A New Month, A New Year – January 2013

30 Dec

Well, there goes 2012 and it sure has gone quick, especially when you look back at the variety of quite significant and extreme weather events that were ‘handed out’ to us this past year. Another year is about to start and seeing we are entering into the ‘heart’ of winter, there are some interesting developments which could make for a particularly interesting January.

The winter so far has generally been quite mixed and overall ‘average’.  Despite a rather cold first half to December with some fairly frequent frosts and even some snow in places, the second half of the month has clearly become far more unsettled.  This has helped to lift temperatures back to nearer average values and not only that cement this year as one of the wettest on records with clearly further flooding to end December and end 2012.

The month ahead, January, I believe could deliver quite a stark variation in conditions with a potentially abrupt change in the weather approximately mid-month, this is primarily due to the expected development of a Sudden Stratospheric Warming event and also other variables including the likes of the QBO (Quasi-Biennial Oscillation).

Taking a look at the first half of the month and the below is what I believe the broader synoptic patterns will look like as an overall average/mean;

First half of January

Overall there is quite good model consistency between the GFS and ECMWF ensembles for high pressure to build from the south and south-west of the UK during the opening week of January and become a dominant feature just to the south of the country.  At times there is a clear signal for the high pressure to build up into the UK and thus produce predominantly settled conditions with a marked ‘ridge’ in the jet stream across more west and north-western areas of Europe.  As a result, whilst perhaps not lasting the whole 15 days, the first half of January looks set to be dominated by higher pressure bringing more in the way of settled conditions and with, thankfully, a marked reduction in the risk of further heavy and disruptive rainfall.  It should be noted that at the moment the high pressure isn’t likely to be one that brings cold and frosty conditions, at least not a first, but instead a lot of cloud is forecast within the short term with patchy rain and drizzle possible.

Now, onto the interesting bit and this relates to the stratosphere.  I have discussed the stratosphere in a blog a few months ago which highlights it has two primary states, that being a well established ‘cold’ vortex and the other being a more disrupted and ‘warmer’ vortex.  This blog and information can be read here

Latest forecast models continue to show a warming event taking place within the stratosphere into early January which is forecast to either split the vortex, displace it or perhaps even do both.  Some charts of interest are below which highlights this current thinking;



Without going into the details too much, both of the above forecast images show a significant warming event is set to take place through the opening week of January as higher pressure becomes particularly dominant within the stratosphere and with a marked increase in temperatures. You’ll notice on both images that the vortex, or what’s left of it, is well displaced from its usual position across the pole and is also split with one main region over North-east Canada and the other over or near Scandinavia. These charts signal a SSW event.


The other factor of a SSW is the reversal of what is known as the zonal winds within the stratosphere.  This is also evident by the negative blue colours on the above image from approximately 60°N and of which are extending from the top of the stratosphere (1hPa) down to near the bottom of the stratosphere and the top of the troposphere (100hPa). This is, yet again, another clear signal for a SWW event.  Finally the below image clearly shows the predicted temperatures across certain areas are forecast to rapidly rise above average into early January in association with this warming event;


Now, what I should add here, which I have also mentioned in the blog from a few months back, is that a Sudden Stratospheric Warming event doesn’t automatically mean cold weather for the UK.  This is an important variable and just because one is forecast doesn’t mean the UK will be plunged into deep cold for weeks.  However, what it does mean is that the affects on the troposphere is likely to be significant and previous SSW events and analysis clearly show that when a SSW event occurs it promotes a highly disorganised polar vortex and allows/aids in the development of blocking (higher pressure) at higher latitudes.  If high pressure can be achieved at higher latitudes then this brings the risk of colder weather affecting the UK and also many other parts of the northern hemisphere.  As an example of high pressure becomes dominant to the north-west of the UK over and around Greenland, then this ‘blocks’ the Atlantic and often brings cold/very cold north or north-easterly winds for several days.

