Prediction for Autumn 2016

[iapennell]

The fundamentals that will drive the prevailing weather this coming season are shaping up to be quite interesting. In July I provided a hint at an Autumn that starts fine in the Midlands and South but that would be chilly and unsettled in Scotland with wet and windy conditions affecting most of Britain from mid-October onwards.  Recent developments on a macro-regional scale point to a more settled and drier season with near-average temperatures, particularly for much of England and Wales. 

During the last month mean sea-surface temperatures in the North East Atlantic to the west of Britain have recovered and the patch of anomalously chilly water has largely warmed out. Sea surface temperatures off the US and Canadian East Coasts are some 3 to 5C warmer than normal for early August and the same is true of waters in the Greenland and Norwegian Seas. Arctic sea-ice extent remains at exceptionally low levels for the season with southernmost extent running from East Greenland near 75N to north of Spitzbergen and thence to the northernmost tip of Siberia. This would encourage sub-arctic depressions to move eastwards in rather more northerly latitudes than usual and to be more intense than normal due to the effect of a stronger baroclinic temperature gradient in high latitudes and the fact that deeper depressions would be needed to support the stronger Westerlies needed to counter-balance tropical easterlies to satisfy angular momentum budgets when such Westerlies blow even closer to the axis of the Earth's rotation. This would certainly imply a relatively stormy late-autumn period for Scotland. However there are other caveats thrown up by recent developments in low latitudes. 

Sea surface temperatures are now well below normal off West Africa and there is a tongue of cooler than normal water across the North Pacific around 25 to 30N. The North Pacific north of 40N is some 3 to 4C warmer than normal for early August. More significantly much of the Equatorial Atlantic and Pacific is currently up to 2C cooler than normal. The La Nina phase of the ENSO Cycle has commenced in earnest. The cool tropical waters have resulted (to date) in a very quiet hurricane season in the Atlantic, there has been just one proper hurricane this summer. In the tropical Pacific it has also been an unusually quiet typhoon season with just TWO typhoons so far this summer. This means that the Intertropical Convergence Zone (ITCZ) is rather less convective than usual across extensive longitudes and thus the Hadley Circulation between the subtropical high pressure belt in the Northern Hemisphere and the ITCZ will be weaker than usual across extensive longitudes. This means weaker tropical easterlies and these need weaker (and less extensive) Westerlies in higher latitudes to counter-balance them so as to satisfy Conservation of Angular Momentum laws. This gives a lot more scope for high-pressure systems to persist well into middle latitudes until later in the Autumn. 

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[iapennell]

Continued)

Two other smaller developments are relevant to this coming season. Firstly the winds high up in the Equatorial Stratosphere have turned easterly. These will impact the Circumpolar Vortex within the next month resulting in a weakening of the Circumpolar Westerlies. The Sun is also past it's active phase of the current Sunspot Cycle and it is becoming quiet. So the Sun will not be sending powerful solar flares to the Earth to impact with the magnetic field to strengthen the Westerlies this Autumn.

A final point has to do with the Moon which reaches an unusually close perigee very close to the occurrence of Full Moon in September, October and November. It means strong tides in the oceans but it also means stronger "tides" in the atmosphere and a bit more of the albeit slight slowing down of that which rotates faster and is a bit closer still to large Full Moons - the subtropical and polar-front jet-streams. That ends up weakening the Westerlies a tiny bit more at times near Full Moon.

For Britain and much of NW Europe the pattern of sea-surface temperature across the North Atlantic will encourage a more accentuated trough off eastern Canada whilst the northerly extent of baroclinic temperature gradients will encourage depressions formed in this trough to travel on a more northerly track than usual. The facts of La Nina, QBO Easterlies, less hurricanes, a quiet Sun and big Full Moons means that these depressions (and the Westerlies on their southern flanks) will not be especially intense. Meanwhile the relatively cooler waters under the southern wave-train of the Circumpolar Vortex to the west of Britain combined with continental cooling of mainland Europe means anticyclonic curvature will be imparted to the upper Westerlies over the UK. This suggests that there will infact be a good deal of fine dry weather this coming Autumn.

I will now provide some more detail of how the Autumn is likely to unfold:

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[iapennell]

Continued) 

September is likely to be fine warm and sunny across England and Wales with high-pressure extending from the Azores and often becoming centred right over the country. Daytime temperatures are likely to hit 21C or above over the Midlands and South. However, in September clear nights with light winds will get chilly with minima regularly falling to 8C or below and early morning mist and fog will occur regularly. Ground frost will occur widely on the coldest nights. From time to time fresher westerly winds and fronts associated with depressions far to the north will bring a little rain to most of England and Wales. 

