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Paul

Model output discussion - 16th Nov onwards

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Any updates about tomorrow's severe gales?

 

The Midlands (well, around here) rarely get winds of 60mph, so it could cause a huge amount of damage and chaos.

 

We're all understandably looking towards the weekend, but there's something extreme just 24 hours away?

Hi , looks a stormy period between 7 pm and 11 pm across much of central and eastern England, Yes damage is quite likely, and disruption, perhaps the worst winds in nearly 2 years in these areas......

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I would like to ask a question for those who are a lot more in the know than my humble self.

Is any body able to define as a rough percentage the overall success of the different model outputs.

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I think the GEFS anomalies tonight highlight the uncertainties involving the upper air evolution. They do proceed to move the trough east on Tuesday, as has been suggested for a day or two, with slight ridging to the SW.  By Thursday, still maintaining the HP GOA, it builds the HP mid Atlantic whilst dropping a trough over the UK so an unsettled NW flow with temps around average.

 

The 11-15 period tends to move the long wave pattern a tad east, ( flattening the pattern which is no great surprise) and developing a weak LP northern Canada. This results in a more zonal westerly flow with temps around average but could bring some wintry conditions to the north with the airflow sourced Canada. But there is much to play for.

http://www.tropicaltidbits.com/

 

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A re-run of 62-63 it is then? :D

 

Do you think that model is likely to verify at that sort of range?  I appreciate it's an anomaly output(?); I just wondered whether the reliability towards February is going to so low that it isn't worth bothering with?

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Do you think that model is likely to verify at that sort of range?  I appreciate it's an anomaly output(?); I just wondered whether the reliability towards February is going to so low that it isn't worth bothering with?

The CFS has produced some rather fanciful 'predictions' over the years. I'd rather take the human perspective for now; but, in all truth; who knows what February's going to be like? Not me! :)

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A re-run of 62-63 it is then? :D

Add to that its not the most reliable site for forecasts either. For me the next 10 days look a complicated picture with a number of scenarios on the table all with an equal chance of verifying.

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Well it wasn't long ago when charts like these from the Ecm 12z op seemed impossible to achieve this month with no sign of a polar maritime incursion let alone an Arctic Blast but here it is and this looks great for coldies next weekend with 522 dam line digging well south. Some of us will have snow showers but even for those who miss out, it's going to feel like winter has arrived over a week early with widespread frosts and I can't wait! :)

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Don't you just love the cloud cuckooness of FI  :D

 

30th November.

 

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Well it wasn't long ago when charts like these from the Ecm 12z op seemed impossible to achieve this month with no sign of a polar maritime incursion let alone an Arctic Blast but here it is and this looks great for coldies next weekend with 522 dam line digging well south. Some of us will have snow showers but even for those who miss out, it's going to feel like winter has arrived over a week early with widespread frosts and I can't wait! :)

 

But we did see a brief polar maritime incursion just on Friday especially further North with wintriness even reported to quite low levels across Scotland but this will be the first Arctic blast of the season. 

 

One positive thing any cold blast will do is too cool the SST's down because I would not be surprised if they are above average at the moment. The detail still looks rather sketchy too me but the main emphasis does seem to be, an ridge into Greenland from quite an unusual starting point and a trigger low to help bring down the colder air from higher latitudes so some sort of cold weather will happen but whether it be a full on blast or something a bit more watered down is still very much debatable. 

 

Someone mentioned the ECM looks dry apart from Northern Scotland but too me, with fairly cold air, low thicknesses then I just can't see how it looks 'dry'. Should be some decent convective weather in eastern areas on that run and there should be some wintriness within those showers also, 

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I would like to ask a question for those who are a lot more in the know than my humble self.

Is any body able to define as a rough percentage the overall success of the different model outputs.

You do have verification statistics showing the accuracy of the outputs. This link should help:

 

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/12Z/

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The ecm anomaly also has the upper trough moving sufficiently east to cut off the cold northerly flow by Tuesday but subsequently treat the mid Atlantic HP a tad differently perhaps allowing a colder NW airstream into the UK. In the ext period the low Canada is developed with a trough Greenland SE to north of the UK giving a westerly zonal flow.

 

Just seen tonight's NOAA which is tending towards the ecm.

 

 

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ECM ensembles this evening highlight the ongoing uncertainty - 6 clusters by day 5.

 

In to the day 10-15 range the ensemble means once again likely to be rather unhelpful with something of a split. The majority of members look to place heights either over or to the NE of the UK, but the spread is rather large. A smaller minority want to re-introduce a more mobile westerly regime, but for now that looks to be the minority solution.

 

But given the uncertainty at shorter range it's worth taking anything beyond the end of this working week with a huge dollop of gritting salt...

 

What looks far more certain is a rather potentially disruptive afternoon/evening across parts of England and Wales:

 

ukgust.pngukgust.png

 

 

SK

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Evening All...After a potent shot of Artic air during the weekend ,we return to the Atlantic, as per the charts below! Gfs  shows the Atlantic in full fury, ecm is really strangely quiet although the same outcome,,,,, :)

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Any updates about tomorrow's severe gales?

 

The Midlands (well, around here) rarely get winds of 60mph, so it could cause a huge amount of damage and chaos.

 

We're all understandably looking towards the weekend, but there's something extreme just 24 hours away?

 

 

A couple of small  fast moving LP's crossing the UK,one tomorrow affecting the areas you mention,and another on Wednesday which looks to give similar strength winds but this time a bit further north.

 

Tuesday..post-2839-0-25155600-1447709364_thumb.gi  Wednesday..post-2839-0-45545200-1447709374_thumb.gi

 

Anomaly charts in good agreement at around the day 10 mark,but detail for the UK very elusive,although unlikely to be a mild setup.

 

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Evening All...After a potent shot of Artic air during the weekend ,we return to the Atlantic, as per the charts below! Gfs  shows the Atlantic in full fury, ecm is really strangely quiet although the same outcome,,,,, :)

I'd love to know how simultaneously the GFS can depict the Atlantic in "full fury" and the ECM shows it "strangely quiet", yet both produce "the same outcome"?

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18z already looking better than the 12z

 

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Saturday ice day?

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Another band of sleet/snow moving down from the NW Saturday night Sunday morning (bank it!)

 

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Stubborn convection persists across the Indian Ocean, amidst pockets of 'noise' bubbling up in an astonishing basin wide