18z model discussion - all aboard the snowlercoaster!

[Turnedoutniceagain]

Good Morning!!

Whats the latest? Did the charts come up with the goods overnight? Are we still looking as though we'll have a snow event here in South Wales?

Will it turn to rain on the back edge or is there a chance that the conditions will be right to completely pass us as snow and leave it dry afterwards for us to actually enjoy it!

Bad news, spring is sprung, flowers out etc etc. I blame the Sais !!!

[kold weather]

Well lookd like the exacts of this snow set-upreally isn't going to be sorted until it arrives by the looks of things, GFS and fax charts still differ quite a bit considering we are now so close. The GFS tears the front northwards with it over N.England by 12z accoridng to the 0z run:

http://www.wetterzentrale.de/pics/Rtavn366.png

At the same time the UKMO fax charts show the front barely north of the M4:

http://www.wetterzentrale.de/pics/brack0a.gif

So clearly timing is still an issue with this.

Still the 0z GFS is actually something of a upgrade as it holds onto the below 0C dew-points for longer so the smnow may well last longer then expected in the south but exactly how long it lasts is the question that even now still can't be answered!

[R.P. McMurphy]

One thing for sure, the Midlands & Wales are going to get a pasting. I don't know yet whether it is going to snow here, I don't know if the front will make it to Manchester. I fear it may stall & stay over the Midlands. Boo Hoo! I have got Thursday off also which isn't so bad, wasn't a bad day to book off eh! So I can model watch alllll night. Anyone else?

[Tigers]

One thing for sure, the Midlands & Wales are going to get a pasting. I don't know yet whether it is going to snow here, I don't know if the front will make it to Manchester. I fear it may stall & stay over the Midlands. Boo Hoo! I have got Thursday off also which isn't so bad, wasn't a bad day to book off eh! So I can model watch alllll night. Anyone else?

Just showed on BBC few mins ago the PPN moving west to east and pretty much fizzling out before getting any further than Manchester by the looks of it.

Are any charts showing pulling in an E/NE if this happens which would be better for the longer term if so?

[Doc]

Met Eireann just said that they would be surprised if most places across Ireland , with the exception of the south, didn't get several cms of snow tonight. I am still a little sceptical!

[West is Best]

Looks like gfs is on one..

Well all the models have now fallen into place behind the GFS. GEM's wild scenario at 12z yesterday has been completely replaced by a GFS-identi-run and with an incredibly warm plume on 12th Feb showing up! The big big change though is UKMO, which also now has taken the GFS route. ECM is also thoroughly zonal and wild.

The only interest in the short term for cold fans is if anywhere will see snow tonight and tomorrow. You all know my views about how marginal it looks, but we shall see! Some front edge snow may occur for a while before rain sets in. Others may have different views.

Well done to the GFS. It has taken a battering from some people on here, but it looks like it has stuck to its guns and if this is how it transpires then it has won the model battle by miles. It's in a different league from the rest.

[TEITS]

The plot thickens here we are 24hrs away from the event and the models still don't agree

Here is what I think will happen based on the Fax charts.

http://cirrus.netweather.tv/fax/PPVG89.png

http://cirrus.netweather.tv/fax/PPVI89.png

Rain turning to snow from the M4 Northwards and spreading as far north as probably N Lincs. The snow in these areas will not turn to rain and will simply just fade away. The areas most likely to see heaviest snowfall is E Midlands/W Midlands/N Wales. During Friday this is likely to remain cold but dry due to precip mostly faded away on front. Into saturday another area of snow will track NE although this time the front shall move further N and to the S this should turn to rain.

Im still unsure if the snow will move as far N as the UKMO is showing let alone what the GFS is showing and like I said to Steve M I believe the main action could be around 60 miles further S. Im basing this mainly on instincts and I just don't believe the precip will be as progressive as the GFS once the front tries to move NE into the block of colder air.

As for beyond this much interest and the prospects of an E,ly remain a possiblity.

[The PIT]

Now will this be a Modern dumping 1cm to 2cm Forecast 10 - 15cm or will be the old type 30cm.

