Model Output Discussion 01/09/17

[karlos1983]

1 minute ago, northwestsnow said:

I was expecting something seasonal mid to long term as per Bluearmy post about ex eps, also the beeb monthly talking about colder and drier weather as we go into December- while we have low pressure sinking into Europe it aint going to mild.

http://www.weathercast.co.uk/services/ensemble-forecast.html?eps=london

very few go into double digits from 24th all the way to the end of the graph, big cluster are showing around 5C Max for London, with some considerably lower than that.

Must admit when I looked at the Met O long range, it didn't fill me with excitement, there is a lot of splinters in bums in that outlook. 

[phil nw.]

14 minutes ago, karlos1983 said:

http://www.weathercast.co.uk/services/ensemble-forecast.html?eps=london

very few go into double digits from 24th all the way to the end of the graph, big cluster are showing around 5C Max for London, with some considerably lower than that.

Must admit when I looked at the Met O long range, it didn't fill me with excitement, there is a lot of splinters in bums in that outlook. 

Yes quite a chilly set karlos,seasonal rather than deeply cold would imagine further north would be quite wintry at times though.

The current NH pattern looks like evolving towards a rather cold mobile pattern in week 2  via Atlantic ridging and European troughing so plenty of polar air in the mix as the jet comes south.

ECM mean day 9

No signal yet though for a Greenland block just ridging and a north westerly flow over the top.Still as said quite chilly and i dare say hill snow and the odd frost will be on the cards from time to time.

[nick sussex]

Just caught up with the outputs. Nice to see the GFS climb down and overall good agreement on the pattern with a few minor differences in the earlier timeframe.

It looks like the all important upstream troughing over Quebec is going to  stall for a time, sending some shortwave energy into the Atlantic.

The key timeframe is between T144 and T168hrs, the trigger shortwave is circled this needs to run se without any residual energy attachment to the upstream troughing. Once that happens you're in the clear to develop the ridge to the nw:

ECM T144hrs

 

ECM T168hrs

I wouldn't look past T168hrs and worry about the later output, we need to get the trigger shortwave into the more reliable timeframe.

For the timebeing my warning system remains at amber!

 

 

 

Edited November 20, 2017 by nick sussex

[Frosty.]

I'm delighted we are not looking at a relentlessly mild mid / longer range outlook, coldies should get to enjoy at least some cold frosty nights and occasionally wintry ppn with snow on hills and sometimes to lower levels with outbreaks of polar maritime which could veer to arctic maritime at times making it a meridional pattern rather than flat zonal..it could be a cold end to autumn / start of winter!..fingers crossed!

[karlos1983]

My computer was the issue. Works now.

 

[nick sussex]

If you look at the ECM ensemble temps for De Bilt there are more colder options today than on last nights ECM.

Of course if the flow was more northerly then northern parts of the UK would show colder values but as we're beginning to see a trend to topple the ridge towards Scandi  De Bilt can be a decent guide in that situation:

 

 

[cheshire snow]

33 minutes ago, nick sussex said:

Just caught up with the outputs. Nice to see the GFS climb down and overall good agreement on the pattern with a few minor differences in the earlier timeframe.

It looks like the all important upstream troughing over Quebec is going to  stall for a time, sending some shortwave energy into the Atlantic.

The key timeframe is between T144 and T168hrs, the trigger shortwave is circled this needs to run se without any residual energy attachment to the upstream troughing. Once that happens you're in the clear to develop the ridge to the nw:

ECM T144hrs

 

ECM T168hrs

I wouldn't look past T168hrs and worry about the later output, we need to get the trigger shortwave into the more reliable timeframe.

For the timebeing my warning system remains at amber!

 

 

 

Ha ha Nick,just had to scroll back 10 pages to find your warning system.

Any chance you can copy and paste it into your future posts.

C.S

[nick sussex]

1 minute ago, cheshire snow said:

Ha ha Nick,just had to scroll back 10 pages to find your warning system.

Any chance you can copy and paste it into your future posts.

