Winter Model Discussion 18Z 13/1/13 onwards.

[lord stratus]

Really well put Dave

Experience also tells us that lp's in this situation dont end up as far North as initially shown, so would not be at all suprised to see the Precipitation making it as far North as say Cheshire across to Mansfield and Skegness but not much further, and all areas south of this Seeing heavy snow and indeed blizzards in some spots.

Will all come to light in future runs, but great looking charts this morning!

As you say probably a south correction over the coming days. Some of the forecasters will have to use a degree of past experience I feel with this weekends event. I was in South Wales during the 78 & 82 blizzards and they don't come bigger than that! The forecasts then seemed more accurate in those days but mainly because we relied only on the BBC forecasts and we weren't forever having mood swings, looking at several model outputs a day! In the 70's & 80's we were served up a forecast and accepted it. I have to say that the met office forecast the 82 blizzard a

week ahead and in the correct area of the UK.

Based on previous channel lows, my experience has been oxfordshire as the snows northern extent.

[swfc]

to be fair given the variance in the output theres not a big void between the oz and 6z to be fair.slightly further east with the low but the generall theme continues imo.what happens beyond the 150hour mark is anyones guess be it anything past 120 looks to be in fi

[TEITS]

One of the problems is if you look at the UKMO/ECM the depth of LP within the vortex is higher.

GEM, NOGAPS, GFS have lower pressures.

[chionomaniac]

I am interested in the possibility in heights building behind that Atlantic trough around days 8-10. Signs are there.

And it may not happen from this run but quite happy with this jet splitting profile at T+162

[TEITS]

And it may not happen from this run but quite happy with this jet splitting profile at T+162

I can't see heights building behind this trough to be honest. Our best chance of retaining the cold weather or seeing a return of it is for the trough to go under with blocking to our N/NE.

[swfc]

Whether or not the 6z varifies or not the pv does even in fi look smashed.

[TEITS]

One trend I have noticed for the medium range is despite a negative AO the NAO is refusing to go negative and actually remains positive.

So what this roughly means is I cannot see any GH and neither can I see mega cold E,lys with upper temps below -10C. Whats more likely is a continuation of what I call cold zonality with LP hopefully tracking NW-SE under the UK. This potentially can give great snowfalls but the word marginal will appear many times over the next 10 days I feel. Great if you like to make snowmen or have a snowball fight.

[bluearmy]

I am interested in the possibility in heights building behind that Atlantic trough around days 8-10. Signs are there.

its something that the models are sniffing around ed. showed to an extent yesterday and my take on the ecm 00z suite is a desire to take the wedge of higher heights furter west where they could certainly have a meeting with an atlantic ridge, pushing the jet even further south.

that remnant of the canadian vortex in newfoundland has been a pain for us in the past post SSW. it does look as though the jet is further south this time though with a definite desire to be aligned nw/se this side of the atlantic.

[Panayiotis]

One trend I have noticed for the medium range is despite a negative AO the NAO is refusing to go negative and actually remains positive.

So what this roughly means is I cannot see any GH and neither can I see mega cold E,lys with upper temps below -10C. Whats more likely is a continuation of what I call cold zonality with LP hopefully tracking NW-SE under the UK. This potentially can give great snowfalls but the word marginal will appear many times over the next 10 days I feel. Great if you like to make snowmen or have a snowball fight.

Doesnt the NAO and AO only reflect what the models are showing?

[WhiteFox]

As has been said already, it depends exactly where the low goes. At the moment, no-one can tell for certain, and a couple of hundred miles either way is going to make all the difference to whether you get a snowfest or not. I doubt very much if anything can be forecast with certainty for this weekend before about Friday night, so i'll not be taking anything as gospel until then.

I think the only way we will see any certainty is if all the models agree that the Atlantic wins out and mild weather returns to all. That is reliant on a strong jet and a reforming of a fairly strong polar vortex however, and I don't see this happening. So, I think we'll continue to see some models pushing further north and East and others keeping the Atlantic further South and West. WRT to the system approaching this weekend, I think we'll have a fair idea of how far it will push against the block by about Thursday, but it's one of those situations where we won't know where the North/East extent of the PPN lies and where the rain/snow line lies until we see the radar on the day!

