Archive | January, 2013

February 2013 – What’s In Store?…

29 Jan

Well there goes another month and we are now well over half way through the winter of 2012/2013 with last of the winter months just around the corner.  January, will, without question, be remembered for quite a distinct and sharp change in the weather compared with the opening week or two. The discussed Sudden Stratospheric Warming event that I made numerous references to in blogs at the back-end of 2012 did occur and without question clearly influenced the weather during the middle and latter half of January.

So what about February and the last of the winter months?

Clearly these final few days of January has seen a marked change once again back towards milder and more unsettled conditions after approximately two weeks of cold weather, but I don’t expect this to be sustained.  Throughout the opening week of February I expect the following broader synoptic pattern to be in evidence;

Jet stream short term

In essence I expect high pressure to be dominant to the south-west and at times west of the UK whilst low pressure remains dominant to the north and north-east.  This is likely to maintain a west and at times north-westerly air flow over the UK overall.  This broader synoptic pattern is clearly evident on the latest GFS and ECM ensemble mean charts for the 5th;

Rz500m7

Reem1681

It is beyond the opening week of February that a change in synoptic pattern may well become more dominant to introduce a renewed risk of colder conditions developing across the UK.  The expected synoptic pattern and broader synoptic evolution looks to be very different to what brought the cold/very cold conditions through January.  This cold weather was produced due to a blocking area of high pressure to the north and north-east of the UK whilst low pressure dominated to the west and south-west.  As February progresses I expected high pressure to be influential to the west and north-west of the UK whilst low pressure is dominant to the east or north-east, as highlighted on the below graphic;

jet stream long term

This pattern is known as a meridional pattern where the jet stream often tracks far north before then tracking south.  It is on the eastern flank of the expected high pressure within the Atlantic that produces north or north-westerly winds and I do expect that this general, broader, meridional pattern to become established beyond the opening week of February and towards the middle of February.  This pattern is likely to lead to colder than average conditions becoming established with perhaps some wintry precipitation at times.  However, what is extremely difficult to comment on is just how much ridging will take place to the west and north-west of the UK.  If that area of high pressure isn’t substantial enough then low pressure systems can easily move over the top of the high pressure and down in to the UK and bringing generally milder conditions and this scenario cannot be ruled out either.

The ECMWF ensemble mean at 240hrs does highlight this broader meridional pattern.  Note how high pressure is attempting to ridge north-wards to the west of the UK whilst low pressure is digging southwards to the east of the UK and thus producing a rather cold north or north-westerly air mass over the UK.

Reem2401

A week or more ago there was the potential for a significant rise in pressure over Greenland through February which would have potentially brought a more sustained period of cold weather.  However, latest data has backed away from that idea and personally I don’t believe we will see a solid, sustained Greenland blocking high pressure developing through February now.  It can’t be ruled out, just like any pattern, but when looking at the medium and longer term, trends are important and without question there has been a trend away from this scenario.

The final third of February has a lot of uncertainty associated with it.  The stark variations that have been evident through this winter so far have made us realise, once again, how volatile the UK’s weather can be and how quickly it can change, as a result I have little or no confidence over the final week or 10 days or so of February at this stage, but a progression back towards more unsettled and milder conditions may well be preferred with time.

So in summary after an unsettled and relatively mild opening week or so of February the cold may well return, but this time most probably from the north  or north-west rather than the east or north-east as high pressure becomes an influential feature to the west or north-west of the UK and as low pressure dominates to the east. A mild, wet and windy month is not preferred at all and whilst there may well be a reduced risk of any Greenland block, I still think overall that February will combine with January in particular to help bring about an overall average if not slightly below average CET value by the end of the winter, which would mean that the winter of 2012/2013 would not fall into the ‘mild’ category and essentially be another cold winter overall.

Kind regards to all,

M.

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