Model output discussion - here comes the beast!

[Summer Sun]

GFS 18z ens is a big shift away from cold after the end of next week

[ScottishSnowStorm]

1 minute ago, Quicksilver1989 said:

Right compared to yesterday some themes are now starting to emerge.

1) The Azores low is going to take a northwards path towards the UK
2) There is potential for mild air to make inroads this evening.

However on closer look things are pretty unchanged from this morning. The 18z ensembles for example still show plenty of runs with cold air winning out down south. Up north there would be many snow showers (or persistant snow in the runs where weather fronts push further north). Anyway I've updated my graphs showing different scenarios again.



Clearly the only thing on here that has changed is that a scenario where the cold pool covers the whole of the UK till saturday appears much less likely now.

However as I mentioned earlier, battleground scenarios where the UK is still under continental air will still see snowfall even if uppers are less cold.

The number of runs supporting a scenario with colder air hanging on until saturday remains unchanged.

Two things could work in our favour:

1) The low weakens as it moves towards the UK and therefore its northwards movement is stunted
2) Northerlies from the Greenland high set in more quickly and keep the warmer uppers away from us.

Both scenarios are very plausible still. A third scenario is that the low remains well to our south but that I think is a low possibility now.

I looked at a group of ECM ensembles, 6 showed milder air taking control by saturday, 16 kept colder uppers over us at the same time.

You could say that the ECM has caught up on the fact that low pressure is coming up from the south but whether this wins out is far from certain. In simple terms ECM is catching up to the GFS. The ops have favoured milder air winning, but that could easily change. The 00z's could show cold air still over the UK by next weekend.

The 18z ensembles don't even look to keep the cold here in the scottish central belt 

[Snowy L]

1 minute ago, Summer Sun said:

GFS 18z ens is a big shift away from cold after the end of next week

Ok wow that's horrific. The fact that so many agree 6 days out on such a complex system is strange though.

[LRD]

1 minute ago, Summer Sun said:

GFS 18z ens is a big shift away from cold after the end of next week

Dear me, that is a huge flip to mild. Let's see what it all looks like this time tomorrow

[Derecho]

2 minutes ago, ScottishSnowStorm said:

The 18z ensembles don't even look to keep the cold here in the scottish central belt 

I'm only focusing up to Saturday, after that its over 168 hours away... far too much time in a situation as volatile as this one.

[pureasthedriven]

4 minutes ago, Quicksilver1989 said:

Right compared to yesterday some themes are now starting to emerge.

1) The Azores low is going to take a northwards path towards the UK
2) There is potential for mild air to make inroads towards Friday.

However on closer look things are pretty unchanged from this morning. The 18z ensembles for example still show plenty of runs with cold air winning out down south. Up north there would be many snow showers (or persistant snow in the runs where weather fronts push further north). Anyway I've updated my graphs showing different scenarios again.



Clearly the only thing on here that has changed is that a scenario where the cold pool covers the whole of the UK till saturday appears much less likely now.

However as I mentioned earlier, battleground scenarios where the UK is still under continental air will still see snowfall even if uppers are less cold.

The number of runs supporting a scenario with colder air hanging on until saturday remains unchanged.

Two things could work in our favour:

1) The low weakens as it moves towards the UK and therefore its northwards movement is stunted
2) Northerlies from the Greenland high set in more quickly and keep the warmer uppers away from us.

Both scenarios are very plausible still. A third scenario is that the low remains well to our south but that I think is a low possibility now.

I looked at a group of ECM ensembles, 6 showed milder air taking control by saturday, 16 kept colder uppers over us at the same time.

You could say that the ECM has caught up on the fact that low pressure is coming up from the south but whether this wins out is far from certain. In simple terms ECM is catching up to the GFS. The ops have favoured milder air winning, but that could easily change. The 00z's could show cold air still over the UK by next weekend.

Very interesting, thanks. Looks like the textbook definition of neck and neck then!

Simply has to be vastly more favourable the further north you are. So for this Gatwickteer, I’ll take the least likely way-southerly track option, thanks. 

[skatefan]

4 minutes ago, CK1981 said:

Cast your minds back to the first SSW. The models were in chaos dealing with the outcome. Many favoured a mild solution, but they were wrong, and at a short time frame.