[Troubleatmill]

As you say probably a south correction over the coming days. Some of the forecasters will have to use a degree of past experience I feel with this weekends event. I was in South Wales during the 78 & 82 blizzards and they don't come bigger than that! The forecasts then seemed more accurate in those days but mainly because we relied only on the BBC forecasts and we weren't forever having mood swings, looking at several model outputs a day! In the 70's & 80's we were served up a forecast and accepted it. I have to say that the met office forecast the 82 blizzard a

week ahead and in the correct area of the UK.

Based on previous channel lows, my experience has been oxfordshire as the snows northern extent.

Indeed the forecasters will discect everything and get it bob on as they do 99% of the time, on chanel lows i agree with that northern extent although i dont see a chanel low here? more a chunk of the Canadian vortex looking like a great big painful zit in the atlantic, anyones game this, dont mean for locations but the uk as a whole.

[Methuselah]

Doesnt the NAO and AO only reflect what the models are showing?

IMO, yes it does...

But, anywho, I certainly wouldn't claim to be sure that the Atlantic influence is going to replace the cold air completely, just yet. It may well do so, but then it might not? The 06Z has hardly done much in the way of clarification, though?

[WhiteFox]

Doesnt the NAO and AO only reflect what the models are showing?

Yes they do, and looking at this FAX chart you can see why the NAO remains neutral to weakly positive:

Unless we get a build of pressure towards Greenland there's nothing to stop Low Pressure systems apporaching from near Iceland. Given the propensity of the jet to track south on the models recently, the block holds firn so we stay cold, so a neutral to weakly positive NAO is not a big problem (although negative would be better of course!).

If it was strongly positive then next to no chance for cold.

[chris55]

EDIT (this was meant for the regional thread, opps, oh well can't be arsed to write it again in there)

UKMO pick of the bunch this morning, a better undercut and angle of approach with the block slightly more robust, it would produce snow and keep the majority of the Westcountry cold.

GFS and ECM are not so good, less robust block and not such a defined undercut,

Such fine margins though and with the Met office talking about the front not even making it in , maybe we will end up somewhere in the middle (that would be great!)

12zs will be interesting, we need the right angle of approach or else we lose the continental flow and warmer air is in the mix.

Edited January 15, 2013 by chris55

[Mark Bayley]

The ECM also supports a more UK wide snow event on Friday (although turning to rain for a time in NI and the far west). Be interesting to see if that band makes it that far, or is pushed further back. The GFS and GEM also show this.

For those interested heres the ECMs takes on Saturdays/Sundays attack. Snow for the Midlands north

Edited January 15, 2013 by Mark Bayley

[TEITS]

Doesnt the NAO and AO only reflect what the models are showing?

Yes and a positive NAO or I should say slightly positive NAO is consisently being shown by the models.

Clearly shown by the Reyjavic/Lisbon SLP means.

http://cdn.nwstatic.co.uk/ensimages/ens.20130115/00/prmslReyjavic.png

http://cdn.nwstatic.co.uk/ensimages/ens.20130115/00/prmslLisbon.png

That for me has been the fly in the ointment so far this winter.

[SMU]

Not much comment- it looks as though its already been said- apart from the GFS will be useless in this situation-

especially the 06z- all it will want to do is plough the energy through to russia-

Stick with the UKMO & the ECM which is currently following the UKMOs trends-

a snow event for many friday- & poss sat- dont be surprised if we stay in the cold all the way through... as fragments of energy are diverted SE as opposed to NE

S

[Cecil Hogmanay Melchett]

it is starting to look like we will see an assault as early as fri now,exciting times

[Troubleatmill]

ECM postage stamps, as TEITS said earlier no point looking further than T72 when this in iself is FI, think this cements that. with LP's tracking NW of Scotland, SE through France with block persisting or full steam ahead right through us. Has anyone known for there to be such an uncertain time for model watching, going on as long as this? quite incredible.

[Coast]

NEW THREAD COMING

[Alexis]

Yes they do, and looking at this FAX chart you can see why the NAO remains neutral to weakly positive:

Unless we get a build of pressure towards Greenland there's nothing to stop Low Pressure systems apporaching from near Iceland. Given the propensity of the jet to track south on the models recently, the block holds firn so we stay cold, so a neutral to weakly positive NAO is not a big problem (although negative would be better of course!).

If it was strongly positive then next to no chance for cold.

The problem with an extremely negative NAO is that the UK can just be sat under an intense high that brings dry weather and not much else.

[Coast]

New Thread here: