October Preliminary 2019-20 Winter Outlook

Okay it’s time to get ready to rumble for Winter 2019-20, so time to delve into the drivers. It’s a big and at some stages technical outlook, so if you want the summary, scroll to the Conclusions section towards the bottom. I encourage everyone to read my explanations and the reasoning, so we know why a winter turns out a certain way, it goes to the forecast or not. Anyway, onto the models….

The model outlook

The ECMWF model argues that winter will feature a Eastern US and Japanese ridge, reducing snowfall. It shows a +NAO, which means more snowfall, but less cold for the European Alps. The snow outlook in this is not good for the UK.

The UKMO seasonal agrees with ECMWF, producing very similar results. Japanese ridge, +NAO and Central US trough, all similar themes.

The North American NMME ensemble model shows warmer than normal temps for Japan and the Eastern US particularly, with more normal (but still relatively mild) temps for Europe and the Western US.

The models convey an overall +AO/+NAO outlook. Some people suggest this to be a point to at least express some question of the drivers. But the only way in my view to properly forecast a winter is to look and assess the drivers seperately and combine them into an outlook. So here we go…

QBO

13bbhFZl14.png
All the years that fit my current forecast for +5 to -10 for this season for QBO values at 30mb, minus strong Ninas and Ninos.

Above is my QBO analog for winter 2019-20. These factor in years that fit within the QBO value range that I am forecasting this year (roughly based on the forecast below).

qbo_wind.jpg
FU Berlin University

My QBO forecast for the next year is the red line in this image.

Key trends to note, based of this:

  1.  -NAO, deep Greenland high.
  2. Massive European trough.
  3. Deep troughing around Eastern US.
  4. Aleutian ridge.
  5. Eastern US pattern driven by NAO.

Probably not the most sturdy patterns imaginable indicated by the composite. But certainly a pattern that could drive snow and cold for the UK/Europe and the Eastern US. It’s also not a bad pattern at all for the PNW, not so great for the Southwest of the US.

Snow & Ice

Let’s start with my intital tweet and expand upon it.

Sources: ECMWF/Accuweather and NASA

So I expect a higher than normal October snow extent over Eurasia to continue. This would improve snowfall chances for Japan, Eastern US and Europe/UK, by forcing a -AO response and creating an environment more conducive to SSWs.

I also expect the current sea ice situation to continue bringing a similar tropospheric response for Japan, Eastern North America and Europe. This is forced by the low Barents-Kara Sea Ice linked to the AO and the stratosphere. The real interesting situation here is the very low sea ice towards the Pacific side of the AO domain.

ENSO

So firstly, we are currently in a Modoki Nino situation. What this means is that there are warm sea surface temperature anomalies in the Central Pacific, as opposed to the the original Eastern Pacific El Nino, closer to South America.

Just for the sake of the exercise and to be comprehensive, I am going to look at Modoki/CP Nino years including and since the 1970s:

The most robust connections to be made from this chart (and I tried various ideas), is the stronger than normal Aleutian Low, the Canadian blocking, and the troughing in the Eastern US. The European part of the composite is less clear, so take this analog as more about the Pacific.

Victor Gensini, with my annotations over it.

The other thing to note is the ENSO effect on the atmosphere. I often use the Atmospheric Angular Momentum charts to help us map out how the circulation around the Northern Hemisphere and ENSO plus various other drivers interact with each other.

I use this chart above to point out the long +AAM cycle over roughly the past year before the NH Summer. Given the cyclical nature of the AAM and the Global Wind Oscillation associated with it, I hedge on the tendency that we would largely lean towards this for much of winter. It is true that we may see more neutral or even +AAM conditions later in winter, January – February, and into Spring, but the start of winter is likely to start with more -AAM conditions, which could contribute to a better than normal start to winter.

Just as a reminder from last outlook, here is the -AAM composite

Lastly, let’s look at the actual ENSO forecast:

Accuweather/ECWMF

So we mostly see a weakish Modoki Nino event, coupled with a positive Pacific Meridional Mode event which warms the sea region close to California and out to Hawaii and the rest of the Pacific. These are all good signs for the Southwest of America, as well as the Eastern US. It also creates a pattern that isn’t so bad for Europe and Japan in terms of snowfall potential. But this year’s ENSO effects will center in the Pacific and downstream for North America.

North Pacific

Accuweather/ECMWF

Our current setup features warm seas across most of the North Pacific, focusing in the Aleutian Sea. This has meant troughing for the PNW and ridging for the Eastern US. However as the winter pattern expands the LWT (Long-wave trough) and the centre of the SSTAs changes, we may see the ridge shift east, shifting the associated trough and ridge east as well.

The anomalies themselves are weakening quite a bit from the current situation. And the forecasts I am looking at show some sort of gravitation towards Alaska of the Warm SSTAs, with the Aleutian warm SSTAs subsiding quite a bit. This may make the synoptic pattern better for the Eastern US and Europe further downstream. But it is also going to decrease snowfall for the Pacific Northwest.

And it also depends on the AAM and associated factors, an Aleutian low may come into play if we see more positive torques and a possible tendency towards a +AAM at some stage, like I was talking above.
 

