General Model Output Discussion:

[Methuselah]

As promised. Please continue...

[pyrotech]

Can one of our experts on here give analysis of current conditions and model predictions. My thoughts are the models show the front stalling over wales and cold air undercutting. With the front pushing southwards over next 24hrs. Anyone abl to confirm if what i read in the models and fax is acurate or not. Huge disapointment in South wales at moment but ive been saying rightly or wrongly that fax chart shows more potential there as day goes on.

[cooling climate]

You will not get any greater expert advice than what the latest faxes are showing other than

up to date satallite and radar.

As for the upcoming freeze as long as max daytime temperatures are +1c or lower so that lying

snow does not thaw (even in sunshine) then anything colder is a bonus.

The GEM model out to t168 seems to be more in line with what NOAA were saying yesterday in

regards to the trough over the eastern US seaboard although the meto update does sound as

though there is more of an east/northeast element to the weather next week.

I would be slightly more inclined to side with NOAA as the meto updates change more often than

the weather itself.

[Dingwantssnow]

You will not get any greater expert advice than what the latest faxes are showing other than

up to date satallite and radar.

As for the upcoming freeze as long as max daytime temperatures are +1c or lower so that lying

snow does not thaw (even in sunshine) then anything colder is a bonus.

The GEM model out to t168 seems to be more in line with what NOAA were saying yesterday in

regards to the trough over the eastern US seaboard although the meto update does sound as

though there is more of an east/northeast element to the weather next week.

I would be slightly more inclined to side with NOAA as the meto updates change more often than

the weather itself.

Hi what were NOAA saying about the trough??

[nick sussex]

I've decided to re-post my earlier thoughts from the previous thread here before the gfs 12hrs run, we need to keep a close check on events over Eastern Canada and the Eastern USA. In terms of NOAA yesterday they expected the Greenland block to be still in control in the later timeframe with the trough over the eastern seaboard edging ne, this is supported by this mornings GEM model in those charts I've posted.

I still think theres one more hurdle to overcome for the uk and this appears towards the end of this weekend when that small low heads ne towards the sw and that small shortwave heads sw from the ne. There is a larger scatter in the ensembles for this time the further south and i think i prefer the ecm solution which drives much more energy into the southern arm of the jet and drops heights well into the Med, a much safer way of extending the cold at this stage.

In terms of the extended outlook we need a little help here from the eastern USA trough. Take a look at these charts from the GEM 00hrs run, note here how the USA trough edges ne'wards and remains deep this helps to stop the Greenland high from retrogressing too far westwards, this then helps downstream by edging the pattern further east with the Scandi trough better aligned as the jet digs south further east. This is a good example of how a feature upstream that perhaps is being overlooked with the current emphasis on near term events can be crucial to events in the UK.

http://www.wetterzentrale.de/pics/Rgem1441.html

http://www.wetterzentrale.de/pics/Rgem1681.html

http://www.wetterzentrale.de/pics/Rgem1921.html

Although the cold spell continued in Scotland and the far north it was the block being too far west which ultimately lead to the less cold conditions further south around Xmas so in this instance the western based negative NAO will always allow chances for less cold or mild air to head ne towards southern Britain and eventually a trough develops too far west sending southerlies northwards.

This is something to keep an eye on in future output, if you want a long cold spell and you're further south especially you want to see the models edge the block further east and go with this trend from the GEM.

[swilliam]

As promised. Please continue...

http://forum.netweat...7entry1679453

Hi Pete,

You forgot to add the link to this thread when you closed the old one again.

[nick sussex]

Nick your links are broken mate

Fixed now , anyway thats what we want to see across the Eastern USA and Eastern Canada, we definitely don't want a west based negative NAO, it gives a chance for low pressure to get too far north towards the UK and eventually milder conditions.

[s4lancia]

I've decided to re-post my earlier thoughts from the previous thread here before the gfs 12hrs run, we need to keep a close check on events over Eastern Canada and the Eastern USA. In terms of NOAA yesterday they expected the Greenland block to be still in control in the later timeframe with the trough over the eastern seaboard edging ne, this is supported by this mornings GEM model in those charts I've posted.

I still think theres one more hurdle to overcome for the uk and this appears towards the end of this weekend when that small low heads ne towards the sw and that small shortwave heads sw from the ne. There is a larger scatter in the ensembles for this time the further south and i think i prefer the ecm solution which drives much more energy into the southern arm of the jet and drops heights well into the Med, a much safer way of extending the cold at this stage.

