Winter 2016/2017: Preliminary Prediction

[iapennell]

As promised I have piece together macroscale developments of sea-surface temperature and regional wind/pressure anomalies to provide a preliminary forecast for the coming winter.During October the global winds, pressure and temperature-patterns across the Northern Hemisphere gravitate towards their winter states, which they will tend to retain until late March.

First thing though we need to list what we know so far:

1) Sea surface temperatures are, in general well above normal across the North Atlantic with anomalies close to 4C for early October in the European Arctic section with anomalies of +6C off the eastern coast of the USA and in the Baltic. The section is part of the mid-North Atlantic about 45 to 55N and 20 to 40W where sea surface temperatures are up to 2C colder than usual. Such warmer than usual waters around the UK would directly warm any winds blowing over them more and would tend to support milder weather and more evaporation from the warmer seas would support increased rainfall. The cool patch in the North Atlantic is sufficiently far west for it to cause the southern part of the strong upper Westerlies to re-curve south over it and just to the east whilst the upper air would be encouraged to "re-curve" northwards having crossed the warmer waters around Britain: This would place an upper trough near to the UK and enhance wet, windy weather.  

2) The North Pacific north of 20N is substantially warmer than normal with sea surface temperature anomalies generally 3 to 4C warmer than normal for early October. However the Equatorial central and eastern Pacific is colder than usual with anomalies up to 2C below normal. The development of La Nina with cool equatorial waters would promote weaker north-easterly Trade Winds over the Pacific between the Equator and a weaker subtropical high-pressure belt centred over warmer than usual waters of the North Pacific around 30 to 35N: Weaker NE Trade Winds impart less westerly atmospheric angular momentum (AAM) to the Northern Hemisphere's atmospheric circulation through frictional interaction with the sea-surface- particularly as less wind means a calmer sea-surface with very low coefficient of friction. There is correspondingly need for less of a sink for accumulated westerly momentum in higher latitudes which implies weaker westerlies reaching Britain with a correspondingly higher chance of cold-air outbreaks from Russia or the Arctic. 

3) Arctic sea-ice extent has recovered remarkably during September and it's extent is close to the seasonal norm east of Greenland but the sea-ice extent remains some 500 km north of its normal October extent north of Alaska and the extreme east of Siberia. Open waters in the Arctic Ocean surrounding the sea-ice remains substantially (i.e. widely up to 4C warmer than normal for October however): This is likely to encourage the Circumpolar Vortex to be contracted as well as displaced towards the UK by up to 200 km, however the warmth of Arctic seas would encourage the strong baroclinic gradients to be shifted towards the Arctic. This lends support to deeper depressions encircling the Arctic close to 70N, particularly in the North Atlantic sector and the warmth of the oceans just to the south of them means rather more moisture latent-heat potential to fuel these storms. The northwards displacement of the Westerlies is likely to encourage them to be strong in any case because they have to blow harder closer to the axis of the Earth's rotation to offset the tropical, subtropical and polar easterlies as required by Conservation of Angular Momentum laws.

4) Also supportive of a mild wet and windy winter is the fact that the Quasi Biennial Oscillation (QBO) at 30mb high above the Equator remains in Westerly phase. During August these stratospheric Equatorial Winds averaged just over 10 metres per second (23 mph) from the west. These stratospheric winds feed down into the general circulation and reach the mid-latitude jet-streams and Westerlies over three or four months. This suggests (strongly) that the coming winter will be mild wet and stormy.

5) The Sun is now entering the quiet phase towards the end of Schwabe cycle 24: Indications are that the Sun is indeed going quieter than it has been for a few years. An active Sun produces Solar Flares which interact with the atmospheric circulation to increase the strength of the Circumpolar Vortex. Instead few (if any) magnetic storms from the Sun will be interacting with the Earth's atmosphere and instead (if anything) that just leaves tidal friction due to the Sun and Moon which affects the atmosphere as well as the oceans. The tidal effects on the atmosphere are very weak but these act to reduce the Earth's rotation by very mall amounts (these are significant over time, which is why Leap Seconds are added at the end of each year). The net effect of all this (weak phase of Solar Cycle, atmospheric tidal friction) would be to weaken the Westerlies a little.

