Model Output Discussion - 16th Jan 12z onwards - Smile While You Post!

[Snowy L]

People saying only snow for the north???

 

Please revisit after you understand what implications the surface cold pool has....

 

 

UKMO is decent for snow for the whole spine of the UK...

 

GFS starting to amplify at 120-150 but not enough this run..

 

S

 

This, I'd agree with those saying no snow on low ground... if we didn't have that surface cold pool already in place. It's going to get very very cold during Sunday night. I'd still say anywhere North of m4 is good for snow, though may be transient for a while in West Midlands and Wales as they see the warmest part of the warm sector.

[craigore]

GFS 6h and 12h for Thurs 7am

 

 

Slightly strong heights over Greenland with westward correction of low to the south.

 

Scandi heights marginally stronger and slightly further NW. Low over southern UK slightly further north...

 

Wonder if the Scandi heights can find a way to link up with Greenland heights down the line with weaker LP putting up less of a fight against the heights to our N/E? If so we could end up with a slider?

Would I be right in thinking we would have snow showers piling in off the N.Sea for the east and South East if this came off ??

[TSNWK]

We'll since the low point of yesterday's UKMO 12z and GFS 18z we have made little steps on each subsequent fun for these two models. This mornings ECM was also step better than Friday evenings run.

Nothing too dramatic, but certainly a little more hope from me that we can squeeze a couple more days out of this cld spell until next weekend.

So with that being said, I fully intend to enjoy the moment and the hunt for small scale features has begun... Starting with a little disturbance drifting down the EA and Sunday evening..

[Jason M]

People saying only snow for the north???

 

Please revisit after you understand what implications the surface cold pool has....

 

 

UKMO is decent for snow for the whole spine of the UK...

 

GFS starting to amplify at 120-150 but not enough this run..

 

S

Assuming you were replying to my post, please can you illustrate this surface cold pool with a chart? Once the winds add an easterly component, yes it gets cold enough, but by then much of the precip has gone. For much of this week the airmass is maritime based not CP.

also, I did not say snow ONLY for the North. In terms of a big snow event though it ain't being shown at the moment and given what is a PM airmass for the next three or four days I simply cannot see a low ground widespread snow event. If by midweek one has occured then you can question my understanding... Not before!

[karlos1983]

it's ok GFS saves the day

Pheeewwwww 

[i luv snow]

Assuming you were replying to my post, please can you illustrate this surface cold pool with a chart? Once the winds add an easterly component, yes it gets cold enough, but by then much of the precip has gone. For much of this week the airmass is maritime based not CP.

also, I did not say snow ONLY for the North. In terms of a big snow event though it ain't being shown at the moment and given what is a PM airmass for the next three or four days I simply cannot see a low ground widespread snow event. If by midweek one has occured then you can question my understanding... Not before!

 

From the way I read them, all the models show both fronts moving through as mainly snow for all, there are numerous charts to illustrate this. Metoffice and BBC both have forecasts saying the fronts will stall trying to push through and turn readily to snow also.

Edited January 17, 2015 by i luv snow

[EML Network]

If only this would come to pass, can you imagine...the entire country enjoying snow

 

This place would be either bedlam, or quiet as we'd all be out dancing around like crazed kids waving hands in the air and zig zagging down the roads yelling and laughing. 

 

knowing my luck that would be the exact moment the local mental assylum van drove past and I'd be picked up and carted off to a crazy home before I'd even made my first snow woman :-)

 

[TEITS]

From the way I read them, all the models show both fronts moving through as mainly snow for all, there are numerous charts to illustrate this. Metoffice and BBC both have forecasts saying the fronts will stall trying to push through and turn readily to snow also.

Not strictly true.

 

The 12Z GFS shows rain with back edge snow except Scotland.

 

http://modeles.meteociel.fr/modeles/gfs/runs/2015011712/gfs-2-72.png?12

 

Next front is more in the way of snow.

 

http://modeles.meteociel.fr/modeles/gfs/runs/2015011712/gfs-2-96.png?12

 

Also Met O forecast for E Anglia refers to rain/sleet for next Mon-Wed.

 

At the moment there is not enough evidence to suggest a widespread snow event or enough to rule one out. The fact is we don't know and won't until nearer the time.

[i luv snow]

Not strictly true.

 

The 12Z GFS shows rain with back edge snow except Scotland.

 

http://modeles.meteociel.fr/modeles/gfs/runs/2015011712/gfs-2-72.png?12

 

Next front is more in the way of snow.

 

http://modeles.meteociel.fr/modeles/gfs/runs/2015011712/gfs-2-96.png?12

 

Also Met O forecast for E Anglia refers to rain/sleet for next Mon-Wed.

 

At the moment there is not enough evidence to suggest a widespread snow event or enough to rule one out. The fact is we don't know and won't until nearer the time.

