Winter Outlook 2020-21

Winter Outlook 2020-21

Executive Summary

This report explores temperature and winter storm expectations during the upcoming winter for the three main population/business zones in the Northern Hemisphere – North America, Europe, and East Asia. Last winter was one of the warmest and least disruptive winters on record – especially in Europe.  As a result, global supply chain disruptions were suppressed and periods of extreme cold, for all practical purposes, were absent. 

This winter is looking much different. The upcoming winter will be driven by three primary variables – trend, the La Nina event in the Pacific Ocean, and the Polar Vortex. The conclusion is that this winter will likely be colder than last winter and feature heightened temperatures variability in all three population zones. Of the three main zones, Europe has the highest probability for colder than normal temperatures. In the U.S., the region with the highest probability for colder than normal temperatures is the western U.S. versus the eastern U.S. Additionally, we anticipate more disruptive winter storm/ice events this winter compared to last winter with the highest probability areas including the western and northern U.S., eastern Europe, and southeast China. 


The era of extremes is firmly in place. This year in the U.S. alone, there have been 17, $1+ Billion USD loss weather/climate events as of late October. Hurricanes, wildfires, heat waves/drought, and severe weather events (such as the derecho in Iowa) are included in this infamous list. This breaks the record (2011 and 2017 had 16 events) and is the 6th consecutive year (2015-2020) in which 10 or more 1 billion-dollar weather and climate disaster events have impacted the United States; this is unprecedented.   

On a global basis, a recent study released by the United Nations indicates that since the turn of the century, there have been 7,348 major weather/climate events.  This is a sharp increase from the previous 20 years when there were 4,212 impactful weather/climate events. The data from this study is portrayed in the graph below.  There has been an increase in every “event” category when comparing the past 20 years to the final 20 years of the 20th Century.  The statistics are clear.  The frequency of extreme weather/climate events is increasing across most of the planet and these events have consequences.  

Figure 01: Total disaster events by type from 1980-1999 vs 2000-2019. Source: United Nations. 

Each event stresses the system. This is the case in human terms (fatalities/injuries, evacuations, loss of property, impacts on employment, forced migration, etc.) and in the supply chain (transportation disruptions, business interruptions, infrastructure damage, production outages, worker availability, price fluctuations, capacity constraints, etc.)   

With the tropical season winding down in the Northern Hemisphere, the next season for disruptions and impacts to the supply chain is winter.  Winter storms, periods of extreme cold/warmth, flood events, and unusual dryness will determine the extent, magnitude, and frequency of supply chain disruptions or lack thereof.  Temperature patterns will largely determine equipment choices for transport of temperature-sensitive products (PFF or Protect From Freeze).

What areas will have highest risk of disruptions from winter storms?  Will the PV (Polar Vortex) cause extreme cold in portions of the U.S., or Europe, or East Asia?  Or, will this winter feature a lack of extreme winter weather like the Northern Hemisphere experienced last winter? This report will discuss the variables that will drive the weather patterns around the Northern Hemisphere during the upcoming winter.  This information will be integrated into a forecast and a discussion of locations that have higher or lower risk of impacts/disruptions going into this winter. First, we will take a look back at last winter which was one for the record books. 

A look back at last winter

The winter of 2019-20 was the warmest winter in recent history in the mid-latitudes – where most people live.  The map below shows the temperature anomalies for the December-January-February period across the Northern Hemisphere (the anomalies are based on the past 10 years and are in degrees C).  The U.S., Europe and East Asia, which are commonly referred to as the Northern Hemisphere population zones, were warmer than normal to varying degrees – very warm in the U.S. and East Asia and exceptionally warm in Europe.  

Figure 02: Northern Hemisphere temperature anomalies (C) during December – February 2019–2020. Source: ERA5 

The area that was colder than normal was the northerly latitudes such as Alaska, northwest Canada, and Greenland.  These areas are always cold in winter but last year, they were 3-5 degrees C colder than the 10-year average.   

The reason for the warmer than normal mid-latitudes and colder than normal northern latitudes lies in the Polar Vortex (PV).  The PV was highly stable last winter which caused a pattern that locked Arctic air up near the North Pole, suppressed flowage of cold air into the mid-latitudes, and inevitably caused a very warm winter for the population zones of the U.S., Europe, and East Asia; more on the PV later in this report.


Figure 03: Population zones in the Northern Hemisphere. 

The Population/Demand Zones 

The Northern Hemisphere has three primary zones of risk for winter weather – U.S. Europe and East Asia. These zones encompass the bulk of population, GDP, and business exposure to environmental issues. Below is a map which shows the location of these zones.  We will now look at the details of last winter in these 3 key areas. 