Scotland will have more changeable weather in September with fresh westerly winds and spells of rain. A few gales will affect the north and west of Scotland but they are unlikely to reach far south. There will also be a good deal of fine weather in between frontal bands and daytime temperatures of 20C can be expected across much of Scotland on such days. Clear nights during these fine spells will be another matter with air temperatures falling close to freezing point with widespread ground frost occurring. 

On the whole September will be warmer than normal in the Midlands and South by about 1C with rainfall well below normal for the time of year. I expect SE England to get well under an inch and a half of rain in September.  For Scotland expect near -normal temperatures and rainfall below normal in the east but a little wetter than normal in the west and far north. 

October normally sees the westerlies off the North Atlantic take a real hold, particularly for Scotland and the North of England. However, in October 2016 the Westerlies will take their time. Falling temperatures over mainland Europe will shift the centre of the high-pressure cells affecting Britain towards the Continent and the Azores High is itself likely to become positioned further south (close to 30N) with sea surface temperatures cooler than usual in these latitudes. It is not at all improbable,  given sea surface temperatures in the Med will still be very warm in October that the Circumpolar Vortex will split with part branching south towards the steepening baroclinic gradient between a rapidly -cooling Europe and surface waters to the south that will still be about 24C then. This is likely to happen if the upper and lower higher -latitude Westerlies are weaker than normal at a time of stronger seasonal cooling over Europe. 

Hence, October is also likely to see a good deal of fine weather and I am now confident that high-pressure will extend across the whole country from the east sometime around mid-October. This will bring dry sunny days with light easterly or south-easterly winds. However with shorter days with lower elevation sunshine and long nights don't expect warmth. Temperatures will reach up to 18C in southern England but it will be near 12C on such days in northern Scotland. At night under clear skies with this continental high-pressure temperatures will drop rapidly and the first air-frosts of the season will occur across much of Britain. 

This mid-October fine spell aside,  there will still be much dry weather for most of England and Wales, with south-westerly winds on the periphery of high-pressure over Europe. This will result in some of the warmest days in October with maxima reaching 20C quite widely. However clear nights will still be cold and fog will occur at times. The passage of depressions across the far North Atlantic will bring some rain at times and cooler days even to southern England. 

For Scotland, Northern Ireland and Cumbria October 2016 will be dominated by stronger south-westerly winds and rather more rain than in September. However there will be plenty of sunshine between the rain-bands though clear nights will also mean patchy frost and fog occurring. 

For most of England and Wales October 2016 is likely to end up with temperatures near -normal but with less rain than normal, particularly in the South and East. Scotland will have October temperatures averaging close to the seasonal average with rainfall above normal in the NW  but below average elsewhere. 

I will make a November prediction closer to the time. 

[iapennell]

For those who are a little disappointed at the absence of a detailed November 2016 prediction, I would not want to make such a prediction three months in advance and spanning an intervening period during which sea surface temperature patterns could again change rapidly. For instance, a large patch of the North Atlantic near 50N was up to 2C cooler than normal in May, but this cool anomaly has now gone and indeed most of the North Atlantic is significantly warmer than usual for early August. This will have a major impact on weather -patterns affecting Britain. I also note that certain macro-scale wind and pressure patterns are quite variable and they are certainly prone to seasonal shifts. The QBO high above the Equator is a case in point, though it has been Easterly over the Summer it could well switch to Westerlies in a month or two (it is supposed to be a two to three year cycle but seems to display considerable month by month variability).  All of this will impinge upon the prevailing weather we will have. 

If I have any general indications for the weather we can expect in November it will be little more than a hunch. At this stage I believe that we have seen the back of cold pools in the North Atlantic for a while and with high-pressure over Europe and depressions hugging 70N, warmer southerly and south-westerly winds will keep the NE Atlantic from cooling much through Autumn. By November the NE Atlantic will (likely) be significantly warmer than the seasonal norm whilst the NW Atlantic cools sharply. Stronger NE Trade Winds in the tropics and sub-tropics will arise from the cooling off of the southern USA, North Africa and South Asia by then and there will be a corresponding need for stronger higher latitude Westerlies to counter-balance these.

