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phil nw.

Model Output Discussions 06z 04/11/16

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6 minutes ago, IDO said:

You do realise that for this cold pool to effect the UK there will have to be strong movement west between now and T94, and that ship has sailed a few days ago. There is no retrogression forecast and that UK high has been modelled to sink SE for many runs. We are within the reliable so this is very doubtful to change.

I think the story has moved on from that missed cold shot to what follows from the next Azores pulse of WAA in the Atlantic from around D6?

 

 

Personally I'm not absolutely convinced on your comment re the ship sailing. All we need is the low dropping from Greenland to come south and disrupt against the block rather than riding it over the top and sinking it. We see this all the time. Not saying it will happen but if we saw any type of undercut then it may well be enough to drag colder uppers closer and certainly the dew points will be low anyway especially off a cold continent. So to have a snow event with a shallow low coming up against the high I actually don't think we're that far from.

  The Azores I think will move northwards but not necessarily be a negative and may pump warm air much further north towards Greenland aka gfs but as ever time will tell.

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7 minutes ago, nick sussex said:

More drama upstream! GFS doesn't phase the Greenland low with the one exiting Newfoundland, the UKMO does. And these differences are at T120hrs.

The differences at that stage mean completely different evolutions past that point. Putting that aside even the UKMO re-amplifies the flow upstream at T144hrs.

Indeed, Nick, and that delay allows a new HP to form around Iceland.

gfs-0-210.png?12

That has ramifications upstream AND downstream cutting off the LP to the south of the British Isles.

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I can't post pictures but that is a cold looking chart at 240, not a big block over Iceland but some very cold air into Scotland.  If that low in the atlantic stalls, which it is doing it looks good.  240 out though so no confidence, just nice to watch being modelled.  There is a decent low pressure in Spain too, this is good news and could lead to a great FI.

Edited by Ali1977

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Lovely 12z +240

gfseu-0-240.png?12gfseu-1-240.png?12

 

EDIT: Oh my 252 come to me please lovely icelantic high

gfseu-0-252.png?12

 

Edited by SN0WM4N

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The latest from NCEP extended discussion:

GUIDANCE STILL SHOWS THE LARGE SCALE PATTERN TRANSITIONING FROM
PROGRESSIVE AND RELATIVELY FLAT MEAN FLOW TOWARD A SLOWER MOVING
AND AMPLIFIED REGIME WITH A DEEPENING TROUGH OVER THE CNTRL U.S.
WHILE MEAN RIDGES BUILD OVER THE ERN PAC AND WRN ATLC.  WITHIN
THIS AGREEABLE EVOLUTION FROM THE MEAN PERSPECTIVE THERE ARE
CONSIDERABLE UNCERTAINTIES FOR INDIVIDUAL BUNDLES OF ENERGY/PSBL
INTERACTION IN THE DEVELOPING MEAN TROUGH... AFFECTING THE FCST
FOR WHAT COULD BE A BROAD AREA OF ACTIVE WEATHER OVER THE
CNTRL-ERN STATES DURING THE FIRST HALF OF NEXT WEEK.  THERE IS
ALSO SOME SPREAD FOR A LEADING SYSTEM AFFECTING THE NORTHEAST.
EXISTING DIFFS HAVE A LESS PRONOUNCED INFLUENCE ON THE FCST OVER
THE WEST.
 

That change upstream is good news but its where we see the jet buckle in the Atlantic that's crucial as to whether the UK is on the cold side of that.

Edited by nick sussex

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Couldn't make it up

gfsnh-0-252.png?12

Bitterly cold air flooding in from the N/NE

BUT we don't get a sufficient undercut 

gfsnh-0-288.png?12

Edited by CreweCold

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7 minutes ago, Severe Siberian icy blast said:

Personally I'm not absolutely convinced on your comment re the ship sailing. All we need is the low dropping from Greenland to come south and disrupt against the block rather than riding it over the top and sinking it. We see this all the time. Not saying it will happen but if we saw any type of undercut then it may well be enough to drag colder uppers closer and certainly the dew points will be low anyway especially off a cold continent. So to have a snow event with a shallow low coming up against the high I actually don't think we're that far from.

  The Azores I think will move northwards but not necessarily be a negative and may pump warm air much further north towards Greenland aka gfs but as ever time will tell.

I think you may be on the right track. Azores high pressure moving northwards to Iceland and cold air on the move south across the UK!  Lovely FI shaping up! And cold air back into Central Europe by t300. 

 

 

gfs-1-288.png

gfs-1-300.png

Edited by Seasonality

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And there we have it, from nothing much to one of the best chart of the season so far in 3 days.  Ha, crazy days,  Lets not get carried away though.

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2 minutes ago, Ali1977 said:

And there we have it, from nothing much to one of the best chart of the season so far in 3 days.  Ha, crazy days,  Lets not get carried away though.

I would not want to rule it out but only one GEFS on the 06z run was even close to the 12z op run and with UKMO going another route and GEM following what we get at T240 from the GEM is:

gem-1-234.pnggem-0-240 (1).png

So hopefully GFS op is onto something as the alternative will not be palatable to many!

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Ha ha! Big knob of -16 850hpa dangling down at 336h.