The U.S.

Figure 04: United States temperature anomalies (C) during December – February 2019–2020. Source: ERA5 

The map below portrays the temperature departures during the December-January-February period last winter. The eastern half of the Lower 48 and adjacent areas of southern Canada were very warm while the western half had more variable temperatures.  The only area that had below normal readings last winter was a few isolated locations in the higher elevations of the Rockies. 

The next map portrays the snowfall anomalies for last winter.  Areas that had less than normal snowfall (negative anomalies) are in the red/yellow shadings while areas that had above normal snowfall (positive anomalies) are shaded in blue/purple. Most of the Lower 48 had below normal snowfall accumulations last winter. An example of this is the I-95 corridor (Boston to New York City to Baltimore) where snow totals, and transportation disruptions, were well below normal.  Hence, this crucial transportation zone had a low number of weather disruptions last year. Above normal snowfall totals were generally confined to areas near the Great Lakes and the Pacific Northwest/southwest Canada. All in all, it was a winter of below normal supply chain and business operation disruptions across most of the Lower 48. 

Figure 05: United States snowfall anomalies (in/mm) during December – February 2019–2020. Source: ERA5 


The winter of 2019-20 across Europe was one of the warmest ever recorded.  The anomalies ranged from 2-5+ degrees C above normal which over a 90-day period, is phenomenally impressive and extremely rare.  As one would expect, the snowfall totals were well below normal across most of the region. The exceptions were some of the coastal areas of the Scandinavian countries, Turkey, and far northern Russia near the Arctic Circle.  The ultra-warm and mostly snow-free season caused a winter with well below normal transportation disruptions, suppressed PFF requirements for temperature-sensitive shipments, and little, if any issues with extreme cold, even at short timescales.  

Figure 06: Europe temperature anomalies (C) during December – February 2019–2020. Source: ERA5 
Figure 07: Europe snowfall anomalies (in/mm) during December – February 2019–2020. Source: ERA5 

East Asia 

The warm theme was also widespread across East Asia last winter, as temperatures were well above normal across most of China, the Koreas, and Japan. The only area with colder than normal readings were sections in, and near, the Himalayas.  In other words, the highly populated areas were very warm, while the small areas that were colder than normal were primarily located in the sparsely populated higher mountain terrain. 

Figure 08: East Asia temperature anomalies (C) during December – February 2019–2020. Source: ERA5 
Figure 09: East Asia snowfall anomalies (in/mm) during December – February 2019– 2020. Source: ERA5 

Snowfall totals last winter were highly variable with well below normal accumulations in Japan while other areas had both above and below normal accumulations. 

Forecast Methodology

How a winter plays out is determined by a unique set of variables.  Each winter the variables differ as some become more dominant than others.  When assessing the forecast for the upcoming winter, the drivers that are the most pertinent are trend, the La Nina event, and the PV. Each variable will be discussed separately and then will be integrated together to determine the areas that have the highest/lowest probabilities of extreme cold/warmth and storm disruptions. 


The variable of trend has to be the starting point when assessing a seasonal forecast. The graphs below illustrate the temperatures during the December-January-February period in the 3 key population/demand zones – the U.S., Europe, and East Asia – over the past 40 years.  In other words, temperatures were averaged out in each individual “box” (see page ### for the specific location of each zone) and plotted.  The first winter on each graph is the winter of 1980-81 while the final point is last winter (2019-20).  The common theme across the mid-latitudes is straightforward – temperatures during the winter are getting warmer.  The trend is the most pronounced in Europe, but the other 2 areas are in the warming category albeit with a bit more volatility. 

Figure 10: United States population zone temperature anomalies during December – February 1980–2020. Source: ERA5 
Figure 11: Europe population zone temperature anomalies during December – February 1980–2020. Source: ERA5
Figure 12: East Asia population zone temperature anomalies during December – February 1980–2020. Source: ERA5 

Does this imply that these regions cannot have a cold winter?  No. East Asia had a cold winter 3 years ago while the U.S. had a cold winter in 2013-14 and a normal one 2 years ago.  The frequency of cold winters, though, is decreasing with time; the frequency of warm winters is increasing with time.  

What about the extremes? 

As winters are getting warmer, does this also mean that it does not get as cold as it used to?  The magnitude of cold during a particular season is noteworthy since it impacts the decision-making process of companies assessing risk of temperature sensitive products such as PFF equipment decisions (reefer, blanket, or dry van).     