6) At least until mid November, the fact that sea-surface temperatures in the tropical Atlantic and Pacific just north of the Equator is likely to enhance tropical storm activity. More hurricanes and typhoons with strong easterlies on their northern flanks that enter the Northern Hemisphere circulation add Westerly AAM to the global atmospheric circulation. This increases the need for stronger Westerlies in higher latitudes to counter-balance them: This strongly hints to late autumn/early winter being wet, mild and stormy. However, from late January onwards the Intertropical Convergence Zone (ITCZ) will be south of the Equator and the fact that sea-surface temperatures in tropical waters just south of the Equator are also warmer than normal now suggests more tropical storms will occur there; Southern Hemisphere tropical depressions (sliding westwards along the ITCZ) have strong westerlies on their northern flank and it is these that will affect the Angular Momentum Budget of the Northern Hemisphere circulation by removing Westerly AAM through frictional impact with the underlying surface: This points to weaker Westerlies coming across the North Atlantic in January/February which would, other things being equal, increase the chances of much colder, drier spells reaching Britain from the east.  

We can now put all this together to get some sort of prediction for Winter 2016/17:

(Continued below)

[iapennell]

continued.)

The warmth of the North Atlantic, the QBO and the northward displacement of baroclinic zones are likely to be the defining influences on Britain's weather (at least through until December). However, the seasonal weakness of the NE Trade Winds combined with the northwards displacement of the main baroclinic temperature gradients is encouraging a strong blocking high to persist over Scandinavia. This will bring a good deal of dry and quite warm weather by day to England and Wales on south-easterly winds through clear nights will be chilly; however there will be no widespread air-frost as yet. This weather looks set to extend into Scotland for a time though here it will be colder. This takes us up to the third week of October and (incidentally) I hinted at a dry cool spell with easterly winds in my first autumn prediction on the basis of the QBO at 50 mb being easterly and the patch of cool water that was (at least in the summer) in the NE Atlantic and I downplayed the prediction of the cool dry easterlies in October with the updated forecast in early September when the QBO turned Westerly and the patch of colder-than-normal water in the North Atlantic melted away only to re-appear later much further west!

From about 18th October onwards things will go downhill rather rapidly as the strengthening Circumpolar Vortex across the North Atlantic shifts it's centre towards Britain a bit and the central Arctic, NE Canada and Greenland quickly become very cold: The contrast between the much colder atmosphere over Greenland and NE Canada and much warmer waters a little further south and east will result in fairly intense baroclinicity with deep depressions pushing east along the sharp temperature gradients. Further tropical storms and the QBO in Westerly phase can only lead to intensification of these storms. However, the pool of cold water in the North Atlantic is liable to shift the southern part of the Circumpolar Vortex southwards and lead to some depressions moving east further south and making a bee-line for Britain; this means all parts of the country are likely to take a battering whilst Scotland and northern England will have quieter chillier weather with fog and ground frost when depressions take the most southerly routes.

So late October-November is likely to be mild and substantially wetter than normal in almost all regions of the United Kingdom with prevailing south-westerly winds. Frost is likely to be infrequent at best and I am not expecting an air-frost for most of us until November. East Anglia and SE England are likely to be the driest and (probably) the only regions not to have rainfall above normal during this period, that said the southerly route of some depressions means that even in these areas there will be substantial rainfall at times- good news for those locations that have suffered water shortages over the summer. On the other hand SW England, Wales, NW England, Northern Ireland and SW and NW Scotland can expect frequent onslaughts of gales and heavy rain with localised flooding, particularly during November. The first snows of winter are likely to occur above 500 metres' elevation in Scotland and northern England by mid-November, most likely when depressions on a more southerly track bring chillier north-westerly winds in their wake.

Summarily: October 2016 England and Wales. Mean temperature (lowlands) of 12C, Rainfall 75 mm; Scotland (lowlands) 10C, Rainfall 120 mm

November 2016 England and Wales: Mean temperature (lowlands) of 8.5C, Rainfall 140 mm; Scotland (lowlands) 6C, Rainfall 160 mm.

