iapennell

27th October 2013 IF you, like me, despair at the persistent south-west winds bringing mild weather in the autumn and the winter months(looks like this October will be the first without air frost for nine years!) there are three culprits to blame for the tendency to persistent Westerlies and south-westerlies off the North Atlantic affecting the British Isles: Firstly the sun beats down on the tropics heating the atmosphere and causing the presence of a zone of hot rising air called the Intertropical Convergence Zone. This zone of hot and moist air sucks in air from cooler latitudes causing the Trade Winds- whilst at high altitudes the tropical air moves polewards. This process becomes more intense in the winter when the subtropical and higher latitudes cool- the strong atmospheric temperature gradient intensifies this circulation known to meteorologists as the Hadley Circulation. Basically, this circulation plays a major role in redistributing heat from the tropics to higher latitudes- preventing winter temperatures falling unchecked in the latitude of Britain. The second factor which mitigates the climate of Britain in particular is the surrounding seas, and the fact that in the late spring and summer months the net radiation budget turns positive as the sun beats down from high elevations each day. This net radiative heating transfers heat to the sea surfaces- heat which is slowly released again (and thus keeps the air warmer) during the autumn and winter months. This further modifies the extremes of cold which could otherwise occur in Britain. However, if it was just for these two factors alone,- the mean air temperatures in Britain would still drop to far below freezing point in the winter months- because a "thermally direct" Hadley Cell circulation would lead to high-pressure, dry subsiding air and clear skies in all higher latitudes. This is because clear, dry atmospheric conditions permit strong net radiation heat loss from the surface and lower atmosphere in the late autumn and winter months in Britain- because this is when the days are short and the sun low in the sky at noon. A third factor makes all the difference, though it also hinges on the other two factors above to be most effective. This third factor that has an all-important impact on Britain's autumn and winter weather is related to the fact that the Earth rotates on it's axis: It is something meteorologists and physicists term the "Law of Conservation of Angular Momentum"; and it explains why winds moving south from high latitudes curve towards the west and why air moving north from low latitudes curves towards the east- in their direction of travel. The effect of this on winds blowing from high to low pressure areas is commonly referred to the "Coriolis Effect". On our rotating planet a Thermally Direct cell with high-pressure in high latitudes and low-pressure at the equator would result in near-surface north-east winds north of the equator, but south-easterlies in the Southern Hemisphere- but this is never observed over entire hemisphere for the reasons I will now explain. Now the Law of Angular Momentum dictates that the total angular momentum of a body unperturbed by any outside force remains constant over time. It means that if extensive easterly winds blow over the globe they would result in the Earth's rotation rate slowing down slightly- and this could only happen if a large chunk of the atmosphere speeded up (i.e blow from west to east- much faster- in view of the atmosphere's small relative mass). This would, of course happen, because the frictional force of extensive easterlies in slowing the rate of the Earth's rotation would cause an equal and opposite force on the atmosphere overall- this is basic Newtonian physics. This in turn results in the upper air moving at ever-greater speeds from west to east; the strong and extensive upper Westerlies would be effective in preventing warm air from the tropics moving to high latitudes at high altitude and where the strong upper Westerlies subside this would [eventually] result in westerlies blowing at the surface. Okay, it does not happen in quite that simplistic a manner- but essentially the upshot is that you cannot have extensive easterlies near the surface throughout either hemisphere for any extended period: This is because of the Law of Conservation of Angular Momentum- which means any extended spell of easterlies over all the Northern (or Southern) Hemisphere would result in Westerlies at high levels blowing at hundreds and then thousands of miles per hour. Although the upper Westerlies over the subtropics and mid-latitudes do get stronger in winter they do not accelerate to this extent- and the corollary of this is that the frictional forces of Trade Wind easterlies in the tropics and subtropics (and blowing out from any Polar or Siberian Highs) must be counter-balanced by the frictional force of Westerlies elsewhere: And Britain, with the relatively warm North Atlantic to the west is at a location of relatively least resistance to satisfy the need for a "sink" for excess Westerly atmospheric momentum. The distribution of atmospheric pressure from the subtropical high to the sub-polar lows is also [thus] a consequence of the Law of Conservation of Angular Momentum- and this causes the winds to come in from the south-west;- bringing to Britain warm air from the Azores! So we have the sun beating down on the tropics causing a zone of hot, moist and rising air, in winter higher latitudes cool more and thus intensify the temperature and pressure gradient driving the NE Trade Winds (these winds blow from the NE due the effects of the Earth's rotation). In summer the sun heats the mid-latitude seas and oceans so that this heat can be released to temper the strong cooling of the winter months over nearby lands. And finally the effects of the Earth's rotation mean prevailing west or SW winds in the autumn and winter months over Britain- these bring the heat from the subtropics and the heat stored in the North Atlantic over the preceding summer across Britain to prevent snow and hard frosts for most of the time. And the depressions- also a product of the summer-sun warmed North Atlantic and the effects of the Earth's rotation are also responsible for the annoying bouts of Wet 'n Windy (as well as mild weather) that dominate the Winter-Half-Year in this country. So there you go!: If we could find a way of slowing down the Earth (or even causing a large volcano over the deep tropics to block out the Sun and weaken the Hadley Cell)- we could reduce this "Need" for Westerlies in higher latitudes;- and in so doing we could solve the problem of Mild, Wet Autumns/Winters in Britain!! Ian Pennell

Sadly, it is looking likely that I will not be recording an air frost in October 2013- very deep depression sweeping across England over next 48 hours; strong Westerlies off the North Atlantic set to dominate the last few days of October- and into November!

Of course, one of the advantages of living in a wild rural area is that there are not so many women and children around who could cause one hassle in the warm weather- but the absence of cold weather until November is still something I dislike: As a weather observer I like to record interesting weather conditions,- raw weather that is beautiful to look at: Cloud with a little drizzle and 12C day after day is naff; but a morning of -5C with thick hoar frost glistening in the morning light (and bringing about blazing golds, crimsons and oranges on the trees) would be fantastic at this time of year. An air frost will also get rid of the bugs, spiders and flies which cause annoyance and irritation- and have now done so for several months. An air frost cannot come soon enough- one is long overdue!!

I live at over 400 metres' elevation in the North Pennines (near Cumbria/Northumberland border)- and the air temperature so far this autumn has yet to drop below 3C; the weather pattern looks like we might get some colder NW winds by Monday/Tuesday- but that could (like recent forecast "northerly snaps") whittle away with higher pressure over the SE and pressure remaining lower west/NW of the UK keeping the warm southerlies/south-westerlies to the month's end: The prospect (with warmer-than-usual waters in the North Atlantic) remains real that mild SW winds will persist and ensure the entire month of October 2013 (even in the North Pennines) has not one single air frost. I don't like this warm, dank muggy (and buggy) weather that allows flies and bugs to persist- without a little air frost the colours on the trees are not anything like as good! By the time we get into November- with the very short days- we should be thinking about winter and the wind would have removed the leaves- brown and soggy-looking! We also need cold weather to set in in October to ensure that the summer is appreciated (if it goes on too long people get pandered to with soft/warm weather much of the year), a good summer is not then so really appreciated. The cold weather also instills some respect into folk (and empathy for others), in really severe wintry weather people pop in to see if elderly neighbours are OK (which they dont do if it's warm); Freezing temperatures keep the yobs that plague many streets in Britain today- firmly indoors!! I also like the weather to turn cold so that little single men like myself can relax if they are out and about in the community: When women and kids are in shorts, etc (as when the weather is warm)- there are some hypersensitive relatives with them who worry that a single man walking down the street near their kids/female friends/girlfriends might be a pervert looking at them (of course they may have their reasons)- but this makes a single man mind have to mind how they go about town. I have had one or two accuse me of following their girlfriends (or them) when I lived in Lancaster some years ago (so I know this aggro happens)!! All this awkward stuff is much less likely to happen in cold weather when fewer kids and women are about anyway (and those that are are bundled up to the nines)- so it's time the weather actually got colder! So, all things considered- this mild October- and having to wait until November for an air frost- SUCKS! Ian Pennell

Even up here in the wilds of the North Pennines on the Cumbria/Northumberland border at over 400 metres elevation the temperature did not drop below 9C last night, and with a warm (if wet) SE'ly wind the temperature has risen to 11C. As far as I am concerned,; What a thoroughly naff October this is turning out to be- looks like we will (for the first time in nine years) have to wait until November for a single air frost! Infact, the lowest temperature it has ever got so far this autumn is 3C. So the leaves are scarcely turning much- except brown; none of the really lovely golds, crimsons and reds on the trees with crisp autumn sunshine this autumn. It would be nice if the churches stopped praying against the cold weather (thus doing their bit to help fight global warming!)- although personally I put the blame at the warm summer that has heated up the North Atlantic so much that low-pressure readily forms (and stays) to the west of Ireland keeping us with these mild southerly winds. There is also a patch of cooler water off Spain to encourage high-pressure there,- thus further strengthening mild south and SW'ly winds over northern Britain! Not one single air frost until November (even in the North Pennines),- such a prospect really bugs me!! Ian Pennell

