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phil nw.

Model Output Discussions 18z 31/01/2016

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Evening all :)

Looking a touch further ahead than the weekend, still huge uncertainty about next week especially from midweek onwards and looking at the GFS Ensembles at T+240, a very mixed bag of options including many cold and many milder. The "battle" between heights to the SW and NE and lower heights to the NW and SE could leave the British Isles in a chill no man's land but the majority currently, it has to be said, favour the Atlantic over a more continental weather pattern.

Beyond that, there's the question of the reforming PV and its position and strength. The OP is on the side of those seeing a strong PV re-constituting in its usual place but many of the Ensembles keep the PV weaker and in different places.

Whatever the weekend brings, next week is still far from clear.

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Disappointing to see ECM faster and flatter across the U.S. again. 

Liking the idea of secondary LP formation across the far S Thu/Fri, makes a lot of sense given the amplification signal upstream with the jet diving well south.

Not sure the initial angle of the frontal system is a done deal yet though; there is some risk that the models are getting carried away with the effects of a supersized air temp. gradient just S. of Greenland days 4-5.

 

The MJO has finally crossed the 4/5 border and the rate of progression over the next few days will be important; models suggest 5 days to MJO phase 6 and then another 3-5 to phase 7. If that verifies, then allowing for propagation time, impacts of phase 6 here would be near 20th, phase 7 near back end of the month. To be talking about phase 6 for early March, the Met Office must be thinking of a far slower progression. Having bet on the wrong horse regarding their being any amplification in the first place (little influence was favoured), I'm not inclined to give their thoughts on the MJO at the moment (but of course I retain great respect for them in the majority of other areas of the field, as global leaders in many areas).

There was a great signal for HLB and a strongly -ve AO from the 00z EC by +384 hours with a deep Eurasian trough. Hopefully that will be retained this evening. 

Looking at MJO analogues, perhaps a phase 6/7 hybrid pattern in the offering?

FebENMJOphase6gt1500mb.gif FebENMJOphase7gt1500mb.gif

In the near term, though, we have a loose 5/6 type pattern but really there's quite a bit of modification away from that, probably from stratospheric influences.

This brings me to the caveat that modification to the 6/7 pattern is certainly a possibility, meaning that all we can really take from it is that there will be an increased tendency for high latitude blocking. The location is not clear, though it does seem an east-based -ve NAO is in with a good shout.

Looking at recent GFS runs for days 10-16, I really can't fathom where the notion of an Azores High extended well into Europe is coming from. Look at the strat. vortex at 30 hPa for example:

npst30.pngnpst30.png

That seems more supportive of mid-Atlantic ridges with the jet digging down across the UK and Eurasia to me. Yet GFS keeps on finding upstream momentum... looking at the AAM/GWO plot doesn't help as a rising trend is seen through 5/6 for that time, which supports reduced momentum. These recent det. runs for week 3 of Feb just seem crazy to me :crazy:

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7 minutes ago, stodge said:

Evening all :)

Looking a touch further ahead than the weekend, still huge uncertainty about next week especially from midweek onwards and looking at the GFS Ensembles at T+240, a very mixed bag of options including many cold and many milder. The "battle" between heights to the SW and NE and lower heights to the NW and SE could leave the British Isles in a chill no man's land but the majority currently, it has to be said, favour the Atlantic over a more continental weather pattern.

Beyond that, there's the question of the reforming PV and its position and strength. The OP is on the side of those seeing a strong PV re-constituting in its usual place but many of the Ensembles keep the PV weaker and in different places.

Whatever the weekend brings, next week is still far from clear.

The GFS ens suite does show a less cold week 2 as we revert to a flow more from the west.

Day 10 500 anomalies and the 850's graph for Warks.

56bce92784769_gensnh-21-5-24011.2.thumb. 56bce97b2323a_viewimage(22).thumb.png.ea

after quite a cold week to come with some sharp frosts.

The Atlantic trough looks like then retreating back towards Greenland where low heights remain to our north west and high pressure is modeled to our south.More a normal Atlantic pattern raising temperatures closer to average or just below as showing on the temperature graph.