Solar

We are currently in a solar minimum with it’s effects peaking upon the world over the next few years. It is correlated with a -AO and particularly -NAO winter, which would mean more snow and cold for Europe and the UK especially. Eastern US and Japan both also gain from this driver’s positioning.

Stratosphere

CFS/weatheriscool

Per the limited tools at my disposal, there are signs of minor stratospheric weakening in November and early-mid December, and perhaps something bigger later in February.

The Brewer-Dobson Circulation is expected to be above normal through the Northern Hemisphere at this point. It’s average in the tropics, and growing in the SH, because of stratospheric temperatures making ozone transport easier if they are colder. I’d say there is a favouring of above normal BDC this season, which means a Sudden Stratosphere Warming and subsequent -AO and -NAO are of a higher probability. I’d say the overall outlook for this driver looks good for Europe/UK, the Eastern US and Japan.

MJO

Tropical Tidbits

The MJO is forecast to be at it’s strongest in December and January. Phase 8-1-2 forcing is expected to be strong. This generally leans towards a -NAO and Scandinavian blocking in Phase 8-1. A lean towards Phase 3 and beyond towards Australia would force a +NAO.

In general the cold SSTs off Australia (Maritime Continent) are set to force a Phase 7-8-1-2 response in early-mid winter. Later in winter, I expect more of a Phase 1-2 and Phase 6-7 pattern focus, but also some of the other MJO phases with potential for some support for +NAO periods. But for the most part, I see a favouring of a -NAO, a potential SSW, more Eastern US snowfall. If anything, this would indicate a later winter for the Southwestern US.

Atlantic

I am not a big user of the Atlantic for forecasting, but for the British and European blog readers, here we go:

ECMWF/Accuweather

The cold “blob” in the North Atlantic may allow for a colder winter for the UK and Europe as a whole. So it’s good for snowfall, especially lower down, but may reduce precipitation a bit.

Conclusion

  • Snow & Ice conditions good for Eastern US, Japan and Europe/UK.
  • MJO largely good for European and UK snowfall, perhaps less so later in winter. Similar for Eastern US and Japan.
  • Oceanic ENSO good for Japan, Southwest US and Eastern US.
  • -AAM good for Europe, Eastern US and Japan, less strong later in winter.
  • Stratospheric conditions favourable for Eastern US, Japan and Europe/UK.
  • Solar minimum favourable for more snowfall for Eastern US, Japan and Europe/UK.
  • Atlantic favourable for a snowy UK winter and colder Europe.
  • QBO favourable for Eastern US, UK and Europe.
  • North Pacific favourable for Eastern US, less so for PNW.

So in terms of what this exactly means, region by region:

  • Japan should be in for an above average winter, particularly Hokkaido. I’ll look at the SSTs in the region and Siberia deeper in the proper Japanese outlook, so keep watch for that.
  • European Alps are forecast to receive a cold and snowy winter. It could be a good one for the Southern Alps, but there should also be good periods for the Northern Alps.
  • It is my opinion that the British Isles will see a snowier than average season, with cold periods. These prospects look best early and especially mid winter.
  • The Eastern US looks like it is set to have a good season as well, focused from the Central US early in the season, but more open to Nor’easters later in the season.
  • California is set to have an above average snowfall season, particularly in SoCal. Less snowfall, the further north you go.
  • The Southwest of US is set to have an above average snowfall season.
  • Utah and Colorado are set to have a slightly above average season IMO.
  • The Canadian/Northern US Rockies are set to have an average to slightly above average season, best falls are early in the season.
  • The PNW is set to have a below average season.

Stay tuned for the specific regional outlooks!

And to conclude the preliminary outlook is some of my forecast maps.

Yellow line is the jetstream. Red is the ridges/highs. Blue is the troughs/lows
Maps are for general purposes only, not specific, as to be expected in Paint.

Thank you for reading this preliminary outlook. I hope you are excited for the winter, and ready to provide long term forecasts 🙂

2 thoughts on “October Preliminary 2019-20 Winter Outlook

  1. Hi Zac, an excellent and comprehensive presentation as usual. We know that there are a lot of variables running into this winter and early 2020 and you refer to many of these. Some, like the Arctic ice extent (still at a record low for mid October), the timing of the full transition of the QBO to east based (may be too late to have much impact on this winter), low solar (which may not impact until next and/or even the following winter) and not least, the ENSO state (pretty neutral seems likely to continue but whether more Nino-like or Nina-like with the battle between the warmer WPAC and the cooler EPAC continuing to wax and wane) could all influence the patterns through this winter. I do feel that we need to be cautious about calling the ENSO state an El Nino Modoki. If we had a similar pattern but with higher SSTs overall and so under El Nino conditions (ie: consistently higher temps in the Nino 3.4 region) then a true Modoki would allow for some more robust correlations. The current (and seemingly ongoing) weak conditions are likely to produce continued variability in the patterns. I’m sure that you are fully aware of this and your regular updates will be even more important than usual. David

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    1. Thanks David. Yes, the ENSO state is not quite solid, and the “Modoki” is not very strong. I certainly am putting more emphasis on the atmospheric component of ENSO, in accords with the GSDM. Appreciate your feedback.

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