Model Output Discussion - The final stretch to Christmas

[snowy weather]

UKMO looks cold on Sunday

 

 

:smiliz19:

bbc weather has heavy rain forecast for saturday night/sunday morning where I live. Surely with those temps it will be snow?

[Mucka]

GFS Op is a poor run but the parallel looks much better and also UKMO still looking good for a decent MLB setting up so not too worried at this stage so long as it doesn't garner support.

[snowy weather]

If you think the gfs has that low too far south then take a look at the ukmo 60 hour chart!! Has the low on the south coast!! Snow event across midlands in that case!!

This may seem like a really stupid and basic question but I am really interested to learn, Why is the low significant? Is it snow?

[Eskimo]

If the UKMO has the track correct, then expect snow from Birmingham northwards, and some wet snow across the Chilterns. The GFS has a large warm sector which limits snowfall to Manchester northwards. 

Edited December 24, 2014 by PerfectStorm

[saint]

bbc weather has heavy rain forecast for saturday night/sunday morning where I live. Surely with those temps it will be snow?

 

 

BBC forecasts wont have updated yet, and also 5 day forecasts are very unreliable. 

[snowy weather]

BBC forecasts wont have updated yet, and also 5 day forecasts are very unreliable. 

when do they update?

[Nick F]

Thanks, and is it good or bad for cold and snow in SE?

 

The passage of the low itself will bring just rain for the SE, but once the low clears into the near continent and colder NEly kicks in, there is potential for a small window of sleet/snow sat eve/night before it turns drier.

[Met4Cast]

GFS(P) building heights towards Scandi. Could we see a classic undercutting pattern on this run?

 

[Neilsouth]

When does the GFS retire and become the new model? Is it next year

[snowy weather]

The passage of the low itself will bring just rain for the SE, but once the low clears into the near continent and colder NEly kicks in, there is potential for a small window of sleet/snow sat eve/night before it turns drier.

thanks for the clarification.

[Met4Cast]

UKMO keeps amplification towards Scandi at 144

 

 

So GFS old is out on its own with flattening out the pattern so soon, which isn't exactly something we haven't seen before.

[nick sussex]

It might be that a shortwave will have to be the trigger to bring in any deeper cold, this would need to eject south near Scandi and head sw'wards, this will then force a high pressure cell further north.

 

We've seen this type of set up before and if this is the newer trend then this is most definitely Code Red!

[Captain Shortwave]

The passage of the low itself will bring just rain for the SE, but once the low clears into the near continent and colder NEly kicks in, there is potential for a small window of sleet/snow sat eve/night before it turns drier.

Indeed, what I see is that low does not engage the cold air to our north east as much, this means the low tracks faster as a shallower feature which is also further south. This I see really as a bad thing as we cannot dig the cold air towards us as the low clears, the result is the models moving to a solution with heights near the UK and cold air going into central Europe.

UKMO and GFS (P) look okay upstream to sheer the ridge and sustain the high over northern Europe

GFS op poor upstream and develops a more Euro high motif and turns conditions milder as we end week 1

So back edge snow and a brief window Sunday night into Monday for some wintry showers in eastern areas before the high builds in and suppresses convection.

Edited December 24, 2014 by Captain shortwave

[Mucka]

The problem with the GFS runs longer term is they do not link the toppling ridge with heights to the east so energy just pushes through NE out of Europe instead of curling back W under the ridge. This in turn allows the ridge to sink S and flatten the pattern. UKMO looks better but it is something we want to see the output moving away from quickly.

 

 

Edited December 24, 2014 by Mucka

[gottolovethisweather]

Well Happy Christmas to one and all at netweather and I was going to attempt a post without mentioning the word snow but on that account I've failed. 

 

Please don't set yourselves up for a fall (literally) with regards to predicting the precipitation type in your backyard at such timeframes as each run is offering up different scenarios right now and will continue to do so until within 24 hours of the event I would suspect.

 

I am fairly confident it will most definitely turn a fair bit colder behind the problematic low providing more wintry chances down the line with some luck. The low is problematic due to in some areas there may well be heavy rain, gales and a true snowstorm for some others. Most current emphasis from the media is on this particular depression being largely a rain-maker but there is still uncertainty regarding this aspect and also as ever, concerning the track of the low. Not only that, there is potential for a secondary feature on the 28th December which may provide more excitement for the cold brigade.

