Model Output Discussion - cold spell to end Autumn

[blizzard81]

Just now, northwestsnow said:

Im not concerning myself with mid Dec ...im not convinced the models have next week sorted yet...:)

I take your point but sometimes the models bizarrely enough can be more certain with the extended outcome but very uncertain as to how they arrive there. If feels like we are in one of those situations. I feel we will end up mild by mid December but the question is how we arrive at that point? Will it be preceded by a mid latitude toppler or a cold snap of sorts?

[comet]

43 minutes ago, feb1991blizzard said:

Nick I think the shortwave spoilers occur because the longwave pattern isn't conducive, so the shortwaves will then appear at the wrong time / take the wrong track to deliver UK cold, I think all the pro's say this anyway, that the longwave pattern drives the shortwave pattern, however, please don't change your analytical style as its brilliant - its the best and simplest way to read the charts and understand what needs to happen to deliver UK setups that deliver cold IMO.

Very true. Sometimes though the models make problems that are not really there ie inventing annoying little shortwaves etc that mysteriously disappear on later output or get brushed aside by a longwave pattern conducive to northern blocking. More than happy with this afternoon and evening model output overall and fully expect to see a much improved ecm tomorrow.

[blizzard81]

6 minutes ago, Paul_1978 said:

Are you allowed to post graphs of that?

I can't post them but I am referring to the debilt ens. 

[blizzard81]

7 minutes ago, feb1991blizzard said:

 

 

So after 240, the ridge never gets any higher / more defined than the 240 mean?

Not sure of the specific synoptics. Waiting for the mean to update. 

[cheeky_monkey]

model still showing the pacific ridge breaking through Alaska into the arctic..still keeps cropping up ...something to keep an eye on 

[feb1991blizzard]

1 minute ago, comet said:

Very true. Sometimes though the models make problems that are not really there ie inventing annoying little shortwaves etc that mysteriously disappear on later output or get brushed aside by a longwave pattern conducive to northern blocking. More than happy with this afternoon and evening model output overall and fully expect to see a much improved ecm tomorrow.

GFS - great, GEFS - great, ECM - poor but better than the 0z so heading in the right direction, ECM eps flaky though apparently, I can only see the 240 mean atm though but its average - 5/10

[chionomaniac]

22 minutes ago, snowbunting said:

Can someone  please tell me what is meant by shortwave and longwave is met terms?

 

I must say the GFS looks awesome. Very potent Nly. Wonder which model will prove right next week.  Part of me thinks the ECM as the GFS would cause havoc in the NW. 

You need a grasp of meteorology - try reading this - you will understand a lot more than just shortwaves by the end!

 

http://www.geologywales.co.uk/storms/upthere.htm

[NorthernRab]

1 minute ago, cheeky_monkey said:

model still showing the pacific ridge breaking through Alaska into the arctic..still keeps cropping up ...something to keep an eye on 

I thought we'd all agreed back in 2014 to call it the Aleutian high when it was term of the year?

[cheeky_monkey]

1 minute ago, NorthernRab said:

I thought we'd all agreed back in 2014 to call it the Aleutian high when it was term of the year?

This side of the Atlantic its called the Pacific ridge..like the Azores High

[knocker]

Further to my post above the EPS 8-13 mean anomaly has some ridging in mid Atlantic but much less amplified then the GEFS so no real suggestion of a split flow and thus a straight forward north westerly flow over the UK portending unsettled with temps a little below average.

[Man With Beard]

ECM ensembles are out on weather.us - At D8, massively in favour of North Atlantic ridge / Scandi trough (i.e. northerly for UK). At D10, ensembles are split - probably slightly in favour of the ridge to the west remaining influential - maybe 30% are like the op with ridging to the south and lows over the top.

[Dennis]

this week outlook; great blocking at Atlantic 

Edited November 28, 2017 by Dennis

[Frosty.]

3 minutes ago, Man With Beard said:

ECM ensembles are out on weather.us - At D8, massively in favour of North Atlantic ridge / Scandi trough (i.e. northerly for UK)

wow that's great news,  I'll happily take that considering what the 00z was showing this morning..hope tomorrow's 00z builds on tonight's 12z output!

[Mucka]

32 minutes ago, Penrith Snow said:

First class post well said.

Its the long wave dog that says the short wave rail not the other way round.

The obsession some people have with short wave behaviour is daft, its the long wave pattern that magtsds.

Andy I 

I think that is a little unfair. shortwave phasing can change the longwave pattern dramatically, but yes if the long-wave pattern is stable, be it typical flat zonal or established block, it will dictate the pattern and not any shortwave activity.

