Big shift in the latest OPI. Now at -1.67. 

Is that where the OPI currently is or where it's projected to be by the end of today's GFS run?

Think it's the projection based on the latest GFS run. I'm guessing it's picking up on the flatter pattern which is appearing in some of the runs now. 

-1.67 to 27th October should still give us a negative OPI for October?

btw, its not out to the end of the gfs run but to day 10. so we have a predicted opi at 21/10 of -2, based on todays gfs 12z out to T240 and the actual data from the first 10 days of october.

as far as i know clem, the opi updates at the end of each gfs run to give a running figure based on the actual numbers up to the current day and the projected number based on the next 10 days. the mean of the previous days numbers should not be relevant.

incidentally, this from the latest ECMWF seasonal update for winter which was issued on the 8th: 

It has a major negative AO

It has more blocking over Greenland now , but still has the strongest blocking over the NW part of N America and over the pole.

of course, this could well deliver a west based -NAO which would make nw europe fairly mild. promising though as it does tie in with what seems to be louder and louder background noise re a -AO winter.

Much better - hardly anyone's mentioned SSW yet

Thank you Riccardo for your contribution and your work looks interesting.

I'm just using the running mean to take out the guess work of the next 10 days predictions to see where we stand as of now. The more days figures that are added to the running mean obviously the less uncertainty and less swings there are.  If we can keep the figure sub -1.5 things could be getting very interesting!

Interesting piece on Joe B's Saturday Summary around the AO and NAO and the current CFS model contradicting its winter forecast with the positioning of above average heights across the Atlantic. 

Clem

Riccardo why did you choose to correlate the OPI with the AO rather than the NAO?

Of course the NAO does not correlate exactly with UK CET-the correlation is around 0.60.

Based on the GFS12z run it's now down below -3 again. I'm surprised because at a glance the 6z and 12z runs both look pretty flat, though TBH I've not looked at them in depth. If Riccardo is around I'd be interested to know what the key differences are between today's 6z and 12z GFS runs in terms of the OPI.

i think it's to do with the angle of the vortex Brian. I wish I could get a better handle on this but I believe that the lower the angle, the more likely it is that a split vortex will ensue rather than an organised one.

it's to do with how organised the polar vortex looks to become as the month progresses. a disorganised vortex as we enter November will promote a better chance of a negative AO in the months that follow. there are other factors at play which will promote feedback mechanisms which also promote a -AO. 

I think low pressure south of Alaska and over southern Greenland and western Russia are signs that the Polar Vortex is having trouble becoming organized.

But this is a subject about which we're all learning as we go along, I think.

At -0.19 based on the GFS6z. Interesting to see what it changes to once the 12z data is being used.

What is the mechanism that's proposed to explain the correlation? r=0.91 is very high, higher than almost any other correlation in the world of climate forecasting even in the tropics (I recall El Nino and regional rainfall correlations are around r=0.7/0.8 at best). Is it simply persistence, i.e. once the atmosphere is organised in a particular way it then remains so for a few months? Or is there something specific about October?

For an index that is atmosphere based, where there has traditionally been thought to be far less persistence than in the ocean, it seems too good to be true. But certainly intriguing.

With such a strong statistical link present in actual values, I would expect dynamical models to reproduce the correlation too and therefore their ensemble forecasts would be much more accurate than they are.

Finally, many winters are a mix with the AO swinging from strongly positive to strongly negative from month to month. Given the 0.91 correlation this would imply the ONI would have to be roughly neutral in any year where the AO swings around intra-seasonally, but that seems counter-intuitive if we consider what dynamical forcing might explain the relationship.

Given how the index is described I'd have thought it could quite easily be independently replicated by sourcing the raw data.

I don't really know anything about the OPI, but all these negative numbers sounds exciting!

anyone know what the proven track record is here OPI + vs OPO - , so how many mild winters have seen with a + & likewise for a negative or is this a untested / unproven theory model at present time?

either way if the minus continues then I am supporting the theory and only time will tell?

interesting none the less, just 16 more days to go.

thanks

The OPI numbers are based on a GFS run but which is the important figure, is it the actual figure at the end of the month or the trend throughout the month. Anyone know?

by the end of tomorrow, we will have more solid data than forecast data re the month as a whole. once we get through the upcoming weekend, the OPI graph should begin to home in on its likely result.  heights are definitely on the drop through the remainder of the month (which would be expected). how far can this take the OPI towards neutral ?

I don't think we're talking about persistence of the atmospheric pattern here. Quite the opposite, in fact. What we're looking for are conditions this month which are associated with an amplified jet in the troposphere. Over the coming weeks and months this should lead to warmth rising northwards (to promote northern blocking) and, at some point, upwards into the stratosphere (your Sudden Stratospheric Warming).

There's no way of knowing when these events will present themselves - a coupled system of oceans and atmosphere is too complex for that - hence your observation that the AO swings from positive to negative during the winter from one month to the next. But there's a fair case that this analysis of October patterns can tell you whether or not a negative AO will manifest itself at some point(s) between December and March.

Disclaimer: O level physics grade B 1977 may not be enough for me to know what I'm on about.