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Model Output Discussion - The Run In To Christmas


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I think one of the stumbling blocks to more amplification of the ridge over the far N Atlantic in across Greenland that we are seeing on the 06z GFS op and the 00z ECMWF is the flow upstream over N America not playing ball.

 

http://www.meteociel.fr/modeles/gfse_cartes.php?mode=0&ech=6&carte=1

 

Using the link above, if you hover over the time frames and work down toward t+150, you can see on the loop that a trough deepens over eastern US, this is what will help amplify a ridge downstream over the NW Atlantic. Problem is, the trough over eastern US does not hang around for long before a flatter 500mb flow develops from upstream - which doesn't allow a block to develop mid-Atlantic. Rather the ridge quickly flattens out.

 

More runs needed, but unless we see the flow more amplified upstream over N America to help slow the trough over the east, then I wouldn't get ready to go panicking buying and stocking up on esstentials just yet! Off topic, but dare I say it maybe the MetO are justified to remain cautious!

Something I commented on yesterday in the previous thread Nick.

The Pacific ridge is less pronounced and downstream the Canadian trough is quickly flattened.

We still see some Atlantic ridging but it won't hold for long under the pressure from the E. Seaboard.

Based on the ens means it looks to be evolving towards an average to rather cold Christmas currently rather than anything severe.

http://www.meteociel.fr/modeles/naefs_cartes.php?ech=180&code=1&mode=0&map=1&runpara=

http://www.meteociel.fr/modeles/ecmwf.php?ech=192&mode=1&map=1&type=1&archive=0

I am certainly not dismissing something colder after the holiday though.

It may be that another attempt to amplify the pattern will appear as that Alaskan +ve ht anomaly remains in the naef ens into the new year.

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Unfortunately, there needs to be a recognition that if we share at *this tentative juncture* the exact nature of what we have as Ops Centre guidance, certain individuals will inevitably extrapolate/wa

If the UK can't get cold from an upstream pattern with a negatively tilted troughing setting up over the ne USA , indeed the best set up since two winters ago then I will seriously consider throwing m

The good news just keeps on coming!   Upstream pattern is falling into place to deliver what many people in this thread want to see, NCEP give us the best update since winter 2012/2013,  indeed I'm

Posted Images

IF anything the ensembles are now even more keen on increasing heights in the greenland locale and the -EPO ridge is stronger.

 

6z gensnh-21-5-264.png?6gensnh-21-1-264.png?6

0zgensnh-21-5-288.png?0gensnh-21-1-276.png?0

 

 

Yes it is typical of the chaotic output that the Op should go for a weaker ridge just as the ensembles give possibly the strongest signal yet for a pattern change and descent into true winter cold.

Hopefully we will get the full combo tonight with all Ops and ensembles strongly on board, but I doubt it.

 

 

graphe3_1000_244_36___.gifgraphe6_1000_244_36___.gifensemble-tt6-london.gif

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what is a channel low please?

Thanks

Snowy weather,

 

A channel low is a low pressure system moving along or slightly south of the south coast from west to east which engages with cold air ahead of it and the result is snow on the northern flank. How far north the snow gets is always open to question but one thing is certain the further north the more likely rain on the southern side. The good thing is a channel low pressure gives the southern half of the country the heaviest snow falls when it happens. The are as rare as the teeth on SM avatar  :acute:  One to watch but as others have said I would not get to excited

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Looking through all 20 runs and not including either the, Op or parrallel. 

 

When looking at solely the 850 Uppers POST 240 

 

5 runs won't deliver the goods

4 runs are close, flirting with cold  but no cigar

11 runs have an extended period of cold weather 

 

bearing in mind it's a + 240 chart , all you can ever do at that time frame is look to see trends, you'd never get all 20 runs going for cold, so I for one like those odds. 

Edited by EML Network
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Netweather headline sums things up perfectly, mild for now but turning colder from the north and if we leap forward to the start of next week the same will apply except next weeks cold incursion is likely to pack a much stronger punch and we will all get some snow and frosty weather during the second half of next week..I don't see any downgrades, just the usual wobbles from run to run which has always been the case when a cold snap / spell is looming..and looming larger and larger is the first proper cold snap of this winter..I am sure of that. :smiliz19:

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Good Morning Everyone,

 

First of all apologies to the Moderators if I have posted this in the wrong thread. Please feel free to relocate it to a more appropriate one if you consider it necessary.

 

I avidly read the model thread every day, but do not feel competent enough to post on it with any degree of clarity as to what I think I see from the charts.