Thus I would expect high-pressure to retreat south-east into Europe as we go into November and deeper sub-arctic depressions will move north-eastwards over Iceland. With warm seas compared to normal likely to persist in the sub-arctic and the rapidly cooling pack-ice likely to remain northwards of its normal extent cold air outbreaks from the Arctic will be slim over Britain yet the strengthening south-westerly gradient over Britain between high-pressure over Europe and deeper depressions well to the north-west suggest to me that November 2016 will be dominated by southerly and south-westerly winds. This would bring lots of grey skies and some drizzly damp conditions to much of the country. It would also bring temperatures well above the November norm. Scotland would be particularly wet and windy with frequent gales in the far North West. Little frost will occur anywhere, except for Eastern England that will get the effect of chillier drier high-pressure off Europe at times. 

However, this is not a firm prediction but a suggestion at this stage as to how November will play out. It could be that the upper Westerlies end up splitting in a major way because of stronger seasonal cooling over Europe under the influence of high-pressure going into November with the relatively weak southerly part of the Circumpolar Vortex breaking away to pass through the Mediterranean. Were that to happen depressions would cross the Mediterranean from west to east and cold easterlies from Russia would affect much of Europe. In this situation the European High would extend west and join up with the rapidly strengthening Asiatic High further east. Were this to happen November 2016 would be much colder and drier with hard frosts occurring frequently across most of the country. 

[Dangerous55019]

Whatever the outcome Iapennell I think you should be applauded for the hard work you've put into this forecast  

[stainesbloke]

1 hour ago, Dangerous55019 said:

Whatever the outcome Iapennell I think you should be applauded for the hard work you've put into this forecast  

Agreed! Very interesting reading and analysis. Thank you for posting.

[MP-R]

Love reading your posts Ian, even if I don't always like what they say haha. Very clearly set out and easy to understand.

I don't think I could handle another November 2015! (other than the opening few days, the PM blast on the 13th and the northerly on the 21st-23rd)

[iapennell]

If you want a rough idea how the Autumn of 2016 might pan out overall I would suggest that the Autumn of 1997 is perhaps the closest parallel in recent times. If you will recall, those of you who are old enough to remember, June and July 1997 were quite changeable and a little on the cool side. However from late July onwards there was some real hot weather and much of August was dominated by high-pressure that was often centred over southern Scandinavia. Very warm SE winds were common and with plenty of hot sunshine many parts of England reached or exceeded 30C. Looking at the forecast pressure charts something similar could happen next week. 

September 1997 was quite changeable and cool across the North but even here there was a good deal of dry sunny weather with some warm days, but also cold clear nights with the first frosts of the season in many places. The South was dominated by high-pressure that bought a good deal of sunny warm weather but also cold nights with ground -frost.  October 1997 continued the fine weather theme and very warm southerly winds brought maxima of 25C to parts of the South at the start of the month. However much colder Arctic air crossed the country during the second week and again on the 24th to 26th; after each Arctic incursion high-pressure dominated bringing clear nights of well below freezing point over most of Britain and chilly sunny days with maxima little over 10C anywhere. I am not expecting quite such sharp early cold and frosts in October this year but I am confident that there will be a week when strong high-pressure from Europe extends over Britain with chilly easterly airstreams. I am certain that the clear still nights that this European High will bring will result in the first air-frosts of the season over much of the country. 

In November 1997 as the high-pressure responsible for sharp late -October frosts slipped east into Europe and North Atlantic depressions strengthened mild southerly winds dominated. There was little frost anywhere though the North West and Scotland was often really wet and windy. I have a hunch (not a scientific prediction three months out) that November 2016 will follow a similar course.

[lassie23]

6 minutes ago, iapennell said:

If you want a rough idea how the Autumn of 2016 might pan out overall I would suggest that the Autumn of 1997 is perhaps the closest parallel in recent times. If you will recall, those of you who are old enough to remember, June and July 1997 were quite changeable and a little on the cool side. However from late July onwards there was some real hot weather and much of August was dominated by high-pressure that was often centred over southern Scandinavia. Very warm SE winds were common and with plenty of hot sunshine many parts of England reached or exceeded 30C. Looking at the forecast pressure charts something similar could happen next week. 

September 1997 was quite changeable and cool across the North but even here there was a good deal of dry sunny weather with some warm days, but also cold clear nights with the first frosts of the season in many places. The South was dominated by high-pressure that bought a good deal of sunny warm weather but also cold nights with ground -frost.  October 1997 continued the fine weather theme and very warm southerly winds brought maxima of 25C to parts of the South at the start of the month. However much colder Arctic air crossed the country during the second week and again on the 24th to 26th; after each Arctic incursion high-pressure dominated bringing clear nights of well below freezing point over most of Britain and chilly sunny days with maxima little over 10C anywhere. I am not expecting quite such sharp early cold and frosts in October this year but I am confident that there will be a week when strong high-pressure from Europe extends over Britain with chilly easterly airstreams. I am certain that the clear still nights that this European High will bring will result in the first air-frosts of the season over much of the country. 

