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phil nw.

Model Output Discussions 06z 04/11/16

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The 12z ECM has furthered a developing suspicion of mine - based on recent model trends - that the low coming in at the weekend might not manage to organise into a broader-scale trough before interacting with the one ahead of it (over Barents/Kara). This means it swings into the base of the old trough as a shortwave feature.

That makes it considerably cooler across most of England Sunday-Tuesday than GFS has been going for.

By Monday the trough is filling in and the jet has dived all the way down to the NW corner of Africa. Had the model not then produced an 'attack of the shortwaves' scenario, expect a cut-off high in the vicinity of Iceland would have fitted in very nicely. Instead we just see faint suggestions of that at +240, with the trough west of Iceland likely to undergo disruption a day or two later in time, leading to low heights extending SE and the ridge from the Azores retreating back west. 

That does, though, assume the Arctic troposphere responding to stratospheric developments in a similar manner to recent GFS/GEFS guidance, as stratospheric height rises, extending from near/over eastern Asia across to first the N. Pole and soon after Greenland, make themselves known. ECM at day 10 is only just reaching the earliest point in time when such a process has been suggested to occur.

In light of Tamara's informative update, I wonder if the more mobile solutions in recent EPS suites are in fact members that show a larger drop in GLAAM than the GEFS mean is now suggesting; a few days back, the GEFS mean showed a very large drop, and the runs were showing HLB having a hard time establishing, at least in a favourable configuration for us to benefit. Since then, the drop has been greatly reduced, particularly within the 10-day range, and we've seen a lot more runs showing the westerlies being pretty much shut down.

If only GEFS were reliable in predicting GLAAM, the upward trend in longer-term values could be taken to imply that the 'floor' that Tamara refers too will indeed be higher than seen in late Sep-early Oct. It's still a positive trend though :)

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4 minutes ago, Man With Beard said:

This is a monster storm on the ECM. Studying this image closely for the English Channel, we have 70 knots at 925hpa (about 80mph) and 85 or 95 knots at 850hpa (100-110mph). 

ecm0125_nat_wind_multi_2016111412_138.jp

This exact scenario was shown on the GFS a few days ago, and there's a few little nasties around on the GEFS - so can't be written off.

Not following the script of this Atlantic-less autumn!

Hopefully it downgrades a bit , BBC not mentioning it yet anyway. It would feel pretty nasty in fairly cold air if it were to come off, not sure indusive for any wintry precip though!!

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ECM low not interacting with cold air as yet.

161114_1200_132.png

161114_1200_132.png

 

The only issue I have with the ECM evolution this evening is that the colder air does not really stay with us other than northern Britain fleetingly if you run the sequence.

http://en.vedur.is/weather/forecasts/atlantic/#type=temp

 

Edited by winterof79

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The ECM op suggests we'll get to the 21st/22nd before warming up ( milding out). I think that looking for the end of a cool to cold spell before it's even started (despite what the GEM model and Summer Sun's analysis might suggest) is well, add in the blanks........ Granted, it is valid to model output discussion, but it is kind of like peeing on someone's chips before they've bought them. 17th through to the 20th/21st November is going to be a cold dominated spell, how cold (i.e. cold enough for the holy grail ice crystals IMBY or your own) we'll have to see. I'm looking forward to cold spell number two, whatever.

EDIT: Singularity's recent post suggests this probability too (an extension to the current 3/4 day cooler interlude). The weekend is set to get VERY intriguing and a forecasting headache for the pros I reckon. Beyond the weekend, all solutions are up for grabs.

Edited by gottolovethisweather

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1 minute ago, gottolovethisweather said:

The ECM op suggests we'll get to the 21st/22nd before warming up ( milding out). I think that looking for the end of a cool to cold spell before it's even started (despite what the GEM model and Summer Sun's post might suggest) is well, add in the blanks........ Granted, it is valid to model output discussion, but it is kind of like peeing on someone's chips before they've bought them. 17th through to the 20th/21st November is going to be a cold dominated spell, how cold (i.e. cold enough for the holy grail ice crystals IMBY or your own) we'll have to see. I'm looking forward to cold spell number two, whatever.

Here here, and its well within the reliable timeframe now! Scotland looks coldest as one would expect with a Northwester but we will all feel the chill and wintry showers won't be exclusive to the north or high ground either..as you say, cold spell number 2 and I don't think it will be too long before that gets considerably added to:santa-emoji:

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54 minutes ago, ajpoolshark said:

hmm...interesting....a shame joe public doesn't have access to ECM dewpoints/thickness charts (if they exist)...that in conjunction with the charts below for the same time frame

144_thick.png?cb=703 168_thick.png?cb=703

It's only a loose guide, but the 528 dam line is right up by the Scottish border at 12:00 on Sunday, dropping slowly south with time to be across the central swathe by 12:00 on Monday.

- but then there's evaporative cooling, 925 hPa temperatures, and so on to consider, which are hidden behind paywalls (assuming they exist at all, at least outside of the ECMWF).

Perhaps a more intuitively promising outcome could occur if the rate of intensification of the low is being overdone. Sometimes when you see a trough stretching out such as the ECM and ARPEGE 12z runs show, all you end up with is an active frontal system with a couple of waves along it. The models have a real habit of assuming at longer-ranges that surface potential will interact with upper winds favourably (which itself relates to the manner of interaction with nearby troughs and ridges).

