General Model Output Discussion

[Severe Siberian icy blast]

Just a quick question to all the experts out there; the 12Z GFS snow risk charts show a lessening of the risk for all of the south as the ppn feature comes in on Sunday. All the 90%+ figures are replaced with 60-70% ones. All those nice purples are replaced by oranges!

Is this is a sign of possible marginality due to slightly higher upper temps or is the GFS just having a wobble?

Thanks!

Hi there im no expert but i do no that the ppn charts and risk charts past 24hrs on the gfs are not worth a second look , they change daily and dramaticly even within hours of an event .

[snowmadchrisuk]

BBC n24 just showed all white and mega snowfall for sunday for the midlands and south of the country

Just had a close look at the 12z Ensembles a little bit more closely and 850's wise we are fine until at least the 13th next Wednesday , after that it is a 50/50 split but the 850 mean never reaching 0. The OP was a mild outlier between 13th-14th and 16th-19th In Leicestershire.

[Nick F]

Stunning ECM at t+168, mild air going to have real trouble infiltrating NE or N to the UK with those lows moving east across western continental Europe to our south:

The upper trough moving in from the Atlantic, is NEGATIVELY TILTED enough not to allow milder air in...

[Nick L]

ECM having none of the GFS shenanigans by the looks of it, this seems pretty cold to my novice eyes!

http://www.wetterzen...cs/Recm1681.gif

Edit: Nick F confirmed my belief

Edited January 7, 2010 by nick2702

[igloo]

im certainly no expert but by looking at the charts at +144 GFS.GEM and ECMWF are all lookvery similar to me so by the looks of things this cold spell may only last another 4-5 days

[andymusic]

Hi there im no expert but i do no that the ppn charts and risk charts past 24hrs on the gfs are not worth a second look , they change daily and dramaticly even within hours of an event .

the gfs nailed the ppn that fell this week mind you when all other models forecasters were all over the place not totally sure where the snow was gonna be

[03jtrickey]

Stunning ECM at t+168, mild air going to have real trouble infiltrating NE or N to the UK with those lows moving east across western continental Europe to our south:

The upper trough moving in from the Atlantic, is NEGATIVELY TILTED enough not to allow milder air in...

The meteociel site is showing 850s of between 0 and -4 for most of England on that chart. Ireland and Scotland are still in <-4 air.

Would that plausibly produce snow, or would we be looking at areas of freezing rain/sleet?

[Tim Bland]

im certainly no expert but by looking at the charts at +144 GFS.GEM and ECMWF are all lookvery similar to me so by the looks of things this cold spell may only last another 4-5 days

Think you are reading the ECM charts incorrectly! The low is forced south and southern england recievs a pasting. This is in line with Will Hands prediction I read earlier. If tthis occours it will allow the block to remain in place to the NE. After dumping a foot of snow we may see a brief thaw before a renewed block and wind back E / NE again.

[Nick.F]

Off topic I know, but I'm really missing the input from our more 'valued' members, one or two are dropping in now and then which is appreciated, but certainly not with the frequency I have become accustomed to over the years. It's a real shame, but I can perhaps understand why they are not frequenting this thread at the moment.

But while there are some who believe this thread is about providing an accurate forecast (which it is not), rather than just discussing potential scenarios and outcomes, it has often seemed a particularly unfriendly and disrespectful place at times.

I sometimes curse the facebook generation and the lack of manners and respect these days, especially online; it is too anonymous. And, I am only 43.

Sorry off-topic, but it needs to be said. Back to the models.

[rich1]

im certainly no expert but by looking at the charts at +144 GFS.GEM and ECMWF are all lookvery similar to me so by the looks of things this cold spell may only last another 4-5 days

There is a low approaching on all 3 charts but it behaves in a different manner and it makes big differences down the line

ECM is the best evolution for cold and it is reckoned to be the best performing model so this one is very much up in the air and it would be brave to back against the status quo

[andymusic]

But while there are some who believe this thread is about providing an accurate forecast (which it is not), rather than just discussing potential scenarios and outcomes, it has often seemed a particularly unfriendly and disrespectful place at times.