In November 1997 as the high-pressure responsible for sharp late -October frosts slipped east into Europe and North Atlantic depressions strengthened mild southerly winds dominated. There was little frost anywhere though the North West and Scotland was often really wet and windy. I have a hunch (not a scientific prediction three months out) that November 2016 will follow a similar course.

What happened in December 1997?

Edited August 9, 2016 by lassie23

[iapennell]

Just now, lassie23 said:

What happened in December?

If I recall correctly December 1997 was mild wet and (towards the month's end) quite stormy too. Then January and February 1998 were milder than normal and quite wet, though there was a short cold snap mid January.

However, global temperature and pressure patterns, not least the much lessened extent of Arctic pack-ice in all seasons compared to 1997 means that the influence on weather patterns will be different. Some high-latitude seas are warmer in all seasons compared to 20 years ago, so it is dangerous to make weather predictions by extrapolation of similar looking seasons in the past, though there are some parallels that can be useful. 

[MP-R]

An autumn like 1997 doesn't sound so bad, as long as it doesn't lead to a winter like 97/98. In fact, other than September, that description doesn't sound too different to last autumn.

[cheese]

I think a winter like 97/98 would be kind of nice actually.. February that year was exceptionally mild, but dry and sunny, in contrast to last December which was exceptionally wet for many places and extremely cloudy everywhere.

Edited August 10, 2016 by cheese

[MP-R]

1 minute ago, cheese said:

I think a winter like 97/98 would be kind of nice actually.. February that year was exceptionally mild, but dry and sunny, in contrast to last December which was exceptionally wet for many places and extremely cloudy everywhere.

Yes February 1998 would be the ideal alternative to something seasonal. Don't think it's worth it though for how the November-January panned out.

[Jakehainton]

Love this thread and a great descriptions thanks mate! 

[Turnedoutniceagain]

No Autumn this year, we're going straight to Winter >> http://www.breitbart.com/big-government/2016/08/12/winter-is-coming-warns-the-solar-physicist-the-alarmists-tried-to-silence/

[Nouska]

You'll be pleased to know the CESM model thinks so too.....

http://www.cpc.ncep.noaa.gov/products/NMME/current/NCAR_CESMtmp2m.html

http://www.cesm.ucar.edu/models/

[Weather-history]

Autumn 1997 was going into one of the strongest El Niños on record, Autumn 2016 is going into La Niña? 

[reef]

7 hours ago, Weather-history said:

Autumn 1997 was going into one of the strongest El Niños on record, Autumn 2016 is going into La Niña? 

Indeed. As well as that, SSTs and Arctic sea ice levels are radically different to then.

SSTs in the Greenland area are exceptionally warm, so I've a feeling we're going to get strong storms spawning there this Autumn. I reckon we'll miss them during September as we'll be under the influence of a mid-latitude block, before October sees the floodgates open.

[iapennell]

Looks like the "Cold Blob" in the North Atlantic has finally warmed out though there is a smaller patch of relatively cool water for the season in the Norwegian Sea. Sea-surface temperatures off West Africa at 10 to 20N and across the Eastern Pacific at 10 to 20N (in the typical tropical depression forming latitudes) are some 1 to 2C warmer than the August norm. Very warm waters for the time of year over North Pacific north of 35N and NW/far North Atlantic. Slight changes to when I made the original Autumn 2016 prediction which suggests more hurricanes/typhoons than originally thought and thus somewhat stronger Westerlies in higher latitudes as the autumn unfolds. I am still confident of a warm, dry September for most (Scotland is likely to be wetter and windier than earlier suggested though) and, in view of higher sea-surface temperatures to the west of Britain I expect September to prove to be warmer than usual across the Midlands and South.

However, confidence in dry settled weather persisting through most of October 2016 as well is less than in my earlier forecast- above average sea-surface temperatures in the NE Atlantic predicates deeper depressions moving east in the vicinity of Iceland (though exceptionally warm waters for the season around Greenland is likely to encourage storm-tracks to be further north than usual. High-pressure is certain to dominate across continental Europe but Britain is more likely to be on the north-west periphery of such highs, leading more to warm southerly and south-westerly winds that bring more cloud. There will still be some warm sunny days in the South early in the month but for those of us who yearn for October frosts and crisp cold mornings there is now an increased likelihood the month will disappoint! This is especially likely to be true for NW England and western Scotland that is much more likely to be under the influence of mild rainy south-westerlies after mid-October. It is still a little too far out to make definitive predictions for November, though it remains a hunch only that November is likely to be mild and overcast with more southerly winds than usual over most of the country.

