As we progress through October, the various teleconnections we look at for winter prediction becomes more important and interesting.

So what do we look for?

Teleconnection / Current Status

• Equatorial Pacific (Neutral-La Nina)
• North Pacific SST Profile (-PDO)
• North Atlantic SST (+AMO)
• Indian Ocean SST (Neutral IOD)
• QBO (west)
• Behavior of the MJO
• Siberian snow cover extent (above average through mid-Oct)
• Solar Maximum
• Arctic Sea Ice extent

Then we break each of the above down to what they actually mean.

Global SST’s as of 10 Oct, 2024.

Let’s start with the North Pacific and first off, note the exceptional warmth south of Aleutians towards Japan but cooling Gulf of Alaska (-PDO). This ‘could’ be a positive for cold lovers…

Then let’s look at the North Atlantic, it remains very warm, esp towards Newfoundland. (+AMO). This profile has been very persistent in the past 24 or so months. By that I mean record warm! That stand out warm pool east of Newfoundland may help in supporting a blocking high over the N Atlantic extending to Greenland.

Now let’s down down to the Indian Ocean, note the generally uniform warm profile throughout throughout the basin except for the cooling off Somalia. This shows a neutral IOD. (Perhaps not as much of a factor for winter).

As for the equatorial Pacific, the strongest cooling is appears central. (Central based La Nina possible!)

The reasons for a stalling of the La Nina development is likely distortion of wind flow likely down to, at least in-part the MJO, the SOI (southern oscillation index) which is a measure of air pressure between Darwin and Tahiti has not been behaving as you would expect for a supposed developing La Nina. This is likely due to an ‘active’ phase of the MJO is the wrong place (west-central Pacific during late Sept/early Oct) and therefore a lack of easterlies generated over the equatorial Pacific which drives upwelling and cooling of the surface waters. This likely now changing…

Latest MJO-ENSO Interaction

The development of La Nina has once again stalled likely due to above reasons.

However, with the MJO returning to the Indian Ocean and Maritime Continent like we observed throughout much of August, those easterly trades should restrengthen over the Pacific.

Rising air over Indian Ocean and sinking over Pacific strengthens the easterlies near the dateline courtesy of winds blowing from high (E Pac) to low (IO/MC)

Weak La Nina is most likely through winter 24-25.

Forecast

CFSv2 and NMME for the upcoming 3-month period shows ‘east-central’ La Nina.

Likewise the NMME

There’s a direct relationship between ENSO and the MJO. When ENSO is either strong + or -, the effects of the MJO tends to be less.

It has to be said, that all of the below, likely was kick started by a rise in the SOI mid to late August, providing a nudge to the MJO.

What’s been happening from TROPICS to POLE to Stratosphere (Sept through mid-Oct?)

We cannot underestimate the power of the MJO (MADDEN JULIAN OSCILLATION). This has undoubtedly become an integral tool in my mid to long range forecasts and it works pretty well for the most part.

A seemingly simple rainfall/thunderstorm enhancing ‘atmospheric wave‘ propagating eastward through the equatorial Indian and Pacific Oceans releases heat north which can dictate the jet stream position, strength and amplitude therefore dictates the upstream and downstream wavelengths (ridges/troughs). It even dictates tropical cyclone productively globally as well as El Nino/La Nina.

It even has influence on our stratospheric polar vortex

Relationship between tropics and pole & effects on polar vortex

What do these various phases correlate to?

Here’s where we’ve been in the past 90 days.

Let’s take August as an example as I believe we’re back as of mid October. Stuck in phase 2-3 then 4-5 (Indian Ocean to Indonesia), we had strong UPWARD motion IO/MC while strong SUBSIDENCE over cent/east Pacific. Surface winds blowing eastwards across the Pacific helped cool equatorial Pacific and this provided a kick to the developing La Nina (& atmospheric response above, the SOI). We also saw a shut down in the tropical Atlantic due to large scale subsidence and also a RECORD STRONG +NAO.

Then came September and October and a shift in MJO into phases 7-8-1 (west to central Pacific), this resulted in strong a reversal in the pressure pattern over the Arctic and North Atlantic resulting in a -AO/NAO. The strong ‘atmospheric mountains’ generated by this eastward progression of thunderstorms within the tropics poking through the shallow ‘polar troposphere’ likely created drag within the stratospheric circulation causing record weak mean zonal winds and SPV displacement. This is at a time when the vortex should be largely undisturbed and strengthening at a steady rate.

Strong positives near stationary blocks were observed over northern North America, Greenland and Ural Mountains, this likely aided a ‘trop to strat’ frictional warming of the stratospheric polar vortex, slowing it’s growth and displacing off the pole.

Spells of arctic source cold entered the mid latitudes in W Europe and central Asia. As MJO re-enters the Indian Ocean and slowly heads towards Indonesia (phase 4-5), the AO/NAO heads positive and milder oceanic influence returns to areas which observed ‘periods of cold’.

As MJO amplifies BACK INTO PHASES 3-4-5 during October, I don’t think there’s a coincidence between this, the lowering of high latitude heights (+AO/NAO) and the likely uptick in 10pha mean zonal wind speeds (strengthening of the polar vortex) during the 2nd half of October.

