Model Output Discussion

[snowmadchrisuk]

Well it is currently Snowing across the Midlands and the South as I speak , Tuesday looks a repeat of today but Snow more likely to settle. Wednesday looks like Some heavy Snow showers may move into the Midlands and SE , and any Precipitation chart after this will not be correct that far out. I think this Cold spell will get extended by a few days and I think on the 00z GFS run the GFS mixes the -10 850's out way to quickly.

[TEITS]

Not according to the ensembles. Just light intermittent flurries. Best chance of snow Wednesday night into Thursday, more especially for eastern Kent.

http://charts.netweather.tv/ensimages/ens.20100208/00/prcpKent.png

I don't mean to be rude but even the higher resolution models such as the NMM/NAE will struggle to accurately predict precip amounts and the GFS operationals even more so. However the ensembles are even more unlikely to predict precip amounts than the GFS Ops!

The only reliable forecasting tool this week is going to be the radar. If I was honest I enjoy the uncertainity and enjoy radar watching.

[nick sussex]

Not according to the ensembles. Just light intermittent flurries. Best chance of snow Wednesday night into Thursday, more especially for eastern Kent.

http://charts.netweather.tv/ensimages/ens.20100208/00/prcpKent.png

The GFS precip charts, infact all precip charts are very unreliable with convective showers off the North Sea, its best to wait nearer the time when the fax charts might show up some troughs, also the NAE model which runs upto 48hrs is worth a look, but as Dave said it will probably come down to just looking at the radar!

Edited February 8, 2010 by nick sussex

[NorthantsSnow]

The GFS precip charts, infact all precip charts are very unreliable with convective showers off the North Sea, its best to wait nearer the time when the fax charts might show up some troughs, also the NAE model which runs upto 48hrs is worth a look, but as Dave said it will probably come down to just looking at the radar!

With such a slack flow though, how much convective activity is realistically going to occur?

[TEITS]

Still some disagreements at +72.

http://www.wetterzentrale.de/pics/Rtavn721.png

Worth mentioning though that at +42 on the 0Z the NAE had the HP further N than the GFS. Only around 80miles but as Tescos say "every little helps"

The GFS is consistent with bringing a band of snow showers on Wed. Although at this stage the GFS indicates these will weaken as they move inland.

[nick sussex]

With such a slack flow though, how much convective activity is realistically going to occur?

As you can see each model changes the strength of the flow so although the general pattern looks consistent we're still not sure which model has called the finer detail correct. If you look at the ECM and UKMO they look to have a stronger flow than the GFS, its really which model you decide to follow, generally for European blocking patterns the ECM/UKMO is what I follow even though the GFS looks much colder for down here with more chances for snow.

[MR EXTREMES]

Morning all, there seems to be a continuing consensus this morning between GFS and ECM into the medium range of more of a west-based -ve NAO developing, which may tend to pull the PV moving down across Scandinavia next weekend SW and the ridge to pull NW/W in across the NE Canadian arctic. ECM tends to pull the expanding PV further W than GFS, looking at the 8-10 day mean H500 comparisons, which may mean southern areas may lose the cold air eventually, but the cyclonic flow and maritime air getting pulled in by a low sat to the north of the UK may mean some significant snowfalls in places where the cold air holds on:

This tendency for the PV dropping down from the higher latitudes and shifting SW to the north of the UK is by no means certain IMO, particularly as the modelling of the PV is an area within the arctic circle with very sparse observations.

On to the weather this week, any snow over the next few days looks to be mainly light as thicker cloud advects in from the N Sea, so a slight covering at best towards eastern areas. Perhaps snow showers pepping up towards the east coasts on Wednesday, as a low-level disturbance runs SSW down the N Sea towards Low Countries. Thursday models suggest a shallow low with fronts affecting Scotland which may bring a spell of snow, further S a more cyclonic and strengthening flow with troughs moving west as colder uppers arrive - which may bring some heavier snow showers Thursday and Friday towards E and SE England.

oh dear so all in all not very good for the medium term.

i tried to stay optimistic i agree this week through up some suprises.

but it would seem the biggest suprise is the breakdown of cold to south of the uk.

it seems things are not working out good right now and beyond nextweek end could be game over for the southern half of the uk but still good to the north.

models have been messy again the last couple of days perhapes fi was to good to be true.

