Model Output Discussion 01/09/17

[SMU]

ECM run pretty much as predicted -

very meridional jet- Scandi ridge phases with arctic high & atlantic trough stalls out.

UKMO looks on the money all be it slightly to far west...

[cyclonic happiness]

all this has an air of 2009 at about this time. even the met office updates.................

Edited November 10, 2017 by cyclonic happiness

[stewfox]

6 minutes ago, Steve Murr said:

ECM run pretty much as predicted -

very meridional jet- Scandi ridge phases with arctic high & atlantic trough stalls out.

UKMO looks on the money all be it slightly to far west...

 

But we will get there in the end ? 

Spporting chart attached

[SMU]

Mate that chart looks like rudolfs been photoshopped over the top...

[Frosty.]

Bring on the cold!..an increasingly chilly weekend coming up and then from later next week onwards looks even better on the Ecm 12z with some low thicknesses between 524-528 dam..beats mild southwesterly  zephyrs  anyday! 

[nick sussex]

Talk about making a drama!

The ECM takes an age to fill out that deep low over the UK and is reluctant to move it east se. The GFS has more margin for error as it has the low further east se with a better ridge to the west from early on, this means theres less chance of phasing issues with energy in the Atlantic.

The ECM miraculously goes from underwhelming at T192hrs and shoots off a shortwave at T216hrs from the troughing in the west Atlantic which cuts se and then some temporary amplification upstream helps develop a ridge to the west, by T240hrs the output recovers with a good set up however the route there is akin to flying round a mountain road in the dark with no headlights.

At any moment it looks perilously close to going pearshaped with coldies hopes stuck at the bottom of the ravine. If you want less grey hair and less shredded nerves cheer on the GFS.

The UKMO looks to have gone rogue this evening caught in between two stalls, it wants to go the high sucked north ahead of the Atlantic low route and its upstream pattern departs from the GFS and ECM.

 

 

 

Edited November 10, 2017 by nick sussex

[chrisbell-nottheweatherman]

1 hour ago, mpkio2 said:

 

Regarding the UKMO 12z t144 - looks good to me!   Look at the bigger picture - its just pinned for the low to head SE as the high builds over Scandi and connect to the ridging growing over Greenland. The Low is negative tilted which will allow for it to go under any high that builds in the GIN corridor.

 

Is it necessarily the case that a negatively-tilted trough automatically indicates that the attendant low will slide south of the ridge, though?  If the eastern flank of the preceding ridge contains a powerful streak with a diffluent left exit, cyclogenesis might surely be sufficiently powerful to send the cyclone NE as it exits the jet, thereby dividing or sinking a ridge unless heights are sufficient to overcome the Pressure Gradient Force?  I appreciate that a confluent trough would weaken any low that develops and would be more likely to send that low beneath the block due to the Coriolis Effect sending the low to the right as it exits, but I'm not sufficiently experienced to be able to determine if this is the case or not.

[SMU]

No you cant have a negative tilt on a NW SE axis trough then expect it to move NE ...

[nick sussex]

Reading the earlier NCEP discussion there’s a lot of uncertainty over the USA and Canada with lots of model divergence from next Wednesday . 

They’re unconvinced by how the models are handling Pacific energy which might result in deeper systems towards the east and over the Great Lakes.

Just looking at the UKMO T168hrs that blows up the low shown at T144hrs hrs to the west of the UK but it seems to build a strong ridge to the west of that low towards Greenland at T168hrs . I’m very dubious of the UKMO given the GFS and ECM aren’t on the same page.

 

 

 

 

[Dennis]

gem model 12z

[mpkio2]

8 minutes ago, chrisbell-nottheweatherman said:

Is it necessarily the case that a negatively-tilted trough automatically indicates that the attendant low will slide south of the ridge, though?  If the eastern flank of the preceding ridge contains a powerful streak with a diffluent left exit, cyclogenesis might surely be sufficiently powerful to send the cyclone NE as it exits the jet, thereby dividing or sinking a ridge unless heights are sufficient to overcome the Pressure Gradient Force?  I appreciate that a confluent trough would weaken any low that develops and would be more likely to send that low beneath the block due to the Coriolis Effect sending the low to the right as it exits, but I'm not sufficiently experienced to be able to determine if this is the case or not.

As you say, if the High to the east as a low rides on the Atlantic towards the UK, isn't strong enough, then yes, technically it will push through the High (But only if the Atlantic jet is strong enough!).

But as @Steve Murr points out, if the High IS strong enough, a negative tilted low will slid under the high as sufficient energy rides under it. It can't then change direction and head NEwards.

Theoretically, the next chart on the UKMO should build a high in GIN corridor, as the small high south of GH builds up as the Scandi ridge builds, allowing for a sufficient ridge to build, sending the low south.

All in conjecture of course...

P.S. Someone correct me if I'm wrong in my explanation...

 

[blizzard81]

The ukmo certainly cannot be discounted. However I happen to think it's 144hr chart would be the best route to decent cold thereafter. Pressure would be sucked up through the UK and join up with the Arctic high leading to an east/northeasterly. Very similar in evolution to Jan 47 but obviously nowhere near the deep cold available to the east as back then. 

 

 

 

[tight isobar]

7 minutes ago, nick sussex said:

Reading the earlier NCEP discussion there’s a lot of uncertainty over the USA and Canada with lots of model divergence from next Wednesday . 

They’re unconvinced by how the models are handling Pacific energy which might result in deeper systems towards the east and over the Great Lakes.

