WInter Model Output Discussion 12z- 28/01/2013

[Rocheydub]

So, as I mused over on the MOD thread a couple of days ago, the key thing with our future weather and potential for proper cold, is the movement of the low pressure system currently modeled (about 120 hours) at the southern tip of Greenland. If that moves up the west coast of Greenland, or the vast majority of it splits up the west side, then we are in a game on scenario, as this will allow height rises to our north, and also drag the PV more Westerly towards west Canada.

Some slight differences (as expected) at 162 with the orientation of that low coming off the eastern seaboard, may actually allow pressure to zip up to Greenland, but it's probably being modeled further south than we'd want, would prefer to see it run up the west side of Greenland away... dragging the PV with it! This would allow pressure rises near Greenland, and the subtle difference to that blob of vortex over Scandi has grabbed my interest too... I like the look of where this run is going... So far.

We'll see!

EDIT: Actually, scrap that. Looks like it will topple quicker on this run out to 180...

The 06 GFS just hinted at this occurring, so I will watch the 12z runs with great interest indeed!

[bluearmy]

the 06z gefs are 'interesting'. the trend is to increase the euro trough (as per ecm consistent output) and in fi the trend is most definitely the ridge over the top. how that manifests itself is unclear and there remains a large cluster of mobile zonal runs.

[snowmadchrisuk]

This is the sort of Westward correction we need as per Member 3 at +180

Edited January 31, 2013 by snowmadchrisuk

[snowmadchrisuk]

As by +240 we get to this ..

[snowmadchrisuk]

And your spread at +240 ... Ensembles throwing out all sorts of options in FI , from raging P/V to no P/V at all...

[Frosty.]

At last, a more wintry trend from the meto today which is more in line with the gfs and ecm op runs, tending to turn colder and showers turning more to snow during the period, rain or sleet showers initially in the south but a much more wintry flavour than recent updates, I think it's probably a lot to do with what mogreps and the ukmo ens are now showing, the ecm ops have always been showing a cold spell next week and now we have that confirmation..at last.

Edited January 31, 2013 by Frosty039

[Man With Beard]

Can't see this chart coming off for the West country from 00z GFS

It is not without precident though. I remember a north westerly sourced from Greenland producing snow showers all down the west of the UK (including N Devon) I think in November 2005/6. As we're in the very coldest part of the year now, I would expect snow all over the UK from this; it would be more marginal in, say, December.

[legritter]

Mornig all ,im very pleased with modells at the moment .i feel we still need a little bit of firming up over next couple of runs but at the moment we are sitting fairly good for a cold spell .things past next tuesday could change very quickly as modells pick up on any disturbances running south or s/east over or close to the UK .and with the sun having a bit more clout in it in early FEB there could be some convective action .and who knows the following week past 9/10th feb we could get some heights to our north .so all looking juicy with the atlantic slowing down a bit and high pressure perhaps becoming more key ,so my glass is half full ,

[Nick F]

After the underwhelming GFS 00hrs run the 06hrs moves back to join the ECM and UKMO with the pattern further west.

Thankfully I think we can bin the 00z GFS op, a look at it against the 00z ECM ens, suggests it being on the milder side of the spread into the medium range. While 00z ECM op was pretty much close to the average throughout.

What's interesting me now is GFS and ECM agreeing on a trend into the medium range to hold back the PV over NE Canada while WAA builds heights NE ahead of the PV towards the GIN corridor while we have deep troughing over Europe. So signs that a more prolonged spell could be in the offing, though still uncertainty over energy across the N Atlantic in this period.

Edited January 31, 2013 by Nick F

[nick sussex]

Thankfully I think we can bin the 00z GFS op, a look at it against the 00z ECM ens, suggests it being on the milder side of the spread into the medium range. While 00z ECM op was pretty much close to the average throughout.

What's interesting me now is GFS and ECM agreeing on a trend into the medium range to hold back the PV over NE Canada while WAA builds heights NE ahead of the PV towards the GIN corridor while we have deep troughing over Europe. So signs that a more prolonged spell could be in the offing, though still uncertainty over energy across the N Atlantic in this period.

Yes I'm a lot more optimistic that we'll see some build of pressure to the ne.

Looking at the big 3 I like the UKMO best at 144hrs although generally theres now good agreement between them. The elongated PV stretching sw/ne does lend itself to some interest to our ne.

The start point re any shortwave track between 144 and 168hrs could well prove crucial longer term also if we can get that build of pressure early to the ne then that could set in motion a longer cold spell.

[BLAST FROM THE PAST]

Interesting t177, trough disruption...E'ly?

BFTP

Well the 06z never got there. Now important point here i think. The 06z goes on to stop the retrogressing HP and goes in favour of lowering heights to NW to stop further retrogression. i think the 06z has it wrong. If the trough disruption occurred as it showed at t177 that secondary LP moves literally N to S. I cannot see anything other than an easterly developing from there as that shows that the retrogression is a stronger signal than a flattening LP development to the NW.

For now the build up continues well, 10-15 target for main retro movement looks on course, with northerly incursions occurring beforehand it looks good for cold temperatures to be in place if an Esterly were to occur to make it more potent.

BFTP

[nick sussex]

Just to explain to newer members why the 144hrs to 168hrs timeframe could be decisive:

Time for one of my paint jobs!

If you look at that UKMO 144hrs chart, the black circle is where we want to see pressure rises, the red circle indicates the formation of a shortwave and where we want it to track, the yellow arrow where we want to see the PV energy go.

As the shortwave tracks s/se it drains some of the energy away from the PV so less eastwards push from that and a better chance we could get some pressure rising in the black zone.

Our start point basically both our margin for error going forward and how good the foundations will be to get to a longer cold spell will probably be laid between 144hrs and 168hrs.

