Model Output Discussion 12z 18/10/2012

[shedhead]

Hi John,

No real surprises or 'secrets'(!) in our briefings of late 're all this; for reference, here's our latest sense of direction into medium range but note this latest issue based on 00z runs (abstracted here from lengthier version). Cheers, Ian

"4. Trend for Days 10-15 : The mostly anticyclonic bias looks set to continue with some agreement in this respect between EC EPS and MOGREPS. More uncertain is the flow direction with EC trending towards a N or NW’ly flow from day 10 (but spreads across all types from day 12), whilst MOGREPS stays SE. Either way, it seems most likely that many S’ern and SE’ern places will see a reasonable amount of fair weather, with sometimes more unsettled conditions further N, but with temperatures tending to fall below normal across all parts.

5. Discussion : There is still a split on the midnight ensembles although all agree on an anticyclonic type. ECMWF would like to go northerly as early as day 8, but now spreads across all types later n the outlook period. MOGREPS would favour an anticyclonic SE throughout"

Thanks for sharing Ian.

[Liam J]

If we were to have -5 uppers over the whole county for example during December then it would be highly likely that any precipitation would fall as snow/sleet. At this moment in time -5 uppers are shown to affect parts of the country in the next week or so, therefore I don't understand why people are doubting that any precipitation could well fall as snow and affect a large part of the UK??.... That's if what we are seeing at the moment on a range of forecasting models actually materializes.

Can anyone shine any light as to why this may be?? I'm still learning so be nice

Lots of info over in the Netweather learning area.

http://forum.netweat...-forecast-snow/

Edited October 19, 2012 by Liam J

[Frosty.]

The weekend is looking fine for many areas but with overnight fog which should clear to bring pleasant temps with sunny spells. however, rain threatens the southeast later on saturday but sunday is looking dry and bright in most areas, after the clearance of overnight fog and temps look a touch milder, the weekend maximum temps generally around 13-15c, maybe 16-17c in the south and southeast, into next week looks a notch or two warmer but temps nearer average for scotland and n.ireland but bright everywhere again with overnight fog which could become slow to clear in places, then possibly much colder towards the end of next week with a wintry blast from the arctic, looking forward to the snowy bbc weather maps...HOPEFULLY

Edited October 19, 2012 by Frosty039

[Radiating Dendrite]

If we were to have -5 uppers over the whole county for example during December then it would be highly likely that any precipitation would fall as snow/sleet. At this moment in time -5 uppers are shown to affect parts of the country in the next week or so, therefore I don't understand why people are doubting that any precipitation could well fall as snow and affect a large part of the UK??.... That's if what we are seeing at the moment on a range of forecasting models actually materializes.

Can anyone shine any light as to why this may be?? I'm still learning so be nice

-5 in December would not guarantee Snow. You need -8c as a guarantee (and even then there are other factors that could make it rain and not snow).

At this time of year the air needs to be colder due to warmer seas and warmer ground temps in order to cause snowfall.

[phil nw.]

I was just having a scan through the outputs since last night to try and get some idea on how much of a cool off we are looking at for later next week.

My overall impression is that the ECM/GFS operationals are still on the colder side compared to mean outputs.

The 006Z Gefs graph here for London and Aberdeen shows this

I then compared the 00z ECM Operational against it`s mean for T168hrs for 850hPa temperatures after the stepdown in temperatures are modelled.

So yes some colder weather to come later next week but at the moment not as dramatic as most of the operational outputs are suggesting.It still looks like the main thrust of cold is headed across Scandinavia and Russia at this stage.

Edited October 19, 2012 by phil n.warks.

[Iceaxecrampon]

-5 in December would not guarantee Snow. You need -8c as a guarantee (and even then there are other factors that could make it rain and not snow).

At this time of year the air needs to be colder due to warmer seas and warmer ground temps in order to cause snowfall.

And after the absolute scorcher of a summer we've had there's no chance of snow to sea level then..! but I understand the marginality of it all especially here in the sheltered NorthWest - thats why some of us have to chase after it all the way to 3k feet asl+ If the amount of ppn (wet) that we also have endured will fall as the white variety we will be snowbound for weeks.But I am sure the law of averages will come in to play as mother nature evens things out and gives us a winter drought - but thats being pessimistic.

