Winter Model Discussion 12Z 15/1/13 onwards.

[surrey slush]

NAE Mods even!!!

Indeed, which means, he binned it. Jesus chinese whispers or what.

[WhiteFox]

i read it the other way the chief is sticking with his modification of the NAE as its out on its own , doesnt mean its not onto something , but currently has little support , we wont know really for another 24h

Yes, that's the way I read it, although it sounded a little ambiguous (I'm sure Ian has more to concern him than updating us on here and it is great that he does). So the NAE is condisdered an outlier, but certainly another possibility. I'm sure John H will confirm just how difficult are these situations to call (as Ian F already has), and note that even Ian Brown seems to have called his family and friends to tell them they may just need a sweater tomorrow!

[Panayiotis]

We await the ensembles to see how much support there is for this superb and amazing run!

[lord stratus]

A Harry met Sally moment.

Looks like something's brewing though, at this stage I like to use past experiences with this set up, a few in the 80's brought huge snow depths so there should be some excitement in this forum this evening. This set up has nearly always favoured the south of the UK for the biggest snow falls.

[Buzz]

As it may have been lost in the scrum, I feel it's worth reiterating what Ian F said a few pages back regarding the GFS precipitation maps:

"Can I just caution re posting / taking as gospel these raw (and often useless) GFS precip/snow probability maps at this juncture. The alogorithm used for these is pretty basic, and I never even bother with them.

A far better route to understanding (at least from GFS) the PPN type prospects for any given area, plus crucial nuances of boundary layer conditions as well as aloft, is to pick-up on the profile soundings plotted for any part of the globe via the excellent http://ready.arl.noa...v/READYcmet.php (we compare these here to our UKMO-GM/NAE tephigrams)."

[Summer Sun]

Deep FI I know but this is an exceptional run from GFS tonight!

[Methuselah]

Where im dubious is how the front even manages to get to my region. Now history tells me it never makes it this far NE. Looking at the UKMO between +72 & +96 and im unconvinced whats its showing.

Usually yes, Dave. But with exception-to-the-rule being all the famous winters (1986 excepted) that we all so love to wax-lyrical about...I'm not saying that the GFS and UKMO are going to be right; just that, if they were, it wouldn't be entirely unprecedented?

[TEITS]

The NAE isn't the end of the world. If you look at the UKMO, GFS you will see that the colder upper temps back W as the front pivots. This isn't shown on the NAE because it only goes to +48. However as the pattern is further E on the NAE then parts of the SW would be at less risk of snow. I feel this is why Ian F said a potential spoiler because he was referring to his region and not the UK.

As for the rest of the GFS and in distant F.I I thought my screen had turned itself upside down!

[swfc]

Well that was an full on 30 mins on here jeez!!!!!!!!!!!.Still no real indicator about the weekens possible events i guess.Possibly staying cold into next week with the chance of occ snow .The pv does look as its given up in the latter stages but as usuall in fi.unsure but interesting times

[randomwalk]

i read it the other way the chief is sticking with his modification of the NAE as its out on its own , doesnt mean its not onto something , but currently has little support , we wont know really for another 24h

i read mods as 'models' - if its modifications its different, but which is it?!

[chionomaniac]

As it may have been lost in the scrum, I feel it's worth reiterating what Ian F said a few pages back regarding the GFS precipitation maps:

"Can I just caution re posting / taking as gospel these raw (and often useless) GFS precip/snow probability maps at this juncture. The alogorithm used for these is pretty basic, and I never even bother with them.

A far better route to understanding (at least from GFS) the PPN type prospects for any given area, plus crucial nuances of boundary layer conditions as well as aloft, is to pick-up on the profile soundings plotted for any part of the globe via the excellent http://ready.arl.noa...v/READYcmet.php (we compare these here to our UKMO-GM/NAE tephigrams)."

For London 12Z

[Jimmyh]

Would it also be wrong to say that the 2010 epic snow event started much the same way like this however i know that the angle of attack was completely different, same principle still applied tho that the embedded cold was there to start with and got colder over the period of time leading to the epic charts which we saw. This has the propensity to be something special all over the country again

[No Balls Like Snow Balls]

i read mods as 'models' - if its modifications its different, but which is it?!

It's modifications. Calm down and Breath, it will be alright.

[johnholmes]

Yes, that's the way I read it, although it sounded a little ambiguous (I'm sure Ian has more to concern him than updating us on here and it is great that he does). So the NAE is condisdered an outlier, but certainly another possibility. I'm sure John H will confirm just how difficult are these situations to call (as Ian F already has), and note that even Ian Brown seems to have called his family and friends to tell them they may just need a sweater tomorrow!

Yes very hard to be sure of just how accurate this run is-pretty amazing really. I've just run various parameters with Extra and I cannot recall in the 8 years on here seeing any GFS run with the zero isotherm over this area for the whole 384 hours. The 850mb temperature, apart from a short spell as the first Atlantic push ocurs is also as if not colder than I have seen on any run before.