Hello, its so lovely to be able to chat about my favourite subject with like-minded folk! Indeed, my money is definitely on a milder, but stormier winter this year. I have close to 30 years of records, and have tended to find that substantially warmer than usual summer half years (with the proviso that the warmth is shifted more June-September) tend NOT to be followed by frosty Octobers (though this rule does not always hold); IF September and October together are then mild and no air frost occurs until November that almost always means a mild winter. Clear examples of such years with warm summers/autumns (and ensuing mild winters) are 1989, 2001, 2004, and 2006.

Hello, I am new to this Forum. I live in the North Pennines (near Alston, just into Cumbria); and I have been a keen weather-observer for many years. I like cold weather, heavy snows and very hard frosts (below -10C) but I am realistic enough to realise that this is usually unlikely in these globally-warmed years. This year proves to be no exception to the general rule. We have just had the hottest summer for several years; sea surface temperatures right across the North Atlantic are over 2C above normal (as reported in September) consequent on the Azores High being further north than usual. The extent of Arctic sea ice is greater than last year but remains below the seasonal norm going through October; and the European Arctic remains ice free to well north of Spitsbergen. This all tends to favour deep depressions forming close to the strong temperature gradient between a warm North Atlantic and the already very cold Greenland/North American Arctic- and the warm North Atlantic right up into the European High Arctic will encourage this cyclonic activity to push well north. This points to persistent, strong west and SW winds and little chance of blocking highs in the Arctic or over northern Scandinavia sending bitter Arctic or Russian airmasses towards the UK. Historically long warm summers, then warm early autumns mean neither early frosts in October, nor really severe winter weather. All of which means it is likely to be November before we even get our first air frost (even here at over 400 metres up in the North Pennines!), there is no reason for deeper lows west of Ireland (and attendant south and SW winds) to change before the end of October: Winter 2013/14 is likely to be milder than usual, though probably also particularly wet and stormy in Scotland and the North. Short Arctic Snaps from the north-west are more likely in February when Greenland and Arctic Canada have cooled sufficiently to permit stronger Highs to form over them; then we may get some snow and a sharp frost. Aside from that temperatures will remain well above freezing point across all lowland Britain, though it is likely that severe gales (the like of which we have not seen for some years) will batter the country from December onwards. Ian Pennell