GFS not looking back UKMO still got the lows to far North for my liking anyway whatever Tomorrow should be interesting.

[Nick F]

The only interest in the short term for cold fans is if anywhere will see snow tonight and tomorrow. You all know my views about how marginal it looks, but we shall see! Some front edge snow may occur for a while before rain sets in. Others may have different views.

Let's see what happens WIB, we know your are wishing it to turn to rain for everyone, probably will turn to sleet and rain south of the M4 but for the Midlands, Wales and parts of E. Anglia it looks to be a snowy day and staying so, no matter how much mild spin you put on it that's pretty much the UKMO fax line of events and they should be trusted most this close.

Further out, Saturday the milder air looks like wining over much of England and Wales eventually with snow turning back to rain, but it may well end up staying as snow over Scotland.

[TEITS]

Well done to the GFS. It has taken a battering from some people on here, but it looks like it has stuck to its guns and if this is how it transpires then it has won the model battle by miles. It's in a different league from the rest.

You are joking right!!.

The GFS has swung wildly IMO and you only have to look at the predicted temps for Sat as an example.

The max temps for Sat have swung from anything from +9C to the currrent predicted temp of around 3-4C. Besides this I think we should wait until the area of SNOW has passed through and then we can take it from there to see who called this correctly!!.

[West is Best]

In a generally difficult situation to call the GFS has been streets ahead of anything else. The others have been all over the place compared to the steadfastness of the GFS. It remains the only 1st class model output.

As for the fax charts, don't start me ...

Incidentally, I am referring to synoptics. Anyone who uses the GFS for an accurate surface temp reading shouldn't.

Edited February 7, 2007 by West is Best

[carinthian]

The plot thickens here we are 24hrs away from the event and the models still don't agree

Here is what I think will happen based on the Fax charts.

http://cirrus.netweather.tv/fax/PPVG89.png

http://cirrus.netweather.tv/fax/PPVI89.png

Rain turning to snow from the M4 Northwards and spreading as far north as probably N Lincs. The snow in these areas will not turn to rain and will simply just fade away. The areas most likely to see heaviest snowfall is E Midlands/W Midlands/N Wales. During Friday this is likely to remain cold but dry due to precip mostly faded away on front. Into saturday another area of snow will track NE although this time the front shall move further N and to the S this should turn to rain.

Im still unsure if the snow will move as far N as the UKMO is showing let alone what the GFS is showing and like I said to Steve M I believe the main action could be around 60 miles further S. Im basing this mainly on instincts and I just don't believe the precip will be as progressive as the GFS once the front tries to move NE into the block of colder air.

As for beyond this much interest and the prospects of an E,ly remain a possiblity.

Morning TEITS,

Thats my feeling. Certainly NGPs goes for a very cold Nely into next week. I think Met Office charts will start to up grade the cold early next week, particularly in the North and East.

C

[One way or another]

Well all the models have now fallen into place behind the GFS. GEM's wild scenario at 12z yesterday has been completely replaced by a GFS-identi-run and with an incredibly warm plume on 12th Feb showing up! The big big change though is UKMO, which also now has taken the GFS route. ECM is also thoroughly zonal and wild.

The only interest in the short term for cold fans is if anywhere will see snow tonight and tomorrow. You all know my views about how marginal it looks, but we shall see! Some front edge snow may occur for a while before rain sets in. Others may have different views.

Well done to the GFS. It has taken a battering from some people on here, but it looks like it has stuck to its guns and if this is how it transpires then it has won the model battle by miles. It's in a different league from the rest.

It's amazing how people can come up with utter nonense to try and justify a point! The GFS has handled this the same as most other models - with uncertainty and constant chopping and changing!

[Snowly does it]

In a generally difficult situation to call the GFS has been streets ahead of anything else. The others have been all over the place compared to the steadfastness of the GFS. It remains the only 1st class model output.