In December there is likely to be small changes to the Westerlies affecting Britain: Above-normal sea-surface temperatures in the Mediterranean (currently +3C or above), cooling over continental Europe and the cool patch in the mid North Atlantic is likely to weaken the westerlies coming into Britain as more depressions get diverted along the southerly wave-train of the Circumpolar Vortex further south (thanks to cooling over Europe and the North Atlantic cool patch). The end of the hurricane season will also help to bring about slightly weaker Westerlies. However, the QBO (currently westerly at 30 mb over the Equator) and the warmth of the far North Atlantic combined with the fact that by December NE Canada, Greenland and the Arctic interior will be extremely cold means some very deep depressions will be racing east in the vicinity of Iceland. As a consequence, December 2016 looks like it will be dominated by strong west or SW winds, frequent gales in the north and west and above-normal temperatures. South as well as north will take a battering but after mid-December there is a stronger hint of colder drier conditions from continental Europe as the depressions on the more southerly routes are diverted into the Med and cold easterlies on their northern flanks eventually establishes cold frosty high-pressure conditions over central Europe. There is likely to be clear frosty weather with localised freezing fog for the Midlands, Yorkshire and eastern England but Scotland will remain under the influence of strong Westerlies bringing rain and (at times) hill snow above 600 metres' elevation.

Summarily: December 2016 England and Wales. Mean temperature (lowlands) of 6C, Rainfall 130 mm; Scotland (lowlands) 5.5C, Rainfall 150 mm.

January and February 2017 look like producing the coldest weather of the winter although temperatures are still likely to be above average on the whole. The relative warmth of the far North Atlantic for the season is unlikely to have "cooled out" completely by then and the Arctic and NE Canada will be at their coldest: The resulting strong baroclinic zone is only ever likely to spawn deep depressions and these will ensure that the prevailing wind-direction over the UK will be west or south-westerly. Gales and high rainfall will still occur frequently in the north-west and most of the time temperatures will be above-average elsewhere. That said, La Niná in the Equatorial Pacific, the likelihood of Southern Hemisphere tropical depressions whose westerlies will have impacts reducing westerly AAM in the Northern Hemisphere circulation as a whole and the Sun entering a quiet phase will act to counter the QBO Westerlies high above the Equator that would impart vigour to the Circumpolar Vortex. There is no doubt therefore, that despite the very strong baroclinic gradient between Greenland/NE Canada and the North Atlantic that the Circumpolar Vortex will be a bit weaker and focus returns to the North Atlantic cold pool (assuming, of course it is still there- and this quite likely because strong west winds off icy Canada over that part of the North Atlantic has a cooling influence in winter). The North Atlantic cold pool is likely to divert the southern portion of the Circumpolar Vortex south-eastwards and then further east colder conditions over Europe are liable to ensure it moves over the northern Mediterranean and the cyclogenesis there will encourage easterlies over central southern Europe at times which will pull cold air west from Russia, but the (likely) strength of the northern portion of the Circumpolar Vortex will discourage blocking high-pressure over northern Scandinavia. 

What this means, then is that central Europe will be under the influence of a westwards extension of the Euro-Asiatic winter high-pressure belt with very cold air at times during the latter part of the winter and this is likely to bring spells with much colder south-easterly winds to England and Wales at times during January and February. The coldest and most-persistent of these spells (likely to be in early February 2017) will bring minima below -5C widely across the region with daytime temperatures struggling to get above freezing point. The passage of this cold air across the North Sea will lead to shallow convection and some snow-flurries from London northwards to Yorkshire and coastal NE England. Inland it will remain dry and clear with localised freezing fog patches at night. More widespread snowfall over England is likely to be at the end off such cold spells as milder moist south-westerlies pushes against the very cold air still near the surface and as such lying snow will be short-lived and tend to thaw quickly as the mild south-westerlies sweep in at the surface.

Before we get too excited though, the strength of the Circumpolar Vortex (the northern parts of it, that is) is likely to prevent icy south-east winds reaching most of Scotland and Northern Ireland where mild, strong Westerlies will remain very much in charge and where (consequently) rain gales and mild temperatures will remain the order of the day. That said, colder westerlies following the passage of deep sub-arctic depressions eastwards will bring regular snowfall to Scotland above about 400 metres' elevation and conditions will be arctic at times on the highest summits. Even further south mild south-westerlies will occur more frequently than cold south-easterlies and these will bring mild temperatures (maxima of 10C or more at times) and (to the west) heavy rain and gales. Owing to their likely proximity to high-pressure over Europe much of the time East Anglia, Yorkshire and SE England are likely to be a little drier than usual in January and February.

February is also likely to be when Scotland gets it's coldest weather- it is liable to come on north-westerly winds following the passage of one or two deep depressions to the north of the country. Such cold is likely to be sharp but short-lived with a day of widespread snow-showers followed by a frosty night or two as a ridge of high-pressure moves in, temperatures will drop below -5C at least once during the month over most of northern Scotland.

