Early Winter (November & December) Forecast Review

[ December 11, 2018 ] - Back in October, MeteoGroup and Prescient Weather presented two live webinars, detailing the highlights of our winter forecast. After last winter ended on an extremely cold note, with the "Beast from the East" sweeping in, there was much attention on what this coming winter would bring to Europe, with the webinars attended by hundreds of organisations.

Through November and so far this December, our forecast has been verifying well. We predicted that early winter would see sustained periods of mild weather over northern, western and central Europe, with some exceptionally mild weather at times. Any cold spells here would be short-lived and of relatively low magnitude. Meanwhile, eastern parts of Europe into western Russia and the Black Sea areas were more exposed to some cold spells.

The chart below shows an example of 3 of our statistical analogue forecasts, predicting the chance for warmer than normal temperatures in early winter over Europe. As you can see from the observed anomalies in November, the forecast is going to plan so far, with more mild weather over western and central Europe after the short cold snap this week.

We also flagged up the potential for wet weather over Spain in November and strong winds at times over northern Europe in December, as shown in this slide, which was part of our winter webinar presentation. We have seen examples of both of these weather types so far.

In contrast to observed European weather to date this winter, back in September and October some well-respected long-range forecast models predicted a cold and blocked early winter, and this was also reflected in the forecasts issued by many other weather providers.

However, our holistic approach to forecasting (with class-leading methodology, software and analysis tools) combined with our team of experienced meteorologists gave us the edge, which was also the case in predicting the hot and dry summer over northern Europe along with the warm autumn over central and north-eastern Europe.

Rest of winter:

On some occasions, the forecast 'drivers' that influence the weather over Europe are all acting in the same direction. This leads to us issuing a high confidence seasonal forecast and the end user can normally expect a successful forecast. However, back in October, we already flagged up that mid-late winter would be a more challenging prediction. We identified several opposing forecast drivers for Europe. Even now, some of the best model guidance and statistical indicators that we use to generate the seasonal forecast are still suggesting a cold outcome, while others are predicting mild!

One important factor we are keeping a close eye on currently is the Stratospheric Polar Vortex. This is a belt of strong high altitude westerly winds that blow around a pool of bitterly cold air over the North Pole. Last February, this polar vortex completely collapsed in dramatic fashion and triggered the bitterly cold weather. After a strong start to this winter, the polar vortex again appears to be losing strength, but more slowly and less dramatically than in February. A slowly weakening polar vortex during December and into January could threaten some widespread colder weather into parts of Europe during mid-late winter. It is a risk factor that needs to be considered.

Our updated seasonal range forecast for late winter will be issued to subscribers later this week, with all the details, discussion and our expert view on the most likely outcome.

Value of Sub-Seasonal and Seasonal Forecasts:

Whilst we issue seasonal forecasts once per month to look ahead at the big picture for the next 3-4 months, MeteoGroup also issues Sub-Seasonal forecasts, twice per week, with a horizon of 4-6 weeks. These forecasts bridge the gap between traditional short-range forecasts and the seasonal range. They can pick up on crucial details such as sudden stratospheric warming events (SSWs) and incoming sudden cold spells. For example, in mid-January last year, we were able to warn users about the increasing threat of a significant cold spell for late February, giving them advance notice of up to 6 weeks (for a review of forecast performance during the ‘Beast from the East’ see here).

White Christmas over the UK!?:

Despite snow falling quite widely on Boxing Day evening over the UK last year, the Big Day itself avoided the snow. The last widespread White Christmas in the UK was in 2010, when snow lay widely and fell in some areas, too. This year, unfortunately, it could be more a case of 'let it blow' rather than 'let it snow', as fresh westerly winds and rather mild and wet weather seems more likely than a picture-postcard white scene. It's still too early to be 100% certain, though, with a small chance (currently around 10%) winds could flick around to the north to give a transient cold snap and perhaps a few wintry showers. This occurred in December 2004, after a rather mild month overall.

Matthew Dobson, Senior Energy Meteorologist, MeteoGroup