Thanks to the ECMWF freeing up a lot more of their range of graphical NWP products, the long range seasonal forecast is now available for up to four clear months ahead, and it’s a vast improvement on the three month long range ‘contingency planners’ forecast that you can access from the UKMO. For one thing it’s not just kind of weird graph of expected temperature and rainfall anomalies averaged out for a single region like theirs is, the ECMWF output is in the form of monthly maps for any region in the world of anticipated terciles, extremes or anomalies for temperature and rainfall.
The bad news, at least for the winter 2020-21 each month, at least temperature wise look remarkably similar. In fact I’ve never seen mean temperature anomalies for the whole of Europe look so consistently alike for four consecutive months like this. That’s not to say that this couldn’t happen, but according to this forecast, winter looks like a slightly muted affair of last winter, with mild or very mild temperatures across the whole of Scandinavia, Mediterranean, and much of central and eastern Europe. The good news is that the areas closest to average in Europe, thanks to a developing cold pool in the North Atlantic south of Iceland, will be the UK, France, the Benelux countries and northern Spain.
It has just been brought to my attention that buried deep in the Met Office web site they do publish probabilistic guidance for temperature and rainfall up to six months ahead that they update monthly. The product is similar to those produced by the ECMWF but the maps are much smaller and don’t include forecasts for individual months. I’ve included a screenshot example from it below, which not surprisingly forecasts a very mild winter for 2020-21 across Europe just as the ECMWF do. Let’s hope in the future they can find a bit of development time to increase the size of their postage stamp sized maps and split them into individual months. It might be handy if they included a more detailed map for the whole of IONA, with mean maximum and minimum temperature anomalies, because let’s face it terciles or quintiles are a fairly crude and very broad brush way of doing things, especially when it won’t be too long before Exeter will soon have the computing power of a £4.1 million pound Isambard 2, the largest Arm-based supercomputer in Europe.