An important development to keep an eye on is the patch of relatively cool water in the Norwegian Sea, if this persists and grows into the autumn this increases the likelihood of high-pressure near Scandinavia developing later in the autumn which would in turn encourage drier colder easterly winds.

ps. to date remarkably few hurricanes and typhoons in the tropical Atlantic and Pacific respectively. If this state of affairs can hold through September we can anticipate a better chance of at least one or two frosty October nights, bringing some nice colours on the trees for most of the country.

[damianslaw]

Fingers crossed we don't see a relentless surge of mild southwesterlies or southerlies in October and November, which would deliver woeful conditions here, incessant rain, low cloud, poor visibility and generally dull miserable conditions, mind its the safest bet given our weather on balance predominantly arrives from a SW quarter. We shall see. The last 3 autumns have seen cold SST values to the NW of us and in the main have delivered very mild conditions and at times very wet conditions, but this year things are quite different.  Its just one factor but would be good to know which years had a similiar SST profile going into autumn as we have now. 

 

[iapennell]

6 hours ago, damianslaw said:

Fingers crossed we don't see a relentless surge of mild southwesterlies or southerlies in October and November, which would deliver woeful conditions here, incessant rain, low cloud, poor visibility and generally dull miserable conditions, mind its the safest bet given our weather on balance predominantly arrives from a SW quarter. We shall see. The last 3 autumns have seen cold SST values to the NW of us and in the main have delivered very mild conditions and at times very wet conditions, but this year things are quite different.  Its just one factor but would be good to know which years had a similiar SST profile going into autumn as we have now. 

 

Having looked at the QBO anomaly, it is still in a negative (easterly) phase though there are signs it is trending towards positive (i.e. anomalous westerlies) and that could well be the case by late-autumn. Easterlies in the Equatorial Stratosphere filter downwards and into the global circulation to have a weakening effect on higher-latitude Westerlies a month or so later, so that there is a hope that the Equatorial Westerlies (if these occur by October) don't come into play to affect our weather-patterns until late November or December. The QBO anomaly for August is still (just) negative and it will have the effect of weakening the Circumpolar Vortex for September-October, but not by much.

Sea surface temperatures in Baffin Bay and off the East Greenland Coast above 70N are running 4C or more warmer than usual for the time of year and I am confident that, at least during September and early October, this will put the strong baroclinic gradient between the rapidly-cooling sea-ice in autumn and much warmer seas rather further north and so the major storm tracks will be north of the Arctic Circle. This certainly boosts the likelihood of high-pressure extending across much of Britain to bring fine warm weather (though with some chilly nights) during the earlier part of the season.

[Gael_Force]

10 minutes ago, iapennell said:

Having looked at the QBO anomaly, it is still in a negative (easterly) phase though there are signs it is trending towards positive (i.e. anomalous westerlies) and that could well be the case by late-autumn

Can you expand on this please as I see the index is still in westerly phase. I know different levels are measured differently but thought the 30mb was the accepted one when following progress.

http://www.esrl.noaa.gov/psd/data/correlation/qbo.data

[iapennell]

1 hour ago, Gael_Force said:

Can you expand on this please as I see the index is still in westerly phase. I know different levels are measured differently but thought the 30mb was the accepted one when following progress.

http://www.esrl.noaa.gov/psd/data/correlation/qbo.data

These are the sites I have been going by to gauge the QBO:

http://www.cpc.ncep.noaa.gov/data/indices/zwnd200

and

I have to say I did not see the 30 mb one! However, if that takes just a couple of months to work down through the Equatorial Stratosphere and thence into the general circulation of higher latitudes that difference of 10 metres per second towards westerlies could make a significant difference as to how the latter half of Autumn 2016 plays out! 

 

Edited August 20, 2016 by iapennell

[iapennell]

It is interesting to note that, at least at the 50 mb and 200 mb levels there is an anomalous easterly flow high above the Equator. This will probably affect the Westerlies encircling the Arctic within the next month but the anomalous Westerlies at 30 mb over the Equator will kick in during October. If so, this lends support to the assertion of a dry warm September for many but wet, windy but mild after mid-October.

[Gael_Force]

Thanks for replies, Ian. Your links are new for me but interesting to see the divergence being talked about in the 30 and 50mb graph. Whether this unusual departure has any bearing for the weather on the ground, we'll see in due course.