Model output discussion - The run up to Christmas

[kold weather]

1 hour ago, Singularity said:

I recall Tamara saying in 2018-19 that a Greenland block that’s partially over Canada is more likely to reach far east  enough to put the UK in a cold airmass during Dec-Jan than in Feb-Mar. To do with seasonal wavelengths... though I think a fully west-based NAO could still be trouble unless it was VERY negative (does happen!).

I think the 00z GFS did that to an extent, though it wasn't a true west based block, it had a huge stonking upper high that was big enough that it surpressed the jet enough to prevent us ending up on the mild side even.

 

[SMU]

Interesting uodated ICON 120

[Sweatyman]

16 minutes ago, Mike Poole said:

Better ICON 18z, here T120 compared to T126 on 12z:

Centre of low is further east and better ridging into Greenland.  But to be honest, this model is playing catch-up!

more elongated which is good.

[chionomaniac]

If this below average spell was hitting us in March then we could write off settling snow. It isn’t, and it is a long time since a below average spell hit not long after the winter solstice

[Mike Poole]

15 minutes ago, North East Blizzard said:

That Greenland block is insane, has to be the form horse now. His response tweet was due to a video released by the met today that mentioned high pressure over the UK, seemed to contradict their text forecast and pretty much every model we see. I can only guess Glosea was showing something different, who knows, could be right but looks unlikely now. 

No GloSea5 or MOGREPS aren’t showing anything different, I’ll bet my car!  They are deliberately downplaying it in my opinion probably for Covid, Brexit, panic buying reasons - see MO updates thread, not wanting to derail this thread.  

Edit no idea why the T6 chart is there, but merry Christmas everyone anyway...

Edited December 23, 2020 by Mike Poole

[Catacol]

2 hours ago, winterof79 said:

#cactol surely that's good for the split with the Russian High. 

I’m still in the split camp despite some of the big US guns calling major displacement. But to be honest I’m not that bothered - I’m just loving the chase at the moment. It is important to realise that since mid Dec all we had really is a gradual upgrading trend once we got beyond the failed ridging prior to Xmas. How often do we see a general upgrading trend? I remember 2010 and certainly 2018 but no other moment that sticks in my memory. We have had a host of downgrading contexts though over the years.

Yes - returning to your point I do see a split - partly a gut instinct as much as a technical read of the situation - and as I have pointed out numerous times this season so far we have such an active pacific jet working in a Nino type of setup that I just don’t see a backtrack. The MJO is favourable, the GWO orbit points to some wind flow support for ridging (or at least no obvious forcing back to a flat pattern), the hyperactive pacific jet is going to keep meridional flow dominant (with a EAMT on the near horizon that could be particularly big) - and the Ural High remains a semi permanent friend in terms of the long term misery it has poured at the vortex along with a tendency for an Aleutian low in a Niña season that statistically should be featuring a North Pacific ridge more obviously.

I’m as happy as a pig in sh*t. My JFF forecast the other day might just come to pass - cold air looks to be embedding and signs of an Omega Greenland block that was the next link in the forecast chain are beginning to pop into NWP. This will make it cold providing the block doesn’t retrogress towards Canada (a slight concern if the pattern is sharpened any further by the next jet surge) and then watch for the vortex split with downwelling impacts that might have us in a serious easterly flow come mid winter. Things can always go wrong - we all know this very well - but right now the upgrading gradient and general medium term horizon is very encouraging.

Short term - a forecaster’s nightmare next week. Some daft posts today declaring rain for all away from high ground. The low inbound next week is not barrelling in from the west - it is dropping down from Greenland and pulling air in from Scandinavia as it arrives. Forget pouring over model attempts to project temperatures in such a deep system with such sharp pressure gradients. Look at the wind vectors, consider the source and be 100% sure that there will be cold sectors wrapped up in the midst of that deep system. For sure rain will feature....and for sure so will snow. Wall to wall snow for all - nope. Chances for spectacular local falls as highlighted by Chio - yes. It may not stick around and it may be messy and changeable - but it represents the START of an extremely interesting phase/spell of winter weather. And from this starting point I’m seeing no evidence of an Atlantic return.

Edited December 23, 2020 by Catacol

[Skullzrulerz]

9 minutes ago, Steve Murr said:

Interesting uodated ICON 120

Maybe some snowfall with that polar low just west of Scotland?

[SMU]

1 minute ago, Skullzrulerz said:

Maybe some snowfall with that polar low just west of Scotland?

More so the one in the SE for the midlands.

Deep snow there from the icon at 114.

[Allseasons-Si]

The ICON has a band of snow 27th-28th pushing down the country from the NW and pivoting through the midlands south.

[sheikhy]

1 minute ago, Allseasons-si said:

The ICON has a band of snow 27th-28th pushing down the country from the NW and pivoting through the midlands south.

Moving east and more in line with ecm!!midlands looks  a big target with the first of the snowfalls in this upcoming cold spell!!

[saintkip]

2 minutes ago, Allseasons-si said:

The ICON has a band of snow 27th-28th pushing down the country from the NW and pivoting through the midlands south.