I will shy away from creating a graphic of how I think the synoptic patterns will evolve beyond mid-January simply because it is anyone’s guess for now.  However, the science being the SSW is sound and I do believe that given the above information and also other information, that as January progresses a far more blocked pattern will likely develop and as a result will bring an increased risk of colder conditions affecting the UK towards and beyond mid-January.  Clearly the details as to how cold, how long any cold will last and its origins are unknown and will be for a number of weeks.  But I urge caution at writing off this winter, there is a long way to go and I do believe eventually the ‘cold’ will arrive.

A Happy New Year to all followers and readers.



Possible Stratospheric Demolition & Final Winter Thoughts…

27 Nov

With just a few days of autumn left and an autumn which has produce quite a few extremes, the attention now turns towards winter.  I’ll add at this junction that (time willing) I’ll produce a blog looking specifically at December in the next few days. In this blog I wanted to directly focus my attention and information on the state of the stratosphere as we now enter into winter.

Many may well have heard of the ‘stratosphere’ in recent months and also within the last year or so as this particular ‘variable’ has been given more and more scientific attention.  Some people believe that the stratospheric conditions aren’t the be all and end all when it comes to affecting the weather across the UK during the winter and in a way they are correct.  There are a large number of variables which come in to play, but equally I can disagree and argue that comment with substantial evidence, of which I have acknowledged myself over the last few years.  Without question, the conditions of the stratosphere do affect the weather across the UK and the northern hemisphere during the winter and early spring period.

In one of my previous blogs, which explains the two primary different states of the stratosphere (https://matthugo.wordpress.com/2012/10/01/stratospheric-conditions-winter-weather-analysis-information/) I give a perfect example of how the stratosphere can directly affect the weather within the troposphere and a perfect example of that was last December.  Now without going over those details, I wanted to take a look at the state of the stratosphere up to present day and what is forecast to happen in the coming days;

Initially, through this autumn, the stratosphere has cooled (as it should) at quite a significant rate to say the least and generally this progression would often lead to a pattern as evident last December.  However, for a number of factors, including the likes of the QBO (Quasi-biennial Oscillation) these particularly potent stratospheric conditions haven’t been able to filter down into the troposphere this autumn and are now highly unlikely to do so.  The rapid drop in temperatures across the polar stratospheric region can be seen on the below 2 images;

As can be clearly seen on the first image in particular the temperatures have now dropped below -80C which is pretty much as low as they can go. Within the second image you can see that at this time last year the temperatures were very similar, but perhaps slightly warmer.  However, there are clear differences, of which I highlighted earlier, this year the stratospheric conditions have been unable to penetrate down into the troposphere and aid the development of a significant polar vortex (http://en.wikipedia.org/wiki/Polar_vortex). To give an example of what the stratospheric vortex looks like at the moment, the below image shows this;

What this image is essentially showing is the temperatures within the stratosphere and also the overall ‘shape’ of the stratospheric vortex.  At the moment, whilst rather elongated, it remains a noteworthy feature and as can be seen within the bottom left of the image the lowest temperature on that chart is -83c (82.5N 2.5W) essentially near the center of the vortex over the polar region.

So what is expected in the coming 7 to 14 days to change this setup?…

Well, without going into the details too much, of which even I am still attempting to get a grasp of, the stratospheric vortex through the winter period can often be at risk of under-going ‘attacks’ from various sources.  These ‘attacks’ help to distort and weaken the vortex and the so-called “holy grail” can be a complete split and relocation of the vortex as well, you may have heard of an SSW (Sudden Stratospheric Warming) event.  At this point don’t forget that a highly disorganised stratospheric vortex has been found (time after time) to aid in the development of northern latitude blocking and a heightened risk of colder weather across the UK and other areas of the northern hemisphere during the winter period than if the vortex is well organised.

So a few more charts of interest;



1) The first image clearly shows a very different vortex within the next 7 or 8 days compared with the actual vortex of present day.  The vortex, as can be seen, has split and of significance is the major warming event taking place over Eastern Russian in association with a major region of higher pressure across Alaska and far eastern areas of Russia.  This is represented by the lighter blue colours and also the patch of pale yellow colour of which represents temperatures of -50C or above.  This may still seem cold but clearly compare that to temperatures of below -80C and that is a marked area of warming.

