General Model Output Discussion

[snowmadchrisuk]

This is what the GFS is showing this morning regarding the breakdown .

It keeps the Precipitation as Snow right out to +168 .

Also to give an example of how Cold the air is over the United Kingdom at the moment , the lowest minimum of this Cold snap has just been recorded at Altnaharra in Scotland of -21.6 . The coldest Min for a long time and only 6 degrees off the lowest recorded min ever in the UK.

As you can see for Cold and Snow lovers the Models are showing A very Snowy week , at least on the lines of last years February event .

This is my 4000th Post ... Have I really been a weather nerd for that long :cold:

Chris

[Yeti]

A cold breakdown is certainly not concrete at all! On Wednesday Bristol was predicted 8C next Saturday and yesterday it was down to -1C. Everything can change from one model run to the other - we've already seen this twice this winter I'm sure.

To me this looks more like bitterly cold southeasterlies:

http://www.wetterzen.../Rtavn1201.html

http://www.wetterzen.../Rtavn1441.html

http://www.wetterzen.../Rtavn1681.html

Keeping pressure low to the south in the Med has to be the key to not letting a ridge extend into the Med. Interesting charts nonetheless. Let's not get worried just yet and take a mild breakdown as sudden as some are making out.

Regards

Those SE'lies are not bitterly cold at all. If that chart is to be believed we can expect 4c minima in the S by Thursday:

http://www.wetterzentrale.de/pics/Rtavn15017.png

Not saying it will happen at all, but people seem to assume that just because the flow is SE'ly it will be cold. Yes, parts of Europe are now bitterly cold and a surface flow from these areas would bring correspondingly cold temps. However the flow is now predicted to have a more southerly element bringing it off France rather than Germany, which is nowhere near as cold (see above chart). We need as much of an E'ly element as possible helped by undercutting low.

[Shiny_Bottom_1]

Well, i'm going to completely contradict myself from the last few days.

The GFS, as it has done for around a week now, shows the 850's creeping above the -5oC for a 2-3 days period (all based on Derbyshire), with them returning below for a 3-4 day period.

Looking at the model comparison, we have a similar set up from the ECM.

However, look at the GFS T2M ensembles. For Derbyshire, it is not until the 18th/19th before we get above 0oC as a max temp.

Personally i'm sceptical about the snow potential, but those, such as Nick F, who have much more experience and knowledge than me (perhaps an understatement), disagree. So, you know who to listen to

Overall, remaining cold...potentially until the end of next weekend/early the following week.

Just to also add regarding the T2M for the ECM. I think i've found them for this mornings run, although the format is slightly different to what I have seen.

There is good back up from the ECM (which also has a similar pressure pattern to the GFS Op) that T2M will struggle to get above 0oC by the end of next week. In fact, the spread is quite impressive, especially as you move through next week, with the higher end of the ensembles remaining at 0oC, but it goes further towards -10oC as well right at the end.

Those SE'lies are not bitterly cold at all. If that chart is to be believed we can expect 4c minima in the S by Thursday:

http://www.wetterzentrale.de/pics/Rtavn15017.png

Not saying it will happen at all, but people seem to assume that just because the flow is SE'ly it will be cold. Yes, parts of Europe are now bitterly cold and a surface flow from these areas would bring correspondingly cold temps. However the flow is now predicted to have a more southerly element bringing it off France rather than Germany, which is nowhere near as cold (see above chart). We need as much of an E'ly element as possible helped by undercutting low.

But if you look at the ensembles, for Kent, 80% (or at least bar the op run + 1 other member) goes for temps of 0oC. I think, at this point, 4oC is much less favourable than an outcome with 0oC. Either way, 4oC is still cold.

[Verglas]

can anyone explain why there seems to have been a constant line of snow showers (still showing remnants on the raintoday animation) down the middle of St.George's channel ?, is it the airflow picking up moisture from the water and instantly turning to snow again ?

[Weather-history]

Those SE'lies are not bitterly cold at all. If that chart is to be believed we can expect 4c minima in the S by Thursday:

http://www.wetterzentrale.de/pics/Rtavn15017.png

If you look at that chart, thats for the south coast, inland its close to freezing.

http://www.wetterzentrale.de/pics/Rmgfs1504.gif

Furthermore, there's a lot of preciptation in that time frame.

Edited January 8, 2010 by Mr_Data

[Shiny_Bottom_1]

Just to back up the point about Kent.

Have a look at the ensembles. The agreement, and the mean of the ensembles, go for 0oC:

[casparjack]

Those SE'lies are not bitterly cold at all. If that chart is to be believed we can expect 4c minima in the S by Thursday:

http://www.wetterzen.../Rtavn15017.png

Not saying it will happen at all, but people seem to assume that just because the flow is SE'ly it will be cold. Yes, parts of Europe are now bitterly cold and a surface flow from these areas would bring correspondingly cold temps. However the flow is now predicted to have a more southerly element bringing it off France rather than Germany, which is nowhere near as cold (see above chart). We need as much of an E'ly element as possible helped by undercutting low.

