Model output discussion-mid Autumn and beyond

[knocker]

4 minutes ago, bluearmy said:

Humour knocker ..... that was my line from yesterday .......

the extended ens are looking quite meh for coldies .....infact possibly quite balmy if we get the mean trough far enough north ......but can we trust the mean ???

Well as always we can look at clusters later blue but speaking form a purely personal point of view I dislike the map projections, (although of course they are geared for their benefit) and thus I find it very tricky to envisage any trends based over five days. That's always supposing of course there are any.

[bluearmy]

7 minutes ago, knocker said:

Well as always we can look at clusters later blue but speaking form a purely personal point of view I dislike the map projections, (although of course they are geared for their benefit) and thus I find it very tricky to envisage any trends based over five days. That's always supposing of course there are any.

The clusters are intriguing to me ..... they generally seem to switch post day 10 and yet as far as I know, the last eps upgrade brought all members to the same resolution out to day 15.  It’s feasible that the 24 I/o 12 hour difference at that timescale is responsible but I would have thought my brain would have coped with that .......

[bluearmy]

Clusters looks a bit messy ......

 big spread of broad solutions ............

[I remember Atlantic 252]

anyone else concerned about Thursday's potential flooding? GFS been showing washout for days, timed for the day too

[phil nw.]

The Atlantic still seems favourite to win through by the end of next week.

Looking at the eps for Friday's clusters we can see solid agreement. 

No doubt  latest modeling has extended the life of the Scandi.high which a few runs ago appeared to be on the way out by then.This has created some interest in that any breakthrough by the Atlantic may be delayed but latest charts from the GFS06z run still show the change arriving pretty much as expected by the 13th.

 

The other point is the lack of any deep cold getting far enough west to give us a chance of rain turning to snow as the fronts approach.At this stage away from high ground in the far north it doesn't look like we will see any snow  with windflow coming of the Atlantic and dew points above 0c.

The approaching Atlantic lows are indeed initially blocked by the high but it looks like the fronts will eventually cross the country by the weekend.

The Atlantic jet still with plenty of vigour heading towards us.

Edited December 8, 2018 by phil nw.

[phil nw.]

2 hours ago, bluearmy said:

Clusters looks a bit messy ......

 big spread of broad solutions ............

Yes just scanned GFS/ECM ens and any number of scenarios possible Blue.The only thing i could take from them is the probability of a southerly tracking jet and some buckling but where the ridges and troughs will go remains very unclear.

 

I suppose one good thing is no solid sign of the usual westerly pattern that we normally get in December.

[knocker]

Interesting-to look briefly look at the two lows that experience explosive cyclogeness that puts huge pressure on the block as they track a tad further east.

At T68 the second one is just being spawned in the baroclinic zone off the Carolinas and both follow a very similar route on the jet

Edited December 8, 2018 by knocker

[I remember Atlantic 252]

12Z GFS, shorts, flip flops Xmas Day, on this run, just for fun I know

[knocker]

At T144 the ecm has a main low WNW of Ireland with a double frontal structure edging east over the Irish Sean and western Ireland. In the bext 12 hours they do struggle across the UK bringing windy conditions and not a little precipitation. Most of this will be of moderate rain but dew points are quite low so snow where the main front hits the cold a distinct possibility, especially on the higher ground. Obviously this is merely musing at this range.

But whilst this has been going on the next low from the breeding ground is tracking south and further east of the first low and deepening as it swings across southern Britain  If this panned out, which obviously it will not at this range , it would bring heavy rain and gales/.

[Singularity]

 

Regardless of the precise outcome for later next week, it's a fascinating time to observe the models work toward a solution. There's the potential for further unusually large adjustments, due to the fact that the models are not only correcting away from Nina-like to Nino-like pattern configuration, but in doing so are moving troughs away from where they are most able to utilise the higher than usual potential vorticity lent by the stratospheric polar vortex lobe in the Greenland-Iceland vicinity. Mid-late next week, this area approximately spans from due west of the UK and south of Iceland to due north of the UK (accounting for typical offset of vortex boundary between the troposphere and the 30 hPa stratosphere level). Troughs moving into this area become more vigorous and hence more progressive in nature.

So there's a strong positive feedback onto progressiveness error associated with projecting a Nina-like pattern of troughs moving across the UK instead of staying out west; the errors are amplified.

