Model Output Discussion 26/10 2012 >

[summer blizzard]

Exactly the same experience I have even dating back to the old BBC Snow-watch days

I can only assume it was simply the greater range of data available that produced this belief (a belief that I too held during the years you mention)

SK

I started on there.

I suspect it may have verified better in winter when those winters were full of shortwaves which the GFS does best on, it may be that simply ignored what went on outside winter for the most part.

[Zenarcher]

The Zipping Friday low has been slightly upgraded on the 18z. This would produce a notable wind event and I would imagine a substantial amount of rain.

Yes would bring gusts over 70mph, interesting to watch this and see how it develops.

Gust Chart From NW Extra,

[summer blizzard]

Snow potential on Sunday and Monday?

GFS suggesting air temperatures around 2C.

[lorenzo]

Couple of up close shots of that Kamchatka ridge, Going to take some breaking down, not surprising to see it hanging on until the very death on the GFS low res.

[Panayiotis]

http://modeles.meteo...snh-2-84.png?18

T84 & the GFS has the first welsh Gridpoint snow under T96 since the first cold wave at the weekend...

S

As i live in South Wales, it would be really interesting if this occured, but can someone explain why its only in this part of the UK where this snowfall will occur?

[Mark Neal.]

Couple of up close shots of that Kamchatka ridge, Going to take some breaking down, not surprising to see it hanging on until the very death on the GFS low res.

This is a question from someone who is still new to these words but is that Kamchatka ridge..a good thing to happen going into the early beginning of winter regarding cold prospects?

I have also been keeping an eye on the models, and it does seem as S&S pointed out that Friday could be a very wild day for parts of SE England as a potential secondary low develops, which in return could see some high wind speeds especially for those close to the coast and also eastern areas.

[Isolated Frost]

Couple of up close shots of that Kamchatka ridge, Going to take some breaking down, not surprising to see it hanging on until the very death on the GFS low res.

Where are those charts from L?

[Robbie Garrett]

The Zipping Friday low has been slightly upgraded on the 18z. This would produce a notable wind event and I would imagine a substantial amount of rain.

Yes would bring gusts over 70mph, interesting to watch this and see how it develops.

Gust Chart From NW Extra,

Very worrying for the South East, as that could be out quite a bit due to the ongoing developments around the Northern Hemisphere such as Sandy. Will be interesting to see what happens over the next few days.

[AWD]

GFS 0z quite clearly shows the secondary low that develops to the SW.

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=78&mode=0

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=84&mode=0

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=90&mode=0

On this run alone, it looks to run through the channel and therefore keep the worst of the winds for the French coast.

[lorenzo]

Another LP system meets the Greenland shredder on the ECM morning run. The Greenland High taking on all systems coming at it with gusto and firing them up Baffin Bay.

In terms of patterns becoming entrenched on the models, this is surely now in with a good shout of continuing as a trend.

@MarkNeal - In terms of this ridge as GP stated sets the Longwave pattern for NH. One impact is the Jet and the increased introduction of meridional flow. Very different for a year a go where there was a flat zonal pattern. From 192 on GFS 00z, Jetstream still not tanking at us at all.

Another factor is the continuous tropospheric forcing brought about by the ridge(s) on the Polar Vortex, and it's usual migration around the NH, whilst Strat temps are cooling, anomalous ridges disrupt it setting up home, as per the NAEFS post above you can see the heights feeding into the polar regions. Random chart from ECM archive 2011 sees a better organised pool of cold.

In terms of what it means further down the line, keep watching, cannot second guess things . The interest I have in the large blocking anomalies is from the SSt pattern of this year going into Autumn / Winter. Well advertised above average SSts leading into the timeframe.

@IF

[weather_it_will]

GFS @T372 showing a fairly widespread snow event with a northerly.

GEFS ensembles also favouring support for colder upper air at the end of the run

with more chances of snow in this period from about 11th November.

Obviously FI but the trend is there for a colder outlook.

Edited October 30, 2012 by snow is falling

[Liam J]

As i live in South Wales, it would be really interesting if this occured, but can someone explain why its only in this part of the UK where this snowfall will occur?

The GFS charts on Meteociel especially the precipitation/snowfall charts leave something to be desired, and certainly need viewed with a dose of salt when trying to determine precipitation given the resolution + that time scale ahead (snow difficult to pin down within 24hrs at times) . More detailed charts from the GFS 00z do not show any snowfall over the UK - courtesy of Netweather Extra.

The 'zipper' low has been pushed a tad further south on the GFS 00z and a downgrade in terms of wind speeds, not really surprising when looking at the other outputs as the GFS is out on it's own blowing this little feature up - something the GFS is pretty good at.

Edited October 30, 2012 by Liam J

[Gibby]

Good morning. Here is the morning take on a set of very unsettled 00z outputs from GFS, UKMO and ECM.

