Although the latest run (12z) GFS has retreated from late next week’s arctic blast, the ECMWF remains firm in bringing down the strongest shot of cold yet into Ireland, the UK and western Europe.

The next 5 days or so looks rather quiet with a flattening of the upper pattern beyond this weekend where we’ll see the return of a chillier northwest flow. The boundary separating very cold from mild will be positioned almost directly above the UK but we’ll see that boundary begin to sag south through the middle part of next week thanks to the presence of a low which will pass just north of Scotland.

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You can see the 540 and 546 line sitting over the northern UK next Tuesday, that’s the boundary. Winds will be stronger and colder along that 540 line and will be noticeable over Northern Scotland where it should be a good deal cooler than on the South Coast of England.

The jet stream will be streaming over northern Scotland so I suspect MOST of the UK even out to mid next week, should remain fairly pleasant temperature wise.

Suttle change, according to the latest ECMWF appears to come later Wednesday as the boundary begins to sag south introducing fresher air and a stronger WNW wind which should contain hefty showers.

By Thursday, the game changer.. low pressure will pass just north of Scotland and it’s this which will drive a cold front southeast over the UK. What’s going to be interesting is how cold will the air be on the north side of the cold front because if it’s cold, then we could have a situation in which we see rain change over to snow and another question would be, could it snow down to low levels?

By Friday that low has deepened to 972mb over southern Norway and is producing quite the temperature fall over the UK with rain changing to snow, possibly to low levels too.

Notice the jet sinking south, opening the door to the arctic.

By Saturday the model has a 1036mb ridge extending from the Azores up to Iceland while another, somewhat weaker ridge is north-south oriented over eastern Europe while a 980mb low spins over the Gulf of Bothnia, aiding in the southward plunge of arctic air over the UK.

The 6z Sat jet is seen directly over the UK, driving bitterly cold air due south. If this is correct, many northern parts of the UK may have a tough time hitting freezing Saturday, especially if there happens to be snow on the ground.

Here’s a rather cold 850mb temperature profile Saturday with widespread -10C air at 5,000ft.

So, even if we do get this blast of arctic air, the big question always remains, what about snow? As per usual, it always boils down to availability of moisture and just how cold the column is. Get the lowest mile of the atmosphere below freezing and you’ve got snow but it’s always a tough call and a pure guess this far out.

Here’s the latest ECMWF snow  chart through 240 hours. Notice most of the continent and a good deal of the UK is seen to have snow on the ground.

Closer look at the UK.

If this cold comes, another question will be, how long will it last? Let’s just keep an eye on this firstly but my hunch just now is that this comes in and will be TEMPORARILY replaced by milder air off the Atlantic again. Keep in mind that the NAO through the next 10-15 days appears to hold largely neutral which suggests a continued PROGRESSIVE pattern. Interestingly the AO is going positive which tells me we must really watch out for that next flip back into negative in both the NAO and AO. If this comes to western Europe with a near neutral NAO and positive AO, then when those indexes flip, then the motherlode of arctic air and trough may go straight to western Europe and lock in place into Christmas and New Year.

This is ‘priming’ time. Notice the arctic shots which have come down have been progressing westwards as waters around the UK cool.

Thought I would throw up the first stratospheric temperature charts of the season and no surprise to see there’s no sign of any warming just yet.

24 hrs

120 hrs

240 hrs

Still a little early! Remember if we get some warming over the pole, there’s a 6-10 day lag before we see the results here in the mid-latitudes.

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