 

gfs-1-336.png

Edited by Seasonality

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The previous cross-model-agreement at t144 on the 0z's of GFS/UKMOGEM has all but been shattered and FL lowered down again on the current 12z's. :closedeyes:

GFS 12z t120:
gfsnh-0-120_xes0.png

GEM 12z t120:
gemnh-0-120_zsp9.png

UKMO 12z t120:
UN120-21_gbg9.GIF

Again, they all look the same on the broad-scale of things, but the devil is in the details! :diablo:GFS allows for better amplification in the atlantic, whereas both GEM and UKMO don't:

GFS 12z t192:
gfsnh-0-192_zpw3.png

GEM 12z t192:
gemnh-0-192_ilw5.png

UKMO 12z t144:
UN144-21_bzy5.GIF

Just need to wait and see what the ECM has to say!

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4 minutes ago, gottolovethisweather said:

And I haven't heard any complaints about the UKMO

Not seen any praise either because too me it's a poor run tbh. Can see the Atlantic coming back eventually with that run seeing as there is no amplification whatsoever

Im very skeptical about the GFS runs when it comes to amplification and even more so after the infamous Greenland high fail but it shows what could happen if things fall into place.

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Just now, Geordiesnow said:

Not seen any praise either because too me it's a poor run tbh. Can see the Atlantic coming back eventually with that run seeing as there is no amplification whatsoever

Im very skeptical about the GFS runs when it comes to amplification and even more so after the infamous Greenland high fail but it shows what could happen if things fall into place.

The UKMO run is actually fairly decent going forward from day 6..compare it to the GEM and they're night and day upstream...with the UKMO being fairly amplified across Canada.

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3 minutes ago, Geordiesnow said:

Not seen any praise either because too me it's a poor run tbh. Can see the Atlantic coming back eventually with that run seeing as there is no amplification whatsoever

Im very skeptical about the GFS runs when it comes to amplification and even more so after the infamous Greenland high fail but it shows what could happen if things fall into place.

Completely agree, Ecm needs to be good tonight before we can have any confidence, whatsoever. interesting model Watching times ahead!

Edited by Connor Bailey Degnan

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I think what we want to see is no middle ground solution otherwise you could end up with the GEM which to be frank is a pile of crxp!

If the Newfoundland low is going to phase with the Greenland one you want it done quickly, for this reason the UKMO at T144hrs is passable as its started phasing at T120hrs, much depends on how much ridging we can get into Greenland as the Canadian high is shunted a bit further east ahead of that amplifying central USA trough.

The GEM phases those lows later and then the amplification upstream puts the UK on the wrong side. So we want either the GFS solution which keeps a lobe of high pressure between the lows or at worst the UKMO.

 

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Some encouragement on the GFS 10 day chart but as with this upcoming spell we need to get high pressure further NW for any sustained wintry blast.

With all the background signals I felt we could achieve that but unfortunately upstream has proved faster and flatter than expectations resulting in a UK high rather than something further NW, not bad for late Autumn though.

Perhaps this next attempt, should it materialise will fair better?

Long way to go, first thing is to see it repeated and backed by the ensembles and other models come on board with the sharpening of the long-wave pattern in FI.

Edited by Mucka

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A Fairly decent 12z overall me thinks

 

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It really is knife edge stuff regarding early December.

I think the best we can hope for is an early blast of winter, 2 or 3 days of well below average temps with snow.

Following on, probably turning milder before maybe unleashing a beast, well atleast I hope.  Let's me optimistic :)

gens-21-1-216.png

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The Op is out on it's own a little at 240, there are some interesting GEFS members though.  For giggles, we have an actual Northerly hurricane on P15.

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Plenty of dry weather over the next week or so giving everywhere a chance to dry out

Cx4hvHeXgAQUrRl.jpg

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15 minutes ago, Singularity said:

What's really struck me today is that there's a continuing signal for the pattern to try and re-amplify in 2nd week of Dec regardless of what happens with the early-Dec attempt. Indeed such a signal remains for the foreseeable, as much as it can be hard to assess from the GFS/GEFS runs given the trouble it has resolving jet stream disruption/tight meandering in lower-res (past +240 hours).

The better efforts from GFS tend to leave us under a large amplified ridge that's trying to build poleward, during which time the lower vortex looks to be under a new wave of attack (usual caveats apply!). This suggests to me that the extreme model drama may continue for at least another fortnight, because even as we (finally) resolve next week's potential, there will be a new round of perhaps greater potential (given better tropical forcing - but stratospheric is awaiting at least a little clarification) coming into view.

With this in mind, I strongly advise not getting too hung up on what goes on with respect to next week, else you  may have little sanity left to face up to what happens afterward :shok:

I'm not going to lie - the extreme model volatility is proving strenuous for me as well, despite my inherently cautious approach.

 

Yes 12z GFS ensembles starting to get on board with blocking trying to take hold again in Atlantic sector between day 10 and 15, much more encouraging set than recent efforts even if there is no obvious cold signal.

I took a step back myself after model fatigue was creeping in and it looked like there was nothing of interest likely to develop until week 2 of December but now here I am again.:nonono:

Hopefully those cold ECM members in this mornings ensembles will have a few new friends later tonight but would also be nice to see a sharper trough/ridge/trough solution develop from the Op this evening days 9/10 but I'm not getting hung up on every run - not just yet anyway.

graphe3_1000_265_93___.gif

Edited by Mucka

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