Summarily: January 2017 England and Wales. Mean temperature (lowlands) of 5C, Rainfall 100 mm; Scotland (lowlands) 5C, Rainfall 140 mm.

February England and Wales. Mean temperature (lowlands) of 4.5C, Rainfall 90 mm; Scotland (lowlands) 4C, Rainfall 130 mm.

The predictions are fairly preliminary at this stage, this being 5th October.  If and when any of the fundamentals underpinning the prediction change in any major way I will update this forecast for Winter 2016/2017.   

[northwestsnow]

Thankyou for taking the time and effort in posting this Ian-

[skifreak]

Well winter 2014 was milder than the poor winter of 2012 in the Scottish mountains. No lift served Snowsports the whole of March in 2012, unprecedented since commercial operations begun. Yet 2 years on an even milder winter delivered the most snow to Western mountains in living memory. A re-run of 2014 I'd take (going to get lynched by most for saying that probably)!  

[Ravelin]

38 minutes ago, skifreak said:

Well winter 2014 was milder than the poor winter of 2012 in the Scottish mountains. No lift served Snowsports the whole of March in 2012, unprecedented since commercial operations begun. Yet 2 years on an even milder winter delivered the most snow to Western mountains in living memory. A re-run of 2014 I'd take (going to get lynched by most for saying that probably)!  

Not by me. Although that winter was relentlessly wet even on the East coast of Scotland, which normally benefits from the 'rain shadow', I've never seen snow depths so deep at Glenshee. The problem then of course was getting there when it wasn't blowing a hoolie.

Ian, thanks for the forecast, even if personally I hope it's wrong I do appreciate the effort it must have taken to compile.

[iapennell]

Gavin's latest update for the Winter going for a milder than normal season again this year. Interesting that he makes reference to the weak La Nina, the Westerly phase of the QBO and sea-surface temperatures being above normal in the North Pacific. The position of the "Cold Blob" in the North Atlantic being supportive of a mild wet winter because it locks the Polar Front Jetstream into a pattern that sweeps deep depressions to the north of Britain is also interesting. 

These factors, along with likely Sunspot activity (which Gavin also covered), are the ones to look at in making a long -range seasonal forecast at this time of year. You can watch Gavin's prediction for the coming Winter here :

 

[seaside 60]

Thanks for your time in this expansive forecast.

Always a pleasure to read.

Can you tell me against yours and Gavin's ideas, why the MO are hinting at what appears to be quite consistently pointing towards high pressure to the north and lower pressure to the south.

Its a constructive question, does the EC 42/ Glosc see some thing we/you don't or is it just numbers which are likely to change.

To be fair they have been pretty good in recent times.

[karyo]

On 10/10/2016 at 08:20, seaside 60 said:

Thanks for your time in this expansive forecast.

Always a pleasure to read.

Can you tell me against yours and Gavin's ideas, why the MO are hinting at what appears to be quite consistently pointing towards high pressure to the north and lower pressure to the south.

Its a constructive question, does the EC 42/ Glosc see some thing we/you don't or is it just numbers which are likely to change.

To be fair they have been pretty good in recent times.

From what I read from posters who access to those long range models, the ECM seasonal goes for high pressure to the north and low to the south as you say but the latest Glosea update has gone back to a mild winter. The November update will be crucial. 

[weirpig]

16 minutes ago, karyo said:

From what I read from posters who access to those long range models, the ECM seasonal goes for high pressure to the north and low to the south as you say but the latest Glosea update has gone back to a mild winter. The November update will be crucial. 

It all depends what you mean by Mild Karyo,  The Glosea is a watered down version of the September update which mainly goes for average conditions across the Uk,  However far to early to call  what the seasonal outlook well be, never mind trying to put temperature values and rainfall amounts  on each month

[Nick L]

23 minutes ago, karyo said:

From what I read from posters who access to those long range models, the ECM seasonal goes for high pressure to the north and low to the south as you say but the latest Glosea update has gone back to a mild winter. The November update will be crucial. 

Wouldn't say it's crucial, doesn't really have any bearing on what's actually going to happen and may well be completely wrong.

[karyo]

1 hour ago, Nick L said:

Wouldn't say it's crucial, doesn't really have any bearing on what's actually going to happen and may well be completely wrong.

As it is the last update before winter starts it is crucial. 

