General Model Output Discussion

[rich1]

Longer term GFS no where near as good upto 216hrs, this is because the GFS creates a monster low near Greenland at 144hrs:

http://www.wetterzen...s/Rtavn1441.png

This flattens everything somewhat...followed by another very deep low pressure system at 960mbs...

Simply put if those LP's are weaker then that run will be proven very wrong...

That on looks like a typically overblown atlantic low from the GFS which has form for that sort of thing...so am not concerned about that at all

still, who cares, the reliable timeframe looks excellent for once and the UKMO chart looks much better at t144 and maybe more realistic

[Rollo]

Longer term GFS no where near as good upto 216hrs, this is because the GFS creates a monster low near Greenland at 144hrs:

http://www.wetterzentrale.de/pics/Rtavn1441.png

This flattens everything somewhat...followed by another very deep low pressure system at 960mbs...

Simply put if those LP's are weaker then that run will be proven very wrong...

It just seems to like to overdeepen these lows-looks to me like a climbdown will be coming soon.

[snowking]

It is exciting indeed! The models show the heaviest of the snow across the south east Midlands and EA, but everywhere else surrounding these areas looks to get condsiderable snowfall too, including here in Birmingham, especially during the early hours of Wednesday if the models are correct.

This event is far from nailed, but at least now alot of regions stand a chance of getting significant snowfall, not just eastern regions of the UK, although they will undoubtedly get the heaviest falls.

To be honest it depends entirely on who you believe in terms of models

UKMO certainly suggests the above

GFS and NAE going with heaviest falls from the channel shortwave actually S and W of the central midlands

I think a lot of us are going to be rather sleep deprived in the next 48 hours

Im going to get a good nights sleep tonight before the front heads in tomorrow i think!

SK

[MR EXTREMES]

Longer term GFS no where near as good upto 216hrs, this is because the GFS creates a monster low near Greenland at 144hrs:

http://www.wetterzen...s/Rtavn1441.png

This flattens everything somewhat...followed by another very deep low pressure system at 960mbs...

Simply put if those LP's are weaker then that run will be proven very wrong...

yeah i see what you mean kold,

that was being shown yesterday very powerfull low south of greenland letting the other low attack could cause some problems in the medium term and then losing the cold.

or am i reading this wrong?

[Altohumorous]

An awesome UKMO 12z run, by T+144 the high decides to start retrogressing towards Greenland again:

ECM though goes for this, which overall would mean very dry, frosty, culminating in stagnant HP weather, probably becoming cloudy and so even the frosty weather would go. However it's a long way off but it has to happen at some stage in this spell:

That low over central Europe seems a constant spanner in the works of the Scandi high joining the Siberian to the Greenland/Arctic, and that has gone a long way to preventing a widespread frontal easterly snow event, IMO.

Of course it's all relative, and compared to the last 15/20/25 years this has been wonderful! (I won't make the weather gods angry <_< )

[kold weather]

That on looks like a typically overblown atlantic low from the GFS which has form for that sort of thing...so am not concerned about that at all

still, who cares, the reliable timeframe looks excellent for once and the UKMO chart looks much better at t144 and maybe more realistic

Totally agree, I think the only real differences between the UKMo and the GFS is the GFS blows the low up so rapidly and to such an extent that the upper high gets shafted and flattened, I'm sure if it was say the same strength as the more realisitic UKMO of 975-970mbs then the upper high would hold up just nicely.

Will be interesting to see how many ensemble members go with this but unless the ECM also does the same I'm expecting a back track from the GFS. It does show however what could happen if there is too much energy in the jet...

[Neilsouth]

Totally agree, I think the only real differences between the UKMo and the GFS is the GFS blows the low up so rapidly

But the gfs is known for having lows way too deep , it does it every month in one way or another... The amount of times we've seen Bomb low's that are no way as deep as gfs expect

[VillagePlank]

Regarding the occluded front running down the country from midnight tonight (ish)

We can see this on the Theta-W charts ...

