Tag Archives: Christmas weather

The Christmas storm singularity

One of the best articles written regarding weather forecasting is Philip Eden’s ‘Does the Weather Have a Memory?’

The crux of the article is that certain weather types can repeat at the same time of year with one having a 100 per cent probability!

The Christmas storm singularity occurs in 84 per cent of years.

While 84 per cent certainly doesn’t mean ‘nailed on’, in the current set up of models being evenly spread between settled and stormy it can be safely guessed at this range that there will be unsettled weather around on the 25th. Whether it will affect the whole country remains uncertain.

The last big snorter of a Christmas storm I can remember in London was 2013. The entry for the 23rd into the 24th reads.

“Cloudy and breezy start grew steadily duller with rain just before noon. Rain grew heavier with some really strong gusts into evening culminating at 2am. Cloud at one point was 10kms thick. Three deaths related to weather.”

There was chaos nationwide with flooding and power cuts.

https://www.bbc.co.uk/news/uk-25512391

The average wind run for this station shows the singularity as well as the mid December settled spell we are now seeing.

The GFS Scottish Christmas Day blizzard of 2020

With the midnight run of this model bringing the start of the 25th into range the prognosis for the big day is a rare white one – for those north of the border.

The rest of the country is messy mix of sleet and, in London’s case, cold rain with a high of 7C. It looks fairly average for this locality!

The GFS operational chart for 0000 on the 25th

But followers of this blog and elsewhere will know that any model output beyond 72 hours should be taken with a very large pinch of salt.

But while conditions out to 15 days are often very different they can give a general guide to how the atmosphere is evolving in the medium range. The last few winters I’ve been doing this Christmas day model blog have revealed that conditions are sometimes not wildly different from what was hinted at 372 hours before.

Over the last few days the GFS, and other models, has been flip-flopping between cold and mild, a symptom of the current atmospheric situation which suggests that the polar vortex may undergo displacement as we progress further into winter. This could signal colder weather for NW Europe – but exactly where this colder weather will be as we progress to the end of the month is very uncertain – any colder than average weather could remain closer toward Central Europe, as happened in 2008.

Below are charts for each day from the midnight operational run of the GFS model.