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Sudden Stratospheric… what now?

16 February 2023

If you’ve been anywhere near the topic of weather on social media lately you will have seen the words “Sudden Stratospheric Warming” being talked about, a lot. Currently, high above the Arctic the stratosphere is rapidly warming. In the last couple of days it’s warmed by as much as 20C.

When this phenomena, known as Sudden Stratospheric Warming (SSW) occurs it can dramatically weaken the usually strong westerly flow within the stratospheric polar vortex and in some cases reverse those winds to easterly. When the winds reverse at 60N, 10hPa this is classified as a major sudden stratospheric warming and can impact the weather we see at the surface.

The last major impactful SSW was in 2018 when we saw the ‘beast from the east’ late February into early March. This was one of the most extreme responses to a SSW on record, however around 70% of SSW’s lead to cold weather outbreaks across Europe and indeed the UK. So, there’s a SSW happening right now, is it going to turn cold?

Well.. it’s complicated. This SSW looks likely to displace the polar vortex towards the Siberian side of the Arctic but it could be a while before the negative anomalies developing in the stratosphere propagate down to surface levels. Occasionally we can see a “quick trop response” and we see impacts within a week of the SSW, with displacement events though any impacts typically take 2-4 weeks.

What can we expect from our weather for the remainder of February? From the middle of next week (21st – 26th February) high pressure will begin to build to the west of the UK switching winds to a more northerly or north-westerly direction, this will bring in colder air across the UK, especially compared to the anomalous warmth we’ve gotten used to in recent weeks. Widespread frosts are likely where skies clear with the potential for wintriness, particularly over exposed northern hills, the Scottish Highlands for example.

Chart for illustrative purposes only.

This northerly is expected to be fairly brief spanning perhaps a few days before high pressure collapses towards the UK. There is some uncertainty over the positioning of this high so detail for specific locations will need firming up on in the coming days.

Looking further ahead into early March, the aforementioned SSW looks like it will begin to impact the troposphere, how, where & what weather that brings however remains unknown, whilst it can increase the chances of cold weather, it doesn’t guarantee it. We are closely monitoring the evolution of this SSW and tracking it down through the atmosphere, once modelling & confidence begins to improve we’ll do another blog post.