To my mind Theta-W (or wet-bulb, if you prefer) values of 2C sit on the marginal. Less than this means increased probabilities of snow, and greater than this means less probability of snow. This front seems to have marginality mixed in with it, especially the more west you are, and I would hazard a guess that although the heights of 850hPa, and 500hPa are perfect, rather like t/storm forecasting: if one parameter is out ...

I think that areas that fall under the 2C or above categories might well need to be at height to see pure snow, and it might well fall as sleet at sea-level at 2C or above. However should the showers, locally, intensify, snow is likely.

Edited January 4, 2010 by VillagePlank

[TEITS]

TEITS

Been poorly - but am gonna get the bread in and milk supplies. Fortunately, I have a garage just down the end of my road so may well pop out again later to stock up.

I have now upgraded to NW extra - what facilities would you recommend to a novice? Also, when do you think given my location, the serious PPN will arrive tomorrow?

Thanks for your reply, in advance.

SF

Highly recommend the NMM model and also the radar. There is obviously much more and having NW Extra is a valuable tool especially for occasions such as this.

As for tomorrow and to be honest as KW says its a mess. I would expect the front to reach E Midlands/E Anglia during the morning and then move further SE. For your location I would expect snow to reach around lunchtime. However based on the UKMO is during Tues night into Wed the fun and games really begin!

The fax charts which should be out in the next hr will tell us alot more.

Edited January 4, 2010 by THE EYE IN THE SKY

[kold weather]

Thankfully the GFS control run seems to be going along with the UKMO rather then the op run upto 120hrs.

Also just worth noting how much snow could fall in central Europe this week, I think a foot of snow could fall it quite widely, this can only help to freeze Europe up and make our SE/ESE winds even colder again...

[snowfish]

Highly recommend the NMM model and also the radar. There is obviously much more and having NW Extra is a valuable tool especially for occasions such as this.

As for tomorrow and to be honest as KW says its a mess. I would expect the front to reach E Midlands/E Anglia during the morning and then move further SE. For your location I would expect snow to reach around lunchtime. However based on the UKMO is during Tues night into Wed the fun and games really begin!

The fax charts which should be out in the next hr will tell us alot more.

Thanks for that!

[Altohumorous]

Thankfully the GFS control run seems to be going along with the UKMO rather then the op run upto 120hrs.

Also just worth noting how much snow could fall in central Europe this week, I think a foot of snow could fall it quite widely, this can only help to freeze Europe up and make our SE/ESE winds even colder again...

Good point. That easterly, if it lasts and doesn't become a slack northeasterly with North Sea air, has potential. Looks like it will be more of a northeasterly so the North Sea influence is going to remain a large factor as it has often be so far this spell. Until it freezes over of course!

Edited January 4, 2010 by Altohumorous

[Snowaddict]

Thankfully the GFS control run seems to be going along with the UKMO rather then the op run upto 120hrs.

Also just worth noting how much snow could fall in central Europe this week, I think a foot of snow could fall it quite widely, this can only help to freeze Europe up and make our SE/ESE winds even colder again...

Indeed Kold W,

Also note that the Ensemble Mean at T+120 is much better than the 06Z Mean & is far closer to the Euro guidance that we have so far today.

SA

[Frosty.]

GFS 12z brings a milder trend in FI with atlantic lows moving in but it's only 1 run.

[danm]

The latest FAX 24hr is out: http://www.meteociel.com/ukmo/fax/fax24s.gif

Looking messy!

[casparjack]

Regarding the occluded front running down the country from midnight tonight (ish)

We can see this on the Theta-W charts ...

To my mind Theta-W (or wet-bulb, if you prefer) values of 2C sit on the marginal. Less than this means increased probabilities of snow, and greater than this means less probability of snow. This front seems to have marginality mixed in with it, especially the more west you are, and I would hazard a guess that although the heights of 850hPa, and 500hPa are perfect, rather like t/storm forecasting: if one parameter is out ...

I think that areas that fall under the 2C or above categories might well need to be at height to see pure snow, and it might well fall as sleet at sea-level at 2C or above. However should the showers, locally, intensify, snow is likely.