In terms of the extended outlook we need a little help here from the eastern USA trough. Take a look at these charts from the GEM 00hrs run, note here how the USA trough edges ne'wards and remains deep this helps to stop the Greenland high from retrogressing too far westwards, this then helps downstream by edging the pattern further east with the Scandi trough better aligned as the jet digs south further east. This is a good example of how a feature upstream that perhaps is being overlooked with the current emphasis on near term events can be crucial to events in the UK.

http://www.wetterzentrale.de/pics/Rgem1441.html

http://www.wetterzentrale.de/pics/Rgem1681.html

http://www.wetterzentrale.de/pics/Rgem1921.html

Although the cold spell continued in Scotland and the far north it was the block being too far west which ultimately lead to the less cold conditions further south around Xmas so in this instance the western based negative NAO will always allow chances for less cold or mild air to head ne towards southern Britain and eventually a trough develops too far west sending southerlies northwards.

This is something to keep an eye on in future output, if you want a long cold spell and you're further south especially you want to see the models edge the block further east and go with this trend from the GEM.

Hi Nick, yep that is exactly how I see it.

I do think the block is going to drift west though as the PV splits and drops into Scandinavia. I have to say, that whilst I am not saying it will be in the same extreme catagory, there are comparisons that could be drawn between this setup and Jan '87. That cold mass of air to our NE could quite suddenly be racing down towards us if certain things go our way as I still think the charts are dismantling the blocking above us too readily.

Whatever happens, we sure are being spoilt by the charts at the moment!

[kold weather]

Yep Nick thats a great post and I agree, you really don't want to see a west based -ve NAO lasting too long because it will eventually give a real chance of bringing in less cold air, esp the further south you are...however on the other hand it also gives us a fair chance of getting a snow storm...

Probably the best set-up would be for a slight west based -ve NAO which transfers eastwards and topples perfectly over the UK, then we have good building blocks if we can get the PV closer to Canada,

Anyway the 06z is a very good run, though the ensembles are suggestive of it being rather too quick on bringing the high south-eastwards as most bring down the PV towards Scandinavia, however if this happens then the risk of a bland Mid-Atlantic high also increases after the PV is forced somewhat further east..

Hopefully the 12z is good, I'm sure within 168hrs it should be given the model agreement.

ps, given the jet is so active generally I'd suspect if we do get a west based -ve NAO ts going to be very hard to sustain for the cold without some milder interludes at times at least in the south, as we've seen this week as it happens...

[grab my graupel]

Just enough time, before the 12z roll out, to mention that the latest Model Output can be viewed on Netweather:

http://www.netweather.tv/index.cgi?action=nwdc;sess=

The Netweather charts are in a higher resolution than the ones available on Wetterzentrale. Also, they have the advantage of being in English

[rich1]

Annoyingly a bit milder down here on this run up to NYE...4 days of rain if it varied, its trying but this low can change its positioning at short notice I guess

[Eugene]

http://www.wetterzentrale.de/pics/Rtavn1141.png - Great chart at such a close range

Harsh frosts this weekend, at least it won't be mild

[SMU]

Annoyingly a bit milder down here on this run up to NYE...4 days of rain if it varied, its trying but this low can change its positioning at short notice I guess

& then blizzards for the SE- over 1 day of snow-

http://91.121.94.83/modeles/gfs/run/gfsnh-0-138.png?12

S

[Snowaddict]

Both GFS and GME are suggesting a snow event at T+132 - T+140 timeframe on both of today's 12Z outputs...

With low pressure undercutting and approaching from the south, with renewed easterly winds and very cold air in place.

This is definitely something to watch because this is the third GFS run to show this.

SA

& then blizzards for the SE- over 1 day of snow-

http://91.121.94.83/...nh-0-138.png?12

S

Steve, GME 12Z also has this evolution..

As I posted below, GFS is quite consistent on it..

What's your opinion?

[nick sussex]

Not the best of runs from the gfs here in the longer term, the Greenland block retrogresses too much setting up a western based negative NAO, could be a big snow event as the low edges ne'wards but the Scandi trough is too far west here. A small pesky shortwave that heads sw also is troublesome here, you need this shortwave to get its skates on and get to the south of the UK to allow the ridge to back westwards and force the sw low more east rather than ne. As i mentioned earlier this is still a hurdle to overcome later in the weekend.

[rich1]

& then blizzards for the SE- over 1 day of snow-

http://91.121.94.83/...nh-0-138.png?12

S

yep, hopefully if this can stay consistent, could be very interesting

very good run from NYD onwards it seems, I suppose I could live with having to stay indoors till friday if this one came about

[Snowaddict]

Very much liking the UKMO 12Z evolution...

