Model Output Discussion - cold spell to end Autumn

[karlos1983]

short ens look encouraging around the 7th/8th.

Op certainly has support

[warrenb]

In fact on the 8th the Op is a middle ground, with the control clearly taking the low further south along with a fair few ensemble members.

[Geordiesnow]

2 minutes ago, Kentish Snowman said:

I don't get the South Westerlies comment when there is a huge high anomaly forecast to remain to our W / NW and in much of the output up to Greenland?  Atlantic influenced possibly but certainly no sign of a South Westerly Bartlett scenario?

Problem is, some runs have hinted height rises near Greenland but initially not favouring us and with a large high over France and low pressure trying to head in our direction we do end up with a mild South Westerly. Whether we can eventually get a proper Atlantic block again remains to be seen. 

[Paul]

Far too many posts being removed for being off topic this morning. If you want to report/chat about the snow today, please head over to the regional threads where there's plenty of that already going on. If you want to comment on members (past or present), then don't hit submit as this is a weather discussion forum. And if you just want a bit of model banter rather than discussion, then head over to the banter thread. 

Those of you intent on just posting what you like in here regardless are ruining it for others and making extra work for the team, so please think before you post.

[karlos1983]

Pick the bones out of that then 

[warrenb]

1 minute ago, karlos1983 said:

Pick the bones out of that then 

Good, trend clearly down, just the OP goes quicker. 

[Chris K]

18 minutes ago, Kentish Snowman said:

I don't get the South Westerlies comment when there is a huge high anomaly forecast to remain to our W / NW and in much of the output up to Greenland?  Atlantic influenced possibly but certainly no sign of a South Westerly Bartlett scenario?

I do get Geordiesnow's point - T+144 does show what occurs after the High starts to sink into Europe and although the 6z GFS Op run still follows this with another cold blast and snow for some areas, it is still too far away and without cross model agreement to be sure which way it will go. For all we know that SCEuro high may end up being more persistent than the 6z was showing, or it could indeed weaken with heights starting to build towards Greenland again. Multiple options still on the table and for now the roller coaster continues. It is interesting to note how the vortex is still not taking up its usual residency and is struggling to organise fully.

Edited November 30, 2017 by Chris K

[nick sussex]

It really is painful. I just wish the outputs could just agree and deliver a decision!

The GFS run is perfectly possible but so is me going on a diet which never happens!

It really is crunch time though. If the shortwave energy splits to the sw with one running east then a good chance of snow, if not its unlikely.

And if by some miracle that does happen then it means the block is stronger and better orientated which will then have a knock on effect as the PV over Canada shoots some more energy across later.

It's possible the jet track will be se into the UK with colder air close by to engage those.

So not to be too melodramatic but the messenger your shortwave to the sw will be your bellwether. The crucial timeframe is between T144hrs and T168hrs.

We're running out of time before the Death Star nukes Planet Coldie!

We need action tonight and no more waffling from the outputs!

 

[frosty ground]

06z
Much better grouping now
0z

And we swing back the other way

[*Stormforce~beka*]

1 hour ago, Summer Sun said:

Left chart is the 850 temps right chart is the 2m max temp

That still makes no sense to me :-D I read it at the top of the charts but I don't know what they mean. Your talking to a dumb ass here ;-)

[Summer Sun]

1 minute ago, *Stormforce~beka* said:

That still makes no sense to me :-D I read it at the top of the charts but I don't know what they mean. Your talking to a dumb ass here ;-)

Hi, You might want to visit the learner area at some point where any questions you have on the different terms can be answered

https://www.netweather.tv/forum/forum/69-learners-area/

[Kentish Snowman in Yorks]

4 minutes ago, Chris K said:

I do get Geordiesnow's point - T+144 does show what occurs after the High starts to sink into Europe and although the 6z GFS Op run still follows this with another cold blast and snow for some areas, it is still too far away and without cross model agreement to be sure which way it will go. For all we know that SCEuro high may end up being more persistent than the 6z was showing, or it could indeed weaken with heights starting to build towards Greenland again. Multiple options still on the table and for now the roller coaster continues.

Completely agree with all of that and definitely multiple options on the table (more cold than mild in my opinion though) hence why I was surprised the call for early December was mild or very mild which can surely only be conjecture at this stage especially as I have not seen a single run giving the UK a sustained South Westerly.

[damianslaw]

2 minutes ago, nick sussex said:

It really is painful. I just wish the outputs could just agree and deliver a decision!

The GFS run is perfectly possible but so is me going on a diet which never happens!

It really is crunch time though. If the shortwave energy splits to the sw with one running east then a good chance of snow, if not its unlikely.

And if by some miracle that does happen then it means the block is stronger and better orientated which will then have a knock on effect as the PV over Canada shoots some more energy across later.

It's possible the jet track will be se into the UK with colder air close by to engage those.

So not to be too melodramatic but the messenger your shortwave to the sw will be your bellwether. The crucial timeframe is between T144hrs and T168hrs.

We're running out of time before the Death Star nukes Planet Coldie!

We need action tonight and no more waffling from the outputs!

