Winter Model Discussion 18Z 5/2/13 onwards.

[chionomaniac]

Right a new thread for the 18Z GFS.

Will it bring another new trend or will it edge closer towards the UKMO and ECM.

Let's hope so.

Remember to keep on topic, no bickering or trolling and please try and justify your comments with relevent charts where appropriate.

And, no lurking in those shadows.......

[johnholmes]

Can someone explain to an old fella what the fuss is about the PREDICTED weather on ONE model at T+240 please?

Why is it expected to validate, why are you arguing/ discussing will there be snow showers?

Just interested in some constructive comments if that is possible before the pub run which of course is ALWAYS dismissed UNLESS it shows cold!

Edited February 5, 2013 by johnholmes

[snowking]

No it's not, it's a term for when the wind has temporarily gone in one direction after a frontal clearance, which is all what we are looking at here. There is no reason for shower activity. People are looking at blue on the chart and a continental source and jumping to the wrong conclusion.

Or alternatively Ian perhaps people are looking at the modelled upper air temperatures of -10c:

Over sea temperatures of around ~ 6-7c

Along with a decently strong flow:

And thinking hmmm....looks like a suitable thermal gradient for the 'C' word to me...

Here's a link showing you, in vivid detail, the C word:

http://en.wikipedia.org/wiki/Convection

SK

[Long haul to mild]

Can someone explain to an old fella what the fuss is about the PREDICTED weather on ONE model at T+240 please?

Why is it expected to validate, why are you arguing/ discussing will there be snow showers?

Just interested in some constructive comments if that is possible before the pub run which of course is ALWAYS dismissed UNLESS it shows cold!

The chart in question was actually at T144 as the low clears into the continent and is similar on the UKMO and ECM. The GFS doesn't show an Easterly at that point so we can't even use the precipitation charts to see what it thinks!

However, I do appreciate the probable futility of trying to predict precipitation 6 days out!

[Timmytour]

Ian

There is a word the Greeks came up with decades ago, it's called pseudo

Ala pseudo easterly.

Can't we call it a faux easterly?

Well I've let go of the hand of the GFs now and am walking slightly in front ot it. But i can't abandon it all together. If, and it's a big IF, we get the cold in 9-10 days time then it has been there for that one. If, and it's a smaller if now, we get a wintry winter this wekend, there's no denying ECM has been far ahead.

Honest....i want to get on board with the excitement.but just can't yet. but this time tomorrow, if the ECM is still there and the GFS is still tiptoeing closer towards it, me and the GFS are going to be "on a break"

[johnholmes]

The chart in question was actually at T144 as the low clears into the continent and is similar on the UKMO and ECM. The GFS doesn't show an Easterly at that point so we can't even use the precipitation charts to see what it thinks!

However, I do appreciate the probable futility of trying to predict precipitation 6 days out!

my apologies typo error and not checked before I posted. Your comment about GFS is very valid which is in part why I asked the question.

[weather eater]

Can someone explain to an old fella what the fuss is about the PREDICTED weather on ONE model at T+240 please?

Why is it expected to validate, why are you arguing/ discussing will there be snow showers?

Just interested in some constructive comments if that is possible before the pub run which of course is ALWAYS dismissed UNLESS it shows cold!

I wonder whether it’s possible to prove that any 240hr chart has ever verified or even come close. Has anyone got any verification stats for 240hrs, my guess is they would be a pointless exercise and a waste of money to produce?

Just seen Johns mistake but hey it’s a valid question.

Edited February 5, 2013 by weather eater

[Nick F]

First post in here, and a bit of a beginner's question, but here goes. Have been looking at all these cold charts and reading everybody's posts re. snow and easterly winds etc, yet daytime temperatures are set to remain 3 or 4 degrees above freezing quite widely across the UK throughout? Now I know that these forecasts are based on GFS output (I think), but should the ECM be the model that verifies what kind of daytime temperatures would we be looking to experience across the country? My model reading skills aren't high enough to interpret the ECM showings and equate this to ground temps

Thanks in advance to anybody who answers, and apologies if it is a stupid question....