Unfortunately this isn't enough to call a 'blocking high victory' as while a Nina-like pattern is likely to be avoided, the tropical forcing toward Nino-like will become temporarily weaker, and it's not clear whether enough will sustain to force the troughs to stay a good way west of the UK and/or disrupt next week - not even the Thursday one, much as the UKMO 12z has illustrated this evening.

 

Looking further ahead, the anomalously high potential vorticity moves east into western mainland Eurasia, so it will make a huge difference to our weather patterns whether troughs are able to make it over there right away and intensify (keeping the UK pattern flat for a time, then promoting 'backside' - of trough - northerlies) or are forced to track further south and west by a resilient blocking high as it moves toward Greenland (in response to what by then will be increasingly strong Nino-like tropical forcing + the evolving positioning of the stratospheric vortex and anomalous ridge). This will strongly depend on what happens mid-late next week so it's a critical juncture in what we see prior to any SSW impacts starting late this month or early next month.

[knocker]

Continuing with gfs this morning and by Friday it has tracked a less intense low north east and the east over the UK giving quite a wet and windy day,

Quickly followed by a more intense low on saturday bringing strong winds and more rain and some quite warm with temps way above average.

For a time from here there is a shift of emphasis with the subtropical high resurging over western Europe

Edited December 9, 2018 by knocker

[knocker]

Regarding the area of uncertainty the ecm has the block quite strong at 1200 Thursday, so much so the upper trough deconstructs resulting in the front stalling and much of the inclement weather over Iberia with the UK dry but quite chilly in the SE wind.

This more or less remains the case over Friday but the winds are starting to veer southerly as the next frontal system edges in from the west.

The front(s) duly cross the country through saturday and early Sunday accompanied by heavy rain and at this range not worth speculating on any detail involving snow except to say the ecm does have the dew points pretty low.

Edited December 9, 2018 by knocker

[knocker]

I sense that a little Xmas cheer will not go amiss.

[Summer Sun]

Not too bad for the time of year

[knocker]

The gfs this evening in brief (or even briefs given the temp)

A weak front giving patchy rain on Wed

Some trough disruption and more widespread patchy rain on Thursday/Friday

Before the next deep low swings north west of Ireland and the associated fronts bring strong winds and heavy rain over the weekend

Edited December 9, 2018 by knocker

[Methuselah]

Aye Malcolm - there's no need for Sydney to unpack his willy warmer, just yet?

[knocker]

8 minutes ago, Ed Stone said:

Aye Malcolm - there's no need for Sydney to unpack his willy warmer, just yet?

Indeed not Ed, he's out and about and gearing up for the Xmas zephyrs

Edited December 9, 2018 by knocker

[Chesil View]

Well as long as he doesn't mind them Xmas Zephyrs coming from the north he'll fine.lol

[knocker]

The ecm has the trough deconstructing just to the west of the UK on Thursday with some inclement weather tracking east over Iberia but resulting in a  dry and cold south easterly over the UK with temps in the 3-4C range

But Saturday sees the fronts associated with the deep low in mid Atlantic driven across the UK accompanied by heavy rain, possibly some snow on the high ground preceding the front, and strong winds in the much warmer air with temps reaching 13C in the south.

And by the beginning of next week the atlantic is in charge

Edited December 9, 2018 by knocker

[knocker]

God strewth another model thread to encourage the willie wagglers

[Rocheydub]

Just now, knocker said:

God strewth another model thread to encourage the willie wagglers

 Saw it and immediately thought of you!!!

[knocker]

Following on from the short range the ecm runs the cold front though on Saturday giving a very wet and windy day, snow on the high ground in the north, and a marked temp differential by evening. Perhaps around 2 "c in Scotland and 13C in the south of England.

Showers and sunny intervals on Sunday in the fresh westerly but by 1200 Monday another low has developed in the southern quadrant of the Atlantic trough and tracked north east west of Ireland and the associated warm front has done likewise across the UK, Thus more wind and rain but very warm in the warm sector with temps in the 11-12C range which is well above average.

Oh my......

Edited December 10, 2018 by knocker

[knocker]

The EPS continuing with it's recent theme.. Twin vortex lobes Siberia/ N. Canada with weakish Alaskan ridge into the Arctic  Resulting in a strong westerly upper flow to the trough in the eastern Atlantic. Portending unsettled weather with temps around average.

snapshot

 

[Mike Poole]

Well, on the 12z runs, when the Atlantic breaks through, which it will there are some pretty nasty options on the table at T192, main models here:

Three of those look absolutely horrible!

[Summer Sun]

Much milder on UKMO extended