Model output discussion - 5th December 2016 - Into Winter we go

[Daniel*]

Judging by 18z GEFS pour London  

The op looks to have been overly progressive... It is a pretty stark outlier you should be pleased to know, not that it was mild, as indeed Mr Fergusson suggested 850 temps - do not always reveal the true story. You can see some precipitation spikes, therefore I'm wondering the block to w/nw might have more fight in it, by no means is it certain to sink over the UK.

Edited December 27, 2016 by Changing Skies

[AGAL]

1 hour ago, feb1991blizzard said:

The biggest concern of mine is that the 12z's downgraded and although the EC46 sounds great, it was derived from 0z starting conditions, which pumped out a stonking ECM, perhaps the 12z's is the start of the usual downgrades.

How can a model detecting reality that doesn't suit our wishes, be a down grade ? We can program the models to churn out stupendous cold charts,

[AGAL]

1 hour ago, feb1991blizzard said:

The biggest concern of mine is that the 12z's downgraded and although the EC46 sounds great, it was derived from 0z starting conditions, which pumped out a stonking ECM, perhaps the 12z's is the start of the usual downgrades.

Only in our eyes are they downgrades. To the models they are just handles on reality

[AGAL]

5 hours ago, fergieweather said:

PS What is worth noting re UKMO is that the GM isn't modified at Ops Centre beyond T+132. That's considered a reasonable cut-off point for fair medium range steer, in terms of tweaking additional fields such as frontal positions/shortwave elements & associated upper forcing/ppn/cloud cover/ etc.

So what does that mean in terms of weather re: cold or warm

[AGAL]

1 hour ago, Tamara said:

I hope no-one minds me saying so as an ordinary member, but a theme I have been putting forward for some time now (circa 4 weeks) and gets construed at times as "glass half empty"

As stated and reasoned last night, and several times previously, downstream amplification is not assured in terms of being sustained if there is not the latent supply in the atmospheric circulation to ensure it so.

My own eyes continue to be on the GSDM (tropical and extra tropical budgets) and how they are best interpreted with the troposphere/stratosphere relationship - and it is from there that I attempt appraisal of the NWP

 

So what is your forecast for the next 10 days?

[That ECM]

We were teased with the hp drifting ne and not sinking se but GFS and ecm both have it sinking. Some cold weather for the start of the NY and then time to chase the last chart. 

[Whether Idle]

ECM the best at 144 this morning as we head into FI.  Likely the high will sink and the jet ride over the top.  This evenings runs will prove of interest at the 144 juncture.

[radiohead]

ECM ends on a positive note for coldies. 

[Polar Maritime]

The GFS continues to show a very cold weekend with Northerly winds bringing -10/11/12 uppers over a large swathe of the UK with snow showers pushing South. It will certainly feel bitter than of late, In-fact it will feel like Winter.. 

Edited December 27, 2016 by Polar Maritime

[IDO]

What is apparent is that there is a strong signal for Pacific forcing from around D5 right out to D15 on the GFS. This helps promote the omnipresent Azores/Atlantic ridge of this winter; ergo ideal conditions to build pressure north in the Atlantic quadrant. The problem is that the PV remains mobile, shifting sands of lower heights pushing around the NH high latitudes. It looks like this rather than a down tick in the two wave forcing is causing both waves to lose their sharpness and flatten out as chunks of vortex pass north of them.

We keep seeing false dawns, where the models interpret the forcing to split the vortex enough to create a true blocked NH pattern. With little apparent help from strat, top down forcing we are relying on the trop to over power the PV.

The London ens remain below the seasonal average from Sunday till D16 though the op and control remain progressive compared to their members for temporary milder interludes of uppers:

A model nightmare charting the interaction of PV -v- Heights, as we have seen from past model watching, so we can be led up the garden path in such scenarios re optimum winter synoptic's when they show up. Certainly a downgrade in the medium term for those (op), but it remains a cold outlook and so surprises could pop up, and we won't have the lag time if the pattern becomes more conducive to a snowy pattern down the line.

 

[northwestsnow]

Well all things considered and not including that poor gfs0z we are still in the game this morning and further to Ians post some snow potential this weekend.Ecm looks cold, a small milder window then back to cold.Happy!

[West is Best]

GFS0z op out on a limb:

 

 

Lots of spread too:

 

 

 

Edited December 27, 2016 by West is Best

[Ali1977]

The op and ctl have a mild blip which doesn't look correct compared to the ENS, made even more sparing is that they are at different times. A pretty cold set all the same and this Sunday looks particularly cold.

[Newberryone]

Admittedly the change in air mass isn't anticipated  until next Sunday but just by going on the wording of this mornings Met Eireann outlook I can't help but get the feeling they're either being cautious or seeing this potential cold snap as a bit of a damp squib....A very halfhearted affair tbh 

 

 The general outlook is for settled weather for the rest of the week as high pressure (anticyclone) blocks out the Atlantic rain. It is going to get milder too. 
------------------------------------------------------------------------------------------------------------------------------------------------------

Chilly Wednesday night with lowest temperatures around zero to 4 degrees and local frost. 

Thursday: Dry with sunny spells A little milder with highest temperatures 8 to 11 degrees in moderate to fresh southwesterly winds. Mild Thursday night. 

