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North Atlantic Oscillation

March 19, 2020
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By Paul Homewood




If you had not noticed (!), it has been a mild and wet start to the year here in the UK, and also across in NW Europe.

No doubt this will be linked to global warming in due course, but in fact it is simply weather, as the CET chart below proves:



Since the year started, temperatures have consistently been within the normal band. In other the sort of temperatures commonly seen at this time of year.

However, they have also been consistently in the top half of that band, rather than being spread between cold and warm, as would happen most years.

The reason for the weather we have had is, of course, the jet stream, or more precisely the North Atlantic Oscillation (NAO), which has been strongly and stubbornly positive all winter.

The Norwegian Centre for Climate Research CICERO spotted this mild weather coming back in December, and commented on 6th January:

The unusual warm temperatures this winter and forecasts indicating milder winter conditions for January, February and March in Europe are partly due to an atmospheric circulation pattern called the North Atlantic Oscillation, or NAO. This atmospheric circulation pattern explains well the weather we get in Europe, especially in winter.



Our own Met Office explains the NAO phenomenon:


The term ‘North Atlantic Oscillation’ is used by meteorologists to refer to variations in the large-scale surface pressure gradient in the North Atlantic region.

In the average state of the atmosphere, the North Atlantic surface pressure is relatively high in the subtropics at latitudes 20°N to 40°N (‘the Azores High’), and lower further North at latitudes 50°N to 70°N (the ‘Icelandic Low’). The North-South pressure difference determines the strength of the westerly winds across the Atlantic and is known as the North Atlantic Oscillation (NAO).

When the pressure difference is large, the NAO is positive and the westerly winds are strong and storms tend to be stronger, more frequent and travel across northwestern Europe. When the pressure difference is small, they travel across southern Europe. The NAO is also associated with changes in temperature and rainfall in Europe and North America.

The fluctuations in the NAO occur on a wide range of time-scales. There are day-to-day changes associated with weather systems, and slower changes associated with seasonal and longer term variability, which is predictable from November for the coming winter.

NAO impacts

Winter (December-January-February) conditions

When the NAO index is well above normal, there is an increased chance that seasonal temperatures will be higher than normal in northern Europe, northern Asia and South-East North America, and lower than normal in North Africa, North-East Canada and southern Greenland. The patterns for precipitation (rainfall, snowfall) are more localised, with an increased chance of higher rainfall in northwest Europe and lower rainfall in southern Europe. When the NAO index is well below normal, the tendencies are generally opposite. The figures below show where seasonally-averaged temperatures and rainfall are likely to be in the top or bottom one third of observed values, given that the seasonal NAO index is in the top or bottom quarter of observed values.

There is one more part to the jigsaw, though.

As you may have noticed, Greenland should be colder than usual. And sure enough, that’s exactly what we find:




But a colder Greenland also means a drier winter, as mild winters are driven by low pressure systems bringing warm air from the south. In contrast, this winter has seen much colder, drier polar air trapped over Greenland.

And less snow means less build up on the ice cap:


 Greenland Surface Ice Mass


Weather forecasts suggest the return of low pressure to Greenland in the next week or two, so snowfall should accumulate again. But it is unlikely to offset the shortfall so far this winter. In turn we will probably see less accumulation than average come the end of summer.

Now, here’s £50 that says the usual suspects will blame that on global warming!

  1. Broadlands permalink
    March 19, 2020 8:55 pm

    It’s also likely that the usual suspects will not acknowledge that the NAO is a natural condition like the equatorial Pacific ENSO, and is not under the control of anthropogenic CO2. Nor is “arctic amplification”.

  2. Phillip Bratby permalink
    March 19, 2020 9:20 pm

    I don’t think you’ll get any takers on that bet.

  3. The Old Bloke permalink
    March 19, 2020 9:33 pm

    A lot depends on where you are in the UK as to whether you think you have had a mild winter or not. Over the last 110 days in the UK it has snowed on 100 of them. As I say, it depends on where you are.

