General Model Output Discussion

[03jtrickey]

Can any on help with this.

Saturday nights event, for south wales is forecast to be rain!

ACccording to models 2m temps near 0, 850s near -5, 528 dam is beyond. I know its the warm sector but can not see why rain and not snow.

With all that in place would the dew point be above zero and if so what would be needed to drop dew points.

Can someone with model experience explain the reasons for forecast and about dew points (and where on models are dew points shown )

Not for the GFS but for the highly detailed NMM model you can view dewpoints (Point Rosee) on Meteociel here http://www.meteociel.fr/modeles/wrfnmm.php?ech=3&mode=18&map=0

Currently showing the milder sector on Sunday morning with dewpoints of 1/2C

[conor123]

There's not a day with the temperature any higher than 3c here from start to 384hrs finish of the 12z run, just hope those lows going through France next week

track further north to give us snow deprived WEST midlanders something decent.

[Frosty.]

UKMO 12z looks cold all the way to the 24th with no hint of anything mild anywhere near the uk with the jet still hundreds of miles south of the BI.

[tinybill]

There's not a day with the temperature any higher than 3c here from start to 384hrs finish of the 12z run, just hope those lows going through France next week

track further north to give us snow deprived WEST midlanders something decent.

well looking at the models you can have some of ours lol we got between 6 to 8 inches already with the prospect of another 6 coming sunday night plus the weather for xmas day is geting better and better

[West is Best]

12z GFS/UKMO - some of the most interesting synoptics I can recall in some ways. It's as if the whole western European setup is going into reverse. There's certainly no sign of a conventional breakdown now ...

[PB22]

12Z ECM also goes with the cold theme for the run up to Christmas:

http://www.wzkarten.de/pics/Recm721.html

http://www.wzkarten.de/pics/Recm961.html

http://www.wzkarten.de/pics/Recm1201.html

http://www.wzkarten.de/pics/Recm1441.html

[ChartViewer]

12Z ECM also goes with the cold theme for the run up to Christmas:

http://www.wzkarten.de/pics/Recm721.html

http://www.wzkarten.de/pics/Recm961.html

http://www.wzkarten.de/pics/Recm1201.html

http://www.wzkarten.de/pics/Recm1441.html

Hi Paul,

Unfortunately 850 temps do not seem to be so convincing on the ECM run, suspect possibly a

chilly South come Xmas day but nothing that will bring any snow, maybe rain ?...

Further North could be fun though!

Any thoughts?...breakdown on Xmas Eve?

Regards,

CV

[J10]

Well further west there is a warm sector embedded in the flow so yeah the front possibly will be of rain and sleet in the SW ad more western parts of England. In many ways this could evolve in a very similar way as Jan 2004 which saw a sleety mix in the west whilst the central and eastern parts got hit quite hard. The fact its coming down overnight for the south is going to help but we will see...

After initial rain, we had a covering of snow from that event. I would certainly expect some snow at least on hills and on the back edge of the front ( in the west). As you say the fact it is at night help, also help that it so cold here at the moment, which may give freezing rain for some.

[Frosty.]

The ECM 12z even at T+216 to T+240 hours looks rather cold at least and cold enough for snow in the north with low pressure smack bang on top of the uk unless i'm reading it wrong.

[asdasd]

After initial rain, we had a covering of snow from that event. I would certainly expect some snow at least on hills and on the back edge of the front ( in the west). As you say the fact it is at night help, also help that it so cold here at the moment, which may give freezing rain for some.

The warmfront passes relatively quickly, and the freezing rain could fall and freeze on impact, meaning that all subsequent snow will stick. It seems like a few hours of snow for the sw.

[ScottSnow]

Regarding low temps, last year when I was in Aviemore (Scotland) the temp got down to -20C on the night of the 8th. Once the cold becomes embedded temps can really fall away at night. I wouldn't be suprised to see some extremely low minima next week.

This cold spell seems to becoming entrenched with the cold not wanting to go away. I believe the GFS is the best at spotting patterns and the overall trend is prolonging the cold weather.

I would expect that there will be some deep snowcover over higher northern areas by the end of next week.

Hopefully we will see a proper cold spell akin to 'yesteryear' and maybe some will argue there is a shift from the 'even larger teapot' era after last years fairly cold winter. It would be interesting to hear Ian Browns thoughts on the matter.

[snowmadchrisuk]

This is the Way GFS see's it for Saturday night , 99% snow for the Midlands, Blackpool , Manchester and Northern Ireland sort of areas may see a spell of Rain/Freezing rain first , but this looks to turn to snow very quickly . I expect in most places this will be an all Snow event . Temps are -2 widely . In Leicester Wet bulb temps stay below freezing , due points range from -1 to -6 as the night goes on.

[Tom Montalbano]

The most recent METO FAX t72 for midday Mon is an upgrade too.

http://cache.netweather.tv/fax/PPVK89.png

The low off NW Spain could well clear the meridian south of the UK.

Regards,

Tom.

[PB22]

Hi Paul,

Unfortunately 850 temps do not seem to be so convincing on the ECM run, suspect possibly a

chilly South come Xmas day but nothing that will bring any snow, maybe rain ?...

Further North could be fun though!

Any thoughts?...breakdown on Xmas Eve?