2) The second image shows the zonal wind speeds (m/s) up through the troposphere and more specific the stratosphere in relation to latitude.  Of significance here is the negative (blue) colours and contours above 70N across the right of the image.  This highlights a progression towards a highly disorganised and weak stratospheric vortex.

3) Finally the bottom image and more importantly the top 3 graphs show how the temperatures are forecast to rise into early December compared with at present to either near or even above average. Of significance, don’t forget that a warmer stratospheric vortex essentially equates to a weaker vortex and a greater likelihood of potential blocking (higher pressure) within the troposphere.

In conclusion;

Gathering the above information and more together the situation through this autumn has been quite unique.  The behavior of the vortex would (more often than not) have led to a likely period of zonal conditions across the UK as the autumn progressed, but clearly this hasn’t happened.  Despite the highly organised and very cold stratospheric vortex there are now a variety of variables which are forecast to “attack” the vortex within the next 7 to 14 days of which, if successful, may actually demolition the vortex almost completely.  For this to happen at this time of year would (combined with other factors) lead to a heightened risk of more meridional and blocking conditions developing.

So, and finally, combining this data and with other information I believe that the winter across the UK between December and February will end up being colder than average with a greater frequency of blocking patterns leading to cold outbreaks.  Clearly details are not possible, but particularly as we progress through the second half of December and also particularly into January if the stratosphere fails to recover from this potential “attack” then I wouldn’t be surprised to see at least one major and noteworthy cold outbreak across the UK.

It’s all to play for, but I certainly feel that compared with last winter, the coming winter will be markedly colder for the UK.

Time will tell as ever in meteorology and I look forward to looking back on this particular blog come next March to contrast and compare.

Regards to all,


The Importance of High Pressure On the UK In Winter

19 Nov

Well autumn is nearly behind us and attention is most certainly being directed towards the start of December and the first of the winter months.  Clearly there has been a lot of talk about a cold start to the month and that seems increasingly likely.  One of the primary reasons for this is the potential development of high pressure (anticyclone) in and around the UK.  I have produced this blog to bring attention to the importance of high pressure across the UK through the winter and whilst this isn’t a forecast as such, may highlight some of my thoughts for the coming weeks.

As we all know high pressure brings more settled conditions than compared with low pressure.  Now from a UK’s perspective high pressure during the winter is important because it aids to bring the risk of colder conditions from a variety of sources.  Due to the location of the UK geographically and the way air masses move around high pressure, more often than not, higher pressure to the north of the UK in some shape or form, is the main ‘key’ to unlock the door to much colder conditions from the arctic.

Whilst this particular chart is at the far end of the GFS model’s time frame, it is still a good chart to use as an example to illustrate the above comments;


Of primary importance and significance here is the area of high pressure situated to the north-west of the UK.  The high pressure is extensive and extends from eastern Canada (1035mb) to Greenland (1030mb) and then all the way up towards Svalbard and into the arctic (1040mb).  Air masses around high pressure systems flow clockwise which is particularly important because if you get high pressure to the north-west of the UK for example, then in theory the air mass to the right of the high pressure would be from a north or north-easterly source, clearly of which is a cold source through winter.  The other important factor is the low pressure over Scandinavia here.  This is sort of acting to combine with the high pressure to allow a particularly cold region of air to move down across the UK from the north-east.

So this is one way that high pressure is important to the UK in winter, get the high pressure at a more northerly latitude to the north of the UK then the chances of colder weather certainly increase, but isn’t a certainty, then again what is in meteorology!?