Ian

[phil nw.]

Some recent posts are wandering off Model discussion.

Let`s get back on topic please.

If anyone wants to exchange more general views on Wintry weather there is always the Winter thread amongst others.

Thankyou.

[SMU]

I was just having a scan through the outputs since last night to try and get some idea on how much of a cool off we are looking at for later next week.

My overall impression is that the ECM/GFS operationals are still on the colder side compared to mean outputs.

The 006Z Gefs graph here for London and Aberdeen shows this

I then compared the 00z ECM Operational against it`s mean for T168hrs for 850hPa temperatures after the stepdown in temperatures are modelled.

So yes some colder weather to come later next week but at the moment not as dramatic as most of the operational outputs are suggesting.It still looks like the main thrust of cold is headed across Scandinavia and Russia at this stage.

Hi Phil- your building your assumptions on a very shakey deck of cards- especially using the worst GFS run with even worse ensembles ( 06z )

BOTH sets of output ensembles will generally phase out the signal for blocking & more epecially with the GFS slide the blocking further east, For example-

If you have 20 members, 10 with the correct solution & 10 with either a very east solution or no credible soloution at all then the mean will be a long way south & east of where the reality will end up-

I fear that your placing to much faith in the ensemble data, whilst there is inevitably going to be cold into scandi, I would add that instead of western russia I would replace that with western europe.

This is why when you look at the ensemble graph above the operational looks colder than the mean, because the wrong solutions are bringing the mean up -

You need to put more weighting on the operational 12z & 00z GFS BUT know when to discard it when it appears very wrong.

Why is this?

THe ensemble data IIRC will have a lower resolution & the gridding will not pick up small shortwaves until we move towards say 120-144. as a result our trigger low, + the small chunk of vortex over the pole + our western greenland energy will always get either phased out or modelled towards the default pattern in the GFS which is EAST & SOUTH-

As the ensembles pick up the data better so they slowley correct westwards & northwards- the 06z operational which hasnt got a full ingestion of data & is the worst run of the day is then underpinned at an even worse level but lower resolution ensembles where the data & accuracy & integrity is even less.

Watch how the 12z suite should correct the 500 Anomaly further west-

As a test here is the mean at 168 on the 06z

http://www.meteociel.fr/modeles/gefs_cartes.php?ech=0&code=21&mode=1&carte=0

0c line across Scotland & -4c line traversing Norway-

when we should expect

http://modeles.meteociel.fr/modeles/gfs/archives/gfs-2012101900-1-168.png?0

the -4 line across the UK....

S

[snowking]

I was just having a scan through the outputs since last night to try and get some idea on how much of a cool off we are looking at for later next week.

My overall impression is that the ECM/GFS operationals are still on the colder side compared to mean outputs.

The 006Z Gefs graph here for London and Aberdeen shows this

I then compared the 00z ECM Operational against it`s mean for T168hrs for 850hPa temperatures after the stepdown in temperatures are modelled.

So yes some colder weather to come later next week but at the moment not as dramatic as most of the operational outputs are suggesting.It still looks like the main thrust of cold is headed across Scandinavia and Russia at this stage.

I completely agree and given the time of year we will se, as we always do, more modification of the flow showing up as we get closer to t+0

However, given the subtleties involved in developing this pattern, should we not be focusing slightly more on the higher resolution control and operational outputs? Particularly where we have the old trick of control follows op across both the GFS and ECM at present.

I fully agree that expecting lowland snow away from the northern half of the UK is unrealistic without a significant upgrade showing its hand, but this tends to be the rule I follow through the winter months, particularly when we are dealing with either shortwaves of a splitting of energy

Kind regards

SK

[Methuselah]

When interpreting model-runs, as to whether snow can be expected at sea-level, I agree with RD; an 850HPa temp of about -8C or less is generally required...this would, under normal conditions, equate to a SL temp of around +2C?

But, there are other things that also need to be considered, the most important being the dewpoint; dry air will generally increase the likelihood of snowfall, whereas wetter air will reduce it...

That said, when I was up in Inverness (late 2009) sleet fell when the 850HPa temp was -9...

I hope I'm right JH. But, by all means step-in, if I'm not!

