There is a very strong signal of colder than average weather dominating Europe including UK for early December. As MJO has already reached phrase 7 and heading toward phrase 8 later this week, which result to a strong and rare -ve NAO event, allowing high pressure to build across the North.
<- ECMWF MJO forecast
As the high pressure build across Scandinavia and Greenland, the jet stream will become more amplified and eventually weaken which allows some easterly wind to drive in.
However there are some uncertainty on the position of the Iberian low, which directly determine the direction of the air mass.
Here are few examples:
You can see the GFS run shows the low pressure will develop on our west, which import milder southeasterly wind to the UK. In contrast, the ECM run shows the low pressure will develop on our south, bringing colder northeasterly wind to the UK. This can cause huge difference on our temperature for the second week of December (4-10th).
<When low pressure is on the south of the UK
<When low pressure is on the west of the UK
Even though the low pressure developed on our west, it is expected to be pushed south or weaken in the third week of the month (11-17th). At this stage, Greenland high will continue to develop, pushing any low pressures to our south, which likely to import some northeasterly wind again, bringing (significantly) colder than average temperature to the UK. This can also produce some low level snow to the south when the low pressure move toward France.
<Temperature dipping down when the low pressure move to our south
<- The same GFS's run as above bringing back colder weather in the third week of December.
At this stage, the confident on forecasting weather on the Christmas period remain low, but most signals support the idea of calmer and drier for the rest of the December.
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