Thats not strictly true though Richard, the GFS has shifted the track of the LP and the position of the 850 -5 air wildly over the last 2 days, it has only just fallen into this more northerly track, against the grain of the consistent fax charts - tomorrow will see which has it nailed, and more importantly, where it goes after that.

[TEITS]

As for the fax charts, don't start me ...

Incidentally, I am referring to synoptics. Anyone who uses the GFS for an accurate surface temp reading shouldn't.

So let me get this straight then Richard you know more than the entire Met O then do you!!.

Within +72 these charts are always going to be the most reliable sets of charts to use for the simple reason they are based on model/human output. Many people are of this opinion and the only reason I believe you are simply saying this is because of what they are showing. If the GFS was predicting blizzards and the Fax charts were showing otherwise you would be highlighting these instead.

P.S the Min temps of -8C will put a dent into your CET prediction

[West is Best]

P.S the Min temps of -8C will put a dent into your CET prediction :lol:

I've never found the fax charts to be very accurate, and I'm not alone in that view.

[tdubya]

You are joking right!!.

Well said! It's been all over the shop. METO more calm and rational by far.

[TEITS]

I've never found the fax charts to be very accurate, and I'm not alone in that view.

Trouble is though Richard how often do we check the Fax charts accuracy.

What I mean by this is when the weather is benign how often do we check the accuracy of these. Take this week for example they have been spot on with the positoning of fronts/troughs and the only reason why we have studied this is because of our current weather.

Still im not going to allow this debate to spoil my day because I have a lovely thick frost outside with temps of -6C and of course a major snow event to look forward to tomorrow. I shall send you the pics .

[VillagePlank]

Marky's t'pence worth . . . unashamedly aimed for the far S/E corner because that's where I lives . . .

Firstly, the 500hPa. Not the best indicator for snow, so, claiming it's marginal from this chart alone is useless. GFS has the 528dam line receding northwards in some form of sinusoidal shape. Remember that 528dam line describes the distance between 1000hPa and 500hPa in decametres, and this linearly correlates with the mean temperature across the whol 18,000 feet. Therefore beyond this line one would expect the mean temperature to be cold all the way up. This, in no way, provides any description of what the atmopshere is like between cloud base and ground where snow melt might take place. Worth noting that the MetO chart - which some say is the best at this sort <T+24 is the best - at that has the 528dam line covering the whole of the country. Here's the GFS chart:

For the S/E, London, then we can presume that milder air is pushing in from the continent. But as I said before this says nothing about what is going on in the critical area - the surface.

To look at the surface we need to look at the 850hPa - about 1500m up, which, within a frontal system should be around the cloud base - so we therefore have a measure of temperature between the cloud base, and the surface. Remember that the 850hPa is the air temperature at the height specified, and not at the ground

Here you can see that although the temperature of -5C covers the entire country (with the exception of Hampshire and the West Country) the heights divide the country in a North South fashion. The figure I'm looking for is about 1270m of height - which notionally is the distance between the surface and the 850hPa boundary. The smaller, the better for snow - this chart divides the country on a 126dam line, suggesting that the 127dam line is further east (you'd need to see the gridded GFS output to determine exactly where) but based on this output, I'd suggest that the vast majority of this country is under the 127dam line. This line means 50/50 probability of snow and rain. Those west of the 126 line are likely to see snow where it precipitates and where they are also behind the -5C line. So from here the best target point, I'd suggest is West Midlands, and Eastern Northern Wales - if the precipitation gets up that far! Those further East of that line, I'd suggest are sitting on a possibility of 50/50 rain/snow with altitude making a good deal of difference - I'd expect the downs to see snow, and not rain, for instance.

The next two factors I'm going to look at are MinC, and Relative Humidity, and suprisingly for some, I'm going to ignore dew points for frontal snow. The reason for this is that if the RH is low enough then the MinC can be higher and it will still snow (it is also the case that dam levels can be higher for frontal snow - something I've conveniently ignored for brevity)

The RH is about 60% which is surprisingly low considering the amount of precipitation (see below) that is forecast to fall. If you look at the minC then you'll see it as 3C which some may think a little too high. In fact, using various laws this gives a miraculously high chance of snow -I'd estimate it at 90% chance at sea-level. This is not ramping this is the result of the application of known laws.