C.S

Yes I'll do that. The amber alert will remain till the trigger shortwave is at T96hrs! We've had some dramatic trigger shortwave dramas in the past, as long as the toughing over Quebec behaves we should be okay but its best to be cautious.

[Mucka]

Interesting output again today, the models are certainly keeping us on our toes with all this flip flopping.

What to make of it?

As far as getting cold air across the UK I think we are looking at two specific phases or bouts of Atlantic ridging.

The first episode at the end of this week looks fairly short lived at the moment but could bring wintry showers to low levels in the North West for a time if the trough feeds in enough cold air but certainly looks like high ground in the North should get some snow.

ECM suggests there could be further developments here though and a stronger ridge than currently modelled could lead to cut off heights around Iceland. (not currently in the output so low probability but worthy of mention) 

The much more likely scenario and the one being currently modelled is for a shortwave low to form SE of Greenland and dive SE leading to a second phase of Atlantic ridging.

ECM/GFS 168 latest output. We can see the low just NW of Ireland on ECM and West of Iceland on GFS.

Also we can see how ECM is clearly more amplified in the Atlantic region but neither have the amplification required to force WAA up the West side of Greenland and build blocking into Greenland itself so the door is open for the Atlantic push in over the block - if correct this can only result in a toppler scenario.

If we get to that stage how the Atlantic ridge topples will determine what pattern builds in FI and it looks as though all options are open there except the Azores high looks likely to remain displaced for a time with further positive height anomalies in the Atlantic sector which suggests further attempts at blocking toward Greenland.

As things stand we have a mixed bag of milder and chilly weather but no cold spell modelled as yet.

On the other hand we are not seeing typical zonal conditions modelled either.

As far as late Autumn early Winter goes this good for coldies, sometimes we simply have no prospects of getting cold polar air across the UK, not even in toppler scenarios, but one can't help feeling this window of opportunity will not remain open through December so it would be nice to eke out a cold spell while the we have an amplified pattern.

 

 

[Nick F]

1 hour ago, karlos1983 said:

My computer was the issue. Works now.

 

Clear there that the ensemble mean supports the high res run on the 00z run, be interesting if the trend continues, because although we expect the operational runs to chop and change, even the ensemble guidance has made some seismic shifts over the past week in the extended range. We've gone from a Euro high signal in the medium range to a Euro trough in the space of a few days' runs.

Seems that the models may be less reliable when the polar vortex is not driving the show, but high latitude blocking and trop waves are. Though there is the chance that the PV will organise itself eventually as we head into early met winter.

Interesting that yesterday's zonal wind forecasts on the Freie Universitat Berlin site are showing a downward slide in 10-30hPa zonal winds after they were showing an uptick - which suggests the strat PV may not be in such a hurry to re-organise and strengthen for now?

The MJO doesn't really seem to be a key player in the troposphere patterns evolving, as it has been in COD since the beginning of the month and looks to remain in COD for a bit or perhaps emerging in low amplitude in various phases according to which model you look at. Even the strat looks increasingly amplified on Berlin at day 10:

Certainly plenty for coldies to be optimistic about looking at the signals coming from various medium range pointers ... for now.

Edited November 20, 2017 by Nick F

[mountain shadow]

2 hours ago, phil nw. said:

 

ECM mean day 9

No signal yet though for a Greenland block just ridging and a north westerly flow over the top.Still as said quite chilly and i dare say hill snow and the odd frost will be on the cards from time to time.

Hi Phil, bit of a learning question here, but what would a Greenland block look like on these charts? This appears to show above average heights from the mid Atlantic right across the Greenland ice shelf and into the pole.

Is it just that the above average height anomaly is not high enough to get a proper block?

Cheers 

[phil nw.]

49 minutes ago, mountain shadow said:

Hi Phil, bit of a learning question here, but what would a Greenland block look like on these charts? This appears to show above average heights from the mid Atlantic right across the Greenland ice shelf and into the pole.

Is it just that the above average height anomaly is not high enough to get a proper block?

Cheers 

That's right.The red shows above average pressure up there against climatology but if you follow the isobars(black lines)they show roughly the wind direction.Still plenty of energy flowing south of Greenland.

