October Preliminary Northern Hemisphere Winter 2018-19 Outlook

Hello everybody, today we have the last joint outlook for the Northern Hemisphere, before I start producing the outlooks for North America, Europe and Japan and their respective snowfall seasons in Winter 2018-19. We will take a refreshed look at all the factors before us, and look at further progress. This shall begin at an unexpected place… the models.

Seasonal Models

First we being with the NMME, the multi model ensemble portraying the majority of the North American based Seasonal models.

It shows slightly warm temperature anomalies for the Eastern US and Japan, and much warmer anomalies for winter on the West Coast and the European Alps.

The latest UKMO Seasonal run, shows more snowfall for Eastern and Southwest US, average snowfall (still lots of snow) for Japan, and below average for Europe and the PNW.

The latest EC Seasonal run, shows more snowfall for Eastern US and for California, mostly average conditions for Japan and Europe, and poor conditions for the PNW.

Primarily the models (and this includes other models as well) are generally showing a more snowier Eastern US, average for Japan, slightly below average for Europe, and less snowier PNW.

ENSO

If you haven’t read my previous thoughts on the matter, you should definitely check it out here. ECMWF shows a basin-wide ENSO event, which means it will create a strong North Pacific jetstream. This would give California a lot of snowfall, and theoretically make the Eastern US less cold. I believe that this process could bring more snowfall for the Eastern US, because of my belief that the -EPO will hold strong, with the jetstream sliding south over California, driven by a further south than average Aleutian Low, and possibly +EAMT events at various stages of the season, given +AAM is the Niño Phase. None of this delivers a win for the PNW or Southwest Canada, which I expect to be under a ridge for a lot of the season.

In terms of intensity of the El Niño, the NMME shows a weak-moderate El Niño below.

The JMA, CFS and EC models also show similar projections to the NMME mean. UKMO and ACCESS-S (both from different countries, but same dynamical core) shows a stronger El Niño coming into force over winter. I am personally predicting a weak-moderate El Niño from around +1.0-+1.2. Given it’s not particularly warm, it means some of it’s impacts will be muffled. However the atmospheric component could be different.

Speaking of the atmosphere, the latest ECMWF forecast of the Southern Oscillation Index or SOI, shows the atmospheric component weirdly turning like a Niña(positive values). My guess is that this could be the models trying to grasp Niño associated anomalies deep into the Western and Central Pacific. Or perhaps it’s the sign of a major flip. UKMO and JMA agrees, and CFS and the CMA (China) model disagree. There’s also some OLR/Precip forecasts from various models that show a similar atmospheric ENSO difference to it’s oceanic component.

So I reckon we will see a basin-wide El Niño event, which is weak-moderate. The exact effects on particular regions will be zoomed in upon in the individual region forecasts. I will keep discussing ENSO on Twitter (@longrangesnow) and on the 33andrain teleconnections thread for advanced ENSO discussion.

QBO

The QBO is heading from negative to positive, and the crucial 30mb level has now turned positive. The underlying effects of this, mean more chance of a +AO setup, particularly later in the season. This means more snowfall for the West Coast, and less for Eastern US, Europe and Japan.

To explain the QBO a bit more in depth, and explain what it means as an index, here is an advanced abstract from a musing of mine a few weeks back. “However it gives the false impression that the QBO is this one number index, which isn’t what it really is. It really is an Oscillation that goes from 5-10mb all the way down to 90-100mb within the equatorial region in the stratosphere, bounded by more anomalies associated with ground conditions and the Hadley cells below, and the Semi Annual Oscillation (SAO) above it. This means when the QBO is positive and descending at 30mb, it may for example be negative zonal wind anomalies below 50mb to 100mb. This shows that the effects of the QBO are not strictly linear, because of this inconsistency within the same Oscillation, creating different effects depending on the height and phase of the descending QBO. There is also the strength of the QBO to contend with, and whether the trend is for a normal QBO phase progression, or a sudden change in progression. These are all factors which play into the QBO’s effect polewardly towards the Stratospheric Polar Vortex, therefore on it’s tropospheric counterpart and then the general hemispheric circulation”

Snow & Ice

Siberian snow cover is currently below average. But not for long.