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9 minutes ago, stodge said:

 

Whatever the weekend brings, next week is still far from clear.

Interestingly, there is mention of an area of snow to affect SE Scotland slipping down into NE England at the weekend with several cm's of snow, even to low ground and then next week being generally much colder than the weekend with a significant risk of snow, especially for the eastern half of the UK....interesting times for coldies at last!:)

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5 minutes ago, Karl. said:

Interestingly, there is mention of an area of snow to affect SE Scotland slipping down into NE England at the weekend with several cm's of snow, even to low ground and then next week being generally much colder than the weekend with a significant risk of snow, especially for the eastern half of the UK....interesting times for coldies at last!:)

Hi Karl, with all this talk of snow and cold are you going back to frosty ? ;-)

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1 minute ago, Fozfoster said:

Hi Karl, with all this talk of snow and cold are you going back to frosty ? ;-)

Erm no I think I will stay as Karl but frosty weather looks a good bet next week.. as well as increasing snow chances:D

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1 minute ago, Karl. said:

Interestingly, there is mention of an area of snow to affect SE Scotland slipping down into NE England at the weekend with several cm's of snow, even to low ground and then next week being generally much colder than the weekend with a significant risk of snow, especially for the eastern half of the UK....interesting times for coldies at last!:)

Yes that would be associated with a couple of disturbances in the cold airflow coming south showing as those troughs on the fax's.They appear as the colder air cuts in from the north.

fax60s.gif?1fax72s.gif?156bcedae84a21_viewimage(23).thumb.png.7c

these type of features often crop up at the last minute so to speak.Difficult to ascertain amounts and extent but these could well produce more organised bands of snow depending on how they develop.

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Just shifting the topic a little. There has been much talk of Channel lows over the past few days and why said systems look like producing very little of the white stuff this weekend The answer is quite simple non of the lows shown have been classic Channel lows.

A real channel low is not a slider from the northwest that happens to end up in the channel.

A proper channel low is one that moves up along the channel from the west or southwest and scrapes along the bottom of an already entrenched area of high pressure pulling air from the east out of Scandinavia or Russia. The advantage of this in producing snow is that it sucks in a dry cold feed off the near continent .  Real channel lows are incredibly rare Jan 1881 and March 1891 being the best examples.

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HiYer Everyone... Away from the weekend , The models show some real interest in Mondays weather. A strong core of high pressure builds to the northwest of the Uk   dragging some pretty cold air across the nation and with the very cold air across the relatively warm  North Sea filtering westwards the East coast of the Southern half of the Uk may well get loads of snow showers and these may travel well inland.....Now ,from a couple of days ago ...Have the models upgraded the cold ........ A big YES!!!!:cold::)

xpress day.png

xpress dayx.png

xpress dayxx.png

xpress dayxxx.png

snowx.gif

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1 minute ago, KasimWeatherQuarnford said:

That precip. Chart in my opinion shows little. Yes coverings of snow for coastal counties but the wind not strong enough to push these showers far in land bar convection via surface heating which could allow a few inland showers.

Its subject to big change , but very interesting viewing nonetheless...:rofl:

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6 minutes ago, KasimWeatherQuarnford said:

I wouldn't expect too much change given the agreement. GFS produces a hit & miss 0-1 /2cm very tops covering a rather small proportion of Yorkshire, Lincolnshire & east Anglia. As you say there is the potential for a further downgrade. Up to 1026mb for some areas killing off lapse rates by Monday however Sunday evening could be the most interesting in terms of light snow showers for eastern Scotland which should be more dry on Sunday and an area subject to change across Wales / SW during Sunday evening as temps drop could be subject to a light fall.

Monday is a long way off , it will be very interesting to see tomorrows models......:)

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3 hours ago, fergieweather said:

 

3 hours ago, fergieweather said:

tying with UKMO broad notion of possible snow issues parts of central UK depending on retrogression of the Scandinavian high and resultant slowing/stalling of front(s) from W/NW. We aren't going to go big on this at the moment. It's just an early heads-up that this issue might become a problem for travellers etc next week. Hope that explains.