Just looking at the UKMO T168hrs that blows up the low shown at T144hrs hrs to the west of the UK but it seems to build a strong ridge to the west of that low towards Greenland at T168hrs . I’m very dubious of the UKMO given the GFS and ECM aren’t on the same page.

 

 

 

 

Yes nick that pacific waa has been blowing up- then reverting on a large scale throughout' modeling of late.

And will be large scale impactual-or otherwise.

[mpkio2]

Anybody got the UKMO t168 chart to post?

Thanks in advance.

[Summer Sun]

4 minutes ago, mpkio2 said:

Anybody got the UKMO t168 chart to post?

Thanks in advance.

[Man With Beard]

1 minute ago, Summer Sun said:

So the mid-Atlantic ridge probably getting up to Scandi ... it's a close call because if the Atlantic low and Scandi low are a little closer, northern heights won't link through Europe and the mother of all northerlies wouldn't be far to the west of the UK

[mpkio2]

13 minutes ago, Man With Beard said:

So the mid-Atlantic ridge probably getting up to Scandi ... it's a close call because if the Atlantic low and Scandi low are a little closer, northern heights won't link through Europe and the mother of all northerlies wouldn't be far to the west of the UK

Yup. Pretty knife edge stuff in that scenario.

Again, IF the high building over GH and Scandi come to fruition, it SHOULD send it under the high.

The UKMO t168 chart shows the low blowing up a little because it has nowhere to go while the GH and Scandy high builds. Puts us in a "No-mans Land" situation with a lot of rain on offer.

Only one possible outcome out of a bucket load at the moment though, so not all too serious at the moment.

16h November is where we might start to see some consistency....

Edited November 10, 2017 by mpkio2

[bluearmy]

Underwhelming extended eps

[mpkio2]

Latest from Gav'sWeatherVids on the upcoming "potential" cold spell and what the models are showing:

NOTE TO MODS: it's still "Model related" seeing how Gav talks about the models and what they're showing

[karlos1983]

Don’t like the UKMO route, screams west based negative to me.

ECM I’m moderately happy with

GFS hello you naughty thing.

so I’m struggling to figure out where the middle ground is right now... 

[knocker]

The anomalies tonight have thrown up a major conundrum which will need to be resolved before one can be reasonably confidant of the later evolution but more on that later.

In the 10 day time frame pretty good agreement.

Upstream we have the twin vortex lobes Russia and N. Canada with the North Pacific ridge linking to a high cell Franz Joseph Land.  The Canadian  lobe is quite active with associated trough orientated SW and SE and also to the trough to the NW of the UK, There is a fairly flat westerly across North America which splits over the east coast due to ridging into southern Greenland with part of the flow going around the top and part underneath, They converge in the eastern Atlantic to basically a westerly flow over the UK. So the percentage play is unsettled with low pressure tending to dominate but the detail that the det runs need to resolve is tricky with the divided energy flows. Temps a little below average

Moving into the 10-15 period and the problems start becoming apparent as the GEFS and EPS disagree. Essentially what is happening upstream is the vortex lobes become far less organized  and the ridging across the pole is disconnected and even tentatively replaced by low pressure  Downstream the GEFS and NOAA are more or less on the same page with ridging into Greenland and a light north westerly flow to the trough in the vicinity of the UK but the EPS has a much flatter pattern with everything a tad further east and by the end of the period the flow is almost zonal and temps about average. It almost if the pattern is poised on hold but at the moment to my untutored eye there is no obvious route to any significant cold  weather.

 

 

Edited November 10, 2017 by knocker

[blizzard81]

35 minutes ago, bluearmy said:

Underwhelming extended eps

This is what I feared this morning. The Arctic high is a very fickle beast. Like a beautiful woman, the opportunity must be seized quickly as she won't be hanging round for long. 

[chrisbell-nottheweatherman]

21 minutes ago, knocker said:

 

Moving into the 10-15 period and the problems start becoming apparent as the GEFS and EPS disagree. Essentially what is happening upstream is the vortex lobes become far less organized  and the ridging across the pole is disconnected and even tentatively replaced by low pressure  Downstream the GEFS and NOAA are more or less on the same page with ridging into Greenland and a light north westerly flow to the trough in the vicinity of the UK but the EPS has a much flatter pattern with everything a tad further east and by the end of the period the flow is almost zonal and temps about average. It almost if the pattern is poised on hold but at the moment to my untutored eye there is no obvious route to any significant cold  weather.

 

 

Presumably this change to a moderate renewal of the PV (or at least reduced ridging in the polar regions) might be partly attributable to Tamara's discussion the other day of changes in the stratospheric wind distributions.  I also wonder whether there's a correlation between the preference for a more meridional flow in the GEFS and the GFS operationals, while the EPS and ECMWF seem to be indicating something rather more zonal?

Edited November 10, 2017 by chrisbell-nottheweatherman

[ANYWEATHER]

Evening All , so to start ,can we see any Mildies in this forum?  Hands up? Cant see any... Probably not because there is not any real mild on the way...A very potent short cold spell this weekend with icy winds and potentially some record breaking frosts during Sunday into Monday morning for this time of year....it warms up to average and then a very cold of air by next weekend....and the trend continues with some potentially stormy cold conditions at T+240  , a very split vortex displayed by the outer time frame from gfs and ecm .......Interesting Reading....There is certainly a Fight in the Artic....

[bluearmy]

Eps AO/nao combo now bottoming out around -2 before recovering to neutral by end week 2. The heady days of -4 not seen for several runs now.