Model Output Discussion 01/09/17

[Tracy Flick]

As Mucka states, the GEFS 12z ensembles aren't overly excited about standard westerlies in the longer term.

e.g. at day 10 the 'purple' low geop. height values aren't really dominant in the cluster, numbering <5:

[knocker]

This evening's ecm is indicating some light snow in central and northern Scotland tomorrow evening but more substantial falls on the Tuesday low pressure and front.

[bluearmy]

The ops are certainly inconsistent in dealing with the polar heights in the 6/8 day period. 

[Frosty.]

Good to see colder air / blue colours pushing southeast later next week following a mild interlude on the Ecm 12z with some wintry showers in places and frosty nights.

Edited November 18, 2017 by Frosty.

[Iceaxecrampon]

12z a week off.

Anyone say why this isn't delivering as much as it suggests - lack of moisture? - temps?

 

[Man With Beard]

ECM op tonight showing snow next weekend for northern hills - not really at lower levels except NW Scotland.

[Frosty.]

Looking towards the end of the Ecm 12z there is potentially another cold shot lining up to sweep down across the UK beyond T+240 hours with further wintry showers and night frosts..so it appears we are in for some big swings in temperature with some mild days alternating with colder crisper conditions as we head through late november..currently enjoying the frosty nights and hoping for plenty more plus the introduction of snow once winter arrives!☺?

[knocker]

Some indications this evening of a pattern change upstream in the 7-12 range of the GEFS and EPS anomalies, Can't post the EPS but it's not a million miles from the GEFS,

Essentially the Greenland HP weakens and moves east with still an active vortex lobe NE North America which initiates some ridging in the western Atlantic. Thus still a strong westerly upper flow out of the eastern seaboard but less risk of cold air plunging south east of Greenland. Still likely to be unsettled with temps around average.

[nick sussex]

Still lots of uncertainty in the shorter term with where any cold/milder boundary might be. You can see from the ECM ensemble spreads at T96hrs that swathe of higher uncertainty running through Scotland/N.Ireland and the very far north of England:

Both the ECM and UKMO at day 6 could develop some interest, both have a shortwave approach from the sw. If we just look at the ECM you can see that shallow feature  running ne through the UK:

Theres a chance that as this runs ne it could be undercut by some colder air heading se bringing some snow more especially to higher ground.

The issue this far out is how complex the pattern is with reliability poor in terms of the models agreeing on track and depth of shortwaves, but the set up is one where you're likely to get one tracking through the UK.

Theres some relief that the models seem to be edging away from holding a trough aligned ne sw to the west of the UK which would keep a mild sw flow later on.

The upstream pattern is expected to remain progressive which means lots of lows running across the USA and heading into the Atlantic, theres a hint later we might see the jet track a bit more se near the UK.

If the UK is tap into some colder air after this mini battle we'd need to see pressure remain high over Greenland to help disrupt some of that Atlantic energy.

Overall a messy set up coming up, lots of wind and rain in the outlook with a chance of some snow but this mainly in the far north, and that's by no means certain because of the fine margin between that colder Arctic air and the milder air to the south.

Fingers crossed after recent luck things will tip more favourably.

 

 

 

Edited November 18, 2017 by nick sussex

[knocker]

Cannot correct it but in my post above it should read " Essentially the Greenland HP weakens and moves west"  not east.

[nick sussex]

The core of heights over Greenland is slightly further east here and the phasing point with shortwave energy to the sw might get edged further east which would help.

We're only talking small margins here but in those areas with a chance of something wintry this could make a difference.

If that shortwave energy over Scotland could separate from the low to the sw this would improve chances.

Edited November 18, 2017 by nick sussex

[Man With Beard]

18 minutes ago, nick sussex said:

The core of heights over Greenland is slightly further east here and the phasing point with shortwave energy to the sw might get edged further east which would help.

We're only talking small margins here but in those areas with a chance of something wintry this could make a difference.

If that shortwave energy over Scotland could separate from the low to the sw this would improve chances.

I think what maintains the interest for me is the memory of so many failed northerlies because of corrections to the east - for some reason though I can't remember too many eastward corrections when the cold is to the west.

Has anyone else noticed that the GFS is consistently modelling a low of tropical origins to be picked up by the main Atlantic trough between T80 and T92? Doesn't look programmed to have too Mach impact at the moment in terms of wind but it does seem the kind of low that could bomb, given the mix of cold and warm.

Edit - actually strike that, on closer inspection I see over 90 mile gusts in its way to S Ireland and not far from SW England. Not pretty.

Edited November 18, 2017 by Man With Beard

[nick sussex]

You can see the difficulty with the models unable to agree whether one low deepens rapidly to the sw or you have two centres like the earlier GFS run.

Its an unusual set up, we normally see deep  low pressure moving east along the jet here a shortwave sits there waiting for reinforcements from the ne .