Regards,

CV

Hi CV,

For next week I wouldn't be taking quite so much notice of 850hPa temperatures to be honest with the cold well established at the surface. I think most of Britain will stay cold until Christmas now, and what happens beyond the big day itself remains open to question. I certainly wouldn't call any breakdown to milder conditions at this stage.

[snowmadchrisuk]

Hi CV,

For next week I wouldn't be taking quite so much notice of 850hPa temperatures to be honest with the cold well established at the surface. I think most of Britain will stay cold until Christmas now, and what happens beyond the big day itself remains open to question. I certainly wouldn't call any breakdown to milder conditions at this stage. :lol:

Well I see the MJO has re entered phase 7 - Continued Northern Blocking it is then ..

[johnholmes]

I'd agree with PB's assessment above-much as I've tried to post in the Christmas blog-certainly not mild-how cold is still open for changes-truly interesting model watching.

new Alert out for the weekend

[Optimus Prime]

Well the breakdown brigade has shut up at last with no breakdown in sight. Staying cold this week with plenty more sleet and snow. Christmas still a long way off, probably gonna be cold and wintry.

[davehsug]

GFS 18z is disastrous and a huge mess with milder air making it right across the country by t144, leaving us with SW winds by t180.

UKMO and ECM however look much better for prolonging the cold.

I really don't think you can say that to be honest. Until this low thats coming from the North gets here & we have more of an idea what it might do, I think all things are possible.

At the moment I'd place FI at t48 or even lower, in as much as I don't believe a single forecaster could tell me with reasonable confidence what the situation might be like on Monday!

On the whole, every model suggests a slow warming up in the weather from around Xmas day & yet they never quite convince. On the face of it, tonights ECM is the most clear cut & least messy model we've seen for a few days & yet it just doesn't "feel right", if you know what I mean.

We are in very strange synoptic times at the moment & I don't know where we're going!

[Ross B]

I wouldn't say it was that bad, still relatively cold upper air temps and ground temps would still be low. We must be spoiled if we think its bad! (will probably be an outlier anyway)

This however:

[nick sussex]

I really don't think you can say that to be honest. Until this low thats coming from the North gets here & we have more of an idea what it might do, I think all things are possible.

At the moment I'd place FI at t48 or even lower, in as much as I don't believe a single forecaster could tell me with reasonable confidence what the situation might be like on Monday!

On the whole, every model suggests a slow warming up in the weather from around Xmas day & yet they never quite convince. On the face of it, tonights ECM is the most clear cut & least messy model we've seen for a few days & yet it just doesn't "feel right", if you know what I mean.

We are in very strange synoptic times at the moment & I don't know where we're going!

Excellent post Dave and theres no way of knowing what will happen on Monday. It's a very messy synoptic set up, even the met office aren't willing to commit to anything at this stage. I wouldn't be surprised to see any fronts slowing down grazing the south coast and slipping eastwards as they hit the cold pool over the uk.

The whole week is a nightmare to forecast.

[PB22]

After the earlier good agreement of cold until Christmas Day, the 18GFS set has now developed a split for the big day itself:

http://91.121.94.83/modeles/gens/graphe_ens3.php?x=353&ext=1&y=93&run=18

Not a mild outlier until FI, whilst the control went milder even quicker than the operational did. The uncertainty continues!

[Frosty.]

18z looks cold up't north until boxing day but then it all goes very pear shaped, not really bothered as we should get another week of below average temps and a risk of snow more or less daily until then and the behavour of the lows next week is pure guess work by the models. The models woefully underestimated the amount of snow that developed yesterday so if they can screw up at 6 hours notice i'm sure they will at T+192

[Cloud 10]

The 18z pressure ensembles for aberdeen illustrate nicely the uncertainty with next weeks setup.

[Thundery wintry showers]

Looks like many ensembles are bringing milder air into the south for Christmas Day but having it struggle to reach the north:

http://charts.netweather.tv/ensimages/ens.20091218/18/t850Tyne~and~Wear.png

...and this includes the operational run, a relatively mild damp Christmas for the south but a cold one with snowfields for Scotland and northern England.

Still not a great deal of support for a warm-up around Christmas Day for Tyne and Wear, and even less if you try a far-northern location like Aberdeen, where there is strong ensemble support for cold snowy weather to see out the entire remainder of December. The uncertainty continues but at the moment, it is looking iffy whether the south gets a white Christmas and favourable for the north. Bear in mind, though, that the progged breakdown a few days ago was supposed to happen around 21-23 December- now we're looking at Christmas Eve at the very earliest.

People living in the south in particular should not be getting their hopes up about a white Christmas just yet. In the meantime potential for a big snow event for many tomorrow- it may well start off as sleet or rain as the warmer pool of air coincides with the forward edge of the main band of precipitation, but it looks like everything behind the forward edge will be snow for a large majority of the country.

[kold weather]

Yeah models are suggesting a pig of a set-up to really put much detail on, the problem being small shifts in the low pressure complex makes a big practical difference to the Uk's weather, such shifts are going to be hard enough to forecast well for the models as it is, yet alone when there is such a marginal sey-up for snow over the UK.

As TWS said, for now in the south looks like less cold air gets in before xmas, further north and it may be a bigger slog...however this set-up is VERY prone to changing on a whim.