In short today all models show a very similar set of synoptics with just small but subtle differences between the models over the duration of their runs. The pattern is set for the rest of this week. Low pressure is developing and deepening to the North of Scotland with a Westerly wind increasing and backing SW across the UK today. Cloud will spill across the North with some occasional rain and this will become more extensive overnight as it moves to other areas. By tomorrow all areas will be under the influence of a deep Low just to the North of Britain with rain at times everywhere in somewhat milder temperatures. By Thursday a cold front will of moved East across Britain taking a band of heavy rain with it and bringing about a change to colder and brighter conditions with sqially heavy showers of rain, hail and thunder especially near Western coasts with snow on Northern hills. With the Low pressure becoming slow moving and complex all models show the rest of the week and the weekend with very little change as the rather cold and showery pattern continues. Some longer spells of rain are still likely with the greatest risk of this on Friday as GFS in particular shows a small but significant area of wind and rain sccot East across the South.

GFS then moves through next week with the first half seeing very little change as the Low only very slowly fills but even as late as Wednesday it is still close enough to maintain a rather cold and unsettled Northerly feed over the UK with further showers, wintry in the North. around midweek a weak ridge gives a window of dry, bright and frosty weather before a new Low pressure slips SE over Britain with further rather chilly weather with rain at times returning. The rest of FI shows High pressure to the West linking a ridge across to Scandinavia bringing cold and drier weather across the North while the cut off Low to the South of Britain by then sets up a cold and raw Easterly feed across the South with rain at times.

The GFS Ensembles show a colder set this morning with the mean 850's for the run staying below the long term mean throughout. Although there is nothing dramatically cold shown with rainfall scattered about throughout the run and nationwide it will feel quite chilly at times with snow on Northern high ground as cold zonal Low pressure looks the likely dominant pattern.

The Jet Stream shows a flow sinking South of the UK in the coming days and staying there for some considerable time.

UKMO for midnight on Monday shows Low pressure centred over the top of the UK with several more days of cold and unsettled conditions likely from that chart with snow likely on Northern hills.

ECM shows a similar setup with a cold Northerly flow. As the Low drifts away east late in the run reinforcements are fed SE from the Iceland area to keep the rather cold and unsettled theme going until the end of the run. It would be cold enough for snow on Northern hills.

In Summary today the evolution beyond this week has firmed up somewhat with all models now suggesting a continuation of rather cold and unsettled conditions with rain and showers for all at times and snow on Northern hills. The ensembles from GFS are very supportive of this theory too and with the recent Meto update suggesting a forecast which would support such synopses I think confidence is high on a couple of weeks of chilly and wet conditions.

Edited October 30, 2012 by Gibby

[Glacier Point]

So what does a solid longwave pattern centred around Kamchatkan ridge / North Atlantic ridge and NW European trough mean going forward ?

The GEFS mean height anomalt days 11-15 depicts this type of pattern.

If we assume this to be setting the ground for what the H5 anomaly for November will eventually be, then we can look at historical precedent given that patterns at this time of year begin to lock down for the winter.

Our analogues, which are an excellent representation of the three major hemispheric anomalous ridges:

Rolled forward into December:

This idea of a negative (potentially deeply negative) NAO during December has a lot of credence when you consider the range of teleconnective signals, and now seemingly ECM long range modelling.

[Alex]

So what does a solid longwave pattern centred around Kamchatkan ridge / North Atlantic ridge and NW European trough mean going forward ?

The GEFS mean height anomalt days 11-15 depicts this type of pattern.

If we assume this to be setting the ground for what the H5 anomaly for November will eventually be, then we can look at historical precedent given that patterns at this time of year begin to lock down for the winter.

Our analogues, which are an excellent representation of the three major hemispheric anomalous ridges:

Rolled forward into December:

This idea of a negative (potentially deeply negative) NAO during December has a lot of credence when you consider the range of teleconnective signals, and now seemingly ECM long range modelling.

Interesting GP however I don't remember apart from 2010, that many of the more recent analogues ie 2005/2006 winters produced much in the way of cold/snow - Dec 06 was rather like 2011 if I recall it right. 2005 I think cold lovers had to wait until the deep realms of Feb for any decent snow and even then it was questionable compared to some recent years. My question is what was different about them years as it looks like northern blocking was prevelent.

[Glacier Point]

I think the interpretation of what these analogues might mean in terms of temperature and ppn should be seen in the context of the shift in the PDO from 2007.

The principal reason I think for the anomalous ridges is the disconnect that we are seeing between angular momentum and current ENSO signal, which effectively is reinforcing this idea of an El Nino within a cold PDO type scenario. The pattern is effectively a hybrid, which is enhancing the net impacts of low Arctic sea ice and SSTA in the North Atlantic.

[Alex]

I think the interpretation of what these analogues might mean in terms of temperature and ppn should be seen in the context of the shift in the PDO from 2007.

