Archive | November, 2012

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)

2)

3)

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,

M.

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,

M.

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,

M.

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.

https://matthugo.wordpress.com/2012/10/01/stratospheric-conditions-winter-weather-analysis-information/

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;

http://forum.netweather.tv/topic/74587-stratosphere-temperature-watch-20122013/

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,

M.