Model output discussion - here comes the beast!

[yamkin]

Intense SSW is in action & the models have picked this up, hence today's fluctuations. No need to be concerned as the current Beast From The East is still on course.

The SSW graph had to be extended to new parameters to accommodate the intensification of SSW. This intensification is the result of the energy from the recent CME (Coronal Mass Ejection) from the sun. Increased blocking.

[Backtrack]

1 minute ago, bobbydog said:

i shouldn't worry about the uppers too much, as long as we have very low dewpoints it should be fine. 

Which we will do due to the origin of the air  

[bluearmy]

3 minutes ago, bobbydog said:

i shouldn't worry about the uppers too much, as long as we have very low dewpoints it should be fine. 

which is why the ec op this morning was such a big concern as it changed the flow to the extent that dp’s went positive next Thursday with the warm sector - move that pattern west a bit and we can stay negative dp’s , even with the same ‘less peachy‘ solution 

[bradymk]

Astonishing low temps for the morning of week Sunday for Southern Britain from 6z gfs. -9c on the max temp charts, -13c on the min ones attached. 

 

Edited February 21, 2018 by bradythemole

[Met4Cast]

3 minutes ago, yamkin said:

Intense SSW is in action & the models have picked this up, hence today's fluctuations. No need to be concerned as the current Beast From The East is still on course.

The SSW graph had to be extended to new parameters to accommodate the intensification of SSW. This intensification is the result of the energy from the recent CME (Coronal Mass Ejection) from the sun. Increased blocking.

Exactly this. 

A secondary warming has probably increased Shannon Entropy again. Think back to how all over the place they were last week. 

Stick with the ensemble means & clusters in these situations, it offers best guidance. EPS > GEFS

Ignore PPN charts or if you absolutely must look at them at this range, stick with the APERGE, GFS PPN charts are useless even at T24. 

Coldest spell for a few years is all but confirmed, details wrt snow/timing/depth of cold remain uncertain but broad pattern is very good. 

[SizzlingHeat]

Not sure why people are moaning that -8c uppers would not bring snow. Given that the uppers across Poole this afternoon are -4c and the temperature is +7c, the dew point is 0c. This shows continental sources air will bring in lower dew points from the continent rather than higher dew points off the Atlantic if this was from a NW direction. Therefore -8c uppers after the initial -10/12c uppers will result in dew points on the coast of between -3 and -5 with inland regions even lower. Any precipitation therefore is guaranteed to be snow.

[Norrance]

53 minutes ago, East_England_Stormchaser91 said:

It's came down from the north on that run though bud. Right down the spine of the country. The Pennines will be absolutely buried if that comes off. 

Polar lows cannot be forecast at this distance in time. Perhaps someone could provide a link to the Polar Low section in  the learning area so that people can see what to look out for. One iirc is a closed circulation with no fronts.

[bobbydog]

Just now, bluearmy said:

which is why the ec op this morning was such a big concern as it changed the flow to the extent that dp’s went positive next Thursday with the warm sector - move that pattern west a bit and we can stay negative dp’s , even with the same ‘less peachy‘ solution 

its always a concern BA, but far enough away not to worry too much at this stage.

[supernova]

Well we all like a fast and predictable plunge into record-breaking cold (most of us at least) but sadly in most winters the UK does it's best to thwart us at every available opportunity. This year's historic SSW and subsequent cold spell appears rather different to our standard fare on so many levels but looking at some of the emotive posts this morning it's probably worth comparing eggs with eggs. Here's yesterday's 00z run ensembles (GEFS) alongside today's - also from the 00z run, for the same part of the country.

Looking at these charts, I actually think it's fair to say that the deepest cold came in slightly faster on yesterday's run with mean uppers beaching -13 by midday Mon and staying exceptionally cold for the next three days before gradually rising back above -5 by Sun where they sit pretty much until the end of the run.

This morning's uppers on the ensembles still break through -10 on Mon (so plenty cold enough for snow of course and therefore also fine to suggest that the "cold" still arrives on Mon) but the deepest cold doesn't breach -13 until Thursday, some three days later give or take. I can therefore see how some forum members are suggesting the cold has been delayed but really I think it's a question of semantics. The deepest cold is delayed, but overall the pattern is entirely similar.