So as you've probably seen from reading the thread many posts have highlighted the importance of getting the pattern further west because in a nutshell that gives us the best chance of colder weather going forward.

Edited January 31, 2013 by nick sussex

[gottolovethisweather]

Just to explain to newer members why the 144hrs to 168hrs timeframe could be decisive:

Not just of use to newer members either Nick. I like others I'm sure will often get lost in all the explanations offered by the many wise chaps/chapesses on here, without back up from attachments.

[MR EXTREMES]

As by +240 we get to this ..

if this were to come of i think even steve m would eat his hat. never say never im not so sure i think look ne for heights but i could be wrong.

[Frosty.]

Well the 06z never got there. Now important point here i think. The 06z goes on to stop the retrogressing HP and goes in favour of lowering heights to NW to stop further retrogression. i think the 06z has it wrong. If the trough disruption occurred as it showed at t177 that secondary LP moves literally N to S. I cannot see anything other than an easterly developing from there as that shows that the retrogression is a stronger signal than a flattening LP development to the NW.

For now the build up continues well, 10-15 target for main retro movement looks on course, with northerly incursions occurring beforehand it looks good for cold temperatures to be in place if an Esterly were to occur to make it more potent.

BFTP

I agree Fred, although I do think the 6z has made steps towards the ecm compared to the poor gfs 00z. I think we at least have agreement as far as next week is concerned, a cold unsettled windy week with blustery showers turning to snow from the north as the week goes on, even some more persistent wintry ppn at times and frosts becoming widespread, and there are now growing signs of a cold block forming and possibly becoming hard to break down, still hoping for a severe NEly blast though which would really be the icing on the cake and cement february as a month to remember, much in the same way as january will be for it's very snowy spell for some.

[Paul]

Latest from Michael Fish - a mixed bag, some more rain, some drier spells and also some colder weather at times..

[Thundery wintry showers]

It is not without precident though. I remember a north westerly sourced from Greenland producing snow showers all down the west of the UK (including N Devon) I think in November 2005/6. As we're in the very coldest part of the year now, I would expect snow all over the UK from this; it would be more marginal in, say, December.

There's still a fair amount of uncertainty over this north-westerly blast and how much of an impact the warm depression core to our north has, but indeed, I don't think the GFS is being OTT with its prediction of snow showers over almost the whole country. It's the kind of synoptic setup that can deliver large snowfalls to Ireland, northern and western Scotland, Cumbria and the Pennine region, though I think from the Midlands south and near west-facing coasts we'll be looking at wet sleety snow that generally doesn't settle.

I remember the November 2005 outbreak- the tongue of Arctic air caught south-west England full in the face on that occasion. I doubt that next week's incursion will be as potent as maxima for the SW are progged to be in the region of 4 to 6C.

Edited January 31, 2013 by Thundery wintry showers

[Stu_London]

I remember the November 2005 outbreak- the tongue of Arctic air caught south-west England full in the face on that occasion. I doubt that next week's incursion will be as potent as maxima for the SW are progged to be in the region of 4 to 6C.

Have to remember that temps will fall readily to close to freezing in any heavy ppn in these set ups.

Agree for most it will be a non or temp settling snow event especially as bands of showers will move through very quickly

The conventive possibilities is where the fun is at with this system, rather than sustained severe winter conditions - couldn't rule out thundersnow somewhere and if we get a trough a Jan 2004 (??) type event couldn't be completely ruled out

Edited January 31, 2013 by Stu_London

[Snowman.]

The first of the 12z is starting to come out lets see we can get some FI candy.

[Frosty.]

There's still a fair amount of uncertainty over this north-westerly blast and how much of an impact the warm depression core to our north has, but indeed, I don't think the GFS is being OTT with its prediction of snow showers over almost the whole country. It's the kind of synoptic setup that can deliver large snowfalls to Ireland, northern and western Scotland, Cumbria and the Pennine region, though I think from the Midlands south and near west-facing coasts we'll be looking at wet sleety snow that generally doesn't settle.

I remember the November 2005 outbreak- the tongue of Arctic air caught south-west England full in the face on that occasion. I doubt that next week's incursion will be as potent as maxima for the SW are progged to be in the region of 4 to 6C.

I noticed that warm depression core affects northern scotland next tues so the snow showers from monday would turn into persistent rain as the warm core sweeps southeast eventually down towards the southeast with more potent cold uppers then blasting down across the far north, I have a feeling the Northerly next week will upgrade and the uppers (T850hPA) will be pushing towards -10 in the far north and widely -6 to -8 further south by the middle and back end of next week, probably significant snow for areas exposed to the NNWly to Nly Gales. There is a chance that the warm depression core may miss the uk mainland completely and dive down the north sea instead.

Edited January 31, 2013 by Frosty039

[mountain shadow]

Bitterly cold day that I would think.

Gale force north westerlies with heavy squally rain/sleet/snow showers.

http://cdn.nwstatic.co.uk/gfsimages/gfs.20130131/12/120/h500slp.png

The delivering low is further south and east than the 6z, will be interesting to see how this pans out. PV over Canada, a little less intense.

[Stu_London]

The 5th remains impressive to me.

Uppers of -8C on a westerly gale - could be some fireworks.

[Snowman.]

Worst than the 6z so far will it be as bad as the 0z the other day?

[Stu_London]

Worst than the 6z so far will it be as bad as the 0z the other day?

The pattern is fairly consistent in the high res part - ignore post 192

[SMU]

http://www.meteociel.fr/ukmo/runs/2013013112/UN144-21.GIF?31-17

Excellent UKMO day 6 tonight with a shortwave diving south in the atlantic & a wedge of high pressure over Eastern greenland..

Looks good post day 7 / 8 if that varifies-

S