While in phase 3 into 4 and 5 in late Auguast, we saw the development of Storm Lilian.

Lo and behold, back in those same phases and same amplitude now and have have prospects of quite a stormy upcoming weekend.

Followed by higher pressure a week or so from now?

As of 16/17th October, the MJO is LIKELY to return to the west, possibly central Pacific in the next 2-3 weeks (phase 6-7-8) and we’re likely to see the pattern we’ve just observed (-AO/NAO) in the last 2-3 weeks pattern repeat. This may be helped possibly by recent recurving Atlantic hurricanes.

So colder times ahead? While despite the AO/NAO returning to a negative state, there’s no guarantee the ridge and trough will sit in just the right place for cold in your back yard, however there’s increasing likelihood for another spell of colder, likely stronger than what’s been observed during September and October. It’s not how strong those 2-3 brief cold spells we’re but what the pattern is telling us.

The ECMWF sees further friction weakening of the stratospheric circulation in response to another period of strong high latitude blocking over the Arctic.

Longer range models see weak polar stratospheric winds into December and even January.

The DWD is very bullish.

QUESTION: While we expect the MJO to return to colder phases late October into November with prospects of a -AO/NAO return and possible weakening of the polar vortex again, is this temporarily or part of a longer term pattern into winter?

We’ll join up the dots at the bottom…

Highest Eurasian Snow cover For Mid-Oct in a Decade?

Looks like we have the highest Eurasia snow cover for the mid point of October since 2014 according to Dr Judah Cohen.

Snow cover as of 31 October as per latest GFS.

Significance of larger Siberia (Eurasian) snow cover extent in October?

It’s believed that greater snow cover extent, the stronger the Siberian high and therefore the potential for an SSW during winter.

Solar Maximum & West QBO

We’ll have a west QBO this winter. That’s winds blowing westwards within the stratosphere over the equator which typically aids stronger zonal westerlies/jet stream and polar vortex.

Solar maximum 25 has officially been declared by NASA in recent days. Stronger than cycle 24 but weaker than 23, it is however the strongest activity since the 2001 maximum.

We’ve all seen for ourselves or in photos the result of the most recent large CME’s and solar flares emitted from the sun, in the form of aurora sightings.

Some wording from Dr Joe D’Aleo.

When the sun is active, there are more geomagnetic storms and aurora events, there is less low clouds due to diffused cosmic rays, more UV (increasing 6 to 8%) which warms through ozone chemistry and a measurable increase in brightness. There is enhanced warming globally..

Via weatherbell

A quiet sun has lower geomagnetic warming, more low cloudiness over oceans which increases albedo (reflectivity) and lower UV (6 to 8%) which usually means a cold expanded polar vortex. Atmospheric flow patterns tend to be more amplified and persistent.

High solar can mean less blocking except when the QBO is westerly as it is now. The west QBO can mean episodes of a strat warming in the polar regions which allows polar air often trapped at higher latitudes to expand south. Snow is often less in most high flux years.

In short, solar maximum tends to suggest a stronger polar vortex and stronger westerlies which bottle arctic air up over the pole, however with a west QBO, this combo tends in increase probability for weaker polar vortex, greater chance for an SSW and -AO/NAO.

There is higher than usual levels of stratospheric ozone over the pole. This can be attributed to stronger incoming solar radiation.

What we know…

Solar Max, W QBO, Neutral to weak La Nina this winter.

So, we remain in a neutral to borderline weak La Nina at present. The core of cooling appears to be focusing towards the dateline or central Pacific.

Where will the MJO position and how amplified? A central based La Nina wouldn’t be particularly good news for colder lovers. The reason is that this could focus the MJO between Indian Ocean where we have uniform above average waters to Maritime Continent (phases 2-3 and 4-5), these are very +NAO phases with active Atlantic storm track into Western Europe, low pressure near Iceland, high pressure near the Azores.

However, with solar max and high ozone concentration within the polar stratosphere combined with west QBO with promotes greater chance for weaker polar vortex and winds which could override any central based La Nina influence or even the MJO as a whole. Afterall the MJO doesn’t always have influence. Remember back to last winter, it played out well (more so than any polar vortex influence) during late November-December and even early to mid January. Then came the DELAYED but not denied overwhelming influence of El Nino… This squashed the other teleconnection influences including MJO.

While a neutral IOD doesn’t tend to have much influence compared to strong positive or negative, there is still influence with a uniform warmer than normal SST basin.

The warmth within the Atlantic could do two things, provide added fuel to the jet stream and storms OR aid Atlantic to Greenland blocking.

While Solar Max/W QBO favours -AO/NAO, it’ll be interesting to see how the rest of Oct goes regarding Eurasia snow cover and whether this could be another influence favouring weaker/warmer stratosphere.

My hunch is SPELLS of strong -AO/NAO cold into eastern US/Canada and Western Europe November and December. The wildcard comes towards Christmas and beyond. Some models certainly suggest stuff going on with the polar vortex. Time will tell whether we see these swings between strong vs weak or will we see the vortex power up towards Christmas.

While a still believe a front loaded winter is more likely, a potential SSW could throw that thinking out the window for sure.

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