From an intuitive standpoint, one may conclude that since winters are getting warmer, it does not get as cold as it used to.  The data does not support this perception.  The maps below are an example.    

The 2 maps below portray the coldest temperature over the past 2 decades during the winter (December-January-February).  The first set of maps is North America.  On the left is the coldest absolute temperature during the past decade (2010-11 to 2019-2020).  On the right is the coldest temperature during the first decade of the Century (2000-01 to 2009-10).  

For most locations in the northern U.S. and southern Canada, the coldest temperature occurred during the past 10 years versus the first 10 years of the new Century. Hence, the coldest temperature was commonly achieved in more recent times (the last decade) rather than during the first decade of the Millennium.  

Figure 13: United States absolute minimum temperature (C) during December – February 2000–2010. Source: ERA5 
Figure 14: United States absolute minimum temperature (C) during December – February 2011–2020. Source: ERA5
Figure 15: Europe absolute minimum temperature (C) during December – February 2000–2010. Source: ERA5
Figure 16: Europe absolute minimum temperature (C) during December – February 2011–2020. Source: ERA5

In Europe and East Asia, the trends are similar.  During the past decade, most locations have experienced the coldest extremes compared to that of the prior decade.  

In the mid-latitudes, it can still get as cold as it used to but the duration of cold is much less than it used to be – there are less extended periods of extreme cold.  Cold events tend to be shorter in duration, less frequent, and cover small spatial areas.  In general, the “warm ceiling” is increasing but the “cold floor” is staying the same. 

Is the Trend of Storms Decreasing?

At first glance, one might conclude that since winter temperatures are getting warmer, there are less impactful storms.  For most of the mid-latitudes, that is not the case.  An example of this is in the charts below. 

Increasing Storm Frequency

The first chart portrays snowstorm frequency by decade across the Lower 48.  The index used is the RSI (Regional Storm Index – from NOAA). The RSI is an index used to measure severity of winter storms and uses a combination of snowfall, wind, spatial extent of the storm, and the amount of population impacted. The number of storm events has been increasing during the past few decades.  The number of storm events in the past decade is nearly double that of the 1990s. Most of the increase is in the weaker category of storms  (Cat 1) versus the massive, debilitating ones (Cat 4 or 5).  On a regional basis, the increase in storm frequency is concentered in the northern sections of the Lower 48 versus the southern areas.  

Figure 17: United States categorically ranked snowstorms during October – April 1980–2020. Source: Regional Snowfall Index NOAA 

The crucial Northeast quadrant of the U.S., which features one of the most concentrated population zones (the I-95 corridor) and supply chain webs, is one of the areas that is driving this increase.  Storm occurrence has been increasing during the past 4 decades in both the lower category storms as well as the higher category. Hence, the frequency of disruptive events in the Northeast has been increasing on a decadal basis. 

Figure 18: Northeast United States categorically ranked snowstorms during October – April 1980–2020. Source: Regional Snowfall Index NOAA

The physical reason for this increase in winter storm events, and extreme events in general, lies in the oceans.  Ocean temperatures have steadily been increasing during the recent decades.  Below is a graph which depicts ocean temperature during the January – September period for every year starting in 1980 through this year.  The trend is very straightforward. The global oceans have been steadily warming for many decades.   

Warmer water increases the moisture content of the atmosphere via evaporation and in the right circumstance, is a storm enhancer – a multiplier if you will.  This is especially the case in regions that are near the oceans such as the Northeast portion of the U.S.   

Figure 19: Global ocean sea surface temperature anomalies (C/F) during January – September 1980–2020. Source: NOAA 

The La Nina Event 

There are large scale events that can impact the winter circulation patterns around the globe, including many areas of the Northern Hemisphere.  This winter happens to be one of those times.  

During the past 4-5 months, a La Nina event has developed in the equatorial Pacific.  For reference, a La Nina event is a period when SSTs in the equatorial Pacific drop to cooler than normal levels.  This ocean phenomenon impacts the atmospheric circulation initially in the Pacific Ocean and then reverberates across many areas of the globe.  The stronger the “event”, the greater the impact.  

The map below portrays SST anomalies as of.  Water temperatures across most of the globe are warmer than normal as depicted by the red shading.   The large-scale exception is the cooler than normal waters (blue shading) in the central and eastern Pacific near the equator. The location of the La Nina event is highlighted on the global SST map.  La Nina events, along with El Nino events, normally persist for a period of at least 6-9 months. Hence, this winter will be dominated by a La Nina base state. 