 

Good post - yes likely developments all hinge on where energy is transferred into the jetstream, if it maintain a split profile, with equal amounts going into both the north and southern arm, then the GFS 6z output is perfectly plausible, with a marked temp gradient over the UK and the trough forced on a NW-SE path, hence heights will quickly ridge NW behind and we are then exposed to another northerly reload. Less of a split then the trough is more likely to anchor west-east and heights are then unable to ridge NW sufficiently to allow the northerly, but it would probably still be a north-south divide, with cold and possible snow in the north.

The models can't get a proper handle on split jetstream setups, this will be a case of waiting until the very near timescale, there are fine margins being played here, and the potential outcome will be very different as a result, i.e. mild/very mild wet atlantic fest, or a cold/very cold possible snowy battleground set up with the cold quickly winning out. All this at the 144hr timeframe, plenty more runs needed. 

[nick sussex]

I'm wondering whether we're seeing a result of the re-invigorated MJO.

It's interesting that this has come just as the La Nina is weakening which normally allows for less interference.

For those that followed the very in depth discussion from New Hampshire state forecast last night the forecaster is becoming quite melodramatic today and does touch on the MJO.

Its a long read but worth it if you like a mix of techno babble and some Hollywood type over the topness!

Winter is coming. Step back to the present, deep exchange ongoing
over the N Atlantic and W Europe. Highly amplified, a wall is in
place. Nothing abating upstream, the Pacific jet continues to pump
mid-level energy across the CONUS through the zonal flow. Bottling
up, one after another, across the Central N Atlantic, the blocking
wall retrogrades from 30W to 60W longitude over the weekend into
early next week. Slowed to stopped flow upstream, no where to go,
the pattern amplifies, energy becomes displaced around the N pole,
especially as mid-level disturbances jam up across E Canada. S draw
of Arctic air magnified via S shear courtesy of amplified H5 ridging
over Western N America, aided perhaps via MJO contributions.

The jam up over E Canada, going into the following weekend, attention will be
needed upon additional mid-level disturbances as they rotate through
the amplified ridge-trof flow spread across the CONUS. Looking for
sub-tropical connections coincident with strong dynamics and robust
curvature associated with any trof amplification across regions of
baroclinicity that`ll aid in storm development, this as Arctic air
continues to spill S rearward, especially over the N Central CONUS.
It`s behind the cold front that undoubtedly the NE CONUS finds
itself on the cold and dry side of the envelope towards late week
with a potential brush of winter-weather outcomes well N/W as low
pressure develops and deepens over E Canada. Bottled up, we must
watch for additional energy rotating through the amplified pattern,
if there are any storm implications for our region. However, in
evaluating mean ensemble guidance, it`s possible the plug is pulled
across the N Atlantic allowing zonal "escape" flow E by the weekend,
the downstream wall potentially having broken open.

Not sold on the late period 30.0z EC just yet. Considerable spread
in ensemble guidance and a lot of moving parts that are 6 to 10 days
out, low confidence in the forecast further out in time.

So a lot of uncertainty there, the zonal escape flow suggests we might see more mobility by next weekend but the issue is the jet track into the UK. The AO is expected to stay negative which means a better chance the jet will track more south.

NOAA update their December forecast tonight so it will be interesting to see their thoughts as that will effect us in Europe.

Edited November 30, 2017 by nick sussex

[karlos1983]

4 minutes ago, nick sussex said:

I'm wondering whether we're seeing a result of the re-invigorated MJO.

It's interesting that this has come just as the La Nina is weakening which normally allows for less interference.

For those that followed the very in depth discussion from New Hampshire state forecast last night the forecaster is becoming quite melodramatic today and does touch on the MJO.

Its a long read but worth it if you like a mix of techno babble and some Hollywood type over the topness!

Winter is coming. Step back to the present, deep exchange ongoing
over the N Atlantic and W Europe. Highly amplified, a wall is in
place. Nothing abating upstream, the Pacific jet continues to pump
mid-level energy across the CONUS through the zonal flow. Bottling
up, one after another, across the Central N Atlantic, the blocking
wall retrogrades from 30W to 60W longitude over the weekend into
early next week. Slowed to stopped flow upstream, no where to go,
the pattern amplifies, energy becomes displaced around the N pole,
especially as mid-level disturbances jam up across E Canada. S draw
of Arctic air magnified via S shear courtesy of amplified H5 ridging
over Western N America, aided perhaps via MJO contributions.

The jam up

Sounds like that could have been written by none other than our very own @tight isobar 

Edited November 30, 2017 by karlos1983

[nick sussex]

2 minutes ago, karlos1983 said:

Sounds like that could have been written by none other than our very own @tight isobar 

I thought you were going to say me!

I have been known to become quite melodramatic at times. Normally the film analogies get wheeled out when the outputs are beginning to get on my nerves !

[karyo]

16 minutes ago, nick sussex said:

 

NOAA update their December forecast tonight so it will be interesting to see their thoughts as that will effect us in Europe.

I will look forward to that.

[phil nw.]