Preferably you want the weakest low possible and not this bombing type which will take longer to clear off eastwards .

Edited November 18, 2017 by nick sussex

[Man With Beard]

GFS 18Z removes any threat of snow to the UK next weekend, except on a mountain. SWlies all the way. BTW just catching up on the day, I see @Singularityhighlighted the risk of winds on the GFS 12Z earlier but worth stating it had a mini storm hitting Wales at just T107 with mean winds of 120-130 km/h - that's around 80mph, clear hurricane strength.

[nick sussex]

7 minutes ago, Man With Beard said:

GFS 18Z removes any threat of snow to the UK next weekend, except on a mountain. SWlies all the way. BTW just catching up on the day, I see @Singularityhighlighted the risk of winds on the GFS 12Z earlier but worth stating it had a mini storm hitting Wales at just T107 with mean winds of 120-130 km/h - that's around 80mph, clear hurricane strength.

Yes horrid looking output in the medium term from the GFS before a little amplification upstream helps to carve out a ridge to the west with a chance of something colder. Earlier it edged the pattern a touch further south before the bombing low appeared and pushed milder air ne.

[booferking]

Cool wet and very windy and any chance of snow getting pushed to the 10 day mark every run terrible were did this all go wrong.

And there it comes on the 10th day a 2 day toppler

[Frosty.]

Good old reliable 18z..knew it wouldn't let me down, here comes the snow!

[BLAST FROM THE PAST]

Just a quickie, anyone else getting the sense that models are moving towards a more interesting set up with more cold gett8ng involved?  As alluded to the wretched SW/NE train is reducing in longevity rapidly.

I think there is more tweaking to come yet

 

BFTP

[Tracy Flick]

The far reaches of the JMA, while mild for the UK, gives some peace and quiet for Norway and Svalbard.  As others have said, still plenty going on to keep the interest.

[That ECM]

Interesting and with a few more tweaks and cool/ cold flow for many. As is always, being north and having elevation will help. Oh the joys of living in Bournemouth, we have neither but some will be encouraged by this ecm run. Strong winds would be an issue as well.

Edited November 19, 2017 by That ECM

[knocker]

Today. The cloud and rain from yesterday has cleared and with a transitional ridge moving in most places will have a dry and sunny start to the day day albeit a bit nippy in the much colder air. Bur it is rather a brief interlude as the next system is moving east and the cloud from the warm front will start affecting the north west and then the the south west during the day. It wills be accompanied by rain which will as snow over the high ground in the north and particularly Scotland as the warmer air hits the colder air in situ. This will spread to all areas tomorrow as the wave and fronts traverse the country.

So on to the gfs this morning. First a brief overview. It is looking like being very unsettled this week and the beginning of next so the main concern will be rain and the possibility of gales.

After the above wave has cleared we arrive at the complexities of this week By 12 Tuesday we have a complex upper trough to the  WSW running all the way down to north west Africa whilst another trough has slipped south between Iceland and Scotland and is about to phase with it. On the surface this translates to the main depression to the SW with the associated front running from Scotland down to west of the Azores on which a wave has formed to be west of Scotland 995mb at same time. This will bring rain (snow over the hills in Scotland although it maybe too far north) and quite strong winds as it tracks into the North Sea and deepens over the next 12 hours.

The front make little progress south as it comes up against the high pressure to the south east although far enough to introduce colder air over Scotland. Quite important this as another frontal low has formed to be 982mb just off the SW tip of Ireland by 12 Wednesday. Over the next 12 hours this deepens considerable and by 00 Thursday  is 968mb over Ailsa Craig with gales and possible blizzards over the high ground in Scotland and strong south westerly winds and rain further south.

By Friday 00 the intense low has tracked into the west coast of Norway but the cold air behind does not get very far south on this occasion and the next systems that arrive, spawned by the large positively tilted upper trough also track east over Scotland which again could produce snow over the high ground

But the main trough continues to edge east and the next intense little surface low tracks across south England which greatly facilitates the ingress of the colder air to all parts of the UK by the weekend. Best left there as apart from anything else a double espresso is calling.

 

Edited November 19, 2017 by knocker

[knocker]

The ecm  starts differing with the gfs by Thursday when it is much more progressive with  the upper trough which then deconstructs taking the main trough NE into the Norwegian basin and forming a cut off low to the south west of the UK. Thus the colder air is introduced over the UK much quicker in the north westerly gales  and wintry weather behind the intense  surface low.to the NE

 

[bluearmy]

Didn't take long did it ..............

[That ECM]

9 minutes ago, bluearmy said:

Didn't take long did it ..............

The text to your mrs has somehow been posted on here

[bluearmy]

3 minutes ago, That ECM said:

The text to your mrs has somehow been posted on here

an amplification now and again is always welcome !!!

speads and clusters awaited ..........