[karyo]

1 hour ago, weirpig said:

It all depends what you mean by Mild Karyo,  The Glosea is a watered down version of the September update which mainly goes for average conditions across the Uk,  However far to early to call  what the seasonal outlook well be, never mind trying to put temperature values and rainfall amounts  on each month

Ian F said it was going for above average temperatures (albeit slightly) so that's in the mild category. Still better than last winter of course.

[Methuselah]

17 minutes ago, karyo said:

As it is the last update before winter starts it is crucial. 

Crucial to what, karyo?

[feno13]

37 minutes ago, karyo said:

Ian F said it was going for above average temperatures (albeit slightly) so that's in the mild category. Still better than last winter of course.

Could you post the link to where Ian has said it is going for above average temps please . I can not find anything on netweather or twitter. Cheers Darren

[Nick L]

43 minutes ago, karyo said:

As it is the last update before winter starts it is crucial. 

But why? For forecasting purposes perhaps but it will have absolutely no bearing on the winter itself.

[karyo]

7 minutes ago, Nick L said:

But why? For forecasting purposes perhaps but it will have absolutely no bearing on the winter itself.

It won't affect the winter outcome of course but it has done pretty well in recent years. 

[karyo]

17 minutes ago, feno13 said:

Could you post the link to where Ian has said it is going for above average temps please . I can not find anything on netweather or twitter. Cheers Darren

ENSO thread p 34: 

 

[bobbydog]

1 hour ago, karyo said:

Ian F said it was going for above average temperatures (albeit slightly) so that's in the mild category. Still better than last winter of course.

No he didn't, to quote Ian-

"Ah, but still looks a pretty interesting winter period, for various reasons. Some key differences versus EC, but still quite distinct from the output we were looking at this time last year, for winter 15-16!

November is always the more critical point when we expect (hope!) to see closer consensus between these models. Still a way to go before it's worthwhile hanging hat on any particular broad outcome for this winter."

[lassie23]

More importantly I have so far scored a big fat zero on the October Fog Index

[Grimers]

I just think it will snow at least once this Winter here.

Edited October 12, 2016 by Grimers

[karyo]

Bobbydog, if you see at the comment he made before the one you quoted you will see that the Glosea doesn't agree with the ECM sadly. Fingers crossed for a better November update.

By the way, thanks for posting his second quote which also confirms that November is the critical (I said crucial) point! Somebody nobody questioned him when he used that word :-)

[Nouska]

26 minutes ago, karyo said:

Bobbydog, if you see at the comment he made before the one you quoted you will see that the Glosea doesn't agree with the ECM sadly. Fingers crossed for a better November update.

By the way, thanks for posting his second quote which also confirms that November is the critical (I said crucial) point! Somebody nobody questioned him when he used that word :-)

I would not get too hung up on what the seasonal models are showing at this stage of Autumn. Mr Fergusson mentions three models - the three that were used in the winter '15/'16 forecast - how did they perform for last winter from the early November run?

GloSea5, ECMWF and Met France monthly mean sea level pressure for December, January and February. Below, the reanalysis for each of the months.

As you can see, there were months/models well off the mark with their November runs. Because the models run regularly throughout winter, we get updates and these tend to skew perceptions that the early forecast was better than it actually was.

 

 

[karyo]

From the above I can see that Meteo France was way off the mark but Glosea and ECM did reasonably well.

That's what I see. I am not expecting any model to get it spot one but that two did well.

 

[DAVID SNOW]

2 hours ago, karyo said:

Bobbydog, if you see at the comment he made before the one you quoted you will see that the Glosea doesn't agree with the ECM sadly. Fingers crossed for a better November update.

By the way, thanks for posting his second quote which also confirms that November is the critical (I said crucial) point! Somebody nobody questioned him when he used that word :-)

How so true Karyo!

Anyway, it must be obvious that a winter update issued in November, 'should' be nearer the mark, than one released a month or two earlier?

[bobbydog]

5 hours ago, karyo said:

Bobbydog, if you see at the comment he made before the one you quoted you will see that the Glosea doesn't agree with the ECM sadly. Fingers crossed for a better November update.

By the way, thanks for posting his second quote which also confirms that November is the critical (I said crucial) point! Somebody nobody questioned him when he used that word :-)

Karyo. Here is the comment he made before-

"GloSea5 was out today. Quite a different take on things... "

That does not say it will be a mild winter. It leads nicely on to the comment I quoted, ie "key differences versus the EC".

The EC said negative NAO all winter. Glosea differs. How? We don't actually know. At this stage neither is right yet. As he pointed out.