I think you might be right, if you look at the 16:00 hrs reports from the Highlands, Aviemore (228m AMSL) and Loch Glascarnoch (265m AMSL) have heavy cloud and light rain, together with temperatures clsoe to 0c or just above.

We will have to hope that the cold air undercuts more by the time it gets South or we could end up with a bit of a hit and miss situation?

I am going to see if I can find some better synoptic reports to support this one way or the other...

[NorthantsSnow]

The latest FAX 24hr is out: http://www.meteociel.com/ukmo/fax/fax24s.gif

Looking messy!

And they said it would be dry!

Look at all that activity right over our heads.

[VillagePlank]

Thankfully the GFS control run seems to be going along with the UKMO rather then the op run upto 120hrs.

Also just worth noting how much snow could fall in central Europe this week, I think a foot of snow could fall it quite widely, this can only help to freeze Europe up and make our SE/ESE winds even colder again...

Yes, Kold - quite true. I should have checked the ensembles first. The operational, which does show marginal theta-w values, is a degree or so warmer than the mean for the critical time, and is mostly warmer than the other runs at 850hPa - at least they are in Kent (and I presume as similar scenario elsewhere, too) ...

Hopefully, that will make the difference to the Theta-W values and push them the right side of marginal as the front passes across the country.

Sorry guys - I should have checked the ensembles first

[Upgrade]

The latest FAX 24hr is out: http://www.meteociel.com/ukmo/fax/fax24s.gif

Looking messy!

strange looking charts. Are we going to see lots lows tracking NE/ SW against the usual grain of our weather patterns?

[VillagePlank]

I think you might be right, if you look at the 16:00 hrs reports from the Highlands, Aviemore (228m AMSL) and Loch Glascarnoch (265m AMSL) have heavy cloud and light rain, together with temperatures clsoe to 0c or just above.

We will have to hope that the cold air undercuts more by the time it gets South or we could end up with a bit of a hit and miss situation?

I am going to see if I can find some better synoptic reports to support this one way or the other...

My assumption was based on the operational charts, which are, as I said above, every so slightly warmer than the mean, and mostly warmer than the rest - so, hopefully, for all concerned, this pushes everyone (possibly not those in the west) to below the magic 2C.

Still it all seems a little close (doesn't it always!) so I'd advise caution and nowcasting!

Edited January 4, 2010 by VillagePlank

[cooling climate]

Stunning UKMO run tonight and I would fully expect the ECM to be like wise.

I would like to add this snippet, I was in the gym earlier and a news flash or update came on the

radio from the Met Office warning of considerable snowfall for tomorrow and with further snowfall

through Wednesday and Thursday.

I see the GFS is starting its backtrack in the post t96 time frame.

[Tucco]

Big change on latest fax, low over the South Coast instead of the Southern North Sea

http://www.meteociel.fr/ukmo/fax/fax36s.gif

With such a change over a short period of time. The radar is everyones best bet.

Mark

[Snowmoon]

NAE goes for a foot of snow over the Isle of Wight

I'm first to admit that I'm not at all skilled in interpreting these charts, but isn't it saying that the units are in millimeteres and so the amount of snow is therefore 32mm => 3.2cm => ~1.25 inches?

[Rob K]

I'm first to admit that I'm not at all skilled in interpreting these charts, but isn't it saying that the units are in millimeteres and so the amount of snow is therefore 32mm => 3.2cm => ~1.25 inches?

mm of rain. A rough guide is that 1mm of rain will give 1cm of snow, as lying snow is ~90% air!

Great fax charts tonight which are virtual carbon copies of the NAE output:

http://www.meteociel.com/ukmo/fax/fax24s.gif

http://www.meteociel.com/ukmo/fax/fax36s.gif

[Tom D]

I'm first to admit that I'm not at all skilled in interpreting these charts, but isn't it saying that the units are in millimeteres and so the amount of snow is therefore 32mm => 3.2cm => ~1.25 inches?

The golden rule is 1mm = 1cm, give or take a bit :lol: