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Offline Stormchaser  
#1 Posted : 08 August 2013 15:47:35(UTC)
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I figure it's close enough to the next season to start thinking about what could be on the way during autumn 2013.

I've made this a sticky - if the other mods feel it should be unstickied, I won't mind


Now then... I've not seen a lot written on autumn 2013 to be honest, but there is this fantastic video from Gavin P:

http://www.gavsweathervids.com/autumn2013v2.html

 

Elsewhere, I've seen suggestions here and there (on wunderground, for example) that the Arctic is likely to become anomalously cold soon, signalling an early start to winter - a rare occurance in recent times. This could well have quite an impact on the autumn, with any Arctic airmasses coming our way being more potent that normal.

With the signal for a wetter than average autumn that Gavin identifies, the implied mobility, coupled with signs that the Atlantic storms could track some way south of normal, suggests to me a risk of unusually cold northerly blasts on the rear flank of storm systems, possibly with a bit of a continental component thrown in for good measure.


IF the Arctic does become anomalously cold through September and October, then what happens later on in the autumn could be a very big deal, as that's when we either see the PV ramping up and taking control, or high-latitude blocking starting to take over the Arctic instead. In the former case, the cold would tend to remain locked into the Arctic, giving the ice a real boost, with rear-flank blasts being the main source of cold for the UK. In the latter case... well, then you've potentially got exceptional cold being forced into the mid-latitudes!


So there you have my thoughts - make of them what you will. I'm not making a forecast, just discussing possibilities, as is one of the purposes of this thread


If you have any problems or queries relating to TWO you can Email twomoderationteam@gmail.com :)

Homeland: Rural Mid-West Hants nearly 10 miles S of Salisbury (near Fordingbridge). More insights: https://twitter.com/peacockreports

2018's Homeland Extremes:

T-Max: 30.9*C 8th July | T-Min: -7.7*C 28th Feb | Wettest Day: 19.2mm 14th October | Ice Days: 4 (28 Feb - 2 Mar & 18 Mar)

Keep Calm and Forecast On

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Offline Gavin P  
#2 Posted : 08 August 2013 16:09:59(UTC)
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Thanks SC.

The final autumn 2013 forecast from GWV will be released later this month - The early cooling over the Arctic certainly add's an interesting aspect this year....

If sustained the immediate response in September and October may be to become rather unsettled and stormy, especially if things start kicking off in the tropics as well?

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Short, medium and long range weather forecast videos @ https://gavsweathervids.com/

Offline Matty H  
#3 Posted : 08 August 2013 16:11:49(UTC)
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I'm going for a mild and settled autumn leading into a very mild winter.

Source: Personal desire (as good as any😇)

Yate, Nr Bristol

Offline Stormchaser  
#4 Posted : 08 August 2013 18:23:46(UTC)
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Originally Posted by: Gavin P Go to Quoted Post

Thanks SC.

The final autumn 2013 forecast from GWV will be released later this month - The early cooling over the Arctic certainly add's an interesting aspect this year....

If sustained the immediate response in September and October may be to become rather unsettled and stormy, especially if things start kicking off in the tropics as well?

Looking forward to that

As for anomalously cold air draining south and clashing with ex-tropical features and their associated very warm TM airmasses...

It's just hit me that such contrasts might well be what's required for creating the top-end extreme windstorms in the UK. Does anybody know which autumns out of the past few decades have been colder than average in the Arctic? Thanks in advance for any information

If you have any problems or queries relating to TWO you can Email twomoderationteam@gmail.com :)

Homeland: Rural Mid-West Hants nearly 10 miles S of Salisbury (near Fordingbridge). More insights: https://twitter.com/peacockreports

2018's Homeland Extremes:

T-Max: 30.9*C 8th July | T-Min: -7.7*C 28th Feb | Wettest Day: 19.2mm 14th October | Ice Days: 4 (28 Feb - 2 Mar & 18 Mar)

Keep Calm and Forecast On

Offline AlvinMeister  
#5 Posted : 09 August 2013 12:25:51(UTC)
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I know we're not finished with summer, but how many of the models predicted a high pressure dominated July for us?