[edit] A bit misleading as the majority of the S/E is under 70% RH and this reduces the chances to 50% rain/snow [/edit]

So, for the S/E - will there be snow? In a word I'd give chances of around 80% at all levels increasing to 100% with height where it precipates. This covers the period 00z-06z tomorrow.

I hope some found this useful.

Edited February 7, 2007 by VillagePlank

[West is Best]

If the GFS was predicting blizzards and the Fax charts were showing otherwise you would be highlighting these instead.

By the way, I can't think of a single occasion when I've used a fax chart on here or even referred to one, so at least I'm being consistent. I just don't find them very accurate and they have certainly been all over the place the last 7 days. We should be in a raging easterly by now ...

I hope you get snow tomorrow. You might at least for a time. Down here little or no chance, and I fear temps will generally lift too much. I also think I may be safe with my no lying snow in England south of the Pennines. (The official defintion of lying snow being I believe 1cm covering more than 50% as at 09h00 in the morning. Think that's right someone?)

Edited February 7, 2007 by West is Best

[R.P. McMurphy]

Richard, I honestly don't understand where you are coming from? The FAX Charts have been one of the most reliable charts from days ago predicting where this front is going to be and when we are going to have this blast. Yes, GFS did predict this from at least 25th January, but with a few turns for the worse, it's only now it's caught up with the FAX Charts.

I hope the GFS is right with it's prediction because it moves the front further North, whereas the FAX charts don't really let the band of HEAVY snow reach me, and if they do, it's only going to be ligh. I look forward to saturday snow.

[Paul]

The Richard v the rest of the world show is getting a bit tedious folks, can you just agree to disagree please - it's not a requirement that you have to pick up on every point Richard (WIB) makes, and vice versa...

This thread will be locked in 20 mins or so to make way for the 06z.

[fender]

By the way, I can't think of a single occasion when I've used a fax chart on here or even referred to one, so at least I'm being consistent. I just don't find them very accurate and they have certainly been all over the place the last 7 days. We should be in a raging easterly by now ...

I hope you get snow tomorrow. You might at least for a time. Down here little or no chance, and I fear temps will generally lift too much. I also think I may be safe with my no lying snow south of the Pennines. (The official defintion of lying snow being I believe 1cm covering more than 50% as at 09h00 in the morning. Think that's right someone?)

I must say I think your on to a loser there. Depends what time the snow arrives of course. I would expect there to be substantial lying snow in the south, central, and North Midlands also mid and North Wales. Southern England and the SE looks less likely, but cant be entirely ruled out.

[Stu_London]

In a generally difficult situation to call the GFS has been streets ahead of anything else. The others have been all over the place compared to the steadfastness of the GFS. It remains the only 1st class model output.

As for the fax charts, don't start me ...

Incidentally, I am referring to synoptics. Anyone who uses the GFS for an accurate surface temp reading shouldn't.

A couple of points

1) Just before the last cold spell (before it had happened in fact) you were saying how rubbish the GFS was and how ECM handled these situations better (because that particular model was showing your default preferred conditions)

2) The GFS has been far from consistent in the run up to where we are now - two mornings ago - there was no snow for tomorrow (apart from the highlands) and yesterday Thursday and Saturday had a major snow event for most of the UK.

3) Back to point 1 - you are handing out plaudits before the events have panned out.

I have a lot of respect for the technical anaylsis in your posts, however the manner of your posting this morning is in danger of showing you up as a wind up merchant

[7andY]

Just had a quick look at the models. Good old Gloucester! Snow then rain and it's all over, temps to 8deg by midday Thursday 8-(

In the last 15 years, I have seen lying snow (not including showers of just a few flakes!) only twice, and only one of those was over an inch... How does that compare with Carlisle and Abingdon ???!!!

Have fun where you get the white stuff!

Cheers, 7&Y