I sometimes curse the facebook generation and the lack of manners and respect these days, especially online; it is too anonymous. And, I am only 43.

Sorry off-topic, but it needs to be said. Back to the models.

here here - I totally agree - feel like I might get my head bitten off in here for saying the wrong thing!!!!!!!!!!

[Nick F]

The meteociel site is showing 850s of between 0 and -4 for most of England on that chart. Ireland and Scotland are still in <-4 air.

Would that plausibly produce snow, or would we be looking at areas of freezing rain/sleet?

If the temperature is 0C or below from 850mb down to the near the surface, then snow is likely. It will only rain/sleet if milder air mixes in near the surface, that would seem unlikely away from coasts with a cold dry feed off a very cold near continent to the east.

Probably won't verify like this that far out, but t+192 chart from ECM also good:

[Tim Bland]

As expected by T+192 the PV is dropping out of the pole again allowing the AO to fall framaticaly indicating a reload. If you compare this run to the GFS 12z the differences start with this low. If we forget the even larger teapot and look at the clasics then the form horese would be a slider low, the block is very solid and would take a direct westerly hit to shift, not the path this low is taking.

[MR EXTREMES]

But while there are some who believe this thread is about providing an accurate forecast (which it is not), rather than just discussing potential scenarios and outcomes, it has often seemed a particularly unfriendly and disrespectful place at times.

I sometimes curse the facebook generation and the lack of manners and respect these days, especially online; it is too anonymous. And, I am only 43.

Sorry off-topic, but it needs to be said. Back to the models.

i think very much you have a valid point.

on to the models i see ecm is going on and indeed low pressure undercutting,

what the outcome would be on the southcoast im not 100% sure.

i expect sleet but as is bumps into the much colder air perhapes 50 to 100miles north could well get some very snowfall.

i think a reload with high pressure building towards iceland could well be a possibility thease where the idears of gp or along them lines:drinks:.

igloo i dont see what you see.

[Altostratus]

The ECM is nothing like the GFS, as expected. The GFS as per usual has overdeveloped a single area of low pressure. The ECM has smaller eddies spinning off from the main low thus allowing for more energy to flow beneath the block. In turn this allows the cold to hang on for longer and brings the risk of snow to some areas. This will only act to delay the push of mild air, however, the cold air is mixing out and becoming more dilute as time goes by. For a stab at a subzero CET, there needs to be a shift in the pattern with another injection of cold air being needed. I only really see this coming from the north at the moment.

Edit: The ECM out to T+216 is the kind of thing we need to see happen re injection of cold air into the system.

Edited January 7, 2010 by Altostratus

[Thundery wintry showers]

Stunning ECM at t+168, mild air going to have real trouble infiltrating NE or N to the UK with those lows moving east across western continental Europe to our south:

The upper trough moving in from the Atlantic, is NEGATIVELY TILTED enough not to allow milder air in...

I agree- essentially the Atlantic just doesn't have enough "oomph" to overcome the blocking on the ECM, unlike on the GFS, and the negative tilt certainly helps. GFS looks similar to T+144 but keeps low pressure stuck to the SW instead of undercutting the block NW-SE.

Judging by those sub 540dam heights aligning with the 1010mb isobar, thicknesses on that T+168 chart cannot be far from 528dam, and with a flow off the continent that should be enough to support snowfalls away from east-facing coasts of the northeast.

There is the possibility of the setup breaking down in around 6-7 days time as the GFS shows, but on the basis of recent model performances I would have to back the ECM over the GFS simply because the ECM has been consistently accurate out to at least T+144 since the end of last month (T+168 and T+192, apart from a few wobbles here and there, have also been quite good), while GFS has often struggled even at T+96.

[West is Best]

Well the ECM is having none of this fast breakdown that GFS goes for. It has a battle royal with the entrenched Scandinavian high winning.