 

There is one thing that I have been mulling over for some time, which I hope I can explain clearly enough.

 

As John Holmes and others have stated on numerous occasions one should look at the same model run each day to look for possible trends (e.g. the 00z GFS on Monday, Tuesday, Wednesday etc. As there is only 24 hours difference between each output how is it that there is often quite a variance?

 

Also as there is only 6 hours difference on GFS between outputs to give an example why is there often quite a difference between the 12Z and the 18Z as they both I presume use the same Supa Dupa Computer using the same input data availability. If GFS, for the sake of argument began their first output 5 years ago how is it that the different outputs vary so much? Would they not come closer together with each 6 hours output?

 

 

Kind Regards

 

Dave

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Within the swinging to and fro, the extended ecm 00z want to slowly sink the Atlantic ridge across us ( as the london temps illustrate, this mean cold remains) and the 06z gefs seem to be in the camp where the pattern potentially remains insitu with further ridging to our nw.

All in all, whatever the detail, a very positive place to be hemispherically as we end the year and head into the heart of winter.

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Good Morning Everyone,

 

First of all apologies to the Moderators if I have posted this in the wrong thread. Please feel free to relocate it to a more appropriate one if you consider it necessary.

 

I avidly read the model thread every day, but do not feel competent enough to post on it with any degree of clarity as to what I think I see from the charts.

 

There is one thing that I have been mulling over for some time, which I hope I can explain clearly enough.

 

As John Holmes and others have stated on numerous occasions one should look at the same model run each day to look for possible trends (e.g. the 00z GFS on Monday, Tuesday, Wednesday etc. As there is only 24 hours difference between each output how is it that there is often quite a variance?

 

Also as there is only 6 hours difference on GFS between outputs to give an example why is there often quite a difference between the 12Z and the 18Z as they both I presume use the same Supa Dupa Computer using the same input data availability. If GFS, for the sake of argument began their first output 5 years ago how is it that the different outputs vary so much? Would they not come closer together with each 6 hours output?

 

 

Kind Regards

 

Dave

When there are major shifts between outputs run to run it generally means that the pattern is very volatile and could go one of several different ways which is why I don't take credence to individual runs and hence why I only commentate on one run a day (the 00zs). This eliminates any post stress that occurs after every 6 hour run doesn't show what was shown on the preceding one and gives the models a chance to iron out such swings into a more calculated 24 hour outcome. I admit day to day too provides some interesting comparisons at times usually when cold weather threatens the UK. Every brick has to fall in the correct place for the UK to receive the holy grail of snow and cold most want to see and there is a 90% chance of that not happening on an island such as ours lying on the Eastern end of a large Ocean as we do and with a usual prevailing Westerly wind across it . It only takes something seemingly quite small synoptically to move in a different way to expected to mean quite different results at the surface.

Edited by Gibby
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Interesting JMA week 2 anomaly and ties in with the latest runs from the main models: post-14819-0-27981200-1418905966_thumb.p

 

Shows the colder upper anomaly over the UK and the ridge. A bit too far east really but as it's a 7 day anomaly so difficult to get specifics as small margins will make big differences to surface conditions.

 

Week 3-4 keeps it colder than average: post-14819-0-90170700-1418906240_thumb.p

Edited by i'm dreaming of...
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Very good 06Z GEFS set IMHO. Better than the 00Z by a distance.

GFS(P) only really loses its way after 240 hours when it enters low res, so can (probably) be discounted. Less of a west based bias as well on this suite.

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Looking through all 20 runs and not including either the, Op or parrallel. 

 

When looking at solely the 850 Uppers POST 240 

 

5 runs won't deliver the goods

4 runs are close, flirting with cold  but no cigar

11 runs have an extended period of cold weather 

 

bearing in mind it's a + 240 chart , all you can ever do at that time frame is look to see trends, you'd never get all 20 runs going for cold, so I for one like those odds. 

Looking at the ens 06z IMBY a big change from the 00z ( sorry cant post) I want snow but ATM keeps going into FI 

t850East~Dunbartonshire.png

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Are you feeling okay IDO?

With both the GFS and ECM ensembles better than the operationals, I'm expecting the 12z's to be even better this evening.The Christmas period will most likely be cold with snow for some, that is the most important trend to take in my opinion.

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Looking through all 20 runs and not including either the, Op or parrallel. 

 

When looking at solely the 850 Uppers POST 240 

 

5 runs won't deliver the goods

4 runs are close, flirting with cold  but no cigar

11 runs have an extended period of cold weather 

 

bearing in mind it's a + 240 chart , all you can ever do at that time frame is look to see trends, you'd never get all 20 runs going for cold, so I for one like those odds. 

