Model output discussion - proper cold spell inbound?

[khodds]

11 minutes ago, geordiekev said:

3600 posts, confused or just devils advocate? Nice contribution to the MO

As you are most likely aware, some members of NW don’t just purely post on the MOD thread... hence the high post count (I don’t post very often due to unhelpful posts like yours... it’s not very welcoming is it?)

back to the regionals I go then....

[Frosty.]

Looking at the GEFS 6z mean, most of the week ahead looks very cold with some inland spots at freezing or sub zero, especially tues / wed and next Saturday so expect plenty of frosty / icy weather and some snow at times too!..beyond the week ahead also indicates below average temps..in other words..cold!

[andymusic]

latest euro 4 in range of Tuesday's event

[WalsallWeather123]

Not much accumulating snow expected by the ICON. A few flurries expected inland on Tuesday but not amounting to anything

[tight isobar]

Below average!!..

And dont be surprised to see further squashing above the line....

@decline

6z london ens.

[Chesil View]

Just now, tight isobar said:

Have a butchers..

Vortex annihilation!!!

DVI2cowVMAEmXz9.mp4..

Massive implications...

@strat warming

Very interesting TI and look how the broken piece of the vortex drops south behind our cold block then heads west. 

[tight isobar]

3 minutes ago, Broadmayne blizzard said:

Very interesting TI and look how the broken piece of the vortex drops south behind our cold block then heads west. 

Exactly!!!?

Edited February 4, 2018 by tight isobar

[stodge]

Morning all

Certainty a variety of opinions and expectations regarding the coming week and so much of it is expectation and managing that. For some winter is about feet of disruptive snow lasting for days for others it's simply about cold, clear, crisp and very frosty weather. I'd love to see a good old foggy frosty anticyclone - ice days in London but no snow.

Never mind, the weather will give what it gives and we take what it gives.

Looking to the medium term as usual this morning and that means St Valentine's Day or February 14th if you prefer - starting with ECM 00Z OP at T+240:

The ECM run is the classic sine wave of colder and milder interludes - indeed, a typical winter outlook. The T+240 chart is typical - pressure low to the NW and building to the SE with a weak HP over southern England and northern France. Could the HP ridge into Scandinavia or will the deep LP near Iceland continue east ? For the British Isles, it's fairly benign for most but with increasing wind, cloud and rain to the far north-west.

GEM 00Z OP at the same time:

Not markedly different. GEM has been dragged kicking and screaming to the upcoming cold spell and maintains a strong Atlantic profile with a 940MB LP over or just to the west of Iceland and a strong deep vortex back toward Canada. Pressure rising over Europe and a SW'ly airflow over the British isles so fairly mild and benign if breezy but the frontal rain is close and a clear transition to colder PM air  on the horizon.

GFS 00Z OP at the same time:

For the normally most progressive of the models, GFS keeps the block and the colder air in situ over northern Europe far longer than GEM/ECM but the Atlantic is closing in with the very deep LP we've seen elsewhere so rising temperatures bringing rain and wind (snow on the front edge) to western parts and probably further east. Further into FI the jet slows and begins to disrupt south or SE offering some teases for cold fans.

GFS 06Z OP at T+240 (6 hours further on):

Very different, A stronger northern arm of the jet but a broad rise of pressure from the Azores through the southern part of the British Isles into Scandinavia so dry and increasingly cold with frosty nights for the south but mild with drizzle or rain further north. Into far FI and mosre eye candy is pressure rises continue as the Atlantic slows to a stop and we get into a colder scene with LP to the south and heights to the north.

GFS 06Z Control at T+240:

Control close to the OP at this point which is always encouraging for model continuity but the evolution from there is different with a large anticyclone setting up to the west of Ireland so nothing particularly remarkable in the outlook with any colder conditions restricted to the far south east.

Of all the morning charts, this is perhaps the most informative of all:

The 10HPA Strat temperature continues to tell the story of a split vortex from next weekend and repeated assault son the vortex remnants as the month goes on:

The GEFS at T+240 also tell a story:

http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=1&ech=240

It's a story of model uncertainty as the month moves on and it's little surprise with the strat developments. It's worth repeating - a split vortex doesn't guarantee us a winning hand but it buys us a seat at the table. The GEFS are sniffing at the possibility of a weakening Atlantic, a split jet (and plenty looking at sending the energy SE rather than NE) and various permutations of HP evolution and orientation many of which would draw colder air to the British Isles.

