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.

M.

 

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