You’ve probably heard the term *Sudden Stratospheric Warming* or SSW being thrown about on weather forums in the last few years and indeed more recently the term has started to appear on TV forecasts too, but what does it actually mean and what type of weather does it bring to the United Kingdom?
Sudden Stratospheric Warming is quite a long and complicated thing to explain so I’ll try and keep it as basic as possible – Temperatures in the Polar Stratosphere can dictate the type of Northern Hemispheric pattern that we see. A colder Polar Stratosphere increases the temperature gradient between the Arctic and the Tropics during the winter months, this helps to strengthen and organise the Polar Vortex often giving us here in the UK wet & mild weather.
A warmer Stratosphere does the opposite however, it decreases the temperature gradient between the Arctic and the Tropics which in turn reduces the strength of the Polar Vortex giving a higher risk of Northern Blocking which as you probably know, increases the chances of colder weather for us here in the UK.
Sudden Stratospheric warming is a sudden and major warming in the Stratosphere which can disrupt, weaken and split the Polar Vortex giving rise to Northern Blocking, this often heralds a major pattern chance for the Northern Hemisphere. We’re currently in the process of seeing one of these SSW events which on average occur once every 2 years. We are therefore expecting a change from the milder conditions we’ve seen recently to cooler conditions as we move through the course of next week and towards the middle of January.
Forecasts are suggesting that as this warming occurs we’re going to start to see the Polar Vortex split into two separate fragments, one will set up over Canada with the other fragment heading into Russia or Siberia. This will help aid development of high pressure over Greenland turning the Arctic Oscillation into a more negative phase.
We’re forecasting a gradual decrease in temperature through the coming week, initially temperatures will return to around average but we could start to see temperatures dropping below average too as computer models start to suggest high pressure developing to the North, North East and eventually North-West of the United Kingdom advecting colder air towards us.
There’s still a lot of uncertainty over how cold things are going to get and whether we’re going to be seeing any snowfall or not, but there is good support within the outputs to suggest a cool down is likely.
– Through the course of next week, temperatures will move closer to the seasonal average, perhaps dipping below by the end of the week
– It’s likely to be largely dry throughout the week but I can’t rule out the odd spell of rain or drizzle pushing into Northern and Western parts from time to time.