Model Output Discussion 29th December - Into mid-Winter.

[MattTarrant]

Just a quick showcase of how much the orientation of the high makes so much difference to the 'prospects'. Much more amplified on the 12z 

6z 228h Vs 12z 222h

 

[frosty ground]

GFS shows a very Unstable flow from the North West turning to a more Northerly. 

[karyo]

1 minute ago, Johnp said:

More zonal? I'd use the word meridional for this run so far.

I agree! Hence we manage to get some colder uppers in this run.

[Singularity]

  

It's a deep low but look at the orientation of the trough-ridge combo.

The low should disrupt and heights tend to rise N of the UK. Lets see if GFS can handle that...!

[There's a storm a coming]

1 minute ago, Singularity said:

  

It's a deep low but look at the orientation of the trough-ridge combo.

The low should disrupt and heights tend to rise N of the UK. Lets see if GFS can handle that...!

Unfortunately GFS can't handle it! The last couple of days GFS had been churning out great FI but today seems to have gone downhill with the dreaded Azores high just not leaving us alone

Tasac

[radiohead]

Not too concerned about the break down of cold in the low-res deep FI. The T240+ charts will be different again on the 18Z, 0Z etc. The more important thing is that the onset of the cold shot is edging closer to the reliable timeframe.

[Singularity]

Just now, There's a storm a coming said:

Unfortunately GFS can't handle it! The last couple of days GFS had been churning out great FI but today seems to have gone downhill with the dreaded Azores high just not leaving us alone

Tasac

Indeed. That little kink in the isobars just W of Ireland is as far as it manages to get - but admittedly I didn't expect that shortwave low to move across quite so quickly. Typical eh?

In any case the low in question is far enough away that it may never become an issue in the first place, for all we know 

[radiohead]

12Z GEM is on board with the cold shot. Though uppers aren't as cold here.

[bluearmy]

Just now, radiohead said:

12Z GEM is on board with the cold shot. Though uppers aren't as cold here.

They never are on gem

its a known model bias (well to us anyway) when there isn't a continental flow 

wouldn't be looking beyond day 8 max on the ops which leaves us in an interesting position 

 

[radiohead]

Just for fun.

[knocker]

Very predictable the GFS didn't run the cyclogenisis idea again. Note the difference

Edited January 5, 2017 by knocker

[phil nw.]

36 minutes ago, Team Jo said:

without wishing to nag,some recent posts would probably be best suited to a PM conversation or the banter thread.......if we could keep on topic for the imminent runs, that would be super!

 

Thanks!

To keep this thread a better read 7 of those posts have been moved to the banter thread here

Please all keep posts  relevant to current model outputs and use the other threads if it's general chat and banter.

Thanks.

 

[Nouska]

7 minutes ago, frosty ground said:

GFS shows a very Unstable flow from the North West turning to a more Northerly. 

Surely this cold an upper air mass could give a chance of polar low formation. It's originating over Greenland and following some of the favoured routes as in the papers linked by Knocker and John Holmes.

Of course, we have to get it to verify but I'm more confident than usual, having looked at the finer detail for the ECM model on the Icelandic site. Both bring this in but there are issues with timing and no doubt shortwaves once we get to five days out.

The EPS 00Z T850 mean +192 at circa -8C is nothing to be sniffed at.

[northwestsnow]

Just wondering how long its been since those in the north west have seen a good old fashioned polar north westerly.

I guess as ever geography playa a part in preferences but if i were on high ground in NW Britain i think i would be getting interested now....

Edited January 5, 2017 by northwestsnow

[winterof79]

3 minutes ago, northwestsnow said:

Just wondering how long its been since those in the north west have seen a good old fashioned polar north westerly.

I guess as ever geography playa a part in preferences but if i were on high ground in NW Britain i think i would be getting interested now....

2009 Jan,several shots.

[Seasonality]

2 minutes ago, Nouska said:

Surely this cold an upper air mass could give a chance of polar low formation. It's originating over Greenland and following some of the favoured routes as in the papers linked by Knocker and John Holmes.

Of course, we have to get it to verify but I'm more confident than usual, having looked at the finer detail for the ECM model on the Icelandic site. Both bring this in but there are issues with timing and no doubt shortwaves once we get to five days out.

The EPS 00Z T850 mean +192 at circa -8C is nothing to be sniffed at.

Is it not quite rare for them to get so far south and I think they weaken rapidly over land? Still, they are very difficult to model and chances are that one wouldn't appear in the NWP and would require nowcasting using satellite images.

[MattTarrant]

Just thought i would post this as its a very good tool. The new Metcheck Super Ensemble. The attached chart is for my home town of Tiverton (61m).

Some good agreement now with only three runs from the 60 runs showing positive 850mb temps. I would approximately say that 60/70% show around the -4/-5 mark with around 7 or so showing -9/-10   

Edited January 5, 2017 by MattTarrant

[knocker]

10 minutes ago, Nouska said:

Surely this cold an upper air mass could give a chance of polar low formation. It's originating over Greenland and following some of the favoured routes as in the papers linked by Knocker and John Holmes.

Of course, we have to get it to verify but I'm more confident than usual, having looked at the finer detail for the ECM model on the Icelandic site. Both bring this in but there are issues with timing and no doubt shortwaves once we get to five days out.

The EPS 00Z T850 mean +192 at circa -8C is nothing to be sniffed at.

You weren't casting your eyes on this little fella by any chance ?

 

Edited January 5, 2017 by knocker

[marksp]

well to my untrained eye the 12z looks a better run early on.

the trough in the mid west USA seems to dig further south, in turn creating more amplification which results in high pressure rises over Nova Scotia, causing the Atlantic trough to drop more favourable over 

the UK, bringing in the cold quicker. T144 to T162 seem critical as always.

thats my thoughts (could be wrong ?)

[knocker]

2 minutes ago, northwestsnow said:

Looks fairly cyclongenic to me old bean? In fact loiks very snowy cyclongenic, or have i missed your point?

Completely, old bean but not  very surprising.

Edited January 5, 2017 by knocker

[ItNeverSnowsInWindsor]

I have a feeling the charts for next Tues and Weds aren't showing enough trough disruption over the low countries as I'd expect with all the cold air in North Europe.

 

[Scandinavian High.]

Looking cold with some snow showers in the north maybe some pushing south on this chart..but no big freeze yet and  sustained colder weather but it could change..

[radiohead]

Lows like this on the 12Z GFS could sweep down at relative short notice in this type of flow and deliver quite a bit of snow to almost anywhere in the right conditions.

Edited January 5, 2017 by radiohead

[MattTarrant]

2 minutes ago, abbie123 said:

Looking cold with some snow showers in the north maybe some pushing south on this chart..but no big freeze yet and  sustained colder weather but it could change..

Yes no big freeze, but as ever the cold spell could increase or reduce by a day depending on the extent of ridging in the Atlantic. I would expect a 2-3 day period from current runs.  

[Nouska]

11 minutes ago, Seasonality said:

Is it not quite rare for them to get so far south and I think they weaken rapidly over land? Still, they are very difficult to model and chances are that one wouldn't appear in the NWP and would require nowcasting using satellite images.

There was a beautiful example hit Brest a few years back and some of the most spectacular ones have travelled a long way down the North sea with huge snowfall as they landed. I'll be trawling the close-up satellite pictures from the IMO site if it turns out anything like modelled.

The most recent one was a bit questionable as it started life as a baroclinic leaf to the east of Iceland - didn't really matter as it did the convective thing on its travels south and crossed central/southern England with a good amount of snow to please the chionomaniacs amongst us.