That’ll do nicely 

[iowpompeylee]

1 minute ago, Allseasons-si said:

The ICON has a band of snow 27th-28th pushing down the country from the NW and pivoting through the midlands south.

Those charts give snow for the south! I will take that every day of the week! As I’m sure lots of others in the forum will!!  

[Day_9]

I can’t really understand the charts, there are no guides to what are the lines, whats the colours, is yellow good? Purple? Which one and when.  Nowhere can you find the info to learn.  
 

however, since pretty much November, the entire trend has been cold.  Consistently. That tells you all that you need to know 
 

 

[Catacol]

2 hours ago, kold weather said:

We are probably early enough and the set-u good enough aloft that we can afford to roll the dice on this one. If it fails and we end up in a SW atlantic wave train I suspect we will get another bite of the cherry and things will rapidly switch back to cold. Just a gut feeling if it does end up too far west. We've come mighty close to that on both the 06z and the 12z deep in FI on the GFS.

The increasingly meridional pattern is trying to shorten the wavelengths and this risks pulling the block west, but at the same time seasonal forcing would favour longer wavelengths and the MJO is likely to work in our favour. If the impact of pacific jet activity pulls that ridge a bit to the west I don’t think it will be a long term thing. Fine lines - but the direction of travel in general remains blocking in the Greenland/Iceland sector. Longer term pressure may rise over Scandy too though that will depend I think on the precise nature of strat events.

Edited December 23, 2020 by Catacol

[sheikhy]

That icon band of snow reminds me of the late december 2000 snow that swept through most of england!!gave a depth of about 10 or 12cms here in leicester!!will never forget that snowfall!!temps were at -4 when it hit!!started at 3am and did not relent till 9am!!started heavy and finished heavy!really big fat fluffy flakes!!following few days temps were in the negatives and snow stuck around solid!!

[chionomaniac]

2 minutes ago, Day_9 said:

I can’t really understand the charts, there are no guides to what are the lines, whats the colours, is yellow good? Purple? Which one and when.  Nowhere can you find the info to learn.  
 

however, since pretty much November, the entire trend has been cold.  Consistently. That tells you all that you need to know 
 

 

Have you checked out the net weather learning area. There are great guides there to help you understand 

[DanDorsetUK]

3 minutes ago, iowpompeylee said:

Those charts give snow for the south! I will take that every day of the week! As I’m sure lots of others in the forum will!!  

Hell to the yeah! Shows we could get a surprise next week down here yet!

[ALL ABOARD]

2 minutes ago, Day_9 said:

I can’t really understand the charts, there are no guides to what are the lines, whats the colours, is yellow good? Purple? Which one and when.  Nowhere can you find the info to learn.  
 

however, since pretty much November, the entire trend has been cold.  Consistently. That tells you all that you need to know 
 

 

Hi, 

In simple and as a starting point. 

Yellows-reds high pressure 

Blues-purples low pressure 

Tighter the lines together (isobars) windier it is. 

[Met4Cast]

The EC clusters are insane.. full on Greenland blocking.

Most importantly, teleconnections are supportive of a Greenland high for the next round of amplification. There is however a possibility of a -wNAO which would prevent the coldest air reaching the UK.

[georgiedre]

7 minutes ago, Allseasons-si said:

The ICON has a band of snow 27th-28th pushing down the country from the NW and pivoting through the midlands south.

Looks good for nw wales... what better during lockdown than a local walk in snowdonia 

[WxHerts]

Shame I don't seem to be able to access archive ICON high-res charts on meteociel, but that's a huge dumping and so am just curious as to how good it is with the modelling of snow events specifically (I'm talking magnitude rather than placement obviously).

[Day_9]

1 minute ago, chionomaniac said:

Have you checked out the net weather learning area. There are great guides there to help you understand 

Yea but i can’t see where to read an 850 chart, or a 500 for that matter.  

[iowpompeylee]

3 minutes ago, Rapodo said:

Hell to the yeah! Shows we could get a surprise next week down here yet!

I think in the next few weeks, nowcasting will be at the forefront for us all at some point! Exciting model watching. In fact the best in a few years I feel.. 

[kold weather]

Worth noting the ICON typically is overly conservative when it comes to snowfall in these types of situations (it showed nothing till the day back in early December) so the fact we have the ICON on board showing snowfall is hugely telling to me that we will be on the right side of marginal

Don't get too hung up on the exact positon of the lows/fronts, they will shift around probably quite drastically from run to run, these secondary low features are nightmares to forecast.

But from an IMBY point of view, I give the ICON a thumbs up, its close enough to my area to provide interest.

I said a while back that the 27-29th period interested me, and the GFS ensembles have done a half way decent job in the super extended range flagging up the possiblity, though it was way overboard with the blocking in the end.

Edited December 23, 2020 by kold weather

[chris55]

3 minutes ago, Day_9 said:

I can’t really understand the charts, there are no guides to what are the lines, whats the colours, is yellow good? Purple? Which one and when.  Nowhere can you find the info to learn.  
 

however, since pretty much November, the entire trend has been cold.  Consistently. That tells you all that you need to know 
 

 

It just takes time. There’s a lot to take in. Read the forum and you’ll slowly pick it up.  

There is also a good section of guides somewhere on here. 
 

Have fun.