In wztl form compare next to it with a Greenland high from Nov.2010

   

See how much further north that amplification builds blocking any east-west jet flow forcing it way up to the pole.The core of the strongest +ve anomalies would be much further north over Greenland on the archive chart.As we can see a much different outcome bitter arctic ne winds as i am sure many of us recall.

Height anomaly charts are often a good guide showing for example weaker vortex profiles such we have now but they don't on their own show the actual 500hPa patterns.They just indicate whether pressure is higher or lower than normal for the time of year. 

Edited November 20, 2017 by phil nw.
spelling

[Mucka]

weather front bumping into the cold air could mean rain turning to snow on Northern flank this weekend?

Certainly a sharper trough than 06z with a more Northerly component.

UKMO also backing the pattern West and sharpening compared to previous output

today's 12z and yesterdays compared - a good trend

Edited November 20, 2017 by Mucka

[frosty ground]

3 minutes ago, Mucka said:

weather front bumping into the cold air could mean turning to snow on Northern flank this weekend?

I noticed that, Elevation will probably be needed thou ?

Edited November 20, 2017 by frosty ground

[karlos1983]

not a bad UKMO +120 chart

Probably flatten/topple by 144 I'd imagine 

Edited November 20, 2017 by karlos1983
typo

[frosty ground]

2 minutes ago, karlos1983 said:

not a bad UKMO +120 chart

Noooooo, i cant post images again 

[Connor Bailey Degnan]

Significant snow event north of the low this weekend? Certainly possible. If the gfs and ukmo 12z came off disruptive snow on higher ground in the north. 

 

Thereafter, frequent snow showers piling into more northern and western regions.

Encouraging signs. 

 

Happy coldie here.

[Cheshire Freeze]

Snow showers packing into NW areas here (including mine)

I can dream!

[johnholmes]

That's right.The red shows above average pressure up there against climatology but if you follow the isobars(black lines)they show roughly the wind direction.Still plenty of energy flowing south of Greenland.

Not surface isobars, the chart is for 500 mb, about 18,000 ft, so they are contour lines. Yes the lines do show the predicted direction of the 500 mb flow.

Sorry if I sound a bit pedantic.

 

Edited November 20, 2017 by johnholmes
spelling

[weirpig]

8 minutes ago, CreweCold said:

Snow showers packing into NW areas here (including mine)

I can dream!

Well if this comes off quite a few will see lying snow . Altitude I still think will be key. But what a nice little upgrade on the 12 z  also a lot more ridging  into Greenland after the northerly moves along on this run 

Edited November 20, 2017 by weirpig

[frosty ground]

8 minutes ago, Connor Bailey Degnan said:

Significant snow event north of the low this weekend? Certainly possible. If the gfs and ukmo 12z came off disruptive snow on higher ground in the north. 

 

Thereafter, frequent snow showers piling into more northern and western regions.

Encouraging signs. 

 

Happy coldie here.

But will it re build after......? Previous runs have shown a 2nd Northerly and the Ensembles do back this up.

[phil nw.]

1 minute ago, johnholmes said:

That's right.The red shows above average pressure up there against climatology but if you follow the isobars(black lines)they show roughly the wind direction.Still plenty of energy flowing south of Greenland.

Not surface isobars, the chart is for 500 mb, about 18,000 ft, so they are contour lines. Yes the lines do show the predicted direction of the 500 mb flow.

Sorry if I sound a bit predantic.

 

Fair play John.I should have made that clear,i knew what i meant as i was showing 500hPa charts.

[karlos1983]

GFS looking a lot better in the 144-168 range. Ridging looks better. 

Edited November 20, 2017 by karlos1983

[northwestsnow]

1 minute ago, karlos1983 said:

GFS looking a lot better in the 144-168 range. Ridging looks better. 

Think the jurys out there Karlos- still got those annoying euro heights , they are not helping ..

[Allseasons-Si]

That shortwave has broke off the parent one south of Greenland much quicker one the 12z and therefore heights build quicker,def upgrade