 

Take care all and stay safe.  :w00t:

 

EDIT: the latest GFS P favours the low stalling somewhat into the early hours of Sunday 28th before clearing away into the continent, this what I presumed was shown as a secondary feature whereas it is likely to be a trailing weather front. In time, I expect more attention to be paid to this feature as this would likely produce snow at lower levels with forecast -6 and -7 uppers in the mix. Eyes on the forecasts guys.

Edited December 24, 2014 by gottolovethisweather

[snowice]

It might be that a shortwave will have to be the trigger to bring in any deeper cold, this would need to eject south near Scandi and head sw'wards, this will then force a high pressure cell further north.

 

We've seen this type of set up before and if this is the newer trend then this is most definitely Code Red!

As long as we don't have a Red nose like rudolph!!lol

[nick sussex]

I think the GFS is a non-starter because of its pattern over in the USA, too flat and unless theres been some drastic change in whats to be expected over there then it won't verify.

 

The UKMO looks like its thinking of developing a shortwave in Scandi at T144hrs, this for newbies is the most traumatic way to get an easterly in, you need the right curve back in the jet to take this towards the Low Countries.

 

The shortwave there is effected by the pattern upstream, you need enough dig in the jet to the west of the UK, so its down to the upstream amplification otherwise the shortwave goes se and not sw.

 

All I can say is be afraid, very afraid...................

[Summer Sun]

Once the low pulls away the models are in good agreement for a quiet end to 2014 with high pressure dominating giving us a colder end to the year with some frost and fog

 

 

Similar picture from GFS P

 

[Midlands Ice Age]

My updates from the December20-21st on the situation as indicated below...

 

https://forum.netweather.tv/topic/82046-model-output-discussion-the-run-in-to-christmas/?view=findpost&p=3093531

 

Well things have moved on a good deal now..... and as I and the more experienced posters (eg Tamarra,(with her techical skills). TEITS and other people) have postulated are coming in as was suggested.....

 

First I would like to simplify  the models (from my viewpoint) - 

 

GFS P after forecasting  the 'bomb' from about Dec 15th  - 21st  in the southern North Sea ,  moving part of it to southern Europe and toying with the idea of some mid-level blocking around the UK, lost the signal about the 21st.

But well done in picking this bomb up, Tough it then got lost. I assume that it was the up-coming pattern change that it could not model correctly (vis the mlb over the UK linking up to Scandinavia,  and then with the Russioan beast(still not fully shown - yet) 

 

GFS it appears was fully committed to the zonal Atlantic and couldn't ever see the change of the jet now expected to happen over the UK in the next 3 days. Consequently it could NEVER see the change to colder projections.

 

In general, the GFS was too swift (even the GFS  P picked the low up for 36hrs before it actually appears.)

 

THe ECM did not pick up the evolution of the bombing 'low' until about the 21st. Previously it had picked up something, but was showing an extreme west base bias for the lows, with  very strange  charts showing a string of lows from Iceland to Newfoundland in a straight line. It had obviously picked up something at this stage and it took a lot of weird charts before it came up with a plausible scenario. It appears to have stuck with this for the last 4 days, and has now looked beyond and sees the developed MLB moving to Scandanavia.

 

 PS The 'strange situation' alluded to above  was the one which led to the 56 blizzard and a very cold period in the UK

 

However , what can we deduce?

 

1) GFS handles the ongoing westerly Atlantic regime quite well albeit a little to quick in timing. But fails whenever we have a blocking scenario in and around Europe about to setup. This has happened in the past as well as this occasion.

So reasonably reliable for 'normal' weather, but lacking when we have the situation where we in Euope are very interested in, albeit only happens occasionally.            .From our 2010 experience it forecast the Greeny high quite well.

 

2) GFSP spotted the change in trend VERY well this time,but somehow lost the signal!!!, and went merrily along the traditional route. I feel the fact that it caught the trend first is a big plus for it

 

3) ECM had detected a change in trend was coming up, but was confused about exactly how to handle it. It picked up the signal about 7 days before the event and further more soon went on to identify the succeeding pattern.