The other important feature of high pressure and the UK is if the high pressure isn’t able to get a northerly location but becomes situated across the UK.  This type of pattern in winter brings little risk of wintry precipitation simply because the anticyclone is dominant across the UK and brings settled conditions, as would be expected.  However, what is important is something which is known as an inversion, which develops beneath areas of high pressure and this can still lead to particularly cold conditions at the surface, especially over a period of days.  I have explained this below in a graphic;

Air within a region of high pressure is sinking and warms as it does so until a point is often reached in the lower atmosphere where an inversion develops, where the temperature then suddenly cools (or warms if you’re rising up from the surface). What is important here is that beneath this inversion cold air can be come trapped, particularly after a period of days because as each overnight period comes and goes, as long as the skies are clear, then cooling takes place and over a period of days that results in a gradual drop in temperature. As an example, when the high pressure builds into the UK the initial maximum temperature may be 8C with temperatures falling to near or slightly below freezing at night (as long as skies are clear).  However, the net affect is for the temperature to steadily drop seeing the nights are longer than the days and if the high pressure persists for several days then the maximum temperatures within 4 or 5 days may be nothing higher than 3C or 4C and minimum temperatures fall more significantly below freezing.

So, there we have it.  High pressure is particularly important during the winter period and it would seem that given latest forecast data the end of the month and into early December will see high pressure become an increasingly important factor.

Regards to all,


Rest of November 12 – Thoughts & Analysis

16 Nov

Well there goes the first half of November and with only 2 weeks left of autumn, until December starts, this autumn has been quite an unusual one.  The distinct lack of unsettled and zonal conditions has been noteworthy, despite quite potent stratospheric developments which can aid the development of this trend towards more zonal conditions through autumn.  We are yet to see any significantly cold conditions, despite some frosts at times.  The first half November has followed suite really with a mix of conditions being evident.

The second half of November has clearly been a talking point for some time, particularly in relation to the potential development of colder weather and a broader change in synoptic pattern.  In this blog I’ll attempt to summarise my thoughts and information to give an idea and suggestion of what I believe will develop during the second half of the month.  As an early disclaimer, of sorts, it should be noted that the second half of November is a forecasting challenge for many reasons.

For the time being I expect rather unsettled conditions to continue across the UK and the reason for this is the following broader synoptic pattern across Europe;

High pressure remains influential across southern and eastern areas of Europe as low pressure remains slow-moving in the vicinity of the UK.  As a result for the UK the next week or so looks unsettled.  Without going into the details, areas of low pressure look set to bring showers, longer spells of rain and some windy conditions as well.  This is highlighted well by the latest GFS ENS mean chart for the middle of next week;

So now that is out-of-the-way, what about the all important final quarter or so of November and perhaps into early December?…Is it likely to turn colder I hear you ask?…

My answer at the moment is; yes.  I also expect it to become somewhat drier than average as well.  The below image was a tricky one to try to put together but I believe it summarises the broader synoptic patterns by late November and into early December.  Clearly I expect higher pressure to become dominant to the north or north-west of the UK whilst pressure becomes lower across more southern areas of Europe.  There are definite uncertainties over the final location of any higher pressure and this will be crucial to any potential cold spell.



The longer range forecast models, of late, have been persistently showing a trend towards higher pressure to the north of the UK in some shape or form.  This type of synoptic develop at this time of year often leads to what is known as a negative North Atlantic Oscillation (-NAO) and essentially ‘kills off’ any low pressure systems and zonal conditions that the Atlantic can bring to the UK.

I have to admit the final location of any higher pressure is unknown, but to give one example and that is with higher pressure more directly over the UK is the 00Z ECMWF model;

This is one of a number of possible solutions towards the end of November.  If this synoptic pattern were to materialise then generally the UK would potentially enter into a period of colder conditions with a risk of frosts and fog by night, depending on cloud amounts.  At this time of year high pressure across the UK more often than not doesn’t equal mild conditions, particularly if the high pressure becomes relatively slow moving across the UK over a number of days.  What you should also note on that ECMWF chart is how there are similarities to my chart.  Note how pressure becomes lower across southern Europe and Mediterranean, whilst clearly pressure is rising in and around the UK.

