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

[Panayiotis]

I believe 216 shows not much left of the vortex, no expert though still learning. Its position does suggest no heights over greenland though.

It shows the strat cooling at 216hrs, but the warming which has taken place (now) will filter down the strat and hit the troposphere where it then effects our weather, the cooling then takes place but that would have a delayed reaction to the troposphere as the cooling filters down the strat.

[Cloud 10]

Ill leave this one for the experts does this though suggest less chance of getting height rises into greenland as we move into next week?...and possible lowering of heights where we dont want them to due to cooling up above...might have read these charts completely wrong though...any response appreciated?

T72

T216

Hi CV,i am by no means an expert,but best to look at pressure charts for the stratosphere when looking for any potential blocking in the timeframe you mention.

If we take a look at the 10mb pressure chart from the gfs for 216 hrs,the stratospheric

polar vortex is split wide apart into two pieces.

[fergieweather]

Its to do with timing the GFS is quicker to push the next front in.

I really don't want to sound like Mr Sensible but please folks don't build your expectations up too high in terms of snow amounts or start dusting the sledge off.

These set ups are invariably a complete nightmare to forecast especially if the block is underestimated at this range.

Concur on every count. Exeter still busy on 12z assessment. It's got forecast nightmare stamped all over the broader scale raw output, let alone regional & timing nuances at this range.

[ChartViewer]

Hi CV,i am by no means an expert,but best to look at pressure charts for the stratosphere when looking for any potential blocking in the timeframe you mention.

If we take a look at the 10mb pressure chart from the gfs for 216 hrs,the stratospheric

polar vortex is split wide apart into two pieces.

Many thanks Cloud and others who responded.

[Yarmy]

FWIW, that shortwave modelled by GFS last week (which apparently handles Greenland better) as going E/NE to Northern Scandinavia and beyond has just delivered me between 5 and 10 cm of solid white precipitation. Models, eh?

[Weathizard]

Some of the GEFS do go for the slider low however the uppers are extremely poor on the few that do. Certainly very interesting model watching at the moment.

Edited January 14, 2013 by Weathizard

[fergieweather]

Having just read a fascinating multi-page UKMO analysis for Fri-Sat.... we're no clearer on outcome. In summary: frontal ppn extension NE on Fri v v uncertain albeit expected almost entirely as snow accompanied by Sig windchill; extended 4km models prog 10-20cm snow Dartmoor etc with falls up NE to Mendips but detail untrusted at this range. Of greater significance perhaps is more active frontal push later Sat, more meridionally orientated as per EC, with leading edge snow at least but again easterly extent into Sun uncertain. A truly fascinating and high stakes forecast challenge all round..

[TEITS]

FWIW, that shortwave modelled by GFS last week (which apparently handles Greenland better) as going E/NE to Northern Scandinavia and beyond has just delivered me between 5 and 10 cm of solid white precipitation. Models, eh?

The GFS has not covered itself in much glory over the past week or so and neither to be honest has the ECM at times.

I've pretty much given up viewing the GFS at the moment beyond +72 hence the lack of my posts. Rather than looking at these runs im basing my outlook on the pattern that these models have been displaying over the past few days. The pattern has been very clear, UKMO least interested in bringing an end to the cold spell maintaining some form of heights to our N/NE with the Atlantic making little progression. The GFS most progressive in bringing a return to milder Atlantic driven weather. The ECM inbetween although since yesterday swinging towards the UKMO.

So as it stands for me the UKMO is the leader here. Now looking at the UKMO I would say historically any snowfall will make little NE progression and won't get anywhere near my location. I would suggest that as next weekend gets closer we shall see that LP being modelled further S. I would go as far and say that only the SW & S Wales would be affected by this front.

Edited January 14, 2013 by THE EYE IN THE SKY

[Blackie]

The BOM is a UKMO developed model for Australia, I've also heard it's basically an extension of the UKMO-GM, so on that basis I'd certainly give it some weight.

Shouldn't it be called the POM, then...?

[Jax]

Shouldn't it be called the POM, then...?

I would expect that from a Sheila

Edited January 14, 2013 by Jax

[Cloud 10]

Taking the GFS charts for Saturday at face value (fraught with danger ) shows the sort of

cold we could be looking at this weekend.

dewpoints..

temperatures..

[WhiteFox]

Fax chart at 120 hrs keeps things very cold.

Note everyone: don't forget that the JMA is highly regarded by the Met Office. Shall I start another urban myth and say that the CMA is also highly regarded by the Met Office?

Anyway, just a quick question on that FAX chart; would there be any convergence of upper winds giving streamers of 'wintry showers' from the south east on that chart? I remember seeing something similar with a long stream of showers coming from the Channel Islands back in October, but that was convergence of upper winds whereas I can't tell on the Fax Chart... I've drawn some arrows (poorly) on the bit I mean.

[If Wishes made Weather]

The way things are going Nick will the Atlantic make any inroads at all?

Maybe we will be looking east next week.

IF - and that is a major IF - this is right perhaps we are best understanding the UK as a bit like the hub of a wheel with slider lows moving across to the south and counterbalanced with the Scandi high in the north relocating further west - perhaps as far as Iceland or Greenland. That would then leave the UK into NE air masses and the cold that would entail. It is something like this that the BOM has shown as possible.

[Buzz]

So as it stands for me the UKMO is the leader here. Now looking at the UKMO I would say historically any snowfall will make little NE progression and won't get anywhere near my location. I would suggest that as next weekend gets closer we shall see that LP being modelled further S. I would go as far and say that only the SW & S Wales would be affected by this front.

