Model Output Discussion - 21st - 28th November

[johnholmes]

the combined charts above supplement my post a short time ago.

It shows the combined ECMWF-GFS 500mb anomaly chart for 10 days time (on the left) and the NOAA version from last evening.

[SP1986]

I've never seen a set of ensembles with as little agreement as shown in the 0z set, taken with so much seriousness before, they're actually a mess with little agreement, if there is a trend it follows closely to the average.

There is however a trend to something cooler, but looking at the charts, should this pattern actually evolve (which of course isn't certain), it'll probably be part of a fast moving, mobile pattern - for example a mix of colder, and milder zonal intervals.

I'm certainly not seeing a persistent cold spell developing, but what I am seeing, is a backing away from the persistent mildness that we've had recently.

Certainly a transition to perhaps more interesting weather; strong winds, showers and potentially thundery showers on Pm airmasses.

[bluearmy]

the combined charts above supplement my post a short time ago.

It shows the combined ECMWF-GFS 500mb anomaly chart for 10 days time (on the left) and the NOAA version from last evening.

getting interesting john. that NOAA cpc chart is raw NAEFS output and that model has been rock solid on maintaining the troughing just west and ridging becoming apparent again to our east in a couple weeks time. given that ecm ens are now consistent on bringing the trough into a much more favourable position for cold plus some upper ridging towards greenland, tonights forecaster modified charts will be strongly anticipated.

[peterf]

well i think it's time to renew the full subscription.i'll probably need a refresher course to rember how to work it lol.

[SP1986]

06z looks like textbook cool zonality to me, although whether you can say it's zonality is another question, there are certain more low waiting in the Arctic interior to swoop down, but the run of mild zonality is cut off by high pressure over NE Canada-E USA.

Most likely won't be cold enough for snow outside of Scotland/on hills, and frosts will be limited. I'm not sure whether this setup would deliver lots of cool rain or showers, it looks fairly flat in terms of what it's doing over Britain, but I'm not sure personally how 6z would ride out in terms of weather.

[Iceaxecrampon]

Widespread snow showers above 200-250m across much of western parts, good snowfalls in the lake district, pennines and highlands likely.

Nice - I will be out and about this weekend (above 200m) The fells (or me for that matter) aren't exactly in condition yet for anything silly but its a start.

Although Monday to Wednesday look better..........

Edited November 21, 2011 by Iceaxecrampon

[Strider]

GFS showing awful consistency atm. The 6z is a cooler scenario with larger heights over Greenland and a slider low bringing in an easterly towards the end, before reverting to type...

Edited November 21, 2011 by Strider

[ITSY]

GFS 06Z shows a Scottish Blizzard (with temps down to -12!) and heavy snow for hills of northern England, Wales and N.Ireland. The frustrated majority in low lying England will be left on the average side of cold with rain. A good run on the whole however (given the dullness of late) and snow aplenty for northern altitudes. Let's hope this develops into something countrywide. ECM please.

[November13]

Slight chance of wet snow in Central Scotland. No sign of extreme or even sustained cold!

[SP1986]

I think the issue with this run in terms of getting persistent cold, is at the juncture where the high pressure is weakest, you have a train of developing low pressure knocking on the door, so the high pressure over Canada will be consistently weakened, and it tries to regain strength, but in that particularly scenario it's difficult to maintain any blocking over that area. What really needs to happen is that the Greenland High comes into play, and it's just not at the moment, it's the plateau high that is providing next to no support for other developing highs.

This is symptomatic of a +NAO I believe, but overall it's a pattern change, and whilst it potentially may not be super cold, like last year, it's still a change from a very persistent pattern.

I do imagine the southwesterlies will recommence later into December, but a fair bit of joy for ski slopes, and members living on the higher hills?

[kold weather]

06z is decent for higher ground in the north though outside of that its still going to be cold rain we can expect. Still its an evolution towards a more seasonal pattern. I suspect if that came off as SP sauid we'd be into a mix of milder and cooler spells but nothing too sustained.

0z ECM is certainly interesting though the angle of the main upper low isn't quite good enough to give us the cold air bottled up straight away.

