Its been far too long since my last post, so it must be looking good for me to be doing a blog post eh?
We are on the cusp of a spell of weather the UK has not seen for many years, with the threat of severe cold and snow. More on that in a bit. Let’s have a quick look at the failed easterly in January and why it was never going to amount to anything, and why this is different.
Here’s the ECM prediction from the 3rd of January for the 13th. As you can see it was going for a cold easterly. At the time I thought any easterly was unlikely, why? PV too strong for the high to establish, there was no real stratospheric support for an easterly.
Sure enough, this was as close as we got, the high collapsed like a jenga tower in an earthquake. This time however, things are just a tad different.
We have seen one of the biggest Sudden stratospheric warmings on record.
Here’s the zonal wind plot at 60N 10hpa showing a huge reversal of the polar westerly’s, this has torn the polar vortex in two. With one lobe over Europe and the other over Hudson bay.
If that wasn’t enough to pump the vortex, 2 days ago a warming peaked right where the main Hudson bay vortex was located.
Net result? Total demolition of the stratospheric polar vortex. Thus a higher chance of colder weather based off that, but to add further credence to this, the split was in a near perfect place to allow a Scandinavian high to form, in the troposphere where we see our weather.
The stratospheric high located over Svalbard is pretty much perfect if you want an easterly.So we have support from the strat. There was also the small matter of a massive MJO wave through phase 6 and importantly phase 7. Which also favours higher pressure over Scandinavia. So now we can begin to see why we are seeing historic charts such as this.
We have not seen such synoptics shown for many years, and the sheer depth of cold coming out of Russia heading west into Europe is very rare indeed.
This means that we have the very rare chance of historic cold reaching the UK.
This week then, we will see the high building over Scandinavia and a slack easterly setting up mid week onwards. It will get colder as we get into the weekend with that windchill really starting to make its presence felt. Snow flurrys likely mostly sunday onwards into the following week when we should be getting the deep cold over the UK, making the snow risk more widespread while feeling bitterly cold everywhere. I wont go in to too much detail yet, as the exact orientation of the high is still up for grabs, so associated depth of cold and snow can still change. (GFS and especiallyECM) would have snow depths in the feet)
Little further on there is good confidence in a retrogression of the high to Greenland, like the ECM 12z OP from today.
Here at day 8 we see the high being sucked up towards Greenland, I feel this is more likely than the GFS which brings low pressure too far north and somewhat spoils the retrogression. The result of this would be the UK locked in cold well into March, with northerly or north easterly winds continuing, something which the met office have alluded too in there longer term outlook.
Just a quick muse on even further ahead, I see March and perhaps into April too having a high potential for blocking around the northern hemisphere, in response to the massive SSW. The effects of an SSW are felt for many weeks.
These are the lag times, we are seeing the first pulse here around 10 days, note the pulses 25-30 days and 35-50 days out. So a much higher chance of a cold March here for sure.
Off topic but remember that the NAO (North atlantic Oscillation) does NOT drive the weather pattern. It is simply a reflection of the pattern. It is not an atmospheric driver like the MJO for example, or an SSW, merely a reflection of the pattern in the north Atlantic, I have seen people getting confused about this.
That’s it for me on this one. See you soon.
Get set, it’s coming.