Just to go a bit further, and as others have implied, I'm beginning to wonder if these repeated southwards adjustments may cause the precipitation forecast for Friday and Saturday to miss us all together. It wouldn't be the first time it's happened where a blizzard has been forecast only for it to decide to pay France a visit instead. I remember one time that this happened in the early 80s, maybe 1982.

We'll see, but we must be careful what we wish for ...........

[mike Meehan]

Looking at Friday's fax chart, it looks to me that with the two lows hanging out to the west, one could travel to the north east and the other to the south east leaving the HP mostly intact with the possibility of snow from the southern most once since it is pretty near the channel - I would have thought they would have followed the line of least resistance.

http://www.netweathe...s;type=fax;sess=

Click on 96 hours

Edited January 14, 2013 by mike Meehan

[Panayiotis]

Taking the GFS charts for Saturday at face value (fraught with danger ) shows the sort of

cold we could be looking at this weekend.

dewpoints..

temperatures..

Everything would be colder, if the low tilted further and went under the block like shown on the UKMO and ECM, however charts shown are still cold enough for snow.

[Stoxs]

The way things are going Nick will the Atlantic make any inroads at all?

Maybe we will be looking east next week.

The way this is going and have seen it before , Nick Sussex will be hoping it goes south of him!!

I think the models have calmed down a bit now, more concistancey witht he genearl pattern from each run,

which is a real good thing as there was no chance of making head nor tail of it before.

It will still change, there is no real detail YET for friday and the weekend.

But a 10 day cold spell will do for the starters!

but i would like to see whats on the Main menu!

ahh then the dessert!!

[J10]

Just to go a bit further, and as others have implied, I'm beginning to wonder if these repeated southwards adjustments may cause the precipitation forecast for Friday and Saturday to miss us all together. It wouldn't be the first time it's happened where a blizzard has been forecast only for it to decide to pay France a visit instead. I remember one time that this happened in the early 80s, maybe 1982.

We'll see, but we must be careful what we wish for ...........

Wouldn't surprise me at all for that to happen.

[EML Network]

IMO there are 3 distinct possibilities regarding this coming weekends weather and beyond and only one of them would continue to keep the cold and snow prospects going for the remainder next week.

Scenario 1 see's the Atlantic barrel straight into the UK after a little short lived fight from the block , not sure how long the route back to cold would be there after.

Scenario 2 see's the Atlantic run over the top of the block, I think if this happened it would be a long route back to cold.

Scenario 3 see's the undercut, and the cold weather is extended with snow opportunities for all.

interesting though that we are looking at the weekend already, but we do have a fair amount of agreement up until Thursday, I suspect this is going to be one of those events that only gets nailed down a few days beforehand.

I think there's an equal chance of all 3 right now

Edit * I guess there's an option 4 , which is the Block holds and the Atlantic is repelled, retrogresses, but that's unlikely given the strength of the Low being modelled

Edited January 14, 2013 by EML Network

[Chris D]

Having just read a fascinating multi-page UKMO analysis for Fri-Sat.... we're no clearer on outcome. In summary: frontal ppn extension NE on Fri v v uncertain albeit expected almost entirely as snow accompanied by Sig windchill; extended 4km models prog 10-20cm snow Dartmoor etc with falls up NE to Mendips but detail untrusted at this range. Of greater significance perhaps is more active frontal push later Sat, more meridionally orientated as per EC, with leading edge snow at least but again easterly extent into Sun uncertain. A truly fascinating and high stakes forecast challenge all round..

This is what makes model watching so exciting!

[Dampdorset82]

Taking the GFS charts for Saturday at face value (fraught with danger ) shows the sort of

cold we could be looking at this weekend.

dewpoints..

temperatures..

we as in you, here in the south not so........

[Panayiotis]

IMO there are 3 distinct possibilities regarding this coming weekends weather and beyond and only one of them would continue to keep the cold and snow prospects going for the remainder next week.

Scenario 1 see's the Atlantic barrel straight into the UK after a little short lived fight from the block , not sure how long the route back to cold would be there after.

Scenario 2 see's the Atlantic run over the top of the block, I think if this happened it would be a long route back to cold.

Scenario 3 see's the undercut, and the cold weather is extended with snow opportunities for all.

interesting though that we are looking at the weekend already, but we do have a fair amount of agreement up until Thursday, I suspect this is going to be one of those events that only gets nailed down a few days beforehand.

I think there's an equal chance of all 3 right now

Regarding the UKMO and the ECM and GFS (kind of) have the low going under the block, could you say there is less chance of Scenario 2 and a higher chance of Scernario 3?

[East_England_Stormchaser91]

These are the best charts I've ever seen so far. Potential for dangerous conditions if these charts came off.

[Panayiotis]

Ensembles keep the below average temps throughout the whole run, which is encouraging! However there is a lot of scatter for this weekend (more so than some days of next week surprisingly) and before this get resolved the further outlook remains uncertain.

Edited January 15, 2013 by Panayiotis

[chris55]

Regarding the UKMO and the ECM and GFS (kind of) have the low going under the block, could you say there is less chance of Scenario 2 and a higher chance of Scernario 3?

I don't see number 2 happening, the trends today have been for undercuts, and all model agree on this, none take energy over the block at the weekend. The uncertainty lies with shape/angle/extent of the Atlantic push and where the battle between the warm and cold air lies.