Yes we are getting close to crunch time for the models to finally decide on when and if we get another cold shot around 6-8th December

Looking at the overall pattern we see the vortex still very disturbed with the Atlantic jet split and buckled.Of course this makes for much uncertainty as the upstream Canadian trough ejects those lows into the Atlantic.It's the plotting of these that is clouding the issue.

Day 4

The main indicator that keeps us in the game for cold though is the ongoing -AO signal with the weakened pv

while this profile continues then the jet is always likely to be forced further south than it's normal zonal position.We as ever need that bit of luck next week so that it buckles enough for us in the UK to be on the north side of any battleground between the polar and sub tropical air.

 

I think these potential battleground patterns are the most interesting Winter setups as every chart is eagerly studied as it churns out.

[Derecho]

OK so I haven't posted my summaries just because the output is so uncertain and its difficult to say what will happen after T144, there is a lot going on but I'll do my best to summarise recent developments (!).

So a short while ago we had seemingly strong support for retrogression of the high to the West of the UK, which now looks almost certain not to happen. The key point is here at T+69:

The problem                                                The result

When the flow to the key region is broken up by a disturbance (red box), we get a sinking high over Spain instead. 

This is a hinderance, no question about it but whether we get a delay in the cold northerly or mild SW'lies remains a major uncertainty.

The key thing to look out for is an advection of warm uppers to the region highlighted in the red box mentioned earlier, it is absolutely critical.

One thing to look out for is the SLP over Greenland prior. Those that start building 1050mb+ offer potential, like the 06z GFS. I think UKMO would fall just short of the mark and be more like the ECM.

With that we can then develop a delayed northerly and push the SW'lies away from the UK. This also depends on the position of low pressure to the west of the UK. If we get it just right a snow event would be in the offering with cold northerlies following behind. This is shown by the GFS:



If the Greenland high is too weak then the mild Atlantic air wins out and the northerly doesn't make it to the UK AKA ECM.



Though we still get a more subdued toppler northerly following

Further afield we also face a potentially reawakening North Atlantic given the cold air outbreak over the continental USA. We need strong Greenland heights to divert the energy towards the Eastern USA instead of the far NE Canada. Here in December 2010 (upper) we can see the block holds firm and weakens the energy from a cold air outbreak. ECM on the other hand offers much less (lower).

 December 2010, block forces US cold to E/SE USA, low pressure gets stuck and pumps warm air to the key region
 ECM, US cold allowed to push NW, reinvigorating the jet stream


Overall the cold spell for next week is in major trouble and offers a forecasting nightmare because the effects of small features are huge. In addition to this its Greenland that this cold spell now really hinges on and we know how difficult this region is to model. ECM and UKMO look bad in my opinion, GFS can salvage some decent cold. My interpretation is we should keep expectations low till this process reaches T72 - T96 but it's not too late to write off the cold spell.

UKMO 5/10 - Potential still there but a return to mild weather likely
ECM 4.5/10 - Only offers a brief northerly later for our efforts, a poor run but its tiny issues that are determining outcomes here
GFS 7.5-8/10 - Much better and coldies still have hope to cling on to

Hope this clarifies thing for confused members.

Edited November 30, 2017 by Quicksilver1989

[Frosty.]

Just my opinion but the weather models so far today currently for next week look a right dogs dinner with a mixture of cold, mild, wet, windy, dry, sunny, showery..the colder air favoured the further north you are..not easy for forecasters with the high degree of uncertainty.

Edited November 30, 2017 by Frosty.

[terrier]

Well after reading the latest met update it seems they favour the ecm solution. With mild wet and windy further south. And colder further north. So it would seem the ecm could be on the money again. Looks like we are back to the realms of FI for a possible cold and wintry northerly. 

[weirpig]

Hopefully mods will keep this here. But it's a response from fergie answering my previous tweet  looks very uncertain next week 

Replying to @weirpig and @modernwinter

Yes, GFS has been v volatile lately (=again). There's a more pronounced leaning in 00z EC EPS towards Atlantic mobility/cyclonicity increasing, *but* cold phases still likely at times and all in all, a v uncertain medium range prognosis post-Tues, let alone further out.

[frosty ground]

5 minutes ago, terrier said:

Well after reading the latest met update it seems they favour the ecm solution. With mild wet and windy further south. And colder further north. So it would seem the ecm could be on the money again. Looks like we are back to the realms of FI for a possible cold and wintry northerly. 

Not sure thats correct, it reads like the Met Office model with depression crossing the center of the UK.

[Frosty.]

3 minutes ago, weirpig said:

Hopefully mods will keep this here. But it's a response from fergie answering my previous tweet  looks very uncertain next week 

Replying to @weirpig and @modernwinter

Yes, GFS has been v volatile lately (=again). There's a more pronounced leaning in 00z EC EPS towards Atlantic mobility/cyclonicity increasing, *but* cold phases still likely at times and all in all, a v uncertain medium range prognosis post-Tues, let alone further out.

It does sound a bit cr*p for the south unfortunately as things stand. Perhaps becoming colder at times further north.

[karlos1983]

Meto Updates can be as fluid as the models at times, not to mention very sit on the fency cover all bases. 

They too are pretty uncertain in the medium/extended as are we. So to say that they are going with this mornings EC is probably wide of the mark.