Also has a similar low at T+120..

T+144 doesn't look bad at all to me either..

SA

[SMU]

Both GFS and GME are suggesting a snow event at T+132 - T+140 timeframe on both of today's 12Z outputs...

With low pressure undercutting and approaching from the south, with renewed easterly winds and very cold air in place.

This is definitely something to watch because this is the third GFS run to show this.

SA

Steve, GME 12Z also has this evolution..

As I posted below, GFS is quite consistent on it..

What's your opinion?

I would say evolution looks about spot on- but the track could still vary a little bit ( it will be further south than todays low) but I think its starting to firm up that the south will be looking East then south west for snow at the end of the week-

UKMO is similar but not quite as far north at 12z- very favourbale thicknesses though-

Steve

[Eugene]

Even warm southerlies in FI give cold temps

http://www.wetterzentrale.de/pics/Rtavn3242.png

http://www.wetterzentrale.de/pics/Rtavn32417.png

[Snowaddict]

I would say evolution looks about spot on- but the track could still vary a little bit ( it will be further south than todays low) but I think its starting to firm up that the south will be looking East then south west for snow at the end of the week-

UKMO is similar but not quite as far north at 12z- very favourbale thicknesses though-

Steve

Cheers for that Steve..

Certainly looking very interesting...

M

[Guest North Sea Snow Convection]

The ukmo ppm charts suggest to me that as the cold air digs back south late Thursday, the ppn peps up in the SE corner and that could mean that we see some decent snow that leads into snow showers on Friday. Again, the UKMO ppn chart suggests some snow showers around on the NE'erly during the day. Then there is the chance of some snow early next week as a low brushes to the south. So a very good UKMO this evening indeed.

The GFS is too knife edge as I see it and brings the low a little further north - even if this particular 12z suggests an all snow event. However that could easily be another 50 miles or more north and the outcome would become like this week

However, not worth too much anlaysis as all that is some way off atm. I would rather that the cold beds itself in properly though before any more frontal attacks from the south west if I am honest. Hopefully the GFS is just being too progressive. North sea snow would be much more ideal!

[kold weather]

The 12z FI shows us just how close we are to getting mild southerlies, the surface flow remains just SSE which keeps us dragging in the colder air right upto the 13th...

Still a slightly weaker jet stream would result in a very different FI to what we see here, the trend is starting to become stronger however for the high to sink eventually SE, the exact position is uncertain however...

Also, expect the set-up currently to hold for longer before it all topples down, remember this/last cold spell ended up being 3-4 days longer then expected in the south...

[Altostratus]

I'm surprised it is so quiet in here. That GFS run would deliver buckets of snow to the SW - classic stuff. It will invariably change between now and then but a nice trend nonetheless. In reality I can see the low being too far south to have any influence. Something to watch in the next few days anyway.

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

Bound to change on the next run but nice to look at nonetheless

[nick sussex]

The ukmo ppm charts suggest to me that as the cold air digs back south late Thursday, the ppn peps up in the SE corner and that could mean that we see some decent snow that leads into snow showers on Friday. Again, the UKMO ppn chart suggests some snow showers around on the NE'erly during the day. Then there is the chance of some snow early next week as a low brushes to the south. So a very good UKMO this evening indeed.

The GFS is too knife edge as I see it and brings the low a little further north - even if this particular 12z suggests an all snow event. However that could easily be another 50 miles or more north and the outcome would become like this week

However, not worth too much anlaysis as all that is some way off atm. I would rather that the cold beds itself in properly though before any more frontal attacks from the south west if I am honest. Hopefully the GFS is just being too progressive. North sea snow would be much more ideal!

Evening Tamara

Personally i dont like the ukmo or the gfs, preferably its better to have a stronger ridge backing west so that low pressure runs ene and then be deflected away this is safer where as here the low is running ne with a weaker ridge ahead of it, part of the problem with the gfs is the block edges west too far, people are assuming that the low will do as the gfs says, and eventually head away se again but this is fraught with danger, with the block having edged so far west the scenario could play out in an altogether less favourable way. The UKMO at 96hrs has that shortwave stopping a stronger ridge from the east, then its down to the low to the sw not heading too far ne. I'm hoping the ecm will stick to its guns driving lower heights into the Med and edging towards the GEM 00hrs run where the block is further east and the Scandi trough better aligned.

I don't want to spoil everyones fun here but the angle of attack of that low and the complications of that small shortwave IMO are not a gamble worth taking but again like I've said before its a risk reward thing, people will of course have different views on this.