Model output discussion - winter proper underway

[Chesil View]

Just now, blizzard81 said:

Well, the meto got the forecast for the end of December very wrong. It was gunning for blocking but it looks like the opposite is going to happen. 

Really I thought it was the 17th today not the 31st

[Ravelin]

7 minutes ago, blizzard81 said:

Well, the meto got the forecast for the end of December very wrong. It was gunning for blocking but it looks like the opposite is going to happen. 

Sheesh, talk about jumping the gun. The end of Dec, assuming we're talking the 31st, is nearly 2 weeks away, and only really the GFS to go on at that range.

   

That's the last 4 GFS runs for the morning of the 31st. No real blocking in evidence for us, but such huge differences even within the same model that you'd never bet on any of them to actually be correct.

[bobbydog]

5 minutes ago, blizzard81 said:

Well, the meto got the forecast for the end of December very wrong. It was gunning for blocking but it looks like the opposite is going to happen. 

they can't have got it wrong if it hasn't happened yet...

 

[Singularity]

  

UKMO and GFS seem broadly similar at this point (day 5) but there is a critical difference; GFS has a LP system departing the Pacific vortex lobe and heading across to the Canadian one, while UKMO does not.

  

A day forward and UKMO is doing some fine vortex assaulting via the EPO ridge, while GFS has 'rounded-off' the northern limits of it while also keeping that limit further south.

The more rounded ridge shape sends cold to the SE or even ESE rather than SSE or S, increasing the thermal gradient in the western N. Atlantic with unpleasant consequences unless you're a fan of wind and rain.

If GFS is wrong about this ridge shape then it's making all manner of incorrect suggestions regarding the pattern for late Dec and early Jan this year.

The 'pointier' ridge of the 12z UKMO and 00z ECM runs sets us on a path toward a renewed split of the vortex with one lobe over N. America and the other over Scandinavia or Europe (or a bit of both). The 00z ECM was almost getting there as of day 10.

Hopefully we are seeing a case of GFS' typical NE'ward bias with LPs resulting in that Pacific low behaving in a way that won't actually transpire. In fact the 12z has two potential cases of this happening in quick succession so there's a lot to play for!

 

Best outcome I can think of going forward from day 6 - for the quickest cold weather results - would be if we had something akin to UKMO but then the LP to the N. of Florida engaged with the cold air pushing south toward the SW States and deepened into a large low while stalling out over the NE'rn US.

 

 

The CFSv2 shows us that it's unfortunate we're not seeing more amplification retained days 5-6 i.e. akin to the 00z GFS of a couple of days back; it's the combination of that and a very pointy Pacific ridge (VPPR to save future writing space... ) that leads to such an interesting outcome by days 8-9. Sometimes the model is good fun .

[LRD]

Even without blocking it looks like the polar vortex might threaten the UK from Christmas. Jan 1984-esque

If we can't have 'classic' cold I'd love to see some of those runs - that have the PV close to or over us - verify to see what that would actually produce on the ground (rain, snow, gales - at least it'll be some weather to talk about). With, hopefully, the Az/Euro High pushed way south and south west too

[bluearmy]

1 minute ago, LRD said:

Even without blocking it looks like the polar vortex might threaten the UK from Christmas. Jan 1984-esque

 

The vortex isn’t anywhere near the uk ?

just deep lows passing 

incidentally, Exeter have been predicting a more mobile flow after Xmas for a few days now 

[LRD]

Just now, bluearmy said:

The vortex isn’t anywhere near the uk ?

just deep lows passing 

incidentally, Exeter have been predicting a more mobile flow after Xmas for a few days now 

The modelled purples aren't part of the PV?

Yes, the modelled mobile weather from next weekend shouldn't be a surprise as it's been touted for a while

[bluearmy]

16 minutes ago, LRD said:

The modelled purples aren't part of the PV?

