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,