Much of summer 2013 has been dominated by a POSITIVE AO and NAO which presented a warm to hot July across Europe but this setup also produced a cold summer across the pole which explains why the sea ice is more extensive this year compared to last. These results will likely support a mixed autumn season with an increased chance of an early start to winter.

In this Autumn 2013 Outlook I shall show you what the CFS, CFSv2 and Jamstec model are showing September through November and the 3-months collectively as well as share with you the reasons for why I think what I’m thinking.

Firstly lets look at both AO and NAO and you can see the general trend since spring has been for a positive signal which supports warmth and ridging over Europe with cold bundled up over the Pole which has allowed a much more extensive arctic sea ice cover this summer compared to recent years. However, it remains well below the normal thanks to the warm AMO.

AO

NAO

Notice the positive in both signals from late June through late July when Europe was hot then the signal went negative and we saw the return of cool and unsettled.

You can also see that we’re now entering a strongly positive NAO but the AO interestingly is in fact going negative. This means cold WON’T bundle quite as much over the pole but with a strong positive NAO, the warmth and mean ridge returns to the UK and Western Europe this week into next.

The warmth and mean ridge will linger as long as the NAO stays firmly positive and there is confliction as to how long it holds positive. I suspect it holds through till the end of August then dips and we enter another spell similar to August which brought more Atlantic driven conditions with wind, rain and near normal temperatures. Some spells of warmth followed by heavy rains which could bring flooding from Ireland to Scandinavia down through the Low Countries and into France.

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Below is the latest CFS forecast for September.

September

500mb heights

Temperature Anomaly

Note the model has average temperatures.

As for October, well models are now hinting at a cold month with the mean trough firmly positioned over Western Europe as the NAO and AO is seen to go negative. With the cold building early across the pole and the atmosphere shifting with a southbound jet stream. The feedback of warm SST’s combined with colder than normal conditions over the arctic may bring on that negative AO/NAO which could bring an early taste of winter and the coldest October to Western Europe since 2008. Eastern Europe would be above normal.

Below is the CFS forecast.

October

500mb heights

Surface temperature anomalies

As for November, well the CFS as well as CFSv2 is going all out for a very cold November with even stronger northern blocking than in October with a colder than normal month across most of Europe. Below is the CFS forecast for November. This is hinting at a tanking of both AO and NAO and would likely support cold and snow for much of the continent including the UK.

November

500mb heights

Surface temperature anomalies

While I agree with the overall idea in the long range models, their timing remains uncertain. November was originally warm, now it’s cold and December was originally cold then warm and now back to cold. The seasonal transition with the current water temperature and arctic sea ice profile keeps things uncertain.

Given the current setup, trends and SST’s I believe October is likely to be cold but there is a tendency for another positive NAO/AO episode and while November has a chance of being cold and not unlike 2010, it could just as easily be warm and wet with a positive NAO/AO like we had in 2009. For those with hope of a cold, snowy winter, November can be a good time to get that AO/NAO positive which will allow the arctic reservoir to reload following the chilly October.

Here is December

500mb heights

Surface temperature anomaly

My hunch is that November will be normal to above normal in temperature with above normal precipitation, most of which falls as rain following a cold October in which we could see early snows like we saw in October 2008. December may start warm like in 2009 but then through the month we could see a strong stratospheric warming event which leads to a real deep negative AO/NAO episode which takes us into January 2014.

Want to see the CFS January temperatures?

As for precipitation. Once the blocking setup develops, rainfall will become less through spring but as Joe Bastardi once told me. Where the heaviest rains fall during autumn, that’s where your trough and cold aims for. Another good reason why I think you’d be hoping for a warm and WET November just ahead of the coldest period of the year.