To be fair those 4c temps are along the South and SE coast, the inland figures are more akin to what we might expect from the 'cold flow' off the continent. We do need more of an Easterlt element though to maintain the cold.

[nick sussex]

I'd say this morning theres more chance of a breakdown to less cold conditions but no model paints the Atlantic piling through with sw'erlies.

Even a southerly sourced over France will remain on the cold side as it would take some time for temps to lift much at the surface. It even snowed on the Med coast yesterday with major chaos east of me. France is in the freezer just like the UK!

If we look at all the models theres enough disagreement to suggest it's not going to be straightforward especially as we are seeing a change upstream, although the AO and NAO remain negative, zonal westerlies are expected with a flattening of the pattern over there, so we have to assume some variability in the model output.

Remembering that whilst both AO and NAO remain negative theres always the chance that the models have overestimated the northern extent of the jet stream, in which case the UK remains on the cold side for longer.

What is however of great interest is a possible Channel low which could bring some major snow as it runs eastwards. Altogether still alot of wintry weather to come. If we do see the end of the very cold conditions it would still have been a major throwback to winters of the past and shows it's still possible to get some wonderful synoptics.

[yamkin]

If you look at that chart, thats for the south coast, inland its close to freezing.

http://www.wetterzentrale.de/pics/Rmgfs1504.gif

Furthermore, there's a lot of preciptation in that time frame.

Hi Mr_Data, The latest BBC24 forecasters are playing down the snow on Sun/Mon for S, SW, SE, Midlands & Wales, but these faxes are showing snow. Am I reading the faxes wrong? Sky News forecasters are still going for a snowy period on Sun/Mon.

http://www.meteociel.fr/ukmo/fax/fax48s.gif

http://www.meteociel.fr/ukmo/fax/fax60s.gif

http://www.meteociel.fr/ukmo/fax/fax72s.gif

http://www.meteociel.fr/ukmo/fax/fax84s.gif

Edited January 8, 2010 by yamkin

[Cloud 10]

It should be noted that all models this morning have low pressure heading southeast under the block at +120 hrs.

There are signs of some sort of breakdown on some models after this,but anyone thinking this will happen easily may find their hopes are set in sand rather than concrete!

[03jtrickey]

Hi Mr_Data, The latest BBC24 forecasters are playing down the snow on Sun/Mon for S, SW, SE, Midlands & Wales, but these faxes are showing snow. Am I reading the faxes wrong? Sky News forecasters are still going for a snowy period on Sun/Mon.

http://www.meteociel.fr/ukmo/fax/fax48s.gif

http://www.meteociel.fr/ukmo/fax/fax60s.gif

http://www.meteociel.fr/ukmo/fax/fax72s.gif

http://www.meteociel.fr/ukmo/fax/fax84s.gif

Those looks like upper fronts on the faxes. I'm not sure whether these are conducive to snow?

[aspire27]

It should be noted that all models this morning have low pressure heading southeast under the block at +120 hrs.

There are signs of some sort of breakdown on some models after this,but anyone thinking this will happen easily may find their hopes are set in sand rather than concrete!

Complete and utter confusion for a newbie here guys! Last night you were all saying more cold to come, definately into next weekend etc etc

Now suddenly its all over.....

Anyone really know what the models are showing??

[snowking]

Hi Mr_Data, The latest BBC24 forecasters are playing down the snow on Sun/Mon for S, SW, SE, Midlands & Wales, but these faxes are showing snow. Am I reading the faxes wrong? Sky News forecasters are still going for a snowy period on Sun/Mon.

http://www.meteociel.fr/ukmo/fax/fax48s.gif

http://www.meteociel.fr/ukmo/fax/fax60s.gif

http://www.meteociel.fr/ukmo/fax/fax72s.gif

http://www.meteociel.fr/ukmo/fax/fax84s.gif

Sorry to jump in here yamkin but hopefully I can help...

I think this is the issue of following the BBC graphics too literally. Beyond 2 days the forecaster will literally just slap a paint brush across the map where they see fit. Its far more important to listen to what the forecaster says - I don't rate carol as one of the better forecasters but shes there for a reason! She says in the forecast that there will be persistent light snow right across southern england and also wales

So nope you are not reading the charts wrong

Kind Regards

SK

Those looks like upper fronts on the faxes. I'm not sure whether these are conducive to snow?

Yep these are upper fronts - simply meaning the change of airmass is happening at a far higher part of the troposphere. This is conductive of precipitation, albeit light

SK

Edited January 8, 2010 by snowking

[Totoro]

The models don't know for sure so neither do the good people who are looking at them.

As a rank amateur I'd say that it looks about 50/50 and is still a few days off, so keep watching them models and reading this forum.