Since then, we’ve had a secondary warming. The models will now be in the same position and trying to work out the solution (but with the additional chaos following the first warming)

I firmly believe they will correct to a colder solution, as before.

I don't believe that, how much I would like to: the SSW and secondary warming determined the positioning of the HP's: and that gives too much retrogrssion and a free game for the LP's.  

[BlackburnChris]

3 minutes ago, Summer Sun said:

GFS 18z ens is a big shift away from cold after the end of next week

Northern England alot Colder ... Mean stays around -5

[Southender]

2 minutes ago, Summer Sun said:

GFS 18z ens is a big shift away from cold after the end of next week

Well, no dressing that up is there. Hopefully just lost the plot. Long way away in weather terms but that is the worst set we have seen in a while.

[CK1981]

2 minutes ago, skatefan said:

I don't believe that, how much I would like to: the SSW and secondary warming determined the positioning of the HP's: and that gives too much retrogrssion and a free game for the LP's.  

Yes, you could be right there, I’m just trying to keep positive. A west based -NAO will nail it for us ?

[Summer Sun]

2 minutes ago, BlackburnChris said:

Northern England alot Colder ... Mean stays around -5

Your chart is still the 12z

[skatefan]

3 minutes ago, CK1981 said:

Yes, you could be right there, I’m just trying to keep positive. A west based -NAO will nail it for us ?

Always good to keep positive! But a westbased -NAO is almost bound to happen as I see it.

[Guest]

GEFS all over the place if you look at it from a nationwide perspective. The op run is one of the milder solutions for the south, but not an outlier. It becomes a mild outlier in the mid-term for central areas and in FI a notable cold outlier for the far north.

A crumb of comfort for southerners is that if the low is being overdone in terms of strength by the GFS and in reality it weakens further south than forecast, the GEFS wouldn't be picking that in the ensembles until it was resolved, in which case you'd see a trend back to cool/cold. Similar to what @Quicksilver1989 mentions in point 1 of his post

I sympathise that the 18z ensembles look poor for the south though, no getting around that.

[Derecho]

1 minute ago, Reverse Zonality said:

GEFS all over the place if you look at it from a nationwide perspective. The op run is one of the milder solutions for the south, but not an outlier. It becomes a mild outlier in the mid-term for central areas and in FI a notable cold outlier for the far north.

A crumb of comfort for southerners is that if the low is being overdone in terms of strength by the GFS and in reality it weakens further south than forecast, the GEFS wouldn't be picking that in the ensembles until it was resolved, in which case you'd see a trend back to cool/cold. Similar to what @Quicksilver1989 mentions in point 1 of his post

I sympathise that the 18z ensembles look poor for the south though, no getting around that.

Yup there seems to be more support for bringing in the milder air later next weekend, for Friday though the ensembles can be a bit misleading as uppers around -1 to -4C can still lead to heavy snow whilst the continental airmass hangs above. Anything after saturday though is pure conjecture due to the fact it is far away still. Though I will admit mid term has seen a trend to mild.

This does remind me a fair bit of late December 2009 when deep lows were getting close by and introducing some milder air.



The Greenland high got its back together and we were in the cold.



Lets wait and see what tomorrow brings.

[ScottishSnowStorm]

6 minutes ago, Reverse Zonality said:

GEFS all over the place if you look at it from a nationwide perspective. The op run is one of the milder solutions for the south, but not an outlier. It becomes a mild outlier in the mid-term for central areas and in FI a notable cold outlier for the far north.

A crumb of comfort for southerners is that if the low is being overdone in terms of strength by the GFS and in reality it weakens further south than forecast, the GEFS wouldn't be picking that in the ensembles until it was resolved, in which case you'd see a trend back to cool/cold. Similar to what @Quicksilver1989 mentions in point 1 of his post

I sympathise that the 18z ensembles look poor for the south though, no getting around that.

Strange how it can be the milder option down south but one of the colder here in scotland till nearer the end of the run how often can that happen?

 

[snow mad]

7 minutes ago, Southender said:

Well, no dressing that up is there. Hopefully just lost the plot. Long way away in weather terms but that is the worst set we have seen in a while.