For those wanting snow then the key thing to watch if you have Extra is how the cold air is brought west as the system tends to slide ESE. As has been commented on IF it turns out correct then some pretty high snowfall totals are probable. It is far from accurate but again on Extra look at the snow depth chart just for an idea where this run is suggesting the heaviest fall could occur.

I am NOT for one moment suggesting the preicpitation totals will be correct let alone the snow but it gives an idea of what the model is suggesting this run. Check it out each day for 12z, check it out every run for those parameters for the same times Friday into Saturday if that floats your boat.

To those that are delivered the white stuff in their gardens enjoy, drop your pictures in here then the rest can drool over what might have been.

PLEASE try and be polite to one another and not snipe with playground type comments-please?

Edited January 15, 2013 by johnholmes

[pages]

I fear this may be lost but a question for someone more knowledgeable, Nick, GP, SteveM, BFTP, TEITS...

If the split chunk of PV stays south of Greenland and we end up with a block over Scandinavia/Iceland, is this a great place to be? I'm thinking the chunk of PV will continually give LP a little extra 'ooomph' as they come at us and slide under the block giving us constant fronts approaching from the SW?

I feel this a great post, we need some energy so the lows put up WAA to build the block. Look at the end of the run as the vortex dies a death the heights retreat and the arctic high on its own can't keep the weak lows south enough.

As long as the Canadian vortex stays to the south west of Greenland I feel we are in business and will only lose the cold if it weakens or moves east.

This is the one time the vortex is doing us a favour.

[johnholmes]

As it may have been lost in the scrum, I feel it's worth reiterating what Ian F said a few pages back regarding the GFS precipitation maps:

"Can I just caution re posting / taking as gospel these raw (and often useless) GFS precip/snow probability maps at this juncture. The alogorithm used for these is pretty basic, and I never even bother with them.

A far better route to understanding (at least from GFS) the PPN type prospects for any given area, plus crucial nuances of boundary layer conditions as well as aloft, is to pick-up on the profile soundings plotted for any part of the globe via the excellent http://ready.arl.noa...v/READYcmet.php (we compare these here to our UKMO-GM/NAE tephigrams)."

very very sensible-I have lost count how many times I have urged caution with rainfall predictions let alone snow-remember 7 additional requirements for snow and the skew-t diagrams are always very useful.

both will it snow and skew-t explanations are in the Guides.

[Yarmy]

Deep FI I know but this is an exceptional run from GFS tonight!

10cm snow cover in the North Sea is indeed exceptional.

[Glacier Point]

12z GEM and another undercut for this Sunday..

At this rate I'm glad we're attempting to bring a front in to have a go, the rest are just wimping out.

The inter-run revisions to models at the moment is pretty rare, nearly always going from positively tilted to negative tilted the closer in we get.

Notice also trend for the Canadian PV lobe to drain away and increasing influence of th pv to our NE.

[bluearmy]

gem 12z corrects itself south again wrt to its 00z and finds a nice track for the shortwaves along the jet. less energy than earlier runs in the atlantic. i think we can call that a trend of the 12z's so far. could be a very cold trough across the uk for the end of the weekend and into next week

[pages]

I going to make a bold prediction that from the 12z models that this will be 10 day severe spell that will go out with a whimper when the Canadian vortex loses its strengthen and can no longer feed them big lows that are feeding the WAA and undercutting.

[swfc]

gem 12z corrects itself south again wrt to its 00z and finds a nice track for the shortwaves along the jet. less energy than earlier runs in the atlantic. i think we can call that a trend of the 12z's so far. could be a very cold trough across the uk for the end of the weekend and into next week

Hi ba.im a little bewildered with the rush of comments.will any front past thursday extend across the uk during the weekend.thanks

[snowice]

I continue to be less than convinced that the models have got this one right especially as the models have upgraded the pressure rise to the ne at 120hrs, this most evident on the UKMO 120hrs.

Looks like the forecast just got a whole load tougher!

would that change the snowline from the west?

[The watcher]

Northern Ireland could possibly do well out of that too - hope so for them guys. Quality undercut.

Maybe that'll keep the silly protesters away.

Knife edge stuff for our wee Isle and Ireland at the moment. Exciting times ahead and hopeful that the Eastward progression from GFS 06Z does not come back to haunt.

[bluearmy]

Hi ba.im a little bewildered with the rush of comments.will any front past thursday extend across the uk during the weekend.thanks

looks likely but as dave has alluded, exactly how far northeast will one get before it shears away and dies out. already we are seeing the second front now being modelled to die out as it reaches the eastern side. by tomorrow, will this have been corrected further west ?

[surrey slush]

key thing to watch if you have Extra is how the cold air is brough west as the system tends to slide ESE

Hi John, .... What exactly should I be looking at here.... soo many options on Extra.