At just +120 to +144 hours though, ECM is worth paying attention to.

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GEFS show a marked cooling at the weekend only returning to average or slightly below before cooling down once more toward month end.

Looks fine to me.

graphe3_1000_258.8399963378906_33.259998

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9 minutes ago, Singularity said:

 

 

- but then there's evaporative cooling, 925 hPa temperatures, and so on to consider, which are hidden behind paywalls (assuming they exist at all, at least outside of the ECMWF).

 

Oh they do exist. The 925mb temp at T132 is 9C over Cornwall and 0C over west Wales. :shok:

Edited by knocker

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The GEFS 12z mean does show support for a milder Southerly flow next week, similar to the Gem 12z..time for a slice of humble pie:shok::D

21_192_850tmp.png

21_216_850tmp.png

21_240_850tmp.png

Edited by Frosty.

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2 minutes ago, fergieweather said:

Not mentioning yet as support still inconclusive. We've seen a signal for potential gales/severe gales for a few EC runs (ENS) lately, as I mentioned in a post a few days back, but cursory inspection of 12z stamps suggests circa 15 members running-up something of similarly bothersome look to the DET & CTRL, smack across the country. Many more show the deep-ish cyclonic outcome but with typically with more northerly bias to their genesis. A few run south of UK (just). Ensembles into 15d still trickling out.

Cheers Ian, if the low was to take a more southerly track would that drag some colder air into the equation ? Either way, potential for the first storm for a while.

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NOAA this evening is certainly agreeing with the highly amplified meridional pattern in the 6-10 time frame. Strong ridging in the Atlantic and the trough just to the west of the UK centred just west of Iberia. Obviously the surface detail resulting from this has yet to be sorted but the indications are of something similar along the lines of the GFS det. 

610day.03.gif814day.03.gif

gefs_z500a_5d_nh_41.pnggefs_t850a_5d_nh_41.png

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Eps mean and anomolys continue their painfully slow evolution towards something closer to GEFS in two weeks as the Eastern European high anomoly gradually fades and the southerly jet becomes the paramount driver. at the moment a mid lat high in our vicinity seems favourite and coldies would hope to see it primed for retrogression, should some WAA evolve courtesy of an upstream split. Tough to gauge on the means but currently a slight drift towards west based neg NAO but not much in it. the low anomoly over Siberia edging towards scandi with time. no idea how the clusters play out on the eps and the story of the evening likely to come from the ec 46 in a few hours, should it show some consistency. 

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12 minutes ago, fergieweather said:

...and by 29th, 27 members have us in a chilly cyclonic NW-Wly; 24 in blocked, cold N-NE'ly.

That's Great news, no need to be concerned about next weeks mild Southerly flow shown on the Gem op and Gefs 12z mean lasting long then.:good:

Edited by Frosty.

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EDM1-144.GIF?14-0   EDM1-192.GIF?14-0   EDM1-240.GIF?14-0

The ECM ensembles show a slow drying out process through next week as the trough filled and becomes cut off to our south. Unlike the operational it develops an area of high pressure near the UK with frost and fog certainly a possibility.

The GEFs have a similar set up to be honest

gens-21-1-144.png   gens-21-1-192.png   gens-21-1-240.png

The high is a little bit further west but the trend is there. The GEFs definitely show a strong retrogression trend with a trough developing to our east and temperatures dropping below normal at 850hPa (I suspect surface temperatures will be cool/cold beforehand). 

gens-21-1-300.png   gens-21-1-360.png

So unsettled until the start of next week, then turning drier with frost and fog before something more interesting could develop in the mid to long range. Well if the model output is to be believed at least which probably isn't that reliable given the high level of uncertainty, but just signs that the potential cold start to winter is starting to take shape.

Edited by Captain Shortwave

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17 minutes ago, fergieweather said:

...and by 29th, 27 members have us in a chilly cyclonic NW-Wly; 24 in blocked, cold N-NE'ly.

Hi Ian...or anyone else for a quick reply,

how many members is the 27 out of?? Just to get an idea of the percentage?

cheers

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2 minutes ago, WINTRY WALES said:

Hi Ian...or anyone else for a quick reply,

how many members is the 27 out of?? Just to get an idea of the percentage?

cheers

27 cyclonic , 24 blocked.....51 total!!

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Having said that, 27 in "chilly cyclonic" NWly flow does not rule out the possibility of Atlantic ridge height rises and blocking thereafter, whereas a straight cyclonic Wly would. Add that to the 24 blocked scenarios, and that sounds good to me. I guess only Fergie can tell us whether that is more or less than what the ECs were showing before? 

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A question to the more knowledgeable . GLosea and other seasonal output has indicated and still does to my knowledge point to a blocked start to December . But with 27 members going cyclonic albeit from a Nw quandrant does that suggest a slight shift change ?

Edited by Mark wheeler

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6 minutes ago, Mark wheeler said:

A question to the more knowledgeable . GLosea and other seasonal output has indicated and still does to my knowledge point to a blocked start to December . But with 27 members going cyclonic albeit from a Nw quandrant does that suggest a slight shift change ?

No those 27 members were cyclonic at that specific point in time (end of November) but there's nothing to say that another half of those didn't go on to be blocked a few days later.

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