1102 ian.jpg

 

Thank goodness it is subject to change, because that raw output is completely underwhelming for the Southern half of England and Wales.

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47 minutes ago, mcweather said:

Just shifting the topic a little. There has been much talk of Channel lows over the past few days and why said systems look like producing very little of the white stuff this weekend The answer is quite simple non of the lows shown have been classic Channel lows.

A real channel low is not a slider from the northwest that happens to end up in the channel.

A proper channel low is one that moves up along the channel from the west or southwest and scrapes along the bottom of an already entrenched area of high pressure pulling air from the east out of Scandinavia or Russia. The advantage of this in producing snow is that it sucks in a dry cold feed off the near continent .  Real channel lows are incredibly rare Jan 1881 and March 1891 being the best examples.

Yes the key factor for instabilty for widespread snow is having sharper temperature differences between opposing air masses Atlantic v Polar Continental.

If we compare a fairly recent event from Feb.2009 with our current pattern by looking at the 500/850 charts we can see the differences.

In the Feb 2009 example we see an Atlantic trough coming against a deep cold pool off the continent.We haven't got this in the current setup and this is why it is so marginal. 

 

2009

archivesnh-2009-2-1-12-0.thumb.png.e8b4darchivesnh-2009-2-1-12-1.thumb.png.7e7f4

T48hrs

gfsnh-0-48.thumb.png.c316fb5e06c900b478bgfsnh-1-48.thumb.png.59f4f1cca34a7c76f7d

In Feb.2009 there was an established Scandi.high feeding those -12C uppers into SE England on a stiff easterly meeting low pressure development across the south.Our current setup lacks the sharp boundary between those air masses as we are in  -2 to -4C pm air without any nearby deeper cold pool.

We do see an injection of deeper cold by early next week but by that time pressure is rising as the Atlantic low sinks away into the continent and so most areas will see dry frosty weather until the modeled approach of another Atlantic trough around the middle of next week.

 

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12 minutes ago, The Enforcer said:

Thank goodness it is subject to change, because that raw output is completely underwhelming for the Southern half of England and Wales.

12z EC delivers snow across much of northern/western/central UK by end of Thursday: all of Wales and for England, approx Scarborough down to Bournemouth as eastern boundary; western boundary approx Exmoor to Exeter (plus Dartmoor).  12z UKMO-GM broadly similar ideas (re western bias).  Much water to run under bridge before then, so very low confidence and no individual solution is trustworthy at this point.

Re this weekend, key difference is how 12z EC offers a far less wet day for the south on Saturday (thus also further reducing scope for any snow across e.g. Chilterns, Cotswolds, Downs). UKMO have modified forecast expectations towards this solution (thus also losing yellow wind warning for SW: nonetheless, a few ENS members are still potent). 

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2 minutes ago, fergieweather said:

12z EC delivers snow across much of northern/western/central UK by end of Thursday: all of Wales and for England, approx Scarborough down to Bournemouth as eastern boundary; western boundary approx Exmoor to Exeter (plus Dartmoor).  12z UKMO-GM broadly similar ideas (re western bias).  Much water to run under bridge before then, so very low confidence and no individual solution is trustworthy at this point.

Re this weekend, key difference is how 12z EC offers a far less wet day for the south on Saturday (thus also further reducing scope for any snow across e.g. Chilterns, Cotswolds, Downs). UKMO have modified forecast expectations towards this solution (thus also losing yellow wind warning for SW: nonetheless, a few ENS members are still potent). 

Thank you for this info Ian... as ever very welcome in this thread.... im assuming that the Peak District is in a good spot then?? i know as you said low confidence but at the very least will give me something to hope for....

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2 minutes ago, fergieweather said:

12z EC delivers snow across much of northern/western/central UK by end of Thursday: all of Wales and for England, approx Scarborough down to Bournemouth as eastern boundary; western boundary approx Exmoor to Exeter (plus Dartmoor).  12z UKMO-GM broadly similar ideas (re western bias).  Much water to run under bridge before then, so very low confidence and no individual solution is trustworthy at this point.