 

Salford, Manchester 67m ASL
Offline Stormchaser  
#6 Posted : 09 August 2013 16:11:09(UTC)
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Just posting Gavin's new video here given how relevant it is

Originally Posted by: Gavin P Go to Quoted Post

Hi all,

Here's today video update;

August/September Look-Ahead + Jan 2014 Sneak Peak;

http://www.gavsweathervids.com

All speculation of course.

CFS sure is going for an unusual September pattern, with blocking highs far more prevailent than usual. Ex-tropical storms usually make blocking tricky to sustain during the first two months of Autumn, but sometimes they can produce favourable warm air advection if the pattern shapes up in the right way for that.

It looks like a potential troublemaker for the East U.S. Coast as there could be opportunities for storms to make a left-turn much like Sandy did, turning what would be a recurve out to sea into a possible disaster.


October is then predicted to be the dawning of a new era of anomalously high polar heights. With that comes the need to keep an eye on those Arctic temperatures - could October become memorable for a northerly outbreak or two...?


November has been looking chilly to cold for a while now. As for December... well that's suddenly looking like an epic month of cold and snow, but let's not forget about the range we're now looking at! Also that's beyond autumn and for another thread about 10-12 weeks from now (going by how eager people tend to be to open a winter prospects thread!)


As a footnote and in response to AlvinMeister's question, CFS had the strongest signal for a high pressure dominated July, in fact it persisted with the idea for many months without wavering much.

The Met Office ensemble model was close behind if I recall correctly, but with heights centered more to the NE than has been the reality.

If you have any problems or queries relating to TWO you can Email twomoderationteam@gmail.com :)

Homeland: Rural Mid-West Hants nearly 10 miles S of Salisbury (near Fordingbridge). More insights: https://twitter.com/peacockreports

2018's Homeland Extremes:

T-Max: 30.9*C 8th July | T-Min: -7.7*C 28th Feb | Wettest Day: 19.2mm 14th October | Ice Days: 4 (28 Feb - 2 Mar & 18 Mar)

Keep Calm and Forecast On

Offline Charmhills  
#7 Posted : 09 August 2013 16:43:34(UTC)
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I think the CFS is on drugs for the coming winter!

Duane.

Offline Stormchaser  
#8 Posted : 09 August 2013 16:53:48(UTC)
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Originally Posted by: Charmhills Go to Quoted Post

I think the CFS is on drugs for the coming winter!

http://www.metoffice.gov.uk/images/prob_ensemble/20130701/2cat_20130701_z500_months46_global_deter_public.png

Some support from the Met Office ensemble mean. It and CFS are often not too far apart from one another, it seems.

That small positive anomaly over part of Europe takes some figuring out, though. I would say a west-based negative NAO is implied, except that the negative anomalies over Scandinavia are too far east for that.

All very interesting... and drifting off topic so I'm afraid I must shut the door on winter disucssion now *clunk*


The autumn anomalies from the above model are very similar to the Oct/Nov/Dec ones:

http://www.metoffice.gov.uk/images/prob_ensemble/20130701/2cat_20130701_z500_months35_global_deter_public.png

...which, given that two of the months overlap, implies a very persistent pattern, though with the blocking becoming increasingly focused across the Greenland area as the autumn progresses.

If you have any problems or queries relating to TWO you can Email twomoderationteam@gmail.com :)

Homeland: Rural Mid-West Hants nearly 10 miles S of Salisbury (near Fordingbridge). More insights: https://twitter.com/peacockreports

2018's Homeland Extremes:

T-Max: 30.9*C 8th July | T-Min: -7.7*C 28th Feb | Wettest Day: 19.2mm 14th October | Ice Days: 4 (28 Feb - 2 Mar & 18 Mar)

Keep Calm and Forecast On

jondg14  
#9 Posted : 12 August 2013 10:20:01(UTC)
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Is the anomalously cold Arctic a result of the PV ramping up already? If so I don't know why the Autumn LRFs are fancying high latitude blocking.

Offline bledur  
#10 Posted : 13 August 2013 17:51:39(UTC)
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well as it has been a dry summer in general i think we can expect a fair dollop of rain in september . indeed some charts are showing adrop in pressure to the s.w quite early on. october drier than september but probably quite cold. november on the cold side and foggy

but how many of the models predicted a high pressure dominated July for us?  i think maybe the cfs was but not to the extent it turned out to be.