Perhaps more importantly, not only does it still turn cold on Mon, then get even colder, but the uppers don't rise back above -5 until Wednesday 7th. 

In a nutshell:

- the cold still gets here Monday.

- it gets just as cold as was predicted previously (or at least the mean does).

- the deepest cold might not arrive immediately but It stays colder for longer.

Happy days. 

EDIT: For those who care about such things the 06z ensembles follow an extremely similar profile to last night's 0z run, perhaps fractionally (and I mean barely) less cold, but there are two notably milder members dragging the overall mean in the wrong direction which would explain the difference. Still cold from Monday, still deep cold thereafter, still extended.

Edited February 21, 2018 by supernova

[Frosty.]

While it's quiet..Here are some beauties from the GEFS 6z

[Gowon]

11 minutes ago, yamkin said:

Intense SSW is in action & the models have picked this up, hence today's fluctuations. No need to be concerned as the current Beast From The East is still on course.

The SSW graph had to be extended to new parameters to accommodate the intensification of SSW. This intensification is the result of the energy from the recent CME (Coronal Mass Ejection) from the sun. Increased blocking.

I though CME was bad for aiding blocking

[Thinon]

The GFS and ECM op squeezes the Scandi high southwards, resulting in the convective potential being pushed down into France, and a significant decrease in the severity of the cold for most parts of the UK except maybe the far South/SE.

Considering it's the GFS and ECM ops, this cannot be ruled out.

The next 24 hours will be crucial.

Edited February 21, 2018 by Thinon

[Mucka]

4 hours ago, Connor Bailey Degnan said:

It would suggest the Op is somewhat of an outlier, yes. Here is yesterdays 12z mean chart at 168, and today's side by side. If anything, i prefer the 0z.

Yes if anything today's mean is slightly better in that it is a little further West which would make for a cleaner/colder transition. Just a little further North on the 12z would be nice. 

[BleakMidwinter]

1 hour ago, Man With Beard said:

Here are the clusters from T144 to T240:

 

They pick up brilliantly the move from the Scandi based High to a more Greenland based High.

Looking at how the op fits in with the clusters:

T144 & T168: Bearing in mind that the further north the 546mb line is, the further north the cold pool is into the UK (at these timeframes, not necessarily later!) - 39 ensembles have this line further north than the op, 5 ensembles have this line further south.

T192, T216 & T240: 21 runs close to the op at this point (potential snowstorm from the north), 19 runs see a direct hit from the cold pool (potential snowstorm from the east), 11 runs have us in a battleground situation between the cold pool and air coming up from the south (potential snowstorm from the south)

T264: Only one cluster which I have come to believe means the ECM computer was unable to spot clear enough patterns, so my advice is follow the mean chart. Here's the T300 mean chart - I think you'll see what I mean - no way there will be a great big nothingness over the UK at that time!!

 

So my interpretation (feel free to disagree!) is D6-D7 = emphasis on deep cold + convective snow, D8-D10 = emphasis on snow risk more widely with varying possibilities for cold, D11-D15 = wait and see

 

[removed charts to save filling up the page!]

 

Thankyou so much for this - it REALLY helps novices like me to have the explanation of the range of clusters. It makes it clear that any one cluster is meaningless, but the range of clusters give patterns which are meaningful. I don't think I'd properly understood just how that all worked before, despite several years trying to follow discussion in here! 

Thankyou!!

[The Eagle]

6z NMM 1km (850 hpa temperatures) resi to Monday morning.

 

Edited February 21, 2018 by The Eagle

[Frosty.]

There really is a super strong signal for deep cold to become entrenched next week and lasting well into march as the Ecm 00z ensemble mean shows!...thoroughly exciting times these for coldies, the best for 8 years!!

[East_England_Stormchaser91]

We've been literally so spoilt with stellar runs this week, so much so that now, if a chart is marginally as bad as a previous one for example, it feels like a let down to some, despite in reality if it suddenly popped up in the middle of zonal dross normality, it would still look like the run of the century. 

 

[MattStoke]

Great 6z from the GFS. It is unbelievable that there are any negative posts at the moment.