Re this weekend, key difference is how 12z EC offers a far less wet day for the south on Saturday (thus also further reducing scope for any snow across e.g. Chilterns, Cotswolds, Downs). UKMO have modified forecast expectations towards this solution (thus also losing yellow wind warning for SW: nonetheless, a few ENS members are still potent). 

A big thank you for that information ,this must be the top weather forum around ,exciting times and plenty of interesting synoptics ,i,m pretty sure if tv weather presenters had far more air time which at one time I wrote to bbc about we would not need the web so much ,perhaps its best that we dont get any more info as this would takeaway the hunt a bit .cheers .

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I'm surprised people aren't talking about the snow showing for Wales the south west and central southern England on Sunday. Screen shot from lunchtime Sunday and ECM precip.......

 

image.png

image.png

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2 minutes ago, Tim Bland said:

That's a Gfs precipitation chart?

 

 

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5 minutes ago, Tim Bland said:

 

image.png

Yep, Wales and West Country waking up to a valentine snowfall according 18z GFS, but may change ... -5C T850s digging further south Sunday on last few runs which is good to see.

image.thumb.png.6f4dc02a109c0f8f4557a9c6

 

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Looking dry here for the next 5-6 days I would think. Not much to get excited about.

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Quite a complicated set up here.

First thing is to the ne and how quickly low heights separate near Svalbard, this allows the Scandi ridge and Arctic ridge to join forces.

Then upstream you can see that deep low moving ne across the ne USA this phases with the PV and helps pull this nw'wards , you can see as this happens the energy feeding the troughing to the nw of the UK begins to dissipate and the troughing finally loses its eastward momentum and is attacked from the ne by the developing heights near Svalbard.

If you look at the ECM in particular you can see its much flatter over the eastern USA the low then just runs into the PV and it also doesn't clear low heights near Svalbard.

 

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Well the GFS almost follows the JMA but loses tge scandi high just to quickly -

however this is a real sight to behold

totally stationary air over the UK- very cold in any clear skies with snowcover

it rarely lasts in the UK

image.thumb.jpg.acfe0492e68b908c440bd8f0

s

 

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Just to highlight the importance of the two crucial areas to keep an eye on in future outputs:

So the GFS18hrs run at T114hrs and the ECM 12hrs run to T120hrs:

gfsnh-0-114.thumb.png.caf04bb494f1057609ECH1-120.thumb.gif.545c3b4925fe01333e984

 

The GFS is already beginning to clear those low heights circled red, upstream you can see both it and the ECM are developing that low in the eastern USA.

Then if we move forward to the GFS 18hrs run to T138hrs and compare this with the ECM 12hrs run to T144hrs, the ECM is already past the point of no return, the energy has spilt east towards Scandi and upstream its much flatter, you'll never then get enough trough disruption and also enough pull on that PV chunk in nw Greenland to pull this further nw:

gfsnh-0-138.thumb.png.7e07217de03ef34f43ECH1-144.thumb.gif.dff4fb94caa38c10e3c44

 

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If it wasn't for the development of the Scandi ridge and also rise in pressure/ heights over Svalbard, GFS would not be showing this trough disruption over the UK later next week, rather the trough dropping from the NW remains intact  with energy piling east into Scandi with us back in mobile cyclonic westerlies. I suppose this is the downfall of 12z ECM, that it doesn't build heights over Scandi and Svalbard, though does have brief trough disruption before the return to westerlies.

Having said that, 18z GFS more progressive in pushing through the frontal system  next Thursday before the trough disruption takes place. Ideally would like to see trough disruption take place over western UK with the frontal system stalling over the UK. Less risk then of cold air pushed out from the west eventually as shown by the later frames of the medium range of 12z EC and 18z GFS.

Still, plenty of twists and turns to come next week, as the NWP models, even today with their powerful computers, are notorious for having difficulty handling trough disruption. For now, at least, any mild sectors moving in from the west next week should hopefully be squeezed out as they come up against the cold block over Northern Europe.

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