 

 

Of course we don't know yet either way, but looking at a variety of ppn charts for both days, I have read them falling mainly as snow (maybe the first one turning to rain for a time) with a fairly widespread snow event from both. This of course, may change. Meto UK forecast I have seen suggests snow for many - as did the latest BBC forecast I just saw. Time, as always, will tell - it's gonna be nowcasting on the day in all honesty.

Edited January 17, 2015 by i luv snow

[Geordiesnow]

Chalk and cheese, however, even if the UKMO turns out right a Northerly would follow a couple of days later. Whilst there is no deep cold modelled at present, things will stay below average for most.

 

I can't see a Northerly appearing at all on the UKMO, for anyone who wants any real cold to continue the UKMO is awful to say the least.

 

The GFS reintroduce the slider possibility but with the cold air getting mixed out, its not something that would excite me a great deal but its got more snow potential than the UKMO would. 

 

All in all, pretty bog standard charts after a cold start to the week with the risk of some frontal snow which may even turn too marginal for a lot of areas.

[craigore]

If only this would come to pass, can you imagine...the entire country enjoying snow

 

This place would be either bedlam, or quiet as we'd all be out dancing around like crazed kids waving hands in the air and zig zagging down the roads yelling and laughing. 

 

knowing my luck that would be the exact moment the local mental assylum van drove past and I'd be picked up and carted off to a crazy home before I'd even made my first snow woman :-)

 

Brilliant even us southerners get in..

[SMU]

Here is the surface cold pool ahead of the incoming front-

 

http://modeles.meteociel.fr/modeles/gfs/runs/2015011712/gfs-6-60.png?12

 

Theta Values of 10c & all the cold having mixed down to the surface will provide a very dry adiatic rate

see here

http://meteorologytraining.tpub.com/14312/css/14312_47.htm

 

The front has theta values of 14c behind it - however importantly only 16-18c column ahead-

 

So we have very dry air being replaced by slightly less dry air although all are probably still below the universal lapse rate -

Its when you get a saturated lapse rate from the SW your fubared.

 

I highlighted this last night with the cold air trailing is now coming off greenland instead of sourced from Canada & would be colder uppers & less modified-

Had we still be looking at the original prognosis from 3 days ago look at the modified air entraped in the system

 

http://modeles.meteociel.fr/modeles/gfs/archives/gfs-2015011518-6-96.png?18 

Your looking at theta values of 26c into the mixture the front....

 

As said now, if something like the MEAN of the GFS suite verifies then a large swathe of snow in the UK, with the South & SW/ SE still at risk of mixing due to the closest proximity to either

 

* the mildest column of air in the front

* the onshore breeze from the channel

 

Or both....

 

S

Edited January 17, 2015 by Steve Murr

[Froze were the Days]

it's ok GFS saves the day

Pheeewwwww 

With what?

[Jason M]

All fair enough Steve.

So we're sort of agreeing then really, as there is a real possibility of just rain of sleet (or non settling snow) in the SE, SW, South, South Midlands (I'd add parts of EA as well).

By day 5 no issues as we have a proper easterly drag and theta values nicely down by that point.

Of course it could all change for better or worse.

[Mucka]

Just some basics that folk new to model watching might to look out for when considering whether we will more likely get rain or snow and whether the cold can be more sustained.

 

We want to see the sliding low push South without stalling to the North too much as this would degrade heights to the NE and mix in less cold air.

Also if the pattern can be backed West then that will benefit us as well.

 

Looking at GFS 12z ensembles they are somewhat improved upon recent efforts re any Easterly prospect or lengthening of the cold, these runs are also generally the ones that have a clean slider with better upstream pattern allowing for a second slider and Atlantic ridge reaching into Scandi and strengthening heights to the NE, basically a reload of the current pattern.

 

GFS short ensembles. Central England

 

 

If you compare the 00z, 06z and these 12z you will see that the cold air has slowly been programmed to last 24 hours longer in 12 hour steps. Not much but for a mean not bad and a positive trend.

Edited January 17, 2015 by Mucka

[MR EXTREMES]

If only this would come to pass, can you imagine...the entire country enjoying snow

 

This place would be either bedlam, or quiet as we'd all be out dancing around like crazed kids waving hands in the air and zig zagging down the roads yelling and laughing. 

 

knowing my luck that would be the exact moment the local mental assylum van drove past and I'd be picked up and carted off to a crazy home before I'd even made my first snow woman :-)

 

Indeed I don't expect any here anyway but am instead looking for an easterly.

But the rest of the country looks good if you get the frontal system near you then most certainly snow event.

And the models tonight are dam site better than last night in fact the whole of yesterday.

But I have my fingers crossed for that little extra insurance for us on the south coast.

Still a cold week coming up with plenty of interesting twists and turns to come.

[shaky]

Just some basics that folk new to model watching might to look out for when considering whether we will more likely get rain or snow and whether the cold can be more sustained.

