• 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.


The Weather Perspective Ltd