[No Balls Like Snow Balls]

I think the issue with this run in terms of getting persistent cold, is at the juncture where the high pressure is weakest, you have a train of developing low pressure knocking on the door, so the high pressure over Canada will be consistently weakened, and it tries to regain strength, but in that particularly scenario it's difficult to maintain any blocking over that area. What really needs to happen is that the Greenland High comes into play, and it's just not at the moment, it's the plateau high that is providing next to no support for other developing highs.

This is symptomatic of a +NAO I believe, but overall it's a pattern change, and whilst it potentially may not be super cold, like last year, it's still a change from a very persistent pattern.

I do imagine the southwesterlies will recommence later into December, but a fair bit of joy for ski slopes, and members living on the higher hills?

I do believe there are a few sheep and goats that are members and will welcome the news.

[Iceaxecrampon]

Slight chance of wet snow in Central Scotland. No sign of extreme or even sustained cold!

All short lived - a taster of sorts - as the cold gets shoved away after midweek by a possible 998 low - but I am not looking at that chart too much

[weathe20]

A change is afoot which is more interesting in terms of variants of weather, but appart from that nothing of interest. Looks zonal and very much like normal UK winter conditions.

[BLAST FROM THE PAST]

Ok, an interesting 06z following the 18z. I say again that nothing is set model wise yet, far from it and a very good post from Great Plum as the models are now dealing with a pattern change and need to decide where this goes hence why I said to see how models develop as the week progresses. Even more interest with JH's imput. Colder weather coming? I maintain yes. Will it bring lasting cold? Still not on that train, but at least change is afoot.

I was very interested in Mark Vogan's update. The period 15-20 Dec is a time to look out for and the pattern evolving seems to be heading on his lines, also heading very nicely on RJS lines too.

BFTP

Edited November 21, 2011 by BLAST FROM THE PAST

[Frosty.]

You keep quoting 60f, you may live in a little tropical micro climate but here in the NE most days have been nearer 50 than 60, just a little above average. Yesterday it reached 45f.

I keep quoting 60f because most of southern britain has had several days of 60f+ this november and even scotland has hit 13c on quite a few occasions. The gfs 06z has enhanced the chances of colder zoneality for northern britain and for increasingly cooler zoneality further south so the signs are improving for cold fans at last.

[Kentish Kiwi]

Interesting to note that on the GFS 06z the 528 dam line resides over some part of Scotland from 159h through to 300h. Obviously uncertain at such a time frame but it certainly illustrates the change to cooler conditions in the north that is becoming more of a likelihood.

[nick sussex]

I think we've seen a slight improvement in the output today, although the ECM operational run continues to be a bit of a worry with it having a stronger Euro high.

It's ensembles do however suggest that it might be holding the pattern too far west, I think we will see some troughing extending further east and south, but its really what happens to shortwaves thats very much up in the air.

Because we're trying to remove positive heights from central and southern Europe we need as much eastwards movement in the pattern and these shortwaves to run more se.

I think theres a decent chance we will see some pressure rises towards Newfoundland and its whether these can transfer far enough east to draw high pressure west away from Europe and carve a more nw/se tilt to the jet.

Theres still a danger that the pattern might lock in too far west and some of the really disappointing output of yesterday can't be dismissed until we see the big 3 models pull that displaced Azores high westwards within 144hrs.

Until that happens then I'd put on hold any premature celebrations that we will see at least a more palatable pattern for the majority in here.

[kold weather]

One thing I'm seeing on the ensembles is quite a few runs blow up several lows between 168-240hrs and the ECM also sees this as a possible solution, so I think along with the possible colder shot coming down wind risk is also at an elevated level for a time as well IMO.

Nick, thats my big fear as well, esp given the constant upper low that has held in the E.Atlantic in recent months, might be a big ask to shift the upper lows that far to the east...

[Frosty.]

until we see the big 3 models pull that displaced Azores high westwards within 144hrs. Until that happens then I'd put on hold any premature celebrations that we will see at least a more palatable pattern for the majority in here.

Hopefully we can put the celebrations on real ice soon.

The models are looking better for colder prospects now, they have been abysmal since october but now they show cold air making inroads into the uk and the timeframe is close enough to make it fairly realistic.