Details will chop and change run to run and there is absolutely no point getting hung up on such detail. However, that run shows there is bags full of potential for snow. Plus the fact it is very different to the previous run shows there is still a lot to be resolved once the deep cold arrives.

It has been clear for days that the real cold would arrive between late Sunday and Monday. God knows where the nonsense about it being put back is coming from.

As for the uppers, you could add 8 degrees or more to those in a contintental feed and snow would still fall to low levels.

As for a quick return to milder conditions - No chance at all. You could not as for a better setup for prolonged cold.

Edited February 21, 2018 by MattStoke

[johnny1972]

2 hours ago, danm said:

Are you really being picky over -12c uppers compared to -14c uppers? 

GFS shows -12c uppers into E Anglia on Monday with -10c across most of the east:

We then see -16c uppers closing in on the east coast by Wednesday:

This isn’t just about the east. When you have a set up like the models have shown over the last few days expectations are high for the whole country to be sub -10 850’s at the least. In N.I the 850’s were modelled -13/-14 yesterday and sit now at -8. So a hell of a difference. Yes it is one run and will likely change again but with charts that have appeared it would be nice to see the whole country in on the act. 

[Buzz]

17 minutes ago, Thinon said:

The GFS and ECM op squeezes the Scandi high southwards, resulting in the convective potential being pushed down into France, and a significant decrease in the severity of the cold for most parts of the UK except maybe the far South/SE.

Considering it's the GFS and ECM ops, this cannot be ruled out.

The next 24 hours will be crucial.

No more 'crucial' than the past 24 hours, or the 24 hours prior to that, or the 24 hours prior to THAT ............ in short, the weather is constantly in a state of flux and the computer models are merely running through possible outcomes. They do not make the weather and are often wrong, particularly the further ahead you look.

Edited February 21, 2018 by Buzz

[Chris.R]

Using “Tableaux GEFS” on the 06Z; at T186; 13 members have -12 or lower at 850 HPa; 8 have -14 or lower. Lowest is -15.1. I’d say that’s pretty good! That’s my location as well not somewhere in the East. 

I mean how often would you see such a strong signal there so far out. Quite breathtaking really. 

Edited February 21, 2018 by Chris.R

[danm]

1 minute ago, johnny1972 said:

This isn’t just about the east. When you have a set up like the models have shown over the last few days expectations are high for the whole country to be sub -10 850’s at the least. In N.I the 850’s were modelled -13/-14 yesterday and sit now at -8. So a hell of a difference. Yes it is one run and will likely change again but with charts that have appeared it would be nice to see the whole country in on the act. 

It's arrived in the east at that time on Monday, according to the GFS, but will push west. 

My point was that the timeframe that has been forecast for the cold air to arrive has consistently been sometime between Sunday and early Tuesday. Each run moves this around, as you'd expect. Yes, on the 6z, the cold air that does arrive on Monday isn't quite as cold as other runs (-12c into E Anglia, rather than -14c or -15c) but it is still arriving as previously forecast. 

[memories of 63]

I really hope the snow fall charts are inaccurate and FI is really FI otherwise I'm looking at 30+cm snow on Friday 02 March 

[frosty ground]

17 minutes ago, The Eagle said:

6z NMM 1km (850 hpa temperatures) resi to Monday morning.

 

Saturday Morning Temps

[bluearmy]

8 minutes ago, MattStoke said:

Great 6z from the GFS. It is unbelievable that there are any negative posts at the moment.

Details will chop and change run to run and there is absolutely no point getting hung up on such detail. However, that run shows there is bags full of potential for snow. Plus the fact it is very different to the previous run shows there is still a lot to be resolved once the deep cold arrives.

It has been clear for days that the real cold would arrive between late Sunday and Monday. God knows where the nonsense about it being put back is coming from.

As for a quick return to milder conditions - No chance at all. You could not as for a better setup for prolonged cold.

depends what is construed as negative matt. hopefully everyone sees those post explaining where things might (and are already differing somewhat from expectation) change as being informative. the idea, I guess is that everyone becomes just that little bit more informed and can make their own judgements rather than just relying on others interpretations of the output which could ( dare I say it) be a little less than than objective and possible imby on occasions.