The other part of the split vortex is the dynamic response which, as we've seen before with Wave 2 warmings, is not to immediately break the vortex but to make it tighter and colder. Tropospherically, we get what might be a counter-intuitive response as the jet fires up and we see the kind of deep LPs we are seeing at T+240 this morning. These can be and have been characterised as "the last hurrah" of the PV but the more immediate impact isn't on the PV but on the jet which slows, weakens and starts to amplify but where that will end up is impossible to know at this time. As the vortex itself begins to displace and fragment and the jet weakens further the opportunity for further amplification offers all sorts of possibilities whether from the north, east or both. 

In summary, whatever the coming week brings or doesn't bring, there will be a renewed Atlantic onslaught going into mid month which will likely see a transient return to milder conditions before the pattern change takes hold and we get what we get which may be cold but may not.

 

 

 

[geordiekev]

34 minutes ago, khodds said:

As you are most likely aware, some members of NW don’t just purely post on the MOD thread... hence the high post count (I don’t post very often due to unhelpful posts like yours... it’s not very welcoming is it?)

back to the regionals I go then....

Sorry, I was just commenting on the fact that someone who was a long time member was taking the P out of some valued posters on here. It's easy to get east/west confused when talking about evolution. Just don't think there's a place for ridicule in the way the post was written. Sorry for any offence

Edited February 4, 2018 by geordiekev

[tight isobar]

18 minutes ago, tight isobar said:

Below average!!..

And dont be surprised to see further squashing above the line....

@decline

6z london ens.

Aberdeen's 6z ens...no prizes for- noting.

Where the colder air is/remains!!!

[khodds]

2 minutes ago, geordiekev said:

Sorry, I was just commenting on the fact that someone who was a long time member was taking the P out of some valued posters on here. It's easy to get east/west confused when talking about evolution. Just don't think there's a place for ridicule in the way the post was written. Sorry for any offence

No worries. I don’t think Jethro was taking the mickey, she just was just confused as we all get on here with the variety of opinions/interpretations of the models.  Same thing happens every year! 

Glad that’s cleared up - sorry I bit back, I read your post wrong ?.

onwards to the 12z.... 

[Matthew.]

41 minutes ago, stodge said:

Never mind, the weather will give what it gives and we take what it gives.

Great post Stodge. I’ve noticed as always we’re looking at 200 miles this way or that way could give us very different outcomes. This expected dive in zonal winds I suppose could force the vortex a little Nw so high p sets up more north of the Uk instead of further south as the Gfs shows

[Frosty.]

Looking at the week ahead, as you can see the GEFS 6z mean paints a predominantly cold / very cold picture with some ice days, very frosty, icy nights and there will also be some snow around, pretty much anywhere across the uk at some point..looking at closer range on the Gfs 6z op, the SE is the sweet spot tonight and tomorrow morning as frequent wintry showers turn to snow giving an inch or two accumulation in places, even sea level could get a covering!..

Edited February 4, 2018 by Frosty.

[Ice Day]

Very interesting from Michael Ventrice this morning:

Quote

This some of the worst model volatility I've seen in a long time; Models diverge in their predicts as early as 5 days out. We are extremely limited in our capabilities in providing an accurate forecast today.

I would assume that the forecasted SSW is creating more than a little chaos for the NWP?  I think more than ever we need to treat anything after 120hrs with much scepticism at the moment (unless it's showing cold when of course it will verify!)

[Snowman.]

12 minutes ago, Ice Day said:

Very interesting from Michael Ventrice this morning:

I would assume that the forecasted SSW is creating more than a little chaos for the NWP?  I think more than ever we need to treat anything after 120hrs with much scepticism at the moment (unless it's showing cold when of course it will verify!)

It's likely due to a multitude of factors right now.

The poor struggle of a weather nothing of real interest for 2 months then BAM! It all comes at once.

Edited February 4, 2018 by SN0WM4N

[mb018538]

I would expect charts like this to start disappearing pretty soon if/when the PV splits....somewhere is going into the freezer, it's just whether we have the lucky lottery ticket!

[Singularity]

What Stodge has posted regarding temporary ‘last hurrah’ of the vortex brings to light the conundrum the models are struggling with; the strat-driven signal for an uptick in zonal winds versus the trop-driven signal for a reduction of via lagged impact in N Atlantic of MJO P7 and AAM climb inc. positive MT.