[Lewis]

Good morning everyone,

As i type the precipitation is very light, and guess what! It's snow

Im amazed with the isotherm, have not looked at the models yet.

Congrats TEITS on the snow, and also the rest of you.

[Southender]

Where's the -10 850's gone on this mornings 6z GFS run?

HP further south again...

Edited February 8, 2010 by LeighShrimper

[ribster]

decent charts but not fantastic IMO..lots of dissapating fronts and troughs that wouldnt deliver too much snagged up in the high pressure..lots of areas would be cold and cloudy..but thats about all.

I keep hearing slack flow, dry, cloudy and cold, marginal, exactly like the last cold spell. Yet it has been snowing heavily here this morning (only lightly as I type), which has settled on the grass and beginning to on roofs. So the charts obviously are not the be all and end all, especially when it comes to precip!

[TEITS]

Where's the -10 850's gone on this mornings 6z GFS run?

HP further south again...

Here they are!

http://www.wetterzentrale.de/pics/Rtavn602.png

I do have a message for Badboy though. If you read Nick F excellent summary he does say there remains some uncertainty. Remember during Xmas the models suggested a W based NAO at roughly the same timeframe. However as this moved closer the Block was further E than the models suggested.

[nick sussex]

Where's the -10 850's gone on this mornings 6z GFS run?

HP further south again this morning.

Freezing the fish in the northern Med! I wouldn't take too much notice of this GFS run,it does seem out of line with the general model guidance upto 144hrs.

[Southender]

Freezing the fish in the northern Med! I wouldn't take too much notice of this GFS run,it does seem out of line with the general model guidance upto 144hrs.

I hope so Nick.

That HP is too close to spoiling it all come the weekend.

Still that's a long way off. A rogue run hopefully.

Retrogression shown after anyway, just maybe not as cold in the meantime, if this run verifies.

Basically a really slow evolution. Serioous patience required during this cold spell I think...

Edited February 8, 2010 by LeighShrimper

[Lewis]

UKMO fax charts still look fine, they show a few troughs aswell.

http://www.weathercharts.org/ukmomslp.htm

No need for everyone to be disappointed or too downhearted, T72 is not even nailed yet. There's a lot more model watching to do until we have an exact idea whats going to happen. In modeling terms thurday/friday is a long time away.

[BLAST FROM THE PAST]

Intersting ECM...16th onwards it shows the LP diving south from our NNW and we become cyclonic. The timing seems about right as I said the other day don't be suprised if the block doesn't hold beyond the 14th. It gives way because it retrogrades so far NW and that is the correct signal. This cold spell will be pretty ok BUT I said and still believe that the coldest part of winter has been and gone and this spell won't match January but it will be cold to very cold at times.

BFTP

[TEITS]

I do feel some require a dose of reality.

For starters this won't be a classic E,ly because frankly I joined this forum in 2004 and I still haven't seen one. So what is a classic E,ly you may ask? well for me a classic E,ly is when you have a huge pool of sub -20C uppers in the continent with around -15C in the UK. The positioning and orientation of the block maintains these very cold uppers over several days.

Make no mistake for some people the week will be just dry, sunny, cold. During the weekend we may actually find temps rise slightly as the HP moves NW. However its what happens after this thats uncertain.

[Thundery wintry showers]

Still some critical differences between the GFS and the Euro models, with the Euro models bringing in more of a pronounced NE flow and less of a strong HP over the north-west, which would promote more precipitation for eastern areas and also the cold air getting further west.

I still think the GFS may be overdoing the high pressure like it did back in January, although there is some evidence of backtracking towards the GFS on the UKMO/ECM.

[MR EXTREMES]

Freezing the fish in the northern Med! I wouldn't take too much notice of this GFS run,it does seem out of line with the general model guidance upto 144hrs.

something i did notice on this mornings met office charts it does look like the high is sinking,

but if it shifts again torwards greenland this maybe will help prolong the cold for a little longer,

there does however show troughs on the thursday friday charts but exclusively for the southeast only,

which is i might say a massive change from lastnights countryfile forecast.

i got a bad feeling this is turning into another nightmare output run things not going smoothly.

indeed also cold does seem to be heading into europe with us getting the much more marginal stuff,

looks like more model output to watch before we get our answer.

but i do agree things do seem to be progressing more quicker which could work in our favour or maybe not,

its hard to call right now.