12z ECM would probably be colder at the surface than 12z GFS early next week as the slider low sinks into France. ECM has a stronger east/northeasterly Mon-Tuesday and lower 500mb geopotential heights (cold pooling) than GFS.

Think we need to see how the flow evolves once the slider low sinks SE before we can worry about temps. Greatest chance for snow looks to be towards the east when the slider comes down and afterwards - as the east will be closer to the coldest air.

Although there's a lot of support from the EPS for milder air to move in from the west mid-week next week, I think there's still chance that we may well see another trough disruption to the west similar to the one this weekend - as the models perhaps underesimate the strength of the cold blocking at the surface and the higher heights aloft to the NE.

Edited February 5, 2013 by Nick F

[Bristawl Si]

The chart in question was actually at T144 as the low clears into the continent and is similar on the UKMO and ECM. The GFS doesn't show an Easterly at that point so we can't even use the precipitation charts to see what it thinks!

However, I do appreciate the probable futility of trying to predict precipitation 6 days out!

Plus, the Sunday/Monday 'event' has been progged for a couple of days now by one of the models and the rest are quickly following suit. Devil in the detail still, at this juncture but it seems highly likely that a fair swathe of the country will be 'hit' come Sunday eve/Monday.

[Long haul to mild]

Can't we call it a faux easterly?

Well I've let go of the hand of the GFs now and am walking slightly in front ot it. But i can't abandon it all together. If, and it's a big IF, we get the cold in 9-10 days time then it has been there for that one. If, and it's a smaller if now, we get a wintry winter this wekend, there's no denying ECM has been far ahead.

Honest....i want to get on board with the excitement.but just can't yet. but this time tomorrow, if the ECM is still there and the GFS is still tiptoeing closer towards it, me and the GFS are going to be "on a break"

You might be wanting the number of a good divorce lawyer!

I have been dismayed by the recent performance of the GFS, it only very very slowly amends its output to match the other better performing models. It's like a teenager that goes into a sulk when it knows its wrong but takes a few days before it starts talking to anyone again, by which time it's in a much better mood

[johnholmes]

I wonder whether it’s possible to prove that any 240hr chart has ever verified or even come close. Has anyone got any verification stats for 240hrs, my guess is they would be a pointless exercise and a waste of money to produce?

many moons ago I did something along those lines but looking at the upper air pattern NOT the surface. Some decent results and again my checks fairly recently using the anomaly charts to T+240 and a bit beyond prove that there is some ability to get the upper air fairly correct on about 70% of the time. I have never tried it for the surface and I doubt the % figure would be anywhere near what I got for the upper air pattern.

[lorenzo]

Or alternatively Ian perhaps people are looking at the modelled upper air temperatures of -10c:

Here's a link showing you, in vivid detail, the C word:

http://en.wikipedia....wiki/Convection

SK

Think

may have been looking at this other link http://en.wikipedia.org/wiki/Comedian

10 day verif charts do exist..

Although actually finding 2 charts the same from T+0 to what they were 10 days ago I imagine would be nigh on impossible.

[Long haul to mild]

my apologies typo error and not checked before I posted. Your comment about GFS is very valid which is in part why I asked the question.

No problem John, when the debate started I eagerly went to the GFS charts to check its opinion but only found a much weaker feature with no residual Easterly, which ruined my hopes of being able to prove my theory that there would be instability in the flow!

Still, if we give GFS a couple more days it will have probably caught up by then........

[Gael_Force]

Where is the last thread? - wanted to catch up on earlier discussion.

[Blackjack10]

12z ECM would probably be colder at the surface than 12z GFS early next week as the slider low sinks into France. ECM has a stronger east/northeasterly Mon-Tuesday and lower 500mb geopotential heights (cold pooling) than GFS.

Think we need to see how the flow evolves once the slider low sinks SE before we can worry about temps. Greatest chance for snow looks to be towards the east when the slider comes down and afterwards - as the east will be closer to the coldest air.

Although there's a lot of support from the EPS for milder air to move in from the west mid-week next week, I think there's still chance that we may well see another trough disruption to the west similar to the one this weekend - as the models perhaps underesimate the strength of the cold blocking at the surface and the higher heights aloft to the NE.