Hello, I am new to this site. I am a 44 year old man who lives in the North Pennines (Cumbria/Northumberland border); I have had a strong interest in the weather for many years, and years ago I took a degree in Environmental Science from Lancaster University. Sadly my degree was not good enough, and I could not find work being a weather forecaster or contributing to weather/climate related research, and I have had a number of cleaning jobs for the last twenty years. Alas, I do make sure my knowledge about things meteorological does not go to waste- so I make my debut on this Forum with a prediction about the weather to be expected for Winter 2013/14! Although the Met Office no longer do them, I tentatively offer my predictions for the ensuing winter half-year in Britain for 2013-14 (starting from this month), based on the likely impact of Arctic Ice extent, sea surface temperatures in the North Atlantic and around Britain and the stage we are at in the Sunspot Cycle. On the basis of the fact that sea surface temperatures close to 50N across the North Atlantic remain well above normal after the warm summer (anomaly +2C in Sept 2013, see here:http://www.bobtisdale.wordpress.com/september-2013-sea-surface-temperature-sst-anomaly-update), but sea temperatures are near normal around Iceland this sets the scene for lower pressure over the Atlantic to the west of Britain and a stronger baroclinic temperature gradient over the North Atlantic to encourage deeper depressions: Warm south and SW winds over Britain with deep cyclonic activity south of Iceland has certainly featured through the last week- and looks to persist to the end of October 2013. Another feature of the large-scale weather pattern is the fact that the Arctic ice cap is- although larger than this time last year- remains smaller than the long-term normal extent for October. Arctic ice is at near normal levels for late October over the Canadian Archipelago but remains well north of Spitzbergen in the European sector of the Arctic (see here:http://www.nsidc.org/arcticseaicenews). The edge of the Arctic icecap- being further north than usual will encourage subarctic depressions (which tend to stay close to the intense temperature gradient between the very cold Arctic icecap and the warmer air over the open ocean and ice-free land) to move further north than usual: The higher-latitude Westerlies to the south of these depressions will thus blow in higher latitudes; from a Conservation of Angular Momentum consideration it means that the higher-latitude Westerlies will have to blow even harder to cancel out the total frictional forces of the tropical and polar easterlies- because blowing closer to the axis of the Earth's rotation the frictional torque of the Westerlies would be weakened (thus the Westerlies will have to be stronger to compensate if the move into ever-higher latitudes). The upper Westerlies and the jet-streams will also remain in fairly high latitudes (these tend to be restricted to zones of strong atmospheric temperature gradient- and if these are in higher latitudes because the Arctic Ice extent remains further north than usual then the jet-streams will follow suit): This means no hurricane-force Westerlies impacting the Pamirs, Rockies or Himalayas absorbing some of the "need" for lower-level Westerlies in the Northern Hemisphere (to cancel out the effect of easterlies elsewhere). This also points to stronger Westerlies and south-westerlies blowing across the north Atlantic from this month onwards and through the winter. The sunspot cycle peaked in 2011-12, and is now declining: This means there is likely to be less impact of solar flares causing forces to impact on the upper-atmosphere (solar flares have been known to slightly increase the overall westerly momentum of the atmosphere globally- and ultimately results in deeper subarctic depressions and stronger higher-latitude westerlies). The solar cycle entering a quiet spell would lend itself to weaker Westerlies coming off the North Atlantic; but the other factors as described above (Arctic Ice constrained in high latitudes and a warmer than usual North Atlantic going into winter) are likely to far outweigh the effect of a slightly "quieter sun". All this indicates that there will be deeper depressions forming over Newfoundland- encouraged by the strong temperature gradient between the ice-covered Canadian Arctic atmosphere and the atmosphere over a warmer NW Atlantic Ocean; these will intensify and be encouraged to move north-eastwards into the ice-free (and warmer than usual) Barents Sea. This all means stronger prevailing SW winds over Britain throughout the late autumn/winter of 2013; all of which will actively discourage the kind of blocking patterns that would send frigid Arctic or North Russian airmasses in the direction of Britain. However, I can be certain that Arctic Ice a little further south than in recent years over Arctic Canada combined with a warmer North Atlantic than usual going into the winter will make for storms: The need for stronger west and SW winds from a Conservation of Angular Momentum consideration certainly lends itself to scope for the North of Britain to get some real batterings- we are set to have some of our biggest winter storms in years. Certainly, later in the winter (December onwards) there is likely to be some short Arctic snaps from the north-west as Arctic Canada and Greenland get very cold and Arctic Highs build over them at times: These are likely to be short-lived, but there is certain to be one or two snaps around February that will bring snow even to the south and a clear night or two down to about -5C (the North and Scotland will be colder with minima locally down to around -10C- over widespread snowcover- during these Arctic snaps). In the main, however the stronger-than-usual baroclinic gradient over the North Atlantic will mean strong westerlies and SW'lies, plenty of gales and rain; although the SouthEast will escape the worst of it! Certainly until December there is going to be little frost or snow anywhere in lowland Britain; even from my home in the North Pennines I have a strong feeling (based on the manner in which potential cold-patterns with highs in the North Atlantic keep crumbling away before their forecast onset!) that persistent southerly and SW winds will keep frost at bay to the extent that for the first time in nine years I will have to wait until November to report an air frost! Contrary to what a number of the pundits might think, warm summers then Octobers tend not to be followed by cold winters. The three past years during which I had to wait until November for our first air frost (in all these years too, the summer half-year was warm),- 1989, 2001 and 2004,- were all followed by mild winters with little serious frost or snow. However, by way of disclaimer- a Sudden Stratospheric Warming (SSW) event in the Arctic Stratosphere in December or January could completely rubbish my predictions- and usher in a wintry spell of exceptional severity. It was a SSW that resulted in the unexpected cold snap in January 2013. That said, SSW events tend to be more likely if the Upper Westerlies encircling the Arctic are weak- and prone to any distortion liable to put a big pool of "warm" air high over the Arctic. As I have pointed out above, I do not think the upper Westerlies are going to be weak: So one can discount all those predictions of -20C and heavy snow in January that you might have read in The Daily Mail!! Ian Pennell