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  • Luke Boxall

Stratospheric Index

Following on from Yesterday's Blog - on an "Improved way to look at the Stratosphere (SSWs) - from the current version" - it's worth having a look at some of the surface responses to these phases.

On my website where the tool is housed ( there is a daily construction of how the surface pattern evolves with time after hitting a certain Phase - we'd expect somewhat of a lag between the Stratosphere changes and the Troposphere impact so it's useful to see what the lag is, however to show it on a blog with hundreds of images is not ideal.

So what I've done instead is to show a single image that summarize best the surface effects - I have picked what the temperature out-turns around 6-9 Days after hitting the Phase as this summary unless stated... I'm constantly learning and wanting to try new ideas - so if you have any comments/feedback to any of this please email the Weather Data Service account at:


Phase 1 sees Vortex completely split and removed from the pole - but the left-over vortex is stronger over the US side of the Globe

Very Cold for Eurasia due to strong Blocking High - Phase 1 to begin with can be warm over the E US as left-over low pressures keeps it more volatile but normally ends up trending colder.


Phase 2 sees more of a vortex - strong displacement rather than full split but vortex pushed over to US side of the Globe

Phase 2-3 is when we have a vortex but its shifted over to the US-side of the Globe - for the US it's this displacement event that are the coldest rather than a Split as it drives down Cold Arctic air into Eastern Half of the US - 2014 was well know as the "winter of the Polar Vortex" - it just sat in Phase 2-3. Europe nearer Normal - E Europe-Asia Cold.


Phase 3 sees a stronger vortex shifted more towards the Pole but still US-leaning

Cold US but warmer Europe as we develop more Southerly flow risk - although still cold for E Europe.


Phase 4 sees a very strong Polar vortex - again still shifted slightly towards US

Warm over US/Europe


Phase 5 again sees a very strong Polar Vortex but this time shifted bit more towards Eurasia

Warm over US/Europe


Phase 6 sees displacement event - Vortex shifted over to Pole-Eurasia side of the Globe

Correlates to a brief cooler snap over Europe on Day 0-5 shown above whilst US stays warm to begin with - but Europe snaps back westerly quickly and warmer whereas troughing risks emerge over E US around Day 10 not shown.


Phase 7 sees a strong displacement event - vortex shifted out of the Polar region onto the Eurasia side of the Globe

Eastern US exposed to some cooler spells from troughing but not as strong as Phase 2-3. N Europe Cold - Warm for Mainland Europe still.


Phase 8 sees the vortex completely split and removed from the pole - left-over remains stronger away from the US - Phase 8 is often the aftermath of Phase 1 - where the Strat vortex is dead - often we get the de-coupling occurring here and 10hpa starts to move on it's own back to neutral or even the more bearish states of 4-6 with lower stratosphere blocked.

Eastern US exposed to some lingering cooler spells effecting eastern coasts but not as strong as Phase 2-3 as it affects Mid-West less. With some left-over low pressure over Europe allows something less cold to be mixed in still - slightly cool bias but not as strong as Phase 1-2. Often Phase 8 is preceded by very strong Europe cold as Phase 8 reflects the 20-40 day period after a split. As Phase 8 most often is followed from Phase 1 I suspect mean maps like above of Phase 8 are commonly just showing the 3-4 week aftermath of Phase 1 Split. So I took times when Phase 8 occurred after Phase 7 and the Picture is different US is very warm leading up to it but turns Cold in the first week shown below - Europe is cold over C/E parts leading into it and after but stays warm over W Europe as enough left-over vortex is there to keep a southerly ticking over in the East Atlantic.

I think there is plenty to learn from using these indexes including how different transitions between different Phases leads to different surface influences among many other things to learn.

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