Friday & Saturday: The dry spell is forecast to continue with sunny spells. Mild, blustery days with daytime temperatures of 10 or 11 degrees and not falling below around 8 degrees at night. 

Sunday the 1st January, 2017: A possibility of some rain moving in from the Atlantic.

[northwestsnow]

8 minutes ago, Newberryone said:

Admittedly the change in air mass isn't anticipated  until next Sunday but just by going on the wording of this mornings Met Eireann outlook I can't help but get the feeling they're either being cautious or seeing this potential cold snap as a bit of a damp squib....A very halfhearted affair tbh 

 

 The general outlook is for settled weather for the rest of the week as high pressure (anticyclone) blocks out the Atlantic rain. It is going to get milder too. 
------------------------------------------------------------------------------------------------------------------------------------------------------

Chilly Wednesday night with lowest temperatures around zero to 4 degrees and local frost. 

Thursday: Dry with sunny spells A little milder with highest temperatures 8 to 11 degrees in moderate to fresh southwesterly winds. Mild Thursday night. 

Friday & Saturday: The dry spell is forecast to continue with sunny spells. Mild, blustery days with daytime temperatures of 10 or 11 degrees and not falling below around 8 degrees at night. 

Sunday the 1st January, 2017: A possibility of some rain moving in from the Atlantic.

The colder air will not arrive until sunday but ireland will be less cold than the UK as its closer proximity to the Atlantic high.Thats my interpretation of the irish mets update.

[Newberryone]

1 minute ago, northwestsnow said:

The colder air will not arrive until sunday but ireland will be less cold than the UK as its closer proximity to the Atlantic high.Thats my interpretation of the irish mets update.

That's a very valid point to be fair and one that unfortunately won't over excite some of my fellow cold weather worshippers such January Snowstorm etc  

[Nick L]

Most of the EC 00z ensembles keep the cold theme going right to the end, with the mean generally 2c or so below normal. The graph follows a very similar theme to the GEFS.

Edited December 27, 2016 by Nick L

[carinthian]

Morning all. This forecast chart from UKMO for NY Eve shows how the timing and clearance of the advancing cold front could be a problem on NY Day , especially over Southern England. Clearly there is a thought of a wave formation working up from north of the Azores along the cold front. This can have two effects in the forecast : a) timing of clearance with possible delay b) amount and type of precipitation, thinking of rain turning to snow as colder air under cuts . Obviously these charts can be dropped or change the expected synoptics for the period but looking at the strength of the Euro high its fairly likely of some sort of delay in clearance. Meanwhile ECM reverts back to a colder set up again. Not sure where the UKMO is going after 168t, maybe toppler set up with further chances of renewed Arctic attacks as we go into later forecast period as indicated along the lines of GFS.

C

[Newberryone]

Glad to say the Irish Met service have perhaps decided to join the party...Here's their latest update as issued just within the last 10 min

 

 Saturday night/Sunday the 1st January, 2017: A possibility of some rain moving in from the Atlantic followed by colder weather but details uncertain. 

[snowice]

20 minutes ago, Newberryone said:

That's a very valid point to be fair and one that unfortunately won't over excite some of my fellow cold weather worshippers such January Snowstorm etc  

By 2 January Ireland is under-11 uppers according to Gfs,patience required 

Edited December 27, 2016 by snowice

[shaky]

27 minutes ago, carinthian said:

Morning all. This forecast chart from UKMO for NY Eve shows how the timing and clearance of the advancing cold front could be a problem on NY Day , especially over Southern England. Clearly there is a thought of a wave formation working up from north of the Azores along the cold front. This can have two effects in the forecast : a) timing of clearance with possible delay b) amount and type of precipitation, thinking of rain turning to snow as colder air under cuts . Obviously these charts can be dropped or change the expected synoptics for the period but looking at the strength of the Euro high its fairly likely of some sort of delay in clearance. Meanwhile ECM reverts back to a colder set up again. Not sure where the UKMO is going after 168t, maybe toppler set up with further chances of renewed Arctic attacks as we go into later forecast period as indicated along the lines of GFS.

C

Hi mate!!any idea of how the 168 hour chart is looking today!ecm has gone colder this morning but we really do need a better gfs 06z!

[Sky Full]

Well the models are all in general agreement for a cold interlude at +144 and at least that's almost in the reliable frame?

ECM:

 

GFS:

 

GEM:

  

UKMO:

Now I have heard it said that you need to get the cold in first before anything else can happen.  Don't know where I read that, as it happens, but it makes sense to me.....

 

[carinthian]

3 minutes ago, shaky said:

Hi mate!!any idea of how the 168 hour chart is looking today!ecm has gone colder this morning but we really do need a better gfs 06z!

Hi Shaky, yes the N Atlantic charts at 168t for what they are worth do show a difference. The  ECM hres better has the colder flow cold a bit longer and UKMO indicating a toppler, all a bit of a reversal from last nights same charts , however they change regularly so not set in stone as it were. Overall I think we on the right track to a colder start to the NY.

 C

[sorepaw1]

If this chart was to pull off for around new years day my neck of the woods could have travel disruption and some of the snow showers moving well inland. 

Possibly getting into central and some southern areas.

Still to early to pin point exact areas.

But something to bear in mind. 

[stewfox]

whats happened to Fergie post ?

On my Mobile but not here. Did he say too much ?

Edited December 27, 2016 by stewfox