So in summary, for the time being I expect predominantly unsettled conditions to carry on with a particularly unsettled week next week for many areas of the UK, but especially across the north and west.  I will then ‘stick my neck out’ and make a bold suggestion of a significant pattern change by late November and into early December which will take the UK into a colder and drier spell of weather.  Clearly, and as mentioned earlier, the details are unknown, but my outcome is for late November to now turn colder, particularly compared with of late.

As ever it’ll be interesting to see how things develop and materialise, but the winter woolies may well be needed by late November and into early December.

Regards to all,


Stratospheric Conditions – Updated Thought’s & Analysis

3 Nov

Clearly we are now into the final autumn month and the next 4 weeks or so are likely to prove interesting and also potentially very important in terms of gauging what the opening month of winter may well be like. A month ago I produced a blog taking a specific look at how stratospheric conditions can affect and have an important role on the atmospheric conditions within the troposphere, the region of the atmosphere where all our weather takes place.  Just as a re-cap the link to that blog is below as further information within this particular blog may refer to it.


There have been some interesting developments of late, which at the present time, do tend to point towards the likely development of a more prolonged and sustained period of unsettled conditions across the UK as November progresses.  The primary reason for this is the potential development of the polar vortex either over or very near to the Greenland area.  Referring to the above blog, last December was a perfect example of how a strong polar vortex resulted in the UK experiencing a series of low pressure systems not only over days, but weeks.  There are signs that conditions within the stratosphere may well begin to influence the weather in the troposphere more significantly in the coming weeks.

As an example and give some details as to why, I want to start with the two below images showing the latest temperature predictions within the stratosphere;


The above images are the latest temperatures at both the 30hPa level and also at the 50hPa level, which are approximately 20 miles to 25 miles up into the atmosphere respectively, or more specifically into the stratosphere.  What has been a persistent feature of the temperature at the 30hPa level and above is that there has been a tight core of temperatures at or below -70C.  This can be seen on the first image.  Now, in comparison, note on the second image (50hPa) that intense core/region of cold air isn’t anywhere near as noteworthy.

This distinct difference in temperature within the stratosphere has allowed (amongst other variables) conditions in the troposphere to be far more ‘blocked’ and high pressure dominated so far this autumn.  Clearly if you try to think of September and October combined it has been far from a wet, windy or even stormy autumn.  One of the primary reasons for this is that the very cold air which is developing due to seasonal changes within the stratosphere hasn’t been able to down-well to lower altitudes and affect conditions within the troposphere.  What can happen at this time of year is low pressure becomes dominant across Greenland and the UK is then set into a pattern of zonal conditions with spells of wet and windy conditions affecting many areas.  Again, the perfect example of that kind of setup is last December (see previous blog for the images).

However, and finally, what seems to be taking place now is that there is a signal within the forecast models for the very cold air at very high altitudes in the stratosphere to potentially begin to filter down into other areas of the stratosphere and then potentially into the troposphere.  The ECMWF model today for example, is showing a potential result of this scenario within 10 to 14 days with low pressure becoming dominant across Greenland and the surrounding areas, whilst the UK is then affected by an increasingly zonal flow;

On the above image, note the dark blue and purple colours directly associated with what is termed the ‘Polar Vortex’.  This pattern on the above image is a near-perfect example of a +NAO (North Atlantic Oscillation) pattern.

The temperatures within the stratosphere are highly important and if the very cold temperatures continue to cool further and also extend downwards within the atmosphere, then the end result could well be a more pronounced spell of zonal conditions across the UK as November progresses.  Temperatures across the polar regions have and continue to run below climate averages, despite some short-term minor variations, this can be seen on the below image;

The end result of the current scenario is that if the above trend continues then there would need to be an additional factor(s) to help stop or at least slow down the cooling processes.  As last November (2011) progressed a similar trend developed and for those who are fans of cold and potentially snowy weather will know, the end result was a particularly unseasonal December with often frequent spells of mild, wet and windy weather.  So there is the potential of a similar setup developing this year for early winter.  However, in meteorological terms 3 to 4 weeks is a long time and we will all have to wait and see how things go from here, but I would imagine that as November progresses a more pronounced spell of zonal, wet and windy conditions may now develop.