 

We want to see the sliding low push South without stalling to the North too much as this would degrade heights to the NE and mix in less cold air.

Also if the pattern can be backed West then that will benefit us as well.

 

Looking at GFS 12z ensembles they are somewhat improved upon recent efforts re any Easterly prospect or lengthening of the cold, these runs are also generally the ones that have a clean slider with better upstream pattern allowing for a second slider and Atlantic ridge reaching into Scandi and strengthening heights to the NE, basically a reload of the current pattern.

 

GFS short ensembles. Central England

 

 

If you compare the 00z, 06z and these 12z you will see that the cold air has slowly been programmed to last 24 hours longer in 12 hour steps. Not much but for a mean not bad and a positive trend.

those are brilliant ensembles mucka! Contorl and op massive outliers towardw the end although very worrying that they both together on it!!

[mushymanrob]

People saying only snow for the north???

 

 

S

 

 

erm... thought that was you? " north midlands northward " ....  

never mind...

whats needed to prolong the cold spell and turn it into a proper event is for pressure to build and sit over scandinavia, the azores high is largely immaterial in such situations . theres time yet for pressure to anchor over there, but its not expected to.

[Jason M]

I alluded to this the other day though...Isn't the new gfs op now hi res out to t276 now so would be better at medium term than gefs which go low res at t192 still? Skewed comparisons now maybe till q3?

Think it's high res to 240 :-)

[IDO]

Snow for the SE at the moment from the two fronts crossing Tuesday and Wednesday based on the GEFS remains about 30%. Today's runs around 30-35%, no better for snow chances (0z, 6z & 12z). There are a handful that are not far off giving snow and there are of course three outliers there, that do not even model the slider. Two of the parameters highlighted here:

 

Heights (DAM) 850s:

 

Fine margins.

 

So the SE is still in the game for snow but very borderline though still nearly three days to go. The further west or North you live the better the chances, eg 55% Birmingham and Leeds 75%.

Edited January 17, 2015 by i'm dreaming of...

[lorenzo]

Ive really had to take some time away from the models. It can take over your life. Hunting for cold and snow which i love more than anything else except for kids and fam.just learn to snowboard or ski then you will see snow a least once a year.sometime things need to be put into perspective. Enjoy the next week.ps. mods move if necessary.

 

Just as an example and not meaning to have a go at anyone here, but this is a good example of what isn't model discussion, this is for the other thread. If you feel you have to write - mods, please move, it's a fair clue to anyone that the post is in the wrong place to begin with !

 

Please continue to discuss the model output with the ECM due to roll, and we can all get the model thread we want to read which also excludes boring notes like this from the team and posts being moved around regularly. Thanks !

[Mucka]

those are brilliant ensembles mucka! Contorl and op massive outliers towardw the end although very worrying that they both together on it!!

 

Yeah definitely a slow improvement Shaky.

As for FI there is no signal for any sustained blocking but a strong signal for a Southerly jet.

This suggests further bouts of cold zonal conditions with any milder spells limited and the Azores high generally being pinned to the West so any lengthy settled or mild weather looks very unlikely.

It also suggests there will be further attempts to build ridge, especially toward the West (Atlantic region) so possible cold snaps within less cold zonal conditions(though average or a little below) seems the form of horse going into Feb at the moment.

 

Full Central England ensembles (GFS 12z)

 

[Jason M]

And tonight's award goes to ptrb 2 of the GEFS

http://www.meteociel.fr/modeles/gefs_cartes.php?code=2&ech=312&mode=0&carte=0

Maybe not quite cobra, but certainly still premium lager :-)

Although the return of the Atlantic still looks likely, it's not as certain as yesterday and it may well be that the opp runs are still being too progressive.

[Mucka]

I alluded to this the other day though...Isn't the new gfs op now hi res out to t276 now so would be better at medium term than gefs which go low res at t192 still? Skewed comparisons now maybe till q3?...ensembles always following the new op now maybe?

 

It is a reasonable observation but any trend within the ensemble mean is not really affected by the Op, especially since the Op actually goes against the trend.

Hard to say the Op is more reliable when each run is different from the last as well.

It is something worth considering though.

[snowking]

Comparison from the last 4 GEFS:

 

 

Notice the initial spike from yesterdays 18z around the 22nd with all that uncertainty regarding the slider potential (op and control included!) before slowly the mean flattens out through the day.

 

Does this mean this is the final solution? By no means. But it does go to show how even at relatively short timeframes NWP really struggles with these situations where West meets East. For those newer members this was an almost 'known' bias of the old GFS deterministic run, and it appears that the shiny new GFS det. seems to continue this trend (the GFS ensemble suite also tends to struggle to model these situations, as is apparent from the above).

 

Still a lot of marginality about it and a lot more twists and turns to come, but it's hopefully a perfect example of why nobody should be making any assumptions about any precipitation discrimination during the coming week.

 

SK

Edited January 17, 2015 by snowking