Figure 20: Global sea surface temperature anomalies (C) on November 2, 2020. Source: OISSTv2, NOAA 

The unique item about the La Nina event this year is how it began. The winter of 2019-20 featured a weak El Nino event.  This winter will be driven by a moderate to potentially strong La Nina event.  This transition is important since it dramatically changes the circulation patterns around the Hemisphere. Since it is rather unique, we wanted to investigate this transition. 

The graph below shows the years that transitioned from an El Nino at the start of the year to a La Nina by years end.  Since the turn of the century, this has occurred 4 times and this year will be the 5th.  The warm to cold SST transition years are 2005, 2007, 2010, and 2016. 

Figure 21: Nino 3.4 sea surface temperature anomaly (C) during January – December 2005, 2007, 2010, 2016, and 2020. Source: NOAA

What does it mean?

The map below portrays the temperature anomalies when averaged out during the 4 winters (Dec-Jan-Feb) following the transition from El Nino to La Nina.  There was a great deal of variability around the Hemisphere but here are some trends that showed up.  Of the big 3 demand zones, Europe had the coldest tendency. Temperatures in the U.S. and East Asia were variable.  No area was exceptionally warm.  

Figure 22: Northern Hemisphere temperature anomalies (C) during December – February 2005, 2007, 2010, and 2016. Source: ERA5 

Because of the small sample size, it is not prudent to take a map like this and over analyze it.  All in all, La Nina winters tend to feature a great deal of variability and unlike last winter, portions of the mid-latitudes tend to feature some cold weather.  The takeaway is, that the upcoming winter looks to be different (colder) than last winter’s balmy conditions in the mid-latitudes.

Figure 23: United States snowfall anomalies (in/mm) during December – February 2005, 2007, 2010, and 2016. Source: ERA5

As for snow and storm disruptions, the maps below portray the snowfall anomalies during the 4 transition years. In the U.S., these transition years tend to feature above normal snowfall and a higher frequency of disruptions in the western U.S.  In the central and eastern U.S., most areas tend to experience below normal snow totals – a lower frequency of disruptions. The exception is the far northern locales and adjacent areas of Canada (northern New England, portions of the Great Lakes, and southeast Canada). 

In Europe, when averaging the transition years, most areas tend to have below normal snow totals. This is especially the case in the UK and western/central Europe.  The lower snow totals are on account of the jet stream patterns that tend to develop during these transition winters.  Colder winters tend to be dominated by a east to west flow as cold air from Siberia backs into Europe; the “beast from the east” is a term used to describe these situations.  Since the flow originates in Siberia, it tends to be drier continental air rather than moist air coming off the Atlantic. Colder winters in Europe tend to be drier winters in because of this dominant or mean flow pattern.    

Figure 24: Europe snowfall anomalies (in/mm) during December – February 2005, 2007, 2010, and 2016. Source: ERA5

The Polar Vortex 

Why is it so cold?  – it is the PV!  The PV has attained a life of its own during the past decade (most famously in 2013-14 in the U.S.) and has become a frequently used, and misused, term in daily conversations. The PV is nothing new and has always been extremely important in determining the location, timing, and magnitude of cold air outbreaks in winter.  If one knows what the PV is going to do, one knows in general terms how the winter is going to turn out. 

The stratospheric PV (nearly 20 km above the surface of Earth) is a natural phenomenon that spins up over the Arctic in early autumn, reaches maximum potential in January, and slowly spins down during the late spring. At times, the PV can heavily influence weather patterns across the U.S., Europe and East Asia.

Most of the time, the key to the amount and duration of cold air flowing from the Arctic into the mid-latitudes lies in the stability of the PV.  The maps below are examples of a stable and an unstable PV. A stable PV allows cold air to become trapped in the northerly latitudes and typically produces warmth in the mid-latitudes – where people live.  An unstable PV means that Arctic air is flowing into the mid-latitudes.

The hemispheric temperature anomaly maps – shown below – are examples of the end result of a stable or unstable PV; each map is the Dec-Jan-Feb period.  Last year’s extremely stable PV caused the warmest winter ever recorded in the mid latitudes.  The second temperature anomaly map is the Dec-Jan-Feb period of 2010-11.  That winter featured a weak, highly unstable and displaced PV.  The result was a cold winter across the bulk of the demand zones in the U.S., Europe, and east Asia.    