The principal reason I think for the anomalous ridges is the disconnect that we are seeing between angular momentum and current ENSO signal, which effectively is reinforcing this idea of an El Nino within a cold PDO type scenario. The pattern is effectively a hybrid, which is enhancing the net impacts of low Arctic sea ice and SSTA in the North Atlantic.

Thanks GP, I am still interested in whether hurricane Sandy will alter any of the Atlantic patterns.

[SMU]

http://www.meteociel.fr/modeles/ecmwf/runs/2012103000/ECH1-240.GIF?30-12

Morning All

Day 10 & still blocking in place with no atlantic- a small surface high developing over scandi & with descending air its creating -10C 850's-

So early in the season, so interesting to see- If ANY movement west of that cold is show it will be very much against any climatology for November,infact probably something of the order of a -1 inverse correlation.

Anything from the east is so rare in Nov- I can remember 93, & thats about it...

THe dice are loaded & its not the usual 1 & 2 - its a double 6!

nice!

S

Edited October 30, 2012 by Steve Murr

[SMU]

Thanks GP, I am still interested in whether hurricane Sandy will alter any of the Atlantic patterns.

Not really no

It will temorarily support a ridge in the atlantic to its NE, however give it another 72 hours & it will be a mere spec on the map- just a small bit of energy getting crushed in the jet.

http://modeles.meteo...gfsnh-0-6.png?0 now

http://modeles.meteo...fsnh-0-78.png?0 then

goodbye 50 year storm...

S

Edited October 30, 2012 by Steve Murr

[BLAST FROM THE PAST]

Thanks GP, I am still interested in whether hurricane Sandy will alter any of the Atlantic patterns.

No, more like its track has been determined by the blocking and behaviour of the jetstream, not the other way round.

BFTP

[Nick F]

Remarkably persistent the +ve height anomaly over the NW Atlantic/Sern Greenland - and no signs that it will shift much - ensembles suggests it will perhaps sink SE only to build back north again. Looking at SST anomaly charts, large warm anomaly across the NW Atlantic too - which could be a contributory factor (among other more global influences) to this anomalous ridge through feed back of warmth to the atmosphere:

http://www.netweather.tv/index.cgi?action=charts;type=seatemps;sess=

Certainly the block was responsible for Sandy diverting NW into the NE USA, when normally it would track NE harmlessly out over the NW Atlantic as it encounters the upper westerlies of the PFJ.

Closer to home, looks like we will be locked into a cool/chilly but unsettled pattern for a while yet - with low pressure always close to the north. With time, signs maybe the mean trough edges further east - which may allow colder air to sink south, though no particularly potent northerly showing yet.

[fergieweather]

GFS 0z quite clearly shows the secondary low that develops to the SW.

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=78&mode=0

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=84&mode=0

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=90&mode=0

On this run alone, it looks to run through the channel and therefore keep the worst of the winds for the French coast.

Given support and broad agreement now between UKMO-GM, EC & ARPEGE (albeit the latter with more complex low, structurally), UKMO consider the GFS solution re this deep S England low development as unlikely. Hence our briefings this morning are to emphasize forecast change to the story in this respect over past 24hrs, with just small potential for the GFS solution to be manifested Fri-Sat. We shall see...

[Tom Montalbano]

http://www.meteociel...1-240.GIF?30-12

Morning All

Day 10 & still blocking in place with no atlantic- a small surface high developing over scandi & with descending air its creating -10C 850's-

So early in the season, so interesting to see- If ANY movement west of that cold is show it will be very much against any climatology for November,infact probably something of the order of a -1 inverse correlation.

Anything from the east is so rare in Nov- I can remember 93, & thats about it...

THe dice are loaded & its not the usual 1 & 2 - its a double 6!

nice!

S

Hi Steve,

November 1965, comes to mind, only know that because my wife said that a few days after she was born her mother said that there was snow on the ground. Being a doubting Thomas of course, I did a little research, have a little drool over these charts:

http://www.wetterzen...00119651112.gif

http://www.wetterzen...00119651113.gif

http://www.wetterzen...00119651114.gif

http://www.wetterzen...00219651115.gif

Very unusual to see -10 uppers encroaching from an easterly point and knocking on the door of the East Coast , in mid-November.

November 1965 came in with a CET of 4.5c, 0.1 colder than 1993 and was one of the coldest, snowiest Novembers of the 20th century.

Wouldnt say no to a little bit of that this November!

Regards,

Tom.

Edited October 30, 2012 by TomSE20

[Nick F]

06z GFS still determined to take that deepening secondary low across southern England on Friday - while the other models say no for now. Wind maps shows 50-60mph gusts along the Channel and East Anglia coasts.

[picog]

Strikingly, the ensembles seem to show more rain on the eastern side of the country with both the north and west being drier/less wet.

http://www.wetterzentrale.de/pics/MT8_London_ens.png

http://www.wetterzentrale.de/pics/MT8_Dublin_ens.png

http://www.wetterzentrale.de/pics/MT8_Manchester_ens.png