[nick sussex]

The UKMO 6-10 day further outlook goes with the current trend in the longer range ECM ensembles. So a mixture of rain and some snow over northern high ground, driest in the se.

Generally this synoptic pattern becomes slow moving , this is why its crucial you get enough of a shift eastwards in the pattern and the jet axis nw/se.

The NAEFS is very reluctant to push the trough too far east and does build that pressure nw again so I suspect the window of opportunity is really now as we do see the main PV edged into Scandi.

[Summer Sun]

Thursday is not looking as windy as it was last night now

http://hw.nwstatic.c...6/81/ukwind.png

http://hw.nwstatic.c...6/84/ukwind.png

http://hw.nwstatic.c...6/87/ukwind.png

Worst of the rain is in the North West whilst further east and south it's much calmer

http://hw.nwstatic.c...6/78/ukprec.png

http://hw.nwstatic.c...6/81/ukprec.png

http://hw.nwstatic.c...6/84/ukprec.png

http://hw.nwstatic.c...6/87/ukprec.png

[phil nw.]

Sign's of a pattern change are in the air this morning ... GFS Op one of the Mildest runs , Control one of the Coldest , always a sign that something is about to change. More Cold members than Mild. ECM not bad as it keeps trying albeit failing to build height's out West and it does actually get there on it's later Charts . I note what Phil said last night but I do believe we can still get Cold patterns into the Uk even with a colder than average Stratosphere , If you put it into reverse we had the massive warming in early Jan and it came to nothing for the UK . It's kind of like a job application , warming Stratosphere preferred but not essential .

Hi Chris.

I just wanted to comment on your post.

You have given the impression that i said a cold setup was not possible with a colder than normal strato.--that`s not what i said.

Here`s what i said last night--copied direct from my origional post--

(quote)

Hi Chris,

I have always said if we can get some buckling to the pattern upstream then things would look different but of course we need the wave pattern to fall for us or we could end up on the wrong side of any blocking.

Unfortunately todays output has flattened everything so we have taken a step back for now.

The current strength of the Vortex with a very cold strato. means Northern blocking is unlikely for a while.

In that case we need a meridonal jet that would work in our favour so that we may, for example, get Atlantic ridging --as you alluded to.

We would at least have something like the famous Northerly toppler.

However for something colder that lasts more than 24-48hrs -well i think we are miles away from that at present.

Regards,Phil (end of quote)

Just to clarify i was talking about yesterdays upstream pattern -being flat etc.

Things can and do change and yes it`s possible for a cold pattern to evolve with a strong vortex if for example the main body of it moves away from Greenland. Even then we need amplitude in the flow as i commented on.

Looking at the overnights it`s a very fluid outlook with a trend away from total mildness now so maybe more seasonal fare is in the offing--a lot depends if we can get that Atlantic troughing far enough East to allow more Pm air into the mix later.

The 12z output yesterday showed all the energy running to our north without blocking over the poles so Polar air incursions were fleeting and only for the far north--thats really what i was trying to get across.

Anyway todays another day and we move on.

Hope that clarifys things.

Edited November 21, 2011 by phil n.warks.

[A Winter's Tale]

Slight chance of wet snow in Central Scotland. No sign of extreme or even sustained cold!

Still 4 days away but it's still nice to see the prospect of something wintery near my location. Let's hope that we see more of an upgrade closer to the time as I won't want to miss out on my first snow of the season.

Can I possibly start my snowfall diary a day earlier than last year? Here's hoping!

I think that at the moment the models really are pretty inconsistent at the moment and I wouldn't really bother looking beyond 8 days. However I would say that for a prolonged, nationwide blast of winter within the next 2-3 weeks doesn't look great judging by the pattern the models are showing but to judge December on a few unreliable charts for the first few days of the month is a bit far.

There are 26 days of December after the 5th and anything could happen during that time and I'm sure that at least we'll see something cooler from either cool zonality or polar maritime or incursions or perhaps we could be even luckier with a Scandi High or Mid Atlantic/Greenland High possibly developing in the 2nd half of the month. Then after December....There are two more months of the meterological winter ahead..............................

[kold weather]

With regards to Thursday most models weren't very agressive with it anyway and kept it further NW, its no surprise that is indeed what is actually likely to happen looking at this morning's model runs.