Edited October 19, 2012 by Rybris Ponce

[SMU]

850 Temps are never a good guide to snowfall-

THicknesses are a clearer guide as in an Easterly flow you can see snow in air thats -1c 850 HPA-

Thats for another thread- I will have to dust off my snow guide- 1290 DAM on the 850/1000mb Charts rings a bell- or is it 1280 DAM

http://www.weatheron...S=0&WMO==

heres the 180 chart from the 00z

Heres your guide

Probability:............................90%.....70%.....50%.....30%.....10%

850-1000 hPa(gpm)..............1279.....1287....1293....1297....1302 (un-adjusted)

S

Edited October 19, 2012 by Steve Murr

[phil nw.]

Thanks for your earlier post Steve-re Mean outputs-i didn`t feel the need to recopy it all.

I know you don`t rate the 006z run and i half expected you to say that.

However for some days the majority of Operationals were on the very low side of the ens.suite and if you look at the London ECM ens graph at the point of cooling it shows the same trend.

http://www.weatherca...-tt6-london.gif

I take the point re.the Ens.have a lower resolution so maybe not modelling shortwaves etc.and this is something i will be interested in following as we get closer to see how this might affect the overall pattern.

I know in the past these cold incursions very often get somewhat downgraded and whilst i too enjoy proper Wintry weather in manageable doses i just feel we need to keep some perspective and consider all the outputs.

[SMU]

http://modeles.meteo...nh-0-132.png?12

As expected another pidgeon step west- We are down to a couple of hundred miles now rather than 1000's-

looks like a bullseye hit for the UK

For anyone looking at these 500 Charts-in THIS situation the key colour to get over the uk is the light blue OR darker-

THats the 540 Line

here is is at 138

http://modeles.meteo...fs-0-144.png?12

Heavy sleet & snow showers attacking NE scotland....

Look at the trough line off the west coast of norway...

S

Edited October 19, 2012 by Steve Murr

[liam300]

http://modeles.meteo...nh-0-132.png?12

As expected another pidgeon step west- We are down to a couple of hundred miles now rather than 1000's-

looks like a bullseye hit for the UK

For anyone looking at these 500 Charts-in THIS situation the key colour to get over the uk is the light blue OR darker-

THats the 540 Line

here is is at 138

http://modeles.meteo...fs-0-144.png?12

Heavy sleet & snow showers attacking NE scotland....

S

Wondering how the models will interpret how further south it will go? France??

Further south it goes determines how long it will stay around for...

Edited October 19, 2012 by liam300

[AWD]

Not much of a PV here.

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=192&mode=0&carte=1

Although it does start building by day 10, hence why the HP can't get into Greenland on this run.

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=240&mode=0&carte=1

Edited October 19, 2012 by AWD

[Geordiesnow]

For UKMO standards, thats a pretty good run for those who wants to have a taste of winter!

The cold signal has certainly strengthened on today runs, it is a question whether we can get a clean ridge into Greenland and not have a repeat of yesterdays GFS runs with shortwaves messing everything up.

[swfc]

BIG change post 200 hrs ??????

[Buzzit]

Hi All,

Did anyone happen to watch the documentary on BBC 4 last night - "Tails You Win : The Science of Chance" http://www.bbc.co.uk...rammes/p00yh2rc ? There was a section about 2 3rds in with representatives from the ECMWF Centre and Met office and how they generally use Ensembles and probability - and this also gets related to the Fish episode... well worth watching to get a general appreciation of their treatment of such (and also an extremely good documentary in my opionion in any case). Documentary repeats this Sunday and Monday night

Might go and buy an new coat this weekend the GFS 12z looks even tastier for cold lovers.

Edited October 19, 2012 by Buzzit

[Geordiesnow]

Surprised theres not more comments on the UKMO run, it sends alot of WAA into Greenland, and you get a proper greeny high with a strong Northerly too boot, bound to be some snow showers into Northern and Eastern parts of Scotland with those thicknesses and no doubt cold uppers.

The GFS does not look too shabby either, I think the important thing for any cold set up to develop is to get the heights over Greenland and the models this afternoon have so far agreed on that.