Looking at the ens 06z IMBY a big change from the 00z ( sorry cant post) I want snow but ATM keeps going into FI 

t850East~Dunbartonshire.png

 

 

It does look from that that the operational is something of a wild card for mild temps between xmas and NY

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It does look from that that the operational is something of a wild card for mild temps between xmas and NY

But the mean is about 1.0c above the 00z it maybe disappointing but ATM the chances of cold/snowy weather are waning rather than waxing, just the way the NWP shows, hope this reverses with the 12z output 

cheers r

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Snowy weather,

 

A channel low is a low pressure system moving along or slightly south of the south coast from west to east which engages with cold air ahead of it and the result is snow on the northern flank. How far north the snow gets is always open to question but one thing is certain the further north the more likely rain on the southern side. The good thing is a channel low pressure gives the southern half of the country the heaviest snow falls when it happens. The are as rare as the teeth on SM avatar  :acute:  One to watch but as others have said I would not get to excited

thanks for the excellent answer mate :)

Hopefully it becomes a trend in the later runs.

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Well after reading met office update I would maybe think they have discounted the ECM 00z run. With talk of snow to lower ground in the north. So I would hint at if your say Newcastle northwards you may very well see some snow in the not too distant future. Maybe rest of us might have to wait just abit longer.

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Well after reading met office update I would maybe think they have discounted the ECM 00z run. With talk of snow to lower ground in the north. So I would hint at if your say Newcastle northwards you may very well see some snow in the not too distant future. Maybe rest of us might have to wait just abit longer.

Looking forward to the 12z output..... the MET have already seen it ( I think) waxing not waning, just what we needed

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Like I said, no downgrade to the cold spell next week, just the usual wobbles we come to expect when looking too closely for every possible flaw on each run but from what I have seen, rather than downgrade, the wintry potential and longevity of the cold is upgrading and any change back to a less cold / milder pattern has now been pushed back into the following week so next week could become very exciting for the cold lovers among us..:-)

Edited by Frosty.
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Further to Nick F's post previously, upstream there are some uncertainties with the progress of that troughing eastwards.

 

In terms of the pattern flattening timing here is crucial to the evolution of cold over the UK.

 

So from NCEP these comments on the morning update:

 

 ONGOING DIFFERENCE BETWEEN THE TWO IS A TYPICAL
ONE... WITH THE GEFS MEMBERS A BIT QUICKER WITH THE PATTERN THAN
THE ECMWF MEMBERS. AMPLIFIED PATTERN WOULD TYPICALLY FAVOR THE
SLOWER /ECMWF-LIKE/ SOLUTIONS BUT UPSTREAM PACIFIC ENERGY MAY BE
ENOUGH OF A KICKER TO KEEP THINGS MOVING.

 

In terms of the outputs so far not a big surprise to see the GFS P drop its 00hrs output, its synoptic evolution there was incredibly difficult and actually does come with a high risk of getting the trough filling in situ over the UK.

 

The later GFS P does look a like a trend towards the ECM in terms of some shortwave energy getting thrown ene towards the UK from the sw. It might be only then that the deeper cold might head further south after this clears and the block edges east.

 

This does bring up the prospect however of a Channel Low like situation, you can see from both the ECM ensemble spreads and wind direction component a cluster suggestive of a change in flow over De Bilt , if this Channel Low does appear I'm afraid its going to lead to a deal of IMBYISM in here.

 

The track of the low will correlate with the strength of any blocking, effectively whats positive for medium term cold is a low track which favours the southern portion of the UK, the further north the track the less favourable the upstream pattern because effectively this means the block is further west and placing less forcing on the pattern which allows lows to head further ne.

 

I'm totally neutral here as this doesn't effect me here in France but simply that a low track will not favour everyone in terms of snow, of course this low might not happen but just something to keep an eye on in future outputs and indeed if you get the southerly low track this should still lead to more snow opportunities UK wide going forward.

 

Overall then as long as shortwave activity to the sw doesn't cause too much drama it looks like becoming an interesting festive period, so fingers crossed that everyone in time can see some snow.

Edited by nick sussex
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Last night there was a -10 showing up in the ENS for 2M temps in central England.

 

Now there is a -13.

 

gefstmp2mmaxbirmingham.png?cb=924

 

I wonder if we can go lower than that on the next set?

 

Updated AO forecast 18thDec:

 

ao.sprd2.gif

Edited by SE Blizzards
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