Yes, the modelled mobile weather from next weekend shouldn't be a surprise as it's been touted for a while

They may have been once upon a time but they are long since warmed out by the ocean 

check out the thicknesses 

Edited December 17, 2017 by bluearmy

[LRD]

Just now, bluearmy said:

They may have been once upon a time but they are long since warned by the ocean 

check out the thicknesses 

Noted. Cheers BA

[bobbydog]

16 minutes ago, bluearmy said:

They may have been once upon a time but they are long since warmed out by the ocean 

check out the thicknesses 

which raises an interesting question- when is a PV not a PV?....

[SilverWolf]

47 minutes ago, blizzard81 said:

Well, the meto got the forecast for the end of December very wrong. It was gunning for blocking but it looks like the opposite is going to happen. 

Wow if you’re using tarot cards can I book an appointment? Won’t be looking at the models again as they seem to be changing their mind every 24-48 hours... 

[Cheshire Freeze]

Just now, SilverWolf said:

Wow if you’re using tarot cards can I book an appointment? Won’t be looking at the models again as they seem to be changing their mind every 24-48 hours... 

Do they?

Not from where I'm sitting. The modelling has been fairly resolute for a while now of low heights engulfing Greenland and other areas to our NW. We've seen little to suggest any HLB will take centre stage any time soon around our locale (other than slight hints of Scandi heights in the 14 day timeframe on some ensemble perts and the odd operational). 

The issue is (and this was alluded to as a risk a couple of weeks back) we have lost the amplified trop pattern that was keeping us afloat. Without the amplification in the N Atlantic sector, we're effectively staring down the barrel of a trop PV becoming more and more organised over the next few weeks; the Pacific ridge isn't enough to promote the necessary perturbed nature of the trop vortex. 

We have been in this position year after year, and 90% of the time there is one outcome once the trop pattern becomes uniformly flat- so let's hope we don't get to that stage. If we do, I'd suggest we would need a SSW to get us out of it.

Day 10 GEM shows us where we DON'T want to be heading

[January Snowstorm]

At the moment it seems that all routes lead to a mild zonal spell of weather. Not exceptionally mild but will feel so after the recent cold spell.

For me a white Christmas is more about the week leading into new year so all isn't lost yet. Of course a technical white Christmas day still has a chance albeit a slim one.

 

[ACCOUNT DELETED]

1 hour ago, Daniel* said:

I’m seeing nothing overly mild on GFS 12z.

I keeping hearing about next week being very mild I’m not seeing it myself largely near average I’d say with frost risk not going away, perhaps milder further north. I think some of our more northern members with some elevation *boom* might be a tad excited - on what’s being shown, I however am not. 

I agree, they say for here in Porthcawl near Swansea, it could reach 13-14C by Tuesday. I can't see that happening myself tbh 

[SilverWolf]

1 minute ago, CreweCold said:

Do they?

Not from where I'm sitting. The modelling has been fairly resolute for a while now of low heights engulfing Greenland and other areas to our NW. We've seen little to suggest any HLB will take centre stage any time soon around our locale (other than slight hints of Scandi heights in the 14 day timeframe on some ensemble perts and the odd operational). 

The issue is (and this was alluded to as a risk a couple of weeks back) we have lost the amplified trop pattern that was keeping us afloat. Without the amplification in the N Atlantic sector, we're effectively staring down the barrel of a trop PV becoming more and more organised over the next few weeks; the Pacific ridge isn't enough to promote the necessary perturbed nature of the trop vortex. 

We have been in this position year after year, and 90% of the time there is one outcome once the trop pattern becomes uniformly flat- so let's hope we don't get to that stage. If we do, I'd suggest we would need a SSW to get us out of it.

Day 10 GEM shows us where we DON'T want to be heading

Ok fair enough and apologies I was being flippant. To be honest my knowledge is basic and hardly ever post here unless a question. My statement about them changing has more to do with the interpretations of others on here with much more knowledge. There seem to be disagreements, though perhaps more longer term (i.e. around Xmas time and after). I’ll shut up now and retreat to regional thread! 