[snowking]

Complete and utter confusion for a newbie here guys! Last night you were all saying more cold to come, definately into next weekend etc etc

Now suddenly its all over.....

Anyone really know what the models are showing??

Yet another reason why people shouldnt take anything but a quick glance at the operational runs on their own beyond day 3-4 at a push

Ensemble forecasting slightly better in the longer range but even then with the models clearly struggling judging by the spread of data on the ensemble data sets very uncertain times ahead

[Duane S.]

As anticipated, the breakdown attempt is looming. The ensembles have been showing this for a while now so perhaps its no real surprise. Difficult to get any sort of firm grip on things at the moment, the GFS really goes off on one later on in its evolution with a very messy setup whilst the ECM now backs a less cold period. Some charts go for the cold spell to disappear with a bit of a whimper, some want it to go out with a bang to remember! This is the point of interest I think.

The mass of cold air over us currently and that the fact that the jet stream doesn't seem to want to come home from its holiday in the Med anytime soon indicates that there will be great uncertainty as to what exactly happens come next week. However, we are almost certainly heading towards a less cold spell but there will be plenty of fun and games along the way I'm sure.

[casparjack]

I'd say this morning theres more chance of a breakdown to less cold conditions but no model paints the Atlantic piling through with sw'erlies.

Even a southerly sourced over France will remain on the cold side as it would take some time for temps to lift much at the surface. It even snowed on the Med coast yesterday with major chaos east of me. France is in the freezer just like the UK!

If we look at all the models theres enough disagreement to suggest it's not going to be straightforward especially as we are seeing a change upstream, although the AO and NAO remain negative, zonal westerlies are expected with a flattening of the pattern over there, so we have to assume some variability in the model output.

Remembering that whilst both AO and NAO remain negative theres always the chance that the models have overestimated the northern extent of the jet stream, in which case the UK remains on the cold side for longer.

What is however of great interest is a possible Channel low which could bring some major snow as it runs eastwards. Altogether still alot of wintry weather to come. If we do see the end of the very cold conditions it would still have been a major throwback to winters of the past and shows it's still possible to get some wonderful synoptics.

I agree, I think what everyone must remember is that the 'change' shown is still ages away, even in normal forecast conditions, let alone an unusual set like this. Sure of course we will have a reversion to Atlantic weather at some point, I for one have the feeling that there may well be a great deal more in this yet to come.

It is just as likely that in 48 hours time we will be looking at a completely different scenario again.

Also as you say the Channel low could well deliver yet more interest!

[David-kig]

you know sunday, monday are we looking at snow grains. what do you mean by light snow. snow flurries? how many cms are we looking at here. ruff guess??

Edited January 8, 2010 by David-kig

[nick sussex]

The ECM De Bilt ensembles for the Netherlands show the operational run as being a mild outlier from next Wednesday.

http://www.weerplaza.nl/15daagseverwachting/default_pluim.asp?r=midden

Of course every new trend will always probably start off as some sort of outlier, however for the timebeing it's not well supported. IMO this evening will be important to see whether the models have overreacted to upstream changes, if they have then we're likely to see the jet stream edged further south with the cold hanging on a while longer.

[AtlanticFlamethrower]

00z GEM keeps the block and the cold spell going.

Overnight snow turning to rain on Sunday for the East.

[Jezzer]

What is however of great interest is a possible Channel low which could bring some major snow as it runs eastwards. Altogether still alot of wintry weather to come.

Hi Nick, any idea when that Channel Low is set to have an impact, is that connected to this weekend's snow event?

[Archie_Lewis]

With regards to Sunday most of England and Wales can expect Snow.

The models all agree on this.

Now of course it will not be anything like we have had the past few days but none the less it looks to be persistent and LIGHT.

Im quite looking forward to the walks over the fields with my dog Sunday.

6'' of snow on the ground with a white sky and light/moderate snow falling.

Seriously.... What more could you ask for?

[TEITS]

Rather worryingly the ECM might be an outlier but the control run goes exactly the same way. In these situations you find the ensemble mean will begin to rise should the OP continue with this trend.

As for Sunday and at the moment alot of uncertainity. The UKMO takes the risk much further S and this is shown on the BBC graphics.

Love the GEM to be right this morning.

[nick sussex]

Hi Nick, any idea when that Channel Low is set to have an impact, is that connected to this weekend's snow event? :unsure:

Well most models have this feature around T-120hrs however theres no agreement on the track of this, its an interesting dilemma here if you want the cold to last, if it tracks to the sw only really effecting the far sw this signifies a better upstream pattern with stronger pressure to the ne and hence the better chance for the cold remaining. At the moment it's a difficult forecast and impossible to say how far north the precp could get.

[Altohumorous]

Looking more and more like a breakdown since yesterday to me, certainly in south and west England, Wales and Ireland.

Very surprising really, considering synoptics and most forecasts

Edited January 8, 2010 by Altohumorous