I'm with John Holmes on this one. Having lived through easterlies like the one setting in I absolutely do NOT buy into a fast-breakdown. Yes it might happen in due course, but it will not be instantaneous. Indeed, I strongly suspect a reload of the easterly (as per ECM). It may take two or even three goes for the Atlantic to gain a foothold over the bulk of the UK.

I very much doubt there will be an end to cold weather before the end of next week at the absolutely earliest and the chances of a continuation of cold remain high.

Remember: the models default to westerly flow and are unused to modelling these patterns.

[Severe Siberian icy blast]

the gfs nailed the ppn that fell this week mind you when all other models forecasters were all over the place not totally sure where the snow was gonna be

Maybe but iv lost count the amount of times its been so far out it was a joke!

[Thundery wintry showers]

Remember: the models default to westerly flow and are unused to modelling these patterns.

I agree with the rest of your post, but I remember reading some insightful posts regarding model performances suggesting that the models don't necessarily default to westerly flow. Rather, there is a tendency, especially on the GFS, to overdo the southward movement of polar air and consequently overdeepen depressions, which has the effect of increasing the chances of a fast breakdown and mild south-westerlies being progged, particularly in the lower resolution part of the run.

[Mark Bayley]

If anyone wants the to view the 850hpa temps for the ECM they can here. Staying cold sums it up! Another good ECM tonight. Will await the ECM ensembles now

http://www.meteogrou...f10ca71087.html <<Link

Edited January 7, 2010 by mark bayley

[snowmadchrisuk]

If the temperature is 0C or below from 850mb down to the near the surface, then snow is likely. It will only rain/sleet if milder air mixes in near the surface, that would seem unlikely away from coasts with a cold dry feed off a very cold near continent to the east.

Probably won't verify like this that far out, but t+192 chart from ECM also good:

A little more Info on this :

The 850mb level of the atmosphere is about 5,000 ft. above sea level. Roughly, freezing temps at 850mb can produce snow. However, if temps are warmer between the surface and 850mb, precipitation could still be rain. Sounding data from the models is then useful to determine the temperature at each level of the atmosphere, which helps determine “thicknesses.” Again, roughly speaking, a thickness of 5400 or below will probably provide snow, while thicknesses above 5400 probably won’t.

[nick sussex]

What a surprise no model backs the gfs 12hrs operational run! How it can have that split PV and set up and still end up trying to push milder air in is beyond me and just shows what a useless model this is as soon as European blocking appears on the charts.

[SizzlingHeat]

If anyone wants the to view the 850hpa temps for the ECM they can here. Staying cold sums it up! Another good ECM tonight, stick with that model over the GFS. Will await the ECM ensembles now

http://www.meteogrou...f10ca71087.html <<Link

I find it so amusing, not being such a poster on here but now rather a watcher, at how peoples bias towards which model is showing what they want rather than going with what is being shown.

As for instance, i remember a lot of people on here slagging the ECM off just before xmas because it was not being consistent. The GFS was consistently showing much colder weather whereas the ECM was all over the place. People slagging this model off because of inconsistencies. Now the ECM is showing what people want, every1 is now slagging off the GFS which showed and predicted the cold spell correctly to begin with.

Not having a go, just was thinking at the bias towards the model which looks the best.

Im sure if the GFS was showing the cold weather extending and the ecm was showing it ending, every1 would be moaning about how inconsistent the model is and that every run that doesnt show what people want should be binned.

[john w]

Not so sure sizzling Heat

I do not tend for bias, in fact, i tend for mild but like to see snow for the benefit of everyone else.

The GFS has really not performed well and even the NOAA (The people whose model it is)have stated how badly it has performed. The GFS has always been a bit over-progressive with breakdowns,

I wonder if someone could post the verification charts up to see how well GFS has done ??

[igloo]

What a surprise no model backs the gfs 12hrs operational run! How it can have that split PV and set up and still end up trying to push milder air in is beyond me and just shows what a useless model this is as soon as European blocking appears on the charts.

thing to remember is the models are very similar at +144 its what happens after then which is the biggest difference any one may be right but going by the progressive nature of the gfs it does look a bit quick