Edited by user 13 August 2013 17:54:57(UTC)  | Reason: extras

Offline Stormchaser  
#11 Posted : 13 August 2013 18:18:49(UTC)
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Originally Posted by: jondg14 Go to Quoted Post

Is the anomalously cold Arctic a result of the PV ramping up already? If so I don't know why the Autumn LRFs are fancying high latitude blocking.

Low pressure has dominated up there for much of the past four months, and it looks to crank up a notch or two in the near future, so yes, the PV is already ramping up a bit.

Even so, certain atmospheric forcing can cause the PV to shatter quite abruptly, and it does seem that the models are expecting an event of such nature, though not really until late September or some time in October - September's +ve anomalies are almost at the mid-latitudes, with near average pressure across the pole region. The latter could indicate a change during the month up there, hence late September is possibility for the pattern shift across the polar regions.

If the shift does materialise, it will represent a change to a regime not seen since early April.

If you have any problems or queries relating to TWO you can Email twomoderationteam@gmail.com :)

Homeland: Rural Mid-West Hants nearly 10 miles S of Salisbury (near Fordingbridge). More insights: https://twitter.com/peacockreports

2018's Homeland Extremes:

T-Max: 30.9*C 8th July | T-Min: -7.7*C 28th Feb | Wettest Day: 19.2mm 14th October | Ice Days: 4 (28 Feb - 2 Mar & 18 Mar)

Keep Calm and Forecast On

jondg14  
#12 Posted : 14 August 2013 10:45:40(UTC)
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Originally Posted by: Stormchaser Go to Quoted Post

Originally Posted by: jondg14 Go to Quoted Post

Is the anomalously cold Arctic a result of the PV ramping up already? If so I don't know why the Autumn LRFs are fancying high latitude blocking.

Low pressure has dominated up there for much of the past four months, and it looks to crank up a notch or two in the near future, so yes, the PV is already ramping up a bit.

Even so, certain atmospheric forcing can cause the PV to shatter quite abruptly, and it does seem that the models are expecting an event of such nature, though not really until late September or some time in October - September's +ve anomalies are almost at the mid-latitudes, with near average pressure across the pole region. The latter could indicate a change during the month up there, hence late September is possibility for the pattern shift across the polar regions.

If the shift does materialise, it will represent a change to a regime not seen since early April.

Thanks for the reply. Very helpful.

So I guess a SSW is one such event that can lead to atmospheric forcing capable of disbanding the PV. Obviously though it doesn't have to be a SSW but the models are picking up on something.

caldog  
#13 Posted : 14 August 2013 13:50:49(UTC)
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Hi there, new here, looks like a great community. 

I admit I am nothing more than an amateur on this subject, but looking at Netweather's forecast for september it would seem that they are going for a higher than normal pressure over most of the UK and below average precipitation. 

I am attempting to provide a link with this, but my browser is being difficult, so I will attempt to do so again later. However, as stated on the website this chart is produced with very low confidence. Having occasionally viewed this forum over the last yar or two, I am guessing that they are not particularly reliable. 

Having had a look at the Meto surface pressure charts for the next few days, it is clear that there is not really anything that can really get in the way of the Atlantic low pressure coming in from the south west for the moment. In particular anything from the east or south. If anything, I would expect there to be a fair amount of low pressure from the north west at that stage. 

Again, having said I am an amateur, I am going to have to go for a gut feeling on this one, which is cool and average precipitation. 

ManUtdMatt1986  
#14 Posted : 14 August 2013 14:07:57(UTC)
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I put quite a bit of trust in the upgraded CFS model (the old version was rubbish) as it consistently showed a cold spring 2013 months in advance, picked up on high pressure being dominant in July weeks in advance and was showing another rise of pressure over the UK for the latter part of August back in July.

Like all long range models, the CFS will be prone to error but it is handy when looking for trends I find so I would put some trust in its take on things for the coming Autumn

caldog  
#15 Posted : 14 August 2013 14:23:30(UTC)
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Originally Posted by: ManUtdMatt1986 Go to Quoted Post

I put quite a bit of trust in the upgraded CFS model (the old version was rubbish) as it consistently showed a cold spring 2013 months in advance, picked up on high pressure being dominant in July weeks in advance and was showing another rise of pressure over the UK for the latter part of August back in July.