No unfortunately not, maybe this will be a snap after all. Real shame. Still it is spring soon so looking forward to some warmth (not that I think it will get warm, just not cold enough for snow after the weekend) and I for one would take a 4/5 day really cold snap/spell and then maybe something more seasonal anyway. Just a bit to late in the season. This time of year Some places in Spain has already had temps we would envy in summer so it won’t take long to mix out the cold when it turns south east/east. Really was hoping for something epic!

[Cheshire Freeze]

6 minutes ago, snow mad said:

No unfortunately not, maybe this will be a snap after all. Real shame. Still it is spring soon so looking forward to some warmth (not that I think it will get warm, just not cold enough for snow after the weekend) and I for one would take a 4/5 day really cold snap/spell and then maybe something more seasonal anyway. Just a bit to late in the season. This time of year Some places in Spain has already had temps we would envy in summer so it won’t take long to mix out the cold when it turns south east/east. Really was hoping for something epic!

6 weeks ago, that 0C isotherm would have been much further S in the same synoptic circumstances. Unfortunately that is why it is better to get your cold in January rather than late Feb/early March.

It is what it is this evening. Personally it takes the shine off a cold spell when you can already see the end before it has properly begun. That's what made Dec/Jan period of 09/10 and December 2010 so special. The modelling was producing cold right out to the end of the runs.

Edited February 25, 2018 by CreweCold

[Welsh_Weather]

The fact that the northern blocking has all but disappeared next weekend is telling. But the MO has hinted at the milder weather pushing in just not this soon. 

Edited February 25, 2018 by Welsh_Weather

[ScottishSnowStorm]

Is what we are seeing in the output now because the whole of the PV has been shunted into russia and placing too much pressure on the blocking to allow any easterly winds to exert thereselves on our side of the hemisphere?

[Cheshire Freeze]

Just now, Bristle boy said:

It's only 2 days ago the NW 'big guns' were confidently predicting 2 weeks of severe cold; what's gone wrong? (So to speak). A silence has descended today, on the forum, from NW's most respected posters.

Well we could have done with the Hudson bay vortex not being completely dismantled as quick as it looks to be dismantled. All it has meant is the block scooting E-W all too quickly to quickly set up a western based - NAO. We needed it to hold. 

If you remember a few nights ago, I suggested this was a risk once the modelling got fully to grips with the ongoing warming. 

[skatefan]

2 minutes ago, Bristle boy said:

It's only 2 days ago the NW 'big guns' were confidently predicting 2 weeks of severe cold; what's gone wrong? (So to speak). A silence has descended today, on the forum, from NW's most respected posters. Stunned?

Too fast retrogression of the HP creates a level playing field for the LP's. Impossible to say what will happen but the charts don't promiss much!

[Cheshire Freeze]

The reason we're seeing this accelerate so much is because the modelling now is getting to grips with the full extent of the SSW. Personally I can't see any way back from here post Friday. Others may disagree of course, and I fully respect that. 

We could have been OK had that Troughing dropped down from the NE a little quicker. 

[CK1981]

12 minutes ago, CreweCold said:

The reason we're seeing this accelerate so much is because the modelling now is getting to grips with the full extent of the SSW. Personally I can't see any way back from here post Friday. Others may disagree of course, and I fully respect that. 

We could have been OK had that Troughing dropped down from the NE a little quicker. 

I was hoping the GFS was being too progressive, and I’m trying to remain positive, but after seeing the GEFS, it’s not looking good  

[Tracy Flick]

For those who want the snow to survive for the one weekend (which surely isn't asking too much, is it?)  the GFS 18z is not a concern.  What is a concern is the UKMO and now the latest shift in the ECM run set.

I don't know why they have to run the GFS 4 times a day to 384h:  maybe it's an attempt to buy love and attention by compensating for the lack of quality with excess quantity.  What's a pro forecaster meant to do, publish a new in-depth analysis every 6 hours?  It's an overload of information that muddies the waters rather than making them clearer. 

Anyway FWIW, the JMA + GEM ensemble means still have promise out to a week on Tuesday for much of the country.  I don't expect a shift in tone from the MetO just yet.

If the snow survives one weekend, rather than just wrecking the drive to work then vanishing Friday night, I'll be happy.

[ScottishSnowStorm]

Hopefully this just turns out to be the same as the easterly is going too far south incident we had and over the next 24hrs things get back to how they were looking earlier on