North American Winter Outlook 2019-20

Welcome to my North American outlook, discussing the models and drivers to come to conclusions about the winter ahead. Discussion is reasonably technical, so if one wishes just to see the results scroll to the bottom.

Model Outlook

The above outlook from ECMWF doesn’t form a strong part of my conclusions, but the global model trend has been considered. Here is the summary of it:

  • December and February favourable for the Eastern US
  • January more favourable for the Western US

I can certainly see some of these ideas coming into practice, with a more favourable pattern for the West in January being a possibility with a mid winter lull for the East Coast. But I am more in favour of this happening a bit later in winter if it does.


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 Eastern US. But it’s also a pattern that works well for the PNW, and not so much California and the SW. Basically it’s a pattern that works well for the Northern US, with cold temps not making it south as much.

ENSO

We are in a El Niño Modoki year. The pattern by the oceanic standard would be something like this. It focuses a ridge over Canada, and an Aleutian Low with a deep trough over the East Coast.

But we are also currently in a GWO orbit for the past few months in the negative AAM values. This focuses on deep troughing and cold over the North American Continent. This approach goes okay for the backend of the Rockies, and can actually help create deep cold in Southern US with the jet bringing cold Canadian air equatorward. This is laid out in the composite below.

Here is a composite for -AAM winters:

My take away for the GSDM pattern this season is a neutral to weak-moderately -AAM circuit this winter, particularly in early months. This pattern is good for cold in the Central US, and it actually helps moisture transport up to the East Coast storms.

These patterns are not going to be very favourable for California particularly early-mid winter. If we can see a more +AAM setup later in winter, probably February, it may see more snowfall. It bases a little better for the PNW.

North Pacific

Here is the latest SSTA forecasts for winter. The focus for warmth is in the Gulf of Alaska and immediately around the Aleutians. This helps ridging in this region, but the warmth is not quite on the coast. It is still a pattern that is not ideal for West Coast mountains and better for the Central and Eastern US.

I visualise this pattern in a rough manner below.

The slightly cold SSTAs is an ideal location for our Aleutian Low, which should be further south and west than normal IMO. This may help the West Coast’s chances later on as the warm “blob” weakens over winter and if a more +AAM pattern comes later in winter.

Sea Ice and Snow

Barents-Kara Sea Ice is expected to be a little bit lesser than normal, helping a -AO persist with higher than normal rates of Scandinavian blocking. This does well for the Eastern US, and less so for Western US.

The significantly lower than average sea ice anomalies in the Bering Sea right now and expected to continue into winter are expected to assist in ridging in the Aleutian region.

Taking statistics just after the end of October, Siberian snow extent is higher than normal, which helps invoke a -AO situation and helps the development of a SSW. North American snow cover is also higher than normal, which will help to build deeper cold earlier in the season and keep a cold theme throughout for the interior.

Atlantic

The EC SSTA forecast for the Atlantic side should be focused on the warm SSTs around the Bahamas. This may help to induce SE ridging.

Gulf of Mexico warm SSTAs should help to increase moisture for much of the East Coast. This will become less of a factor as the winter goes on.

Stratosphere

I see a more likely chance than normal for stratospheric warming this winter. Why?:

  1. A descending -QBO will help chances for a SSW later on this winter, particularly for February.
  2. Brewer Dobson Circulation is to be stronger than normal in both of the NH and SH subtropics and average over the tropics this month. I expect a stronger than normal BDC over the winter. This increases ozone in the SPV during the winter.
  3. ENSO factors are sort of supportive at least from the oceanic perspective. The GWO should be more supportive later in the winter.
  4. Higher than normal Siberian Snow Cover and low Barents-Kara Sea Ice supports a SSW during this winter.
  5. Solar minimum is taking place at this point, favouring a -AO and potential stratospheric disruption.

This means that I predict a SSW from mid Jan – March. Current signs of stratospheric weakening could eventuate into a minor SSW with some medium-long term implications, but I think the major event will be later in winter. The implications of this is more snowfall for the Eastern half of North America.

Conclusions

  1. The Interior of the East Coast on the Appalachians and further west is set to have a better than average snowfall season. The East Coastal regions are set to have a mostly average season.
  2. California is set to have a largely below average season. It won’t be absolutely abysmal though, with potentially improving conditions later in the season.
  3. The Southwest of US is set to have a largely average season, with New Mexico doing better than Arizona.
  4. Utah is set to have an average season. Which tends to be pretty good anyway.
  5. Colorado is set to have a mildly above average snowfall season.
  6. The Canadian/Northern US Rockies are set to have a mildly above average season.
  7. The PNW Coastal mountains are set to have a mildly below average season, but I can see them having a better early-mid season compared to California.
  8. The Central Interior US from the Great Plains to the Midwest to the Tennessee Valley is expected to have an above average season for snowfall and deep cold at times.

Thanks so much for reading. 

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 is meant to be interesting information, that can help to see what the season would be like. 

This took a lot of work over the last fortnight, so I appreciate your support. Starting in late November, my long range outlooks for North America will start! They will be produced every 2-3 weeks, looking out into the range of 10-30 days out. Stay tuned. 

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

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