Figure 25a: Example of a weak polar vortex. Source: ERA5
Figure 25b: Example of a strong polar vortex. Source: ERA5
Figure 26a: Example of Northern Hemisphere temperature anomalies (C) during a weak vortex. Source: ERA5
Figure 26b: Example of Northern Hemisphere temperature anomalies (C) during a strong vortex. Source: ERA5 

In early autumn this year, the PV has been unstable. This is a big reason for some of the extreme cold in late October in the U.S. However, that looks to change in November, as the PV is projected to become more stable and stronger than normal especially during the early portion of the month.  This will help contract Arctic air from the mid-latitudes more toward the North Pole.  While much of early November will feature a more stable PV, there are no concrete indications that it will stay that way into the heart of winter – December, January, and February.  

What does this mean for temperatures? The PV is signaling heightened temperature variability this winter.  In other words, it is a mixed signal. There are no early indications of the PV staying stable throughout the core of winter, such as what was the case last year. On the flip side, there are no preliminary indications for a longer duration, unstable PV. Thus, initial indications point to the PV going through periods of stability and instability/movement during the core winter months, which equates to more variable temperatures across the mid-latitudes.  Temperatures this winter look to be highly volatile.  

As is the case every winter, it will be important to monitor the PV and changes in its strength and stability on a week-to-week basis. There is skill in forecasting the stability of the Polar Vortex out to approximately 30 days but after that, skill decreases, and uncertainty rises. This long-term uncertainty is due to smaller scale but anomalous features/events that can force changes to the PV. Some examples of these features/events include recurving tropical cyclones or highly amplified jet stream patterns in a particular region, which typically tend to appear in the forecasts within two-week time scales.

Putting the Pieces Together: Winter Outlook Takeaways

The variables going into this winter are unique when compared to the past few winters. The strong La Nina event will be the underlying base-state that will influence circulation patterns across the globe.  Trend, which is not unique to this particular winter, has to be taken into consideration in the forecast assessment. As is always the case, the PV will be extremely important in the details of extreme cold/warmth and winter storm location/frequency.  The timing, location, and whether the PV is stable or unstable will drive the details of the winter both around the Hemisphere, as well as regionally.  One cannot emphasis enough how important the PV is.    

Putting these drivers together yields the following preliminary key takeaways for this winter:

  • This winter will likely feature more cold air outbreaks around the Northern Hemisphere compared to last winter.  In some ways this is stating the obvious since last winter was the warmest by a wide margin when combining the 3 main demand zones.  We expect some areas to have significantly different temperature/storm outcomes compared to a year ago – mainly in the colder direction. 
  • Of the three demand/population zones, Europe is the likely region that will be significantly colder than last winter. In fact, if we had to focus on the area that has the higher probability of having more frequent cold air outbreaks, it would be Europe. 
  • A common theme this winter is likely to be highly variable (volatile) temperatures. In other words, there will be periods (days-to-weeks) of warmer than normal and colder than normal temperatures. Any extended periods (3 or more weeks) will be determined by whether the PV becomes highly unstable/stable over an extended period of time.  
  • This winter will likely feature a higher number of disruptive storms across the U.S., Europe, and East Asia compared to last winter. In the U.S., the northern and western U.S. are the favored areas for more frequent disruptive storm systems.  Eastern Europe is slightly favored compared to Western Europe for increased disruptive storms while central China is slightly favored regionally in East Asia.


  • In the U.S., this winter will likely not be as quiet as last winter in terms of supply chain disruptions due to storms and cold. This is due to the expected higher frequency of the disruptive storms (snow and ice) especially across the western and northern U.S.  
  • PFF requirements will be much more enhanced this winter compared to last winter. Regionally in the U.S, the western U.S. is favored over the eastern U.S. for longer duration PFF requirements.
  • In Europe, PFF requirements will greatly enhanced this winter compared to last winter. In fact, PFF requirements could register higher than normal as Europe has a higher probability (compared to the U.S. or East Asia) for more frequent cold air outbreaks.  These potential cold air outbreaks would provide a setup for the development of disruptive storm events.
  • Across East Asia, PFF requirements for temperature sensitive product shipments will be much more enhanced this winter compared to last winter. This is due to the expectations of more variable temperatures – more cold air outbreaks compared to last winter.  Regionally, northeast China has higher probabilities for warmer than normal temperatures and thus suppressed PFF requirements.

What’s Next?

This winter forecast is a first assessment for the season; this is the starting point or first step of the process.  In other words, based on the data currently available, this is the initial outlook for the winter of 2020-21.  As is always the case, the situation must be closely monitored throughout the season. 

The Everstream Analytics Team will be providing updates on a weekly and monthly basis via Digests, Webinars, and Reports.  This is especially pertinent when analyzing the PV which will largely determine the details throughout the winter of 2020-21.  

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