The beginning of December is causing a lot of headaches for us forecasters. The computer models we rely on to predict the weather have been very inconsistent and flip flopping from one possible solution to another, at times of such consistency we turn to the ECM 46 day forecast.

This model is an ensemble blend which runs 46 days into the future, far beyond the reach of normal forecast models and we’re going to be discussing what this is suggesting for December.

The first week of December is expected to be rather unsettled with areas of low pressure moving across the UK, occasionally these may drag down some colder air from the North bringing the risk of snow across Northern Hills, this is something Metcast will be keeping a close eye on in the coming days. Follow Snow Watch for wintry updates.

GFS forecast showing the potential for some snow during the first week of December

The second week of December is where models go off in different directions making it hard for forecasters to get an idea. One chart we use is the ECM Cluster chart, this takes the 51 ECMWF ensembles and splits them up to give a general picture of possible weather patterns.

The first cluster in the top left shows high pressure to the North-West of the UK across Scandinavia, 54.9% of the 51 ensembles are suggesting this pattern is a possibility. The cluster chart next to it shows a much more mobile, Atlantic driven pattern and this one has 45.1% support.

You can see how it can be difficult to forecast a particular outcome when the two patterns are almost equally supported, yet both would bring very different weather for the UK.

This is where the EC46 model I spoke about at the beginning comes into play – Unfortunately, I cannot post these charts directly because they are not publicly available but they are very similar to the charts above. Week 1 of the EC46 shows unsettled weather, week 2 shows high pressure building towards the North-West of the UK. Week 3 shows a return to more Atlantic driven weather, however I tend to take anything past Week 2 with a pinch of salt as it does sometimes prove to be unreliable and prone to the same “flip flopping” the shorter range models suffer from.

Here’s a small snippet of the 11-18 day forecast from the EC46 showing height rises across Scandinavia

Going forward, I think we will see high pressure developing across Scandinavia as we go through the second week of December and this will turn things increasingly settled across the UK. There is the possibility of colder weather coming in across the UK from the East however given the finely balanced probabilities we’re dealing with, it’s a little too early to take this too seriously.

Join us tomorrow as we start our weekly look at Christmas 2018, or if you cannot wait until then head on over to our community forum for some festive model watching, tradition talk and more…

Daniel has been interested in weather all his life and learned to forecast the weather during his teenage years. His favourite season is winter and his favourite weather is snowfall and thunderstorms.

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