For anyone with an interest in this area of meteorology may I direct you to the following topic on the Netweather.tv forum;


More frequent information and discussions takes place here and particular attention should be made to the creator of the thread ‘Chionomaniac’ who provides some educational and informative posts on the subject.

Regards to all,




November 2012 – Thoughts & Analysis

31 Oct

We are clearly progressing through Autumn at quite a rapid pace and with October now behind us, attention turns to November.  November, like October, can continue to provide quite significant extremes of weather.  Overall the risk of frosts and wintry precipitation does increase on average as temperatures continue to fall.  Autumn gales can often become noteworthy through this month with notoriously persistent spells of wet, windy and potentially even stormy weather.

At the time of writing this blog I do believe November is likely to be a month of two halves, which, to an extent, helps summarise and discuss the expected weather.  However, what I don’t believe will happen is for November to be a ‘typical’ wet, windy and mild washout.  At this juncture it is worth to highlight the current state of the stratosphere.  Up to present the seasonal fall in temperature across the polar regions has been sort of irregular with some minor falls to below average, but equally then recovering to nearer average.  This can be seen on the below image for example;

As can be seen of late temperatures at the 30hPa level are essentially near average and the stratospheric vortex is becoming noteworthy at high altitudes with some particularly cold temperatures (<-70C) at and above 30hPa.  Out of interest the 30hPa level is approximately at an altitude 40,000ft. What has happened so far this autumn however is that the particularly cold temperatures at these altitudes haven’t been able to descend to lower levels and affect the weather within the troposphere and bring about the significant development of a polar vortex across polar regions, which is one of the reason why October was most certainly not a particularly stormy or frequently mild, wet and windy month.  Overall, I don’t expect a major polar vortex to develop through November either and as a result this creates a particularly difficult month to discuss to an extent, as it may well lead to quite sudden and extreme changes in the weather rather than a more persistent and dominant weather-type.

So what’s the first half of the month expected to be like:

The above pattern may look rather strange, given the position of the high pressure.  However and quite simply, I expect low pressure to be influential across the UK and other northern areas of Europe during the first half of November, whilst pressure is higher to the west and potentially north-west of the UK.  Clearly the above image unfortunately doesn’t extend far enough west, but I expect quite a meridional pattern with higher pressure to the west or north-west of the UK, whilst low pressure dominates across the UK.

This pattern is likely to lead to predominantly cool, if not rather cold conditions, with temperatures at or slightly below average and with clearly precipitation totals above average.  Both the GFS and the ECMWF ensemble mean charts highlight this scenario well;

Both these forecast charts out to 240hrs (10th) clearly show this expected pattern.  The resultant weather throughout a large part of early November is likely to be characterised by rather cold west or north-westerly winds and potentially even northerly winds at times, but nothing sustained.  Showers and longer spells of rain are likely nationwide with some windy conditions as well.  Precipitation is likely to be wintry especially across northern hills and overnight frosts are also possible as well.  The high pressure to the west or potentially south-west as well, may well build into parts of southern areas of the UK at times, so whilst overall I do expect the first half of November to be predominantly unsettled, some drier conditions are temporarily possible.
The second half of the month is interesting.  As I highlighted earlier in the blog at the present time I don’t expect a sudden development of a polar vortex in and around Greenland, so I don’t expect a particularly zonal or unsettled second half of the month, in fact the opposite, which the below image tries to highlight;