As I said, the question marks will come from any potential shortwave development and whether the high that is going to be over us will "erode" away too allow the floodgates to open.

[johnholmes]

Hi John,

No real surprises or 'secrets'(!) in our briefings of late 're all this; for reference, here's our latest sense of direction into medium range but note this latest issue based on 00z runs (abstracted here from lengthier version). Cheers, Ian

"4. Trend for Days 10-15 : The mostly anticyclonic bias looks set to continue with some agreement in this respect between EC EPS and MOGREPS. More uncertain is the flow direction with EC trending towards a N or NW’ly flow from day 10 (but spreads across all types from day 12), whilst MOGREPS stays SE. Either way, it seems most likely that many S’ern and SE’ern places will see a reasonable amount of fair weather, with sometimes more unsettled conditions further N, but with temperatures tending to fall below normal across all parts.

5. Discussion : There is still a split on the midnight ensembles although all agree on an anticyclonic type. ECMWF would like to go northerly as early as day 8, but now spreads across all types later n the outlook period. MOGREPS would favour an anticyclonic SE throughout"

Hi John,

No real surprises or 'secrets'(!) in our briefings of late 're all this; for reference, here's our latest sense of direction into medium range but note this latest issue based on 00z runs (abstracted here from lengthier version). Cheers, Ian

"4. Trend for Days 10-15 : The mostly anticyclonic bias looks set to continue with some agreement in this respect between EC EPS and MOGREPS. More uncertain is the flow direction with EC trending towards a N or NW’ly flow from day 10 (but spreads across all types from day 12), whilst MOGREPS stays SE. Either way, it seems most likely that many S’ern and SE’ern places will see a reasonable amount of fair weather, with sometimes more unsettled conditions further N, but with temperatures tending to fall below normal across all parts.

5. Discussion : There is still a split on the midnight ensembles although all agree on an anticyclonic type. ECMWF would like to go northerly as early as day 8, but now spreads across all types later n the outlook period. MOGREPS would favour an anticyclonic SE throughout"

many thanks for that insight Ian

[Met4Cast]

GEM interested in the Northerly again too

Perhaps slightly better than what the GFS is showing, in some ways!

[johnholmes]

850 Temps are never a good guide to snowfall-

THicknesses are a clearer guide as in an Easterly flow you can see snow in air thats -1c 850 HPA-

Thats for another thread- I will have to dust off my snow guide- 1290 DAM on the 850/1000mb Charts rings a bell- or is it 1280 DAM

http://www.weatheron...S=0&WMO==

heres the 180 chart from the 00z

Heres your guide

Probability:............................90%.....70%.....50%.....30%.....10%

850-1000 hPa(gpm)..............1279.....1287....1293....1297....1302 (un-adjusted)

S

Met O figures are very close to those you show, just +/- 1 or 2DM

When interpreting model-runs, as to whether snow can be expected at sea-level, I agree with RD; an 850HPa temp of about -8C or less is generally required...this would, under normal conditions, equate to a SL temp of around +2C?

But, there are other things that also need to be considered, the most important being the dewpoint; dry air will generally increase the likelihood of snowfall, whereas wetter air will reduce it...

That said, when I was up in Inverness (late 2009) sleet fell when the 850HPa temp was -9...

I hope I'm right JH. But, by all means step-in, if I'm not!

for my Guide see bottom of the first page of Net Wx Guides

[AWD]

JMA looks interesting at T192 with heights looking to build into Greenland better than the GFS, letting the cold air flood into Northern Europe including the UK.

http://www.meteociel.fr/modeles/jma.php?ech=192&mode=1&nh=0&archive=0

NoGaps doesn't have the block as far west as the JMA, so the proper cold air ends up going to the east of the UK, although still cold for the UK.

http://www.meteociel.fr/modeles/nogapse_cartes.php?ech=180&code=0&mode=0&carte=1&archive=0

Edited October 19, 2012 by AWD

[MR EXTREMES]

ok its a start will greenland high maintain its grip over greenland or will the vortex move house.

impressive model outputs across the board.

[The PIT]

Massive downgrade on the indian summer gone down from four days to possibly just two. However the downgrade well within T96 shows that watching a possible cold snap to follow is in very dodgy grounds. Not worth going to the bookies yet me thinks.