We have a perfect example of this with GFS and ECM - GFS longwave dictates tot he shortwaves while ECM shortwaves dictate the later longwave pattern. 

(Should also state that if ECM were more amplified and a little further West at 120 the longwave pattern would likely dictate as with GFS.)

Take 120h, the longwave pattern, jet profile, are much the same.

So how are the longwave patterns so different by 192? (Again it could be argued they are not massively different but just a little later they are, for purposes of this discussion using these)

Because ECM phases the shortwaves which produces a deep Atlantic low 120-144 which then further interacts with the upper trough causing energy push NW and flatten the longwave pattern whereas GFS does not.

The whole angular momentum of Atlantic troughing (upstream) is then completely different to what it would be. (much faster and flatter)

Without those shortwaves existing and phasing it would be a straight route to a solid ridge into Greenland and potent Northerly and prolonged cold spell so how can we say shortwaves don't affect the longwave pattern?

Conversely, as already stated, if the longwave pattern is such that the ridge is already in place then the shortwaves cannot dictate the longwave pattern as they are "trapped" and can only disrupt and likely undercut having far less immediate influence - though they will still influence the pattern given that undercutting could produce a cut off Greenland high while split energy would just maintain an Atlantic block of sorts - quite different longwave patterns with the jet going under and into Europe one way and slitting NW, SE the other. Because longwave patterns are slower to change then the cause/effect of shortwave may not become immediately apparent in a pattern change even where shortwave activity triggers it. (often shortwaves are resolved without dramatic changes to longwave patterns)

It is all about the distribution of energy when low pressure comes up against high pressure and though it is arguable that people tend to be a little myopic when it comes to longwaves and shortwaves, being they tend to concentrate a small area around the UK.

 

 

Edited November 28, 2017 by Mucka

[SMU]

26 minutes ago, cheeky_monkey said:

This side of the Atlantic its called the Pacific ridge..like the Azores High

-EPO ridge

[MKN]

1 minute ago, Frosty. said:

wow that's great news,  I'll happily take that considering what the 00z was showing this morning..hope tomorrow's 00z builds on tonight's 12z output!

Dont read to much into ensembles. They chop and change as quickly as the main output in my experience. 

[feb1991blizzard]

9 minutes ago, Man With Beard said:

ECM ensembles are out on weather.us - At D8, massively in favour of North Atlantic ridge / Scandi trough (i.e. northerly for UK). At D10, ensembles are split - probably slightly in favour of the ridge to the west remaining influential - maybe 30% are like the op with ridging to the south and lows over the top.

Ive searched all through weather.us and I cant find these, can I have a link please?

[tight isobar]

12 minutes ago, cheeky_monkey said:

This side of the Atlantic its called the Pacific ridge..like the Azores High

Alutien/pacific/western seabord...

@ridge all cover it.

Just depends on preference!

[cheeky_monkey]

1 minute ago, tight isobar said:

Alutien/pacific/western seabord...

@ridge all cover it.

Just depends on preference!

well whatever... its worth a watch..where it goes could have a big influence on what happens down stream..ie UK and Europe

[northwestsnow]

Well a couple of fascinating tweets from well respected forecasters suggesting things might be getting interesting for coldies - both appear to be suggesting a locked in -NAO

[Man With Beard]

13 minutes ago, feb1991blizzard said:

Ive searched all through weather.us and I cant find these, can I have a link please?

On the drop down boxes, where it says "master", you'll find the ensembles within this drop down box. It doesn't do 500mb heights but does give surface pressure, so not quite the same.

[Ian Francis]

9 minutes ago, northwestsnow said:

Well a couple of fascinating tweets from well respected forecasters suggesting things might be getting interesting for coldies - both appear to be suggesting a locked in -NAO

do tell

 

[northwestsnow]

Just now, Ian Francis said:

do tell

 

tweets thread 

[winterof79]

1 hour ago, nick sussex said:

Thanks. The longwave gives us the bigger picture but as we know in the UK it’s often at the periphery of the cold , small changes have often bigger effects .

When we see for example a Scandi trough and high to the west the big picture doesn’t show whether the UK had a direct hit of cold or whether it’s too far east.

Globally a few hundred miles isn’t much in terms of the longwave pattern but has huge effects on the weather on the ground for the UK.

So true about how we forget how close we come to severe cold sometimes.2012 being a prime example of severe cold over eastern Europe and didly squat here.

 

[Paul]

Just a quick off topic post (please don't discuss here), the Netweather Winter Forecast is now online