Both can be underestimated by the models, so human input has its work cut out too.

[nick sussex]

Not sure whats happened in this thread in recent days.

The outputs when rubbish for cold seem to cause a lot of sniping and moaning and then when the outputs are more interesting still sniping and moaning!

Anyway can people just get on, the vast majority are really on the same side, as in liking cold weather and snow.

In terms of the outputs its really not a time to be viewing longer range outputs as a done deal because of the MJO and the upcoming SSW both of which are going to lead to some large changes.

As has already been mentioned in these threads the issue of the PV and what happens in SSW events, you often do see  a temporary re-invigoration of that before it weakens.

The current fight between the MJO trying to re-amplify the pattern and the PV trying to flatten things is what we're seeing play out, hence we've seen these eastwards corrections then back again to more westwards ones.

The PV will eventually be floored as the MJO recruits the SSW and together finish it off!

 

[ICE COLD]

Well Guys and Girls the output is far from boring at min . With a cold week to come here and a SSW predicted, I have a really good feeling we're gonna see some BOOM charts/output in the next few days ?. Nice message from IF earlier on regarding SSW , so at least METO are on board for that . Let the crazy times in the MOD begin ?

[ICE COLD]

3 minutes ago, nick sussex said:

Not sure whats happened in this thread in recent days.

The outputs when rubbish for cold seem to cause a lot of sniping and moaning and then when the outputs are more interesting still sniping and moaning!

Anyway can people just get on, the vast majority are really on the same side, as in liking cold weather and snow.

In terms of the outputs its really not a time to be viewing longer range outputs as a done deal because of the MJO and the upcoming SSW both of which are going to lead to some large changes.

As has already been mentioned in these threads the issue of the PV and what happens in SSW events, you often do see  a temporary re-invigoration of that before it weakens.

The current fight between the MJO trying to re-amplify the pattern and the PV trying to flatten things is what we're seeing play out, hence we've seen these eastwards corrections then back again to more westwards ones.

The PV will eventually be floored as the MJO recruits the SSW and together finish it off!

 

Top post nick . Someone that speaks a lot of sense ??. 

[Snowman.]

The GEFS runs that keep the high in the picture if you will early on re-amplify at D10 leading to an easterly wind direction while dry later on gather pace and form some rather impressive HLB, those flatter are less impressive later on. 

If you want to see something that causes a tingle in the nether region then look at P20 straight up would rival Nov/Dec 2010.

[Rayth]

8 minutes ago, nick sussex said:

 

 

Bang on as usual @nick sussex ! Are the Strat and Trop coupled well at the moment ? Reason I ask is after this potential ( and I say potential as I don’t want to jinx) SSW I’m wondering about the lag timeframe until the effects are felt in the troposphere ? 

Edited February 4, 2018 by Raythan

[tight isobar]

9 minutes ago, SN0WM4N said:

The GEFS runs that keep the high in the picture if you will early on re-amplify at D10 leading to an easterly wind direction while dry later on gather pace and form some rather impressive HLB, those flatter are less impressive later on. 

If you want to see something that causes a tingle in the nether region then look at P20 straight up would rival Nov/Dec 2010.

Could post a pic-of a beautiful woman...

But on this occasion...these will do!!?

mr steve murrs sausage come with double egg n, bacon here!!!?

Edited February 4, 2018 by tight isobar

[nick sussex]

22 minutes ago, Raythan said:

Bang on as usual @nick sussex ! Are the Strat and Trop coupled well at the moment ? Reason I ask is after this potential ( and I say potential as I don’t want to jinx) SSW I’m wondering about the lag timeframe until the effects are felt in the troposphere ? 

The trop response varies . Sometimes the reversal propagates down quickly , it’s also effected by the current state of the AO.

Theres a stronger response in terms of the NH pattern if you’re in a more positive or neutral AO state which does seem logical because you in a sense have more explosive energy.

If you’re already in a negative AO phase you have less energy to play with .

The current state of the AO at onset of the SSW looks around neutral so hopefully a bigger shuffling of the NH pattern.

Edited February 4, 2018 by nick sussex

[Man With Beard]

2 hours ago, andymusic said:

latest euro 4 in range of Tuesday's event

Worth keeping an eye over France too to see if the system over there throws a trough north - November 2010 style