CFS Precipitation

September

October

November

Jamstec Forecast

SST’s

Sept-Nov

Surface temperatures

Linking Autumn With The Upcoming Winter

As you can see from the below chart. Arctic sea ice is far more extensive this summer compared to recent times but remains well below normal. It’s still only mid-August and the minimum has yet to occur but given the chill up across the arctic, there may or may not be much more melting. This year’s extent compared to recent years shouldn’t be overlooked for impact later down the road.

Here’s a comparison in Arctic sea ice extent between September 15, 2012 and August 15, 2013. Despite this year remaining well below normal and levels of 1980, 1990 and 2000, What a huge difference!

I am using 2009 as an example but may in fact become an analog year as there are similarities to this year.

I want you to look at the next comparison chart below between September 15, 2009 with August 15, 2013. Note there’s a lot more ice in 2009 but less than this year, however it’s much thicker than our larger but thinner coverage.

The reason I mention this is because a few claimed last weekend that more arctic sea ice this year would ultimately produce less blocking but I’m afraid these are claims without any understanding of the big picture and nothing to back up them. 2009 produced record high latitude blocking despite sea ice being MORE EXTENSIVE than early autumns of 2007 and 2012. In other words there doesn’t need to be barely any ice up there to promote strong blocking. In fact I believe you need enough to produce an adequate reservoir of cold air and less sea ice means less cold. So when and if you have high latitude blocking. The cold that heads south isn’t as potent or severe as there would be if you had a colder summer and autumn. Like anything, it’s all about balance.

Like 2009. This year has the potential to be very interesting with enough ice to allow cold to build faster and stronger but enough surrounding warmer-than-normal waters and the tripole of warm-cold-warm in the North Atlantic to produce the blocking and quite the winter further south.

Despite the more extensive arctic sea ice. It remains BELOW NORMAL as already stated thanks to the positive AMO. Check out the global SST’s below between mid August 2009 and this year. Look at how warm the waters are up across the arctic still. Both years have a lot more sea ice than 2007 and 2012 despite being well below normal with well above normal SST’s.

As for last winter. The early and mid point was warm for North America with spells of cold surrounded by warm over Western Europe (decent spells of severe winter over central/eastern Europe though). Was the arctic sea ice too minimal in autumn? Do we need more extensive summer/early autumn sea ice in warm AMO years like we have now to produce winters like 2009-10? Let’s remember, winter 2009-10 didn’t get going till around December 15 and after that we saw repeated cold and snow which was interrupted by short lived spells of mild. As for 2010 which was the coldest December in 100 years for the UK, it got off to a fast start in November and lasted till New Year then winter ultimately ended as the La Nina came on. The following winter simply never got started in Western Europe but it was a very different story over the continent extending into Asia. North America saw a warm winter!

While we have a long way to go. I believe that given the evidence in front of me with the current ENSO index which remains largely neutral, the trend of the NAO/AO. The extent of summer sea ice and continued chill that will remain up there and the type of water temperature profile we have not only surrounding the UK and across the Atlantic but globally… all this points to a colder-than-normal winter here in Western Europe with strong blocking episodes. While high latitude and North Atlantic blocking looks likely and may last long periods of time like we saw repeatedly in 2009-10 as well as the early part of 2010-11, the key will be exactly WHERE that block sets up. Too close to the UK and you’ve got another winter like 2011-12.

Just how cold and when will the cold come, go and stay remains very much an open question at the moment but will work on timings etc through the next couple of months and present this information to you in my winter forecast at the end of October.

Here are SST comparisons between August 17, 2009 and now.

2009

This year!

Not a whole lot of difference…

As mentioned many times over. For a good SST profile which supports a Greenland block, your looking for warm-cold-warm over the North Atlantic and check out both the Jamstec and CFSv2 water temperatures for winter.

The ENSO is expected to stay neutral, perhaps even rise enough to produce a weak Nino. This supports a cold winter, especially mid to late winter!

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Tags: Autumn 2013 Forecast, Europe Autumn forecast 2013, Fall Forecast 2013, UK Autumn Forecast 2013