  4. March 19, 2020 10:37 pm

    I’ve found it to be mostly cold and miserable.

  5. March 19, 2020 11:38 pm

    A really great post with useful links. Thank you sir.

    • John of Cloverdale, WA, Australia permalink
      March 20, 2020 12:27 am

      Here here!

      • John of Cloverdale, WA, Australia permalink
        March 20, 2020 1:30 am

        Sorry, HEAR HEAR!

  6. March 20, 2020 12:43 am

    Hi Paul, do you know about the nullschool site? it gives you global wind and ocean current data graphically within a 3-hour time frame. you can use the mouse to turn the globe around and find the location of interest.,32.35,275/loc=-44.567,53.925

  7. John of Cloverdale, WA, Australia permalink
    March 20, 2020 1:33 am

    Paul, I laid the AMO index below the CET summer temperature record (from 1850).
    There appears to be a fair match in the cycles. But it may be my eyes.

  8. March 20, 2020 4:56 am

    “No doubt this will be linked to global warming in due course”

    Yes sir. It’s the atmosphere bias of climate science that explains atmos composition in terms of fossil fuels and everything else in terms of atmospheric composition.

  9. Bill permalink
    March 20, 2020 8:33 am

    A question for you Paul. When was the last time that there was no lying snow in the south of England through an entire winter? I remember many mild winters, for example 1988, but the 19/20 pattern was exceptionally persistent was it not? And now, low and behold, classic cold winter synoptics for the end of March!

  10. MrGrimNasty permalink
    March 20, 2020 1:56 pm

    Local BBC news just interviewed eco-nutter Chris Packham on how CV19 was impacting climate change/bio-diversity loss, sorry, the countryside. He was on good form. Such classics as “Farmers will have to self-isolate, they won’t be able to get out into the fields” accompanied by a picture of a tractor toiling away. What a berk. Was there ever a more solitary aspect of a more solitary job!

    • dennisambler permalink
      March 20, 2020 2:00 pm


    • David Parker permalink
      March 21, 2020 9:37 pm

      95 acres cultivated today, ready to plant wheat on Monday. Solitude – marvellous.

  11. dennisambler permalink
    March 20, 2020 2:20 pm

    They know all this, but prefer, or are required, to keep banging the global warming/climate change drum.

    “High-magnitude flooding across Britain since AD 1750”
    Neil Macdonald and Heather Sangster, Department of Geography and Planning, University of Liverpool, March 2017

    “The principal findings of this work are that of the strong correlations between flood-rich/flood-poor phases and solar magnetic activity, AMO and NAOI, (NAO Index) indicating a clear driver for flooding patterns across Britain.

    This work suggests that high-magnitude flood-rich periods relate to negative NAOI across much of the country, in western catchments with a stronger westerly airflow signal significantly correlating to positive NAOI…

    It also identifies the importance of the Atlantic Multidecadal Oscillation as a clear correlation is shown between higher North Atlantic sea temperatures and increased severe flood events across much of Britain.”

    Aberystwyth University: Foulds, S. A., Griffiths, H., Macklin, M., & Brewer, P. (2014). Geomorphological records of extreme floods and their relationship to decadal-scale climate change. Geomorphology, 216, 193-207.

    “..large floods have occurred frequently in the past associated with flood-rich periods and variability of the NAO, SNAO, and the frequency/persistence of different Lamb weather types (LWTs; Lamb, 1972), notably cyclonic and westerly flows

    Monthly NAO values indicate that historical autumn-winter floods occurred during negative phases associated with cyclonic conditions (Table 5), which can give rise to circulating frontal rain bands and documentary references to rainfall continuing over several days (e.g., February 1869, December 1880, and September 1903: Table 2).

    Positive autumn-winter NAO values are also associated with an increased frequency of westerly/southwesterly winds, which can lead to orographically enhanced daily and multiday rainfall totals in upland areas”

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