This year’s record tying super El Nino significantly dominated at least the first half of the 2015-16 winter season. El Nino related or not, it was also another year with a positive North Atlantic Oscillation which has resulted in a warmer than normal December through February period. Lack of blocking has meant the Atlantic flow has ruled but as the season matured, so changes in the upper flow changed.

Arctic Oscillation was positive through December but has been more negative in January.

Only 1 spell throughout the December-February period has there been a negative North Atlantic Oscillation.

The first month (December) turned out record warm and wet across the UK and Europe, helped by a strong polar vortex which led to a strong +NAO/AO. That then led to a powerful trans Atlantic jet stream which drew unusually mild, tropical air north for not just the UK but majority of the hemisphere. El Nino which enhanced the southern branch or subtropical jet brought one deluge after the next to Ireland and the UK.

Within a 30 day stretch, Dec 10 through Jan 10, we saw multiple flash flood episodes.

December 2015 temperature anomaly

Similar to December 2013, storms were strong and frequent.

At the close of December, a mid Atlantic storm system brought a huge hemispheric pattern shift by pumping warmth into the arctic. Weakening of the polar vortex with the first real signs of stratospheric warming from NE Asia to Alaska. With PV displacement towards Eurasia, this instigated a brief -NAO coupled with -AO which allowed a week long cold shot mid January, first of the season.

Many parts of the UK experienced their first real snowfall and we also saw temps drop to -12C at Kinbrace.

Late January and the NAO flipped back positive with Atlantic air stream resuming but with colder air entrainment, sporadic snowfall came and went. This pattern was more ‘typical’ than what we saw in December.

Even gave me the opportunity to go sledging with my daughter Holly for the first time.

As well as experiencing the first taste of winter, January did start off record wet in Aberdeenshire and temps climbed to a toasty 17C.

Despite a taste of winter, mild won out in January overall but for Scandinavia, it was darn cold.

January temperature anomaly

February has been a different month. After a brief regrouping of the polar vortex and cooling stratosphere, we’ve seen another ongoing wave of stratospheric warming. Again, the orientation of this warming has favoured cold in east Asia and North America with westerly dominance on this side of the Atlantic.

Notice in this 30-day 500mb geopotential height anomaly animation how there hasn’t been a connection between North Atlantic and Greenland high.

The difference between January and February is that the return of a -AO has released Arctic, even Siberian origin air south and with eastbound lows entraining much colder air, temperatures have been colder in West Europe with snowfall coming and going. Recent times including now has seen a displaced jet stream further south into Iberia and France, keeping the UK and Ireland beneath a colder air mass.

This setup allowed nights to turn very cold and in fact Braemar recorded a minimum of -14C within the last 10 days which makes for the UK’s lowest reading of winter.

February temp anomaly so far.

Given the chilly outlook through the remainder of February, this month could wind up slightly cooler than normal. February was highlighted back at the end of autumn last year as the winter’s coldest month!

As we head towards March, we have a colder pattern in place with further south jet as well as blocking high pressure between Scotland and Iceland.

There is increasing confidence that the NAO will go negative into March as stratospheric warming is expected to become more favourable for cold over Europe.

Note the below strat warming between initial and 10 days from now is crossing the pole and down over Greenland as well as Canada. This would support more Greenland blocking and colder weather for UK and West Europe.

GFS ensemble shows a colder than normal period now till early March at least.

Canadian showing some nice blocking and a cold solution for UK/West Europe for March.

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