The above EPS Control Forecast shows by nearly the end of October, Siberia is now fully covered in snow, giving the -AO feedback that people want if they want more cold in Europe, and more snowfall in Eastern US and Japan. However I would prefer it if the snow made it to Moscow quicker…. North American Snow Cover is also higher than average, it’s loosely tied to a +AO, but counter to that, it gives plenty of cold for the Eastern US to tap into.

In terms of Arctic sea ice, it is currently well below average in the Laptev-Barents-Kara Sea areas, which all creates more -AO forcing. I don’t expect that to change too much, based on current forecasts.

PDO

ECMWF shows the PDO to be neutral or slightly positive, with the warm anomalies along the North American Coast, but the normally cold anomalies are just neutral. This means the PDO have little effect. However those warm anomalies off the coast, are a key part of my forecast. They help force a -EPO, which means less snowfall for the PNW and more snowfall for the Eastern US. The average anomalies south of the Bering Sea, which are surrounded by warm SSTs, help pinpoint the location of the Aleutian Low.

Solar

As previously discussed, we are in a solar minimum. This creates -AO forcing, correlating with more snowfall for Europe, Eastern US and Japan. Below is the current sunspot index, and forecast. More info on the forecasts here.

MJO

I expect the MJO will go further eastward, and perhaps be a little stronger than your typical El Niño. La Niñas typically have stronger MJOs, than El Niño’s. More on the relationship between ENSO location and the MJO here. This all points to an increased prevalence of the MJO in Phases 7 & 8, into Phase 1. This is echoed by the SST forcing, with warm SSTs around Phase 7,8,1 & 2, and cooler SSTs around Phase 4 & 5. It also is being forecast by Long Range CFS below. This all points to potentially less atmospheric rivers (but more if it can get over to Phases 3 & 4), and more troughing for Eastern North America. Phase 6 & 7 would indicate a -NAO, which would bring more cold into Europe(Phase 3 indicates a +NAO).

Stratosphere

An El Niño, higher Siberian Snow Cover than average, Low Sea Ice around the Barents-Kara Sea region, all indicate a weaker Polar Vortex. In addition, there is potential for blocking coming in from Alaska, and over the Barents-Kara Sea, and potentially also from Greenland. The latest CFS shows 3 members showing a weaker than average polar vortex than average.

This would indicate -AO forcing. It’s worth noting that the polar vortex at 10mb is colder (stronger) than normal for this time of year.

Forming conclusions

So in summary, my forecast is for a rapidly descending to positive QBO, weak-moderate basin-wide El Niño with perhaps some weird atmospheric feedback, neutral/slightly +PDO, strong -EPO, a -AO and -NAO and a much further south than usual Aleutian Low. Also some potential Scandi blocking, and blocking over the Barents-Kara Sea.

This gives us:
1. A warmer and less snowier PNW.
2. A more snowier (with slightly above average temps) California and SW.
3. An average Colorado and Utah.
4. A much snowier Eastern US.
5. A colder Europe, but with average snowfall.
6. A slightly above average snowfall season for Japan.

All of the above has been put into my very rough 500mb height anomalies forecast map for 2018-19 Winter for the Northern Hemisphere.

Please note that this map is to note general trends, don’t go looking for exact locations.

Now we have started to form conclusions, we can continue narrowing down region by region over the next month or so. Thank you so much for reading this seasonal outlook for the Northern Hemisphere.

Disclaimer: Seasonal outlooks tend to have bias and errors, due to the fact that these forecasts are so far out. So don’t use these outlooks to make important decisions. These outlooks are meant to be interesting information, that can help to see what the season might be like.

Thanks again for reading, follow me on Twitter @longrangesnow and subscribe to my email list by clicking on the tab on the main header above. First regional outlook will be Japan in a week or so. I will hopefully see you then.

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