NAO Ensemble Uncertainty Leaves Rest of October Open To Question

I’ve seen a few mentions floating around and some folks have also asked me about the prospects of a late month Greenland block developing and an early taste to winter here in the UK. Right now I am kinda sitting on the fence or at least not jumping too quick as there is a lot of uncertainty in the NAO ensembles these days. It is also worth pointing out that despite a negative NAO at this time of year or indeed even winter, this doesn’t nessesarily mean winter comes to the UK. However the very up and down nature of the ensemble makes it a poor guide in the longer term forecast. Really untill we loose the warmth that’s still around and the atmosphere makes that change towards winter, then the NAO isn’t always the greatest indicator.

In saying all that, though the ensemble has been trending more and more negative, plus given the summer bias to negative, I think I would be kidding myself on if I believed a major positive was coming or I dissregarded what the recent runs have suggested. The return to negative is more likely given the signal over the past 3-4 months. It has been tough to get it positive. The complete opposite to last year.

Here’s the latest NAO ensemble.

The ECMWF is starting to hint at a cold shot times for Scandinavia/Eastern Europe and later, the US again.

What I do feel confident on right now is the major pattern shift over North America. The cold leaves by this weekend but before it does, a major shot of arctic air drives across Canada and also drops into the Northern Tier of the US.

Check this out for Friday.

but then, have a look at Sunday! Response to +NAO?

The big question is how long does this positive phase last before flipping back and the recent ensemble trend has been for a decent drop from the 16th onwards. I suspect the US gets a break from the cold but turns stormier with more Pacific influence freeflowing across the continent in the 6-10 day but beyond that, well I wouldn’t be surprised to see another cold episode.

Even though the arctic air reteats, one cannot rule out the threat of snowstorms, especially for BC and the Pacific Northwest. Cold pools can become trapped within a more positive AO pattern where the main channel of arctic air is cut off but these cold pool within upper troughs can still supply snowstorms within these pattern setups.

Cold Blast coming to Scandinavia/Russia, eventually the UK?

As for Europe, here’s what the ECMWF suggests for next week. Notice the colder air building over Scandinavia and northwest Russia. This may be the seeds to PERHAPS a late October cold shot for the UK but it’s too early to speculate.

Sorry for the short post. This is more food for thought. I shall cover this in greater detail in the next few days!

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  1. calum says:

    Question Mark, Does the JS ever deflect off a UK or Scandi high to the north? i.e. go over the UK and on upto northern Norway? Does that every happen? I think I’ve only ever seen it deflect south of the UK like in you pic.

  2. Jamie says:

    Who needs a cold shot from the arctic late Oct? I’ve had enough of putting the heating on already. Lol

    Lets do the warmth dance i.e. the dance to stay warm in this blooming cold.


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