It’s interesting when looking back at the 500mb anomaly from the last 90 days and see a cold arctic, hence the ‘less melting’ of sea ice compared to 2012, 2013 but still see a predominantly -AO and -NAO. I’ve said for years now that we should watch carefully the ‘trends’ and this year is largely opposite of last year which was bias positive. Largely down to the solar maximum I believe.

Check out the summer. Note the blocking across the high latitudes which extended far enough south to give us another great summer and start to autumn. That northern blocking signified a -NAO/AO summer.

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A negative AO/NAO is often misunderstood as being a COLD signal but a -NAO has different responses to our atmosphere depending upon time of year.

This shows you the predominantly -NAO/AO we had during the past summer despite it being warmer than normal.

Come autumn and especially with warm water surrounding us, we get a different response from that same -NAO.

Back in 2009, we had very warm water surrounding the UK and with a predominantly -NAO into autumn that meant a turn to very wet as the heights lowered and the air cooled. But come winter and we see the natural shift, we get the winter type -NAO. Where it rained a lot during the autumn, that’s where the cold likes to go and did go. My point is that going by the mean and not individual periods, you get a better grasp as to what’s going on and why we go from summer ridge to wet trough to cold trough with that prolonged -NAO signal. Like I say, the NAO was mainly positive last year.

Colder air and lower pressure in late autumn over residual warm water left behind by a warm summer leads to a wet pattern into October and particularly November. Sure we get spikes into psotive with both NAO and AO but given the LONGER TERM TREND, you know it’s only a matter of time before the signal flips back to negative again. We saw that in 2009 and we’re going to that this year. Where it likes to rain a lot during late autumn, that’s where the cold likes to go come the cold season and I think, based on all the evidence shown by the past and present, well there’s a lot more pointing to cold than warm this winter.

NAO was negative back in summer and autumn 2009.

The stratosphere sure is cooling over the pole through the next 10 days.

Initial

120 hrs

240 hrs

After a spell of positive in NAO/AO, the index is going back negative and strongly too. THIS should help trigger our wetter pattern over the next 6-8 weeks.

Especially when you’ve this SST profile around the UK.

That means snow building time over an important part of the world for us here in Western Europe… Asia. Afterall that’s our coldest source region and if the atmosphere plays out right then east, northeast winds should blow over a solid, vast expanse of snow cover. Less snow cover and you get weaker cold air masses.

ECMWF snow chart

36 hrs

240 hrs. See how it expands!

Check out this morning’s video for more on this.

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