 

So maybe we will be able to use the GFSP in future to warn when a change of pattern is imminent. Shown later by all models going AWAL.

 

PLEASE NOTE - THE ABOVE ASSUMING THE FORECAST MLB and HLB do get underway!!!!!!.

 

So where do I see it going now -

 

Well it has gone exactly as I suggested in my first post 7 days ago, and I believe that the high will migrate to Northern Europe, with cold 2M temperatures in abundance. As suggested previously, I think  the cold will be 'locked in' by events to the south west.  This is where our attention must be kept  The jet will try to fire up against the block, It needs to resist for a long cold spell to be established.

 

If this happens we may well end up with channel lows and a 1947 type of scenario, which will have the effect of pulling high pressure back from Scandy and towards Iceland /Greenland (regression), and leaving us in the cold.

 

These types of situation have not occured too often recently, but it looks as if it MAY occur this time.

 

Also of note that it is occuring at the same time, and a very similar way, to the way in which 1962 started, except there the MLB around the north west of the UK, hung around a longtime (4 or 5 days) to allow cold to move into Europe, before the boxing day/ new year blizzards came from the southwest  and cold set  in  for a prolonged period. Eventually regression occured  after a SSW about 3 weeks later.  

 

So, I feel  there are very good prospects for winter to really set in . I have compared to strong winters in the past and we could end up (with a large slice of luck - bad luck at my age) with a composite of 47 and 62. Not something to be sniffed at..

 

HOWEVER we could end up with nothing at all....

 

MERRY CHRISTMAS to all!!!!

 

MIA

Edited December 24, 2014 by Midlands Ice Age

[EML Network]

I think I'll await the ECM and GFS Ensemble suite to come out before reading too much into the 12 z GFS OP , Parallel and UKMO. 

 

I would fully expect to see small adjustments North or South from run to run, of the High pressure and those small adjustment would mean big differences down the line between getting an Easterly setting  or a flattening out of the pattern and a return to mild westerlys. 

 

But what I have seen thus far this afternoon has stepped away from the idea of a Scandi High ever so slightly.

 

What I find encouraging is the continue split of the vortex being modeled further out

 

It should help to keep things interesting from a cold lovers perspective. 

 

 

 

 

[Mucka]

I think the GFS is a non-starter because of its pattern over in the USA, too flat and unless theres been some drastic change in whats to be expected over there then it won't verify.

 

The UKMO looks like its thinking of developing a shortwave in Scandi at T144hrs, this for newbies is the most traumatic way to get an easterly in, you need the right curve back in the jet to take this towards the Low Countries.

 

The shortwave there is effected by the pattern upstream, you need enough dig in the jet to the west of the UK, so its down to the upstream amplification otherwise the shortwave goes se and not sw.

 

All I can say is be afraid, very afraid...................

 

 

I think we need to worry about the downstream amplification as much as worry about what then comes upstream Nick. Without an anchor for the ridge to prevent it collapsing South into Europe there will be less chance of undercut upsteam anyway no matter what the pattern. We need the diving low to be stalled in Europe somewhat instead of just pushing through to aid amplification and connect heights to the NE.

 

It is a bit six of one and half a dozen of the other but I think both areas need watching closely.

[bluearmy]

Always rely on the GEM when we're in a tight spot

[Frosty_wsm]

Always rely on the GEM when we're in a tight spot

Well it is Christmas, the time of miracles so you never know lol.

[Captain Shortwave]

GFS ens

Support some sort of high over Northern Europe and a light continental feed, 850s are not particularly cold but the surface temperatures are (low single figures for most). So still a spell of surface cold to come when the low clears, though we do need things to trend the other way to bring a colder snowy solution

Edited December 24, 2014 by Captain shortwave

[Mucka]

GEM links heights to the NE allowing the flow to loop back West

 

 

This keeps the block from sinking and allows the undercut later.

 

 

This why the link up of heights is important as it props up the high and without it the high would be at a lower latitude and the undercut would very likely not occur later but instread go over the block sinking it

Edited December 24, 2014 by Mucka