Thanks for the answer, appreciate it! So odds are that we will see temperatures a few degrees cooler than those currently forecast, as charts home in on the finer details nearer the time... Fingers crossed the cold pool can fight it out through next week!

[davehsug]

Where is the last thread? - wanted to catch up on earlier discussion.

Seconded, I usually catch up but the last thread has disappeared.

[Cheshire Freeze]

Seconded, I usually catch up but the last thread has disappeared.

Thirded, looks like it's been deleted

[That ECM]

Just got in from work and looked at the ECM and said "get in" out loud. Mrs thinks I have gone mad. Not sure why she needed that for confirmation though. Fantastic, lets hope it looks like this for the next few runs and I can shout get in just to reconfirm her thoughts.

Love the the talk of 30 cm etc. I would take 6 cm here. The beauty of living on the south coast.

[Mark Neal.]

Where is the last thread? - wanted to catch up on earlier discussion.

Can't find it either. Any chance of it being put back up just got in from work and want to catch up

ECM a cracker, been a good winter for snowfall here so far, but winter is still to run!

[Wayneywoo]

Where is the last thread? - wanted to catch up on earlier discussion.

Seconded, I usually catch up but the last thread has disappeared.

Here ya go guys: http://forum.netweat...s/page__st__900

Oh...err....I just went back in my browser and went "back" in to the old thread but copying the link for you guys hasn't worked

Edited February 5, 2013 by Wayneywoo

[Panayiotis]

Just got in from work and looked at the ECM and said "get in" out loud. Mrs thinks I have gone mad. Not sure why she needed that for confirmation though. Fantastic, lets hope it looks like this for the next few runs and I can shout get in just to reconfirm her thoughts.

Love the the talk of 30 cm etc. I would take 6 cm here. The beauty of living on the south coast.

Ha exactly what I said!

The PV on the 18z is considerably weaker compared to the 12z,, and heights have already linked up with the russian high at 42hrs....

Edited February 5, 2013 by Panayiotis

[I remember Atlantic 252]

Can't find it either. Any chance of it being put back up just got in from work and want to catch up

ECM a cracker, been a good winter for snowfall here so far, but winter is still to run!

its on the home page for me, bottom left

[Paul]

Old thread is back, we just hid it for a bit for a quick tidy up

[snowking]

A sign of the times

Last Nights FAX for 12z Friday:

And todays:

That occlusion shifted a fair way west, reflecting the overall trend of the day

SK

[OldMetMan]

Hi folks,

Some interesting similarities right now with the cold spell last month although the current evolution is somewhat different.

Although we are now getting Arctic air flooding S over us, it's not what I would call a "proper" northerly, I would prefer to call it an "eventual" northerly, happening as LP gradually transfers NW/SE pulling in the cold flow behind it. As such, they tend not to last long in my experience as the upper flow over the N and central Atlantic is too flat. For examples of "proper" northerlies try December 1967 or February 1969.

However, the models seem to have been trying for a few days to set up with an easterly, especially the ECM, which in its latest run as a significant HP over Scandinavia.

At 500mb, there are some similarities to what happened in January. The Canadian vortex has moved further E, pushing out into the Atlantic, and an upper ridge seems to be trying to form ahead of it, not very successfully as yet but there are signs that it could. Overall, the hemispheric flow is fairly flat but that can quickly change as we know.

As far as the other models are concerned, there has been a lot of uncertainty as to how the Atlantic systems will behave after this northerly moves away, with some suggesting disrupting short-waves running SE. It seems quite possible with the European upper low amplifying as the current cold air spreads SE.

Normally, with this kind of evolution I would tend to dismiss it for the purposes of significant cold over the UK but after what happened last month, with a fairly weak 500mb blocking pattern, I don't think it would be wise to do so!

I shall be watching to see if we get increasing heights near Iceland, maybe even an upper high cell, if none such happens then we seem to be heading for a rather indeterminate spell of chilly weather. However, if the block returns, we could be in for more significant snow.

Tricky one this but worth following!