[Cheshire Freeze]

Just now, SilverWolf said:

Ok fair enough and apologies I was being flippant. To be honest my knowledge is basic and hardly ever post here unless a question. My statement about them changing has more to do with the interpretations of others on here with much more knowledge. There seem to be disagreements, though perhaps more longer term (i.e. around Xmas time and after). I’ll shut up now and retreat to regional thread! 

There's only one way you'll learn and that's by getting involved  

Your input is just as valuable as anyone's 

Has taken me 8 years on here to get up towards an 'experienced' member and I'm still learning more and more from the more technical minded on here!

[swfc]

Wow what a diff a week makes weather and mood wise.Possibly GP or Tamara could post and steady the ship.Any looks like a fired up pv is looking to build ete  after a week of milder weather.Anyonewith altitude may do well if the said spell transpires and any move north of west may spring a few suprises.Nothing cast in stone tbh so maybe a few twists and turns yet giving the current volatility in the output

Edited December 17, 2017 by swfc

[Weathizard]

1 minute ago, swfc said:

Wow what a diff a week makes weather and mood wise.Possibly GP or Tamara could post and steady the ship.Any looks like a fired up pv ete is all but nailed on after a week of milder weather.Anyonewith altitude may do well if the said spell transpires and any move north of west may spring a few suprises.Nothing cast in stone tbh so maybe a few twists and turns yet giving the current volatility in the output

Is there really volatility in the output though? The flat pattern in the models has been consistent for days on end now really.

Normally the ENS suites are where I look for hope in these situations but there's not a huge amount to talk about there either, you know when the models have got bad... even Steve Murr isn't here offering his 'route to cold' 

[swfc]

Just now, Weathizard said:

Is there really volatility in the output though? The flat pattern in the models has been consistent for days on end now really.

Normally the ENS suites are where I look for hope in these situations but there's not a huge amount to talk about there either, you know when the models have got bad... even Steve Murr isn't here offering his 'route to cold' 

I take your point but the 6zgfs this morning did show be it late on signs of more variable block ete around the uk.12 z has virtually nothing and looks a big switch in a short time period.Imo any change in an area of either low or high pressure could swing things in a short space of time.Granted its not the favoured outcome but who nos over the next set of runs

[Daniel*]

We love you NAVGEM we do oh, NAVGEM we love you... probably the pick of the bunch. Strangely out of kilter with other models regarding the PV monstrosity over Greenland. 

 

[feb1991blizzard]

35 minutes ago, bobbydog said:

which raises an interesting question- when is a PV not a PV?....

IMO, you cant have a displacement event with the PV then setting up over the UK, you can in the US, type in to Google 'Jan 1985 arctic outbreak', this is because there's a landmass from the USA all the way North right to the North Pole, the only way you can have the PV hitting the UK is with ridging into the pole (usually Greenland) splitting the PV and sending a chunk of it south like the second cold spell Dec 2010.

[Methuselah]

1 minute ago, Daniel* said:

We love you NAVGEM we do oh, NAVGEM we love you... probably the pick of the bunch. Strangely out of kilter with other models regarding the PV monstrosity over Greenland. 

 

All that's needed now is confirmation from the BOM!

[swfc]

Ecm does look better than gfs at the 168hr mark with a better flow from the north west . also at 192 hours pacific ridge nearly moving into greenland and maybe dissipating the pv!!!

Edited December 17, 2017 by swfc

[northwestsnow]

5 minutes ago, swfc said:

Ecm does look better than gfs at the 168hr mark with a better flow from the north west . also at 192 hours pacific ridge nearly moving into greenland and maybe dissipating the pv!!!

Unfortunately there is a euro high on the way...it looks hopeless.

:-(

[LRD]

4 minutes ago, northwestsnow said:

Unfortunately there is a euro high on the way...it looks hopeless.

:-(

NH profile isn't without interest though