Longer range forecast information, at the moment, is signalling a potential reversal of fortunes with lower pressure perhaps becoming influential across central and southern areas of Europe, whilst higher pressure may well become dominant to the north of the UK in some shape or form.  This kind of particular setup is difficult to predict and as a result I have low confidence at the moment over the broader synoptic developments during the second half of the month.  However, despite this, I do believe that some colder weather may develop at times later in the month as the weather patterns become more blocked.  Clearly to what extent is unknown, it may well lead to a temporary ‘cold snap’ for a few days, or potentially something more prolonged.  Overall I expect temperatures through the second half of November to be average at best, if not trending slightly below nationwide and precipitation totals may become near or below average.
So in summary November looks to be quite a changeable and interesting month.  I don’t expect a mild, wet and windy month from start to finish.  The second half of the month in particular could become very interesting and from the middle of November onwards the final signs and signals should be in place as well to give a better idea as to how early winter may develop.  This could go really go either of two ways, increasingly unsettled, zonal and mild as per late November and December of last year, or potentially remain quite blocked with a higher chance of colder conditions into December. Safe to say though November is unlikely to be a mild month.

I’ll attempt to review the first half of November mid-month and then also take a look at December towards the end of the month as usual.

Regards to all,


October 2012 – What’s In Store?…

28 Sep

Well there goes one of the autumn months already and September has certainly produced some extremes, as is often the case with September’s.  Many areas of the UK experienced some late summer warmth just after the opening week of the month with temperatures widely above 20C.  This was then in comparison to the middle and latter half of the month which has clearly felt far more autumnal with temperatures generally average at best.  Clearly the stand-out feature of the month was the potent area of low pressure around the 24th and the 25th which clearly brought yet further large and extreme rainfall totals which is in-keeping with the months prior to September.

So what about October?…October can often really bring the ‘true’ signs of autumn with a greater frequency of frosts, especially across northern areas, an increased risk of autumn gales and also perhaps a more notable risk of some wintry precipitation across northern areas as well.  At the moment I expect the following pattern to dominate throughout the majority, if not all of the month;

There is only one particular image to summarise October at the present time, simply because I couldn’t find a distinct difference between the first half of the month and the second half.  Clearly, and just as a quick reminder, September was most definitely a month of two halves, which was highlighted, but October, I believe, looks set to be an unsettled one throughout.  What this forecasts doesn’t highlight is clearly more short-term variations where perhaps higher pressure temporarily builds into the UK before low pressure returns, so that is something to bear in mind, as unsettled conditions from the 1st to the 31st of October is unlikely.  That being said, there is a clear signal for October this year to be predominantly unsettled and cyclonic.

The GFS and ECMWF ensemble charts highlight this trend throughout the first half of the month in particular;

Both these models signal lower pressure to be dominant to the west or north-west of the UK as high pressure is influential further south, which tallies with my original image.  As a result of this broader pattern, the first half of the month in particular is likely to be most unsettled across northern and western areas of the UK with precipitation totals at their greatest here.  This is contrast with more southern and south-eastern areas which may generally experience more in the way of drier and brighter intervals interspersed with some rain and showers at times.

Looking at the longer range GFS ensemble, which covers up to mid-month and the broader unsettled pattern persists;

With the temperature gradient increasing across the North Atlantic as is always the case through October, as temperatures drop quite rapidly across higher latitudes, this increases the risk of more noteworthy and deep areas of low pressure. So given the broader unsettled pattern it does seem likely or at least possible that somewhere down the line the UK will be at risk of some particularly potent low pressure systems, clearly details on this is unknown at this stage. This signal for low pressure throughout the first half of the month can be seen quite clearly on the latest GFS ensemble graph for central areas of the UK;

Despite some spread in the ensemble members which does lead to some uncertainty, at the moment the general trend is towards lower pressure with little signal for higher pressure to become influential. The second half of October, as is always the case, has a lower confidence given the time frames involved and the synoptic evolutions can change and as usual I’ll review the first half of October and look more closely at the second half of the month around the 15th.

So, in summary.  I expect October 2012 to be quite a typical October month across the UK with lower pressure dominating rather than higher pressure and thus bringing quite a cyclonic month.  Temperatures may well vary from north to south, with still the risk of some warmer days across the south as areas of low pressure to the west or north-west bring up some temporary warmer air from the south-west, but equally cooler, if not colder, north-westerly winds may develop at times as well.

Regards to all.