. In short, the current extreme block may also be an indication that the coming winter will likely see more blocking than the previous one (a theme consistent with the summer blockiness).

I agree with your thoughts Don...some of these analogs I had on my radar for a while especially the neutral enso years...October 2012 could end up with the lowest AO monthly value if it stays negative the rest of the month...

[e pluribus unum]

1979 and 2003 were the other neutral positive ENSO winters on that list, 1981 was also neutral.