We’re now entering deeper into autumn with winter fast approaching. October is pushing ever closer and this transitionary month can be a critical telltale month as to what we may expect later down the road. It was Joe Bastardi a few years back who said to me that often (not always), where the wettest weather and trough sets up during October/November is often where the cold will focus on during that winter. This occured beautifully in November 2009 which was a weak El Nino year which had a mostly negative NAO summer, like we’ve seen this year.

The summer of 2009 has good similarities to this year with the cold PDO, weak warm AMO, weak Nino, negative biased NAO which lead to a similar summer. Though undoubtedly this summer has been far more extreme in terms of UK rainfall and US heat, perhaps due to the colder, PDO and warmer AMO as well as the flip between the back to back la nina to el nino.

I wanted to post on what the models are currently showing and quite frankly, right now they’re all over the place but remember that they’re changing all the time so they aren’t the best guidance tool in my opinion.

What is a better form of guidance is looking at the current players against a similar setup in the past.

Water temperatures play a major role and right now it’s worth showing you Sept SST anomalies with recent nino years.

This year’s Sept SST’s.

Notice the horseshoe of cold over the North Pacific showing the strong cold PDO signal. The warmth along the Central America/South America coast indicative of the El Nino.

Here was 2009 around this time when there was a similar weak el nino.

Notice (2) key differences between this year and 2009. 1) the Pacific was warmer, 2) the north Atlantic was colder so the two major influences (PDO and AMO) are stronger in the opposite direction.

Despite the cold PDO and warm AMO last year, the la nina significantly cooled the Pacific with this years el nino development and likely reaction to the cooling. This ‘reactive el nino’ within a cold PDO also happened in 2009. Reactive because la ninas are far more likely within a cold PDO and they tend to be weak and centrally based which leads to colder conditions over the US with jet stream pahsing leading to storminess across the Southern and Eastern US. In 2009, November was mild to warm with a mainly zonal flow with a positive NAO and AO. This allowed the cold to build over the arctic and I believe this is beginning to set up this year too but there could well be some troughs which drop into particularly the western US like we saw with the coolish October in 2009. That winter shaped up to be quite the cold season for both sides of the Atlantic as well as across large parts of Europe and Asia.

Here is what the SST’s where in late December 2009.

Notice the significant cooling of the north Pacific and the tripole of warm-cold-warm over the north Atlantic. Why is that significant? The Atlantic tripole is well known to favour blocking and the autumn saw a positive NAO/AO before the dramatic flip to negative and it remainded mostly negative throughout that winter to near record values. Could we see a similar SST profile in both Pacific and Atlantic this year?

Here’s what the Jamstec model showing SST’s for this winter (DJF).

There is clear similarities between 2009 and this winter IF the Jamstec model is correct with seeing the tripole favouring blocking as well as the cold north Pacific and the central based el nino.

Below is the mean 500 mb height anomalies for this winter off the Beijing model.

Notice where it has strongest heights in the means for winter, right where water temps are warmest over the Davis Straits and Greenland so it’s seeing the blocking. However, what it has in terms of air temps doesn’t make sense given it’s upper air pattern.

Below is what the latest Jamstec model has. Notice the warmth in the north. Again it’s seeing the blocking with practically all of the Lower 48 well below normal but the Northeast is slightly above normal. That I disagree with too given where the blocking is likely to set up. I also think there is colder over northwest and northern Europe.

To conclude,

I think this autumn will present storminess with a spell of negative in the NAO and AO during October but right now it’s going positive with medium range models showing a flattening out of the upper flow across the hemisphere. Storminess with a rollercoaster in temperature is likely. We could see a spell of very wet weather again here in the UK and over large parts of the US East.

The winter is likely to be cold and snowy across parts of the South and Eastern US with frequent blasts of arctic cold coming down from northern Canada. A period between mid December and mid January could be very cold with perhaps a major East coast blizzard followed by an arctic outbreak which locks in as a major stratospheric warming event covers the pole. The UK could also see this with a strongly negative NAO. So, for us here in the UK, we could see several days with snowfall followed by major cold. Like in 2009-10, we’re likely to see repeat spells of snow followed by cold which lasts through March. In between there will be short lived warm spells but cold is never far away.

Tags: europe winter forecast 2012-13, uk winter forecast 2012-13, united states winter forecast 2012-13, us winter 2012-13