The 2018-19 winter forecast is based on and factoring in all atmospheric/oceanic drivers currently in play. This year’s forecast will take into consideration the current ENSO index (El Nino Southern Oscillation), the global as well as Atlantic SSTA (sea surface temperature anomaly) profile, arctic sea ice extent and current status of the solar cycle. There are other aspects which will be looked at.

Background

Here are the main factors taken into consideration for the upcoming 2017-18 winter for Europe. Global SSTA’s can have significant influence on the atmosphere above, especially mid and late winter.

Current.

A few things stand out clearly in the above chart. The Pacific as a basin is warm (especially the further north) and Atlantic cool (especially the further north).

On the face of it, the warm north/northeast Pacific (Gulf of Alaska) could lead to stronger than normal high pressure extending into Alaska, NW Canada leading to downstream troughs and cold surges into the central and eastern USA.

The cooler waters surrounding and south of Greenland could support more troughiness and low pressure west, northwest of the UK but it’s a question of how strong of a jet stream shall we have which shall determine the level of ‘maritime’ influence. That can be determined by two factors, 1) the temperature gradient over North America and 2) temperature gradient in both Atlantic (temp anomaly) and atmosphere above.

Here’s the CFSv2 projected SSTA’s for the 3-month winter period.

Interesting how the model has all ocean basins warm. Can I just say now, that will NOT be the case.

Other factors to consider

The global temperature is slowly coming down following the Super El Nino from a couple of years ago. Each super El Nino drives the global temperature up (in the form of increased water vapour into the atmosphere), a La Nina (cooling of the equatorial Pacific) typically follows a strong El Nino often helping drop the global temperature from above to below normal.

However the global temperature has risen further with each of the last 3 Super El Ninos. The 1997-98 Super El Nino had a higher start point for cooling than the 1982-83 Super El Nino and it would appear we have an even higher start point for cooling now following the 2014-15 Super El Nino compared to 1997-98. Point is we are beginning the cooling from a warmer ‘start point’ and this is essentially leading to less global cooling with each passing Super El Nino.

What will be interesting to see over the next 6 months will be how much of a drop in global temperature shall we see this winter?

Eurasian snow cover during October was low this year compared to previous years. A study found that high October snow cover across Eurasia during late autumn tended to strengthen the Siberia high. This in turn was said to increase the likelihood of blocking and colder winters for the US and Europe.

However this indicator proves unreliable in my opinion as recent big snow covers have not enhanced high latitude blocking or brought cold winters. In fact 2009 saw little October snow cover across Eurasia yet we experienced record high latitude blocking and the coldest winter since 1978-79.

Other, more complex and long term factors worth considering

Other players which are more complex and more challenging to read in the long term but is linked to the current status and behavior of solar cycle. The Quasi-biennial oscillation (QBO) is a measure of equatorial zonal winds within the tropics.

A more typical westerly QBO usually correlates to a stronger westerly flow through the mid latitudes and less amplification. This tends to be stronger around solar maximums whereas an easterly QBO is the reversal in the upper winds and often aids the development of high latitude blocking. This becomes more common around solar minimums.

Also, there is the Maddan Julian Oscillation (MJO), a pulse of increased convection which circles the equatorial region of the planet. The MJO often has greater influence during low solar years with more amplification of upper air pattern.

We are currently nearing the end of solar cycle 24 with the minimum expected by 2020. This can and will affect all of the above drivers, even controlling the cooling and heating of our vast oceans.

With the lowest sunspot activity in some 80 years and the approach of a solar minimum, one has to assume that our planet is ready to turn down the thermostat.

The strength of the stratospheric polar vortex will determine the availability of the cold for the mid latitudes. A weak vortex will help create a weaker jet stream and a weaker jet stream will make for increased blocking patterns. It’s difficult to say at this point whether we’ll go into December with a weak or stronger polar vortex with cold stratosphere.

Keep in mind, as the solar cycle nears the minimum, there’s greater possibility for weaker PV’s and SSWE’s (sudden stratospheric warming events). Impossible to say if we will see that this winter.

The verdict: What can we expect this winter?

I have two major conflictions for this winter. 1) Our planet is very warm BUT we are approaching a solar minimum.

With a very warm north Pacific/Gulf of Alaska, warm off the US East Coast and more importantly, the likely maturation of a modoki, central Pacific basin El Nino, there is an increased possibility for a cold and snowy winter from the Northern Plains to Carolinas.

The warm Gulf of Alaska may be good for the US but may not so much the UK. We only need to go back to the winter of 2014-15 to see why. Despite a weak polar vortex and frequent southward plunges of arctic air into the US, this air met abnormally warm air  over the Caribbean. This thermal clash drove a stronger than normal Atlantic jet stream and fired one deep low after the next across the UK.

I’m in two minds about the cold North Atlantic. This could support more trough west and over the UK while ridging holds near France which keeps us mild and wet OR we have a less strong jet with less temperature contrast over the US and across the Atlantic which means blocking over Greenland and down over the Atlantic, overriding the cool ocean feedback.

The behavior of the PV will be crucial. If we get a weakening vortex into early December in a year where we have a modoki El Nino, look out for colder, snowier times for the UK.

At this point, I believe a fairly average, perhaps slightly above average November is on the way for rainfall.

A wetter November is what we want to see when it comes to cold winters. Joe Bastardi of Weatherbell highlighted years ago. Where the rains fall heaviest, this can signal where the cold is headed for winter. We saw a textbook example of this in 2009.

So, November looks fairly unexciting winter weather-wise. Unfortunately, given the likely stronger than average PV over the next 4-6 weeks, I believe early and mid December remains mild and firmly Atlantic driven.

384 hours from now.

Stronger PV’s lead to this pattern.

However, given the low solar and modoki El Nino, I believe change could occur (similar to 2009) by around Christmas/New Year with a weakening PV and increase in blocking.

Winters with modoki El Ninos within a near minimum solar cycle tend to favour greater potential for mid winter SSWE’s (sudden stratospheric warming events) and colder 2nd half’s to winter. (colder mid January, February). Could the February 2018 SSWE repeat sometime in early/mid January?

All in all, I believe winter will be fairly benign this side of Christmas but could turn pretty wild from mid January with colder, perhaps much colder January and February.

The Canadian has an interesting look with classic Greenland block/cold pattern for February.

The CFSv2 500mb mean height for the full winter is quite interesting with arctic/Greenland blocking.

Monthly break down indicates clear cut mild.

CFSv2 500mb for December

January

February

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