Could Indian Ocean Thunderstorms Trigger a Late December Sudden Stratospheric Warming Event?

Written by on December 12, 2018 in Rest of Europe, United Kingdom & Ireland with 0 Comments

I’ve held off for about a week or so on talking about the stratospheric polar vortex because we all know how modelling suggests one thing only to let us down with the opposite. We know the stratospheric polar vortex has been under a degree of stress and as a result it’s been stretching and flexing.

This stress may lead to little or nothing, especially for Europe. A good example of this was back in the 2013-14 winter which saw stratospheric warming from Siberia to North America (similar to now) which allowed a piece of the vortex to dive into the US a few times that winter. For us, we saw one deep low after the other sweep across the British Isles and Ireland, powered by a powerhouse jet stream which was triggered by polar air colliding with Caribbean air. This likely enhanced the absense of a negative NAO.

The below 10mb temp chart shows why we observed a strong ridge over Alaska but lack of ridge over Greenland. In fact the Icelandic trough was strengthened, helped by the position of PV and strength of the trans Atlantic jet stream.

However, the models are quite consistent at a major warming from Asia across the Arctic and crucially down over Greenland. If we get that siege of warmth sweep over much of the Arctic basin and down over Greenland, then a conducive to Europe SSWE is likely.

The current stress and stretching could be an early indicator of an impending SSWE.

This looks promising.

Credit: Tropical Tidbits

Joe Bastardi of Weatherbell has pointed out the large scale thunderstorm activity currently over the central and eastern Indian Ocean. Not only does this support a phase 3 of the Madden Julian Oscillation which supports a warm pattern for the United States (now developing), but more importantly, the large scale heat release from these thunderstorms bump up against the Himalayas  and rise vertically  through the troposphere into the stratosphere.

This could be the cause of the SSWE the models are now seeing.

The below chart shows the convection extending from Indian Ocean across the Pacific and into NW North America which leads to rising heights over the US which pulls Pacific air across the US, this is then telegraphed across the Atlantic but notice depth of convection is less… The jet stream is not strengthening as it should and that could be an indication of high latitude blocking developing down the road. Stronger than normal westerlies tend to it harder for the atmosphere to develop a meridional blocking pattern.

Credit: Tropical Tidbits

With the right ingredients in place, weak westerlies tend stratosphere to troposphere coupling.

So, if we manage to get this late month SSWE, what next?

A current large-scale negative (low pressure) over positive (high pressure) will reverse and the arctic floodgates will open. Of course the million dollar question may be, where will the cold end up? IF we get strong positives over Alaska and Greenland, then the warm pools should settle over Alaska, western Canada and Greenland while cold troughs lock in over the eastern US and UK.

The potential for our coldest January and February since 2010 is on the table if we get the above.

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