Like all long range models, the CFS will be prone to error but it is handy when looking for trends I find so I would put some trust in its take on things for the coming Autumn

If it is a new version then I am all for giving it a chance :) I remember having a look at the old version of CFS a couple of years ago, and it seemed like it was repeatedly wrong. You can probably see why I wanted a bit of consensus on the new version before making my mind up! As always with forecasts though, I tend to take them with a pinch of salt. :)

ManUtdMatt1986  
#16 Posted : 14 August 2013 14:46:09(UTC)
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Originally Posted by: caldog Go to Quoted Post

Originally Posted by: ManUtdMatt1986 Go to Quoted Post

I put quite a bit of trust in the upgraded CFS model (the old version was rubbish) as it consistently showed a cold spring 2013 months in advance, picked up on high pressure being dominant in July weeks in advance and was showing another rise of pressure over the UK for the latter part of August back in July.

Like all long range models, the CFS will be prone to error but it is handy when looking for trends I find so I would put some trust in its take on things for the coming Autumn

If it is a new version then I am all for giving it a chance :) I remember having a look at the old version of CFS a couple of years ago, and it seemed like it was repeatedly wrong. You can probably see why I wanted a bit of consensus on the new version before making my mind up! As always with forecasts though, I tend to take them with a pinch of salt. :)

I think the new version  (CFS V2) is pretty good for long term trends, and much better than the old one (CFS V1). Poor for the specifics but then it was designed more toward picking up long term trends.

Offline roger63  
#17 Posted : 15 August 2013 09:07:59(UTC)
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http://www.cpc.ncep.noaa.gov/products/CFSv2/htmls/euT2me2Mon.html

This seems to be the latest CFS temperature output output.Looks pretty average over the UK .Postiive temp anomaly over SE Europe mainn feature.

Offline roger63  
#18 Posted : 15 August 2013 09:33:01(UTC)
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http://www.metoffice.gov.uk/research/climate/seasonal-to-decadal/gpc-outlooks/glob-seas-prob#20120901&months46&global&temp2m&3up

Just a follow on the latest 3-5 month  European temperature forecast from METO.( you need to set to july 2013 date)

Suggests a warmer than average Autumn.Also cant see any sign of a cold Arctic ( or is it off the map?)

Edited by user 15 August 2013 09:37:23(UTC)  | Reason: Not specified

Offline nouska  
#19 Posted : 15 August 2013 10:02:24(UTC)
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Roger, that is not the most recent run of the CFS - you need to use E3 for latest run.

A look at both models for the same parameters shows the expected Arctic anomalies in similar positions.

http://i.imgur.com/z6G8T6x.png

http://www.cpc.ncep.noaa...esInd3/glbT2mSeaInd2.gif

Offline Stormchaser  
#20 Posted : 15 August 2013 10:03:51(UTC)
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http://www.cpc.ncep.noaa.gov/products/people/wwang/cfsv2fcst/imagesInd3/glbz700MonInd5.gif

Can't really trust those 2m temp. projections from CFS... I mean, it shows a positive temp anomaly from the above 500mb anomaly setup!

That's probably down to it overcooking the Atlantic - it nearly always has raging storms in the Atlantic even during periods of strong high-latitude blocking.

That's why I only really pay attention to the 500mb anomalies, because if it does show anomalous high-latitude heights, then we can more realistically interpret what that would really mean over what the model actually comes up with at the surface.


Looking at the Met Office probability outlook, the overall signal does to be for an Autumn more settled and warmer than averagem though it's not a very strong signal once you factor out the 2m temp anomalies shown over the oceans (those depend largely on the SST anomalies and won't respond so readily to pattern changes).

The high-Arctic i.e. close to the Pole is not visible on those maps. I think the signal for at least the first part of the Autumn is for the cold to remain locked into the Arctic close to the poles thanks to a notable Polar Vortex.

If you have any problems or queries relating to TWO you can Email twomoderationteam@gmail.com :)

Homeland: Rural Mid-West Hants nearly 10 miles S of Salisbury (near Fordingbridge). More insights: https://twitter.com/peacockreports

2018's Homeland Extremes:

T-Max: 30.9*C 8th July | T-Min: -7.7*C 28th Feb | Wettest Day: 19.2mm 14th October | Ice Days: 4 (28 Feb - 2 Mar & 18 Mar)

Keep Calm and Forecast On

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