[Southender]

Hmmmm. Not sure what to make of this run.

I think being realistic, we have to take anything shown after +72 with a pinch of salt.

Edited February 8, 2010 by LeighShrimper

[TEITS]

Even at +36 the 06Z GFS has the HP too far S compared to the 06Z NAE.

http://www.wetterzentrale.de/pics/Rtavn361.png

http://expert.weatheronline.co.uk/daten/proficharts/en/nae/2010/02/08/basis06/euro/prec/10020918_0806.gif

0Z/06Z GFS F.I illustrates why beyond this weekend is uncertain.

Edited February 8, 2010 by THE EYE IN THE SKY

[Guest]

something i did notice on this mornings met office charts it does look like the high is sinking,

but if it shifts again torwards greenland this maybe will help prolong the cold for a little longer,

there does however show troughs on the thursday friday charts but exclusively for the southeast only,

which is i might say a massive change from lastnights countryfile forecast.

i got a bad feeling this is turning into another nightmare output run things not going smoothly.

indeed also cold does seem to be heading into europe with us getting the much more marginal stuff,

looks like more model output to watch before we get our answer.

but i do agree things do seem to be progressing more quicker which could work in our favour or maybe not,

its hard to call right now.

How far can the high sink since the jetstream is propping it up??

I thought that was usually the problem with our high pressures, that the jet ran over the top (i.e. to the north) and sank them into Europe. Surely this time the high will at worst just sit there since most of the energy is in the southern arm of the jet.

[BLAST FROM THE PAST]

How far can the high sink since the jetstream is propping it up??

I thought that was usually the problem with our high pressures, that the jet ran over the top (i.e. to the north) and sank them into Europe. Surely this time the high will at worst just sit there since most of the energy is in the southern arm of the jet.

Correct, it can't sink too far and IMO the 06z shows its southernmost position....but is likely to adjust a tad further north as it becomes reality. Retrograde NW is the hemispheric movement so adding that all up I think await adjustments north. Like last week with the SW'lies from Cuba which many fell for being the spot on solution and being so far off the mark, and the way winter panned out with sudden changes and adjustments look no further than t96. The SE will get heavy snow by Friday and I wouldn't be suprised if many experinced temps remaining at or below 0c.

BFTP

Edited February 8, 2010 by BLAST FROM THE PAST

[MR EXTREMES]

Even at +36 the 06Z GFS has the HP too far S compared to the 06Z NAE.

http://www.wetterzen...cs/Rtavn361.png

http://expert.weathe...020918_0806.gif

0Z/06Z GFS F.I illustrates why beyond this weekend is uncertain.

i agree it does seem a little quick yesterdays country file had it futher north and there indications where also for it to move north around thrusday/friday with snow forecast to move into wales ni and southwest england.

12 hours later this totally different.

mmmm strange.

[Nick F]

How far can the high sink since the jetstream is propping it up??

I thought that was usually the problem with our high pressures, that the jet ran over the top (i.e. to the north) and sank them into Europe. Surely this time the high will at worst just sit there since most of the energy is in the southern arm of the jet.

Yes, there should be no worries of this block sinking, as the main thrust of the upper flow is under cutting the block, though an eddy in the upper flow off the main jet around the ridge is keeping the block maintained. What we have this week to our west and northwest is a classic omega block whereby the single main jet runs such of the block.

Alternatively you can have diffluent blocks where the jet bifuricates into a northern and southern arm, but these blocks tend to more likely sink when more energy starts going into the northern arm which tips the balance. Here's a good diagram which explains the 2 types of block:

Although the block probably wont sink as it is undercut by the southerly jet, it may shift NW which could allow the PV north of Scandi later this week to shift far enough SW next week to set up an upper low just N or over Nern UK, which could turn things less cold in the far south. But too far off to worry about yet:

[Weather-history]

This is how it could have been if GFS 06z from last Monday turned out correct. Don't think there would have many snow reports for today!