With winter fast approaching we felt it’s time we looked in more detail as to what could be expected over the coming winter months.
Of course as many of you will know forecasting isnt an exact science and the multitude of variables make long range forecasting particularly difficult.
To come up with a better idea of what may happen over a long range we have to rely on current large-scale patterns that persist over months rather than weeks, such as La Nina/El Nino, QBO, Solar activity, etc. – rather than the teleconnections of AO (Arctic Oscillation), NAO (North Atlantic Oscillation) and MJO (Madden Julian Oscillation) – which are only useful in a relatively short period of time.
One particular factor we look at is the state of the ‘ENSO’ (El Nino Southern Oscillation) This year has seen a shift towards what is known as LA Nina.
This is the waters of the Tropical Pacific cooling. At present we are seeing a weak La Nina.
Now the reason this may be a factor is because La Nina has been linked to a tendency to reduce the westerly winds which bring the UK mild air, particularly in early winter. And a La Nina phase of the ENSO has been linked to suppressed temperatures globally too, though this more likely during a strong event than a weak/moderate event that is currently being seen.
Another important factor is to look at what is happening high up in the Stratosphere as The tropical stratosphere is home to the QBO (Quasi-Biennial Oscillation) – a pattern of high altitude winds which alternate between westerly and easterly direction in regular cycles which help make predicting this part of the puzzle a little more straight forward.
The QBO influences the North Atlantic Oscillation (NAO), a pattern of seesawing atmospheric pressures that dominate European weather.
When the QBO winds are in a westerly/positive phase, pressure differences over the North Atlantic tend to be greater, which strengthens the jet stream which increases chances of mild and stormy winter weather.
This winter, the QBO is expected to remain in an easterly/negative phase, which increases the likelihood of northern Europe having a good shot at a colder, drier winter.
Another key factor that could help towards seeing a colder winter is the upcoming solar minimum, This combined with a negative NAO has the potential to see a weaker Polar Vortex allowing high pressure to assert more influence at northern latitudes forcing cold air south.
Then we have the SST’s, Sea surface temperatures have flipped over the last year seeing warmer temperatures on the Eastern side of the U.S which increases the chance for low pressure systems to form further south and enhancing Northern blocking.
In summary of all the above it is worth remembering the number of factors in predicting day to day weather makes the job of a long range forecast extremely difficult which is enhanced when dealing with a forecast for the UK given its relatively small size and large body of water in the shape of the Atlantic. We can often see the general weather pattern be one conducive to cold conditions overall for North West Europe yet the UK still manages to find itself slightly to warm for snowfall.
Overall however we feel there is an increased chance that the UK will see a colder winter than the last 4 years with temperatures at or just below average for the 3months December to February.
That in itself will be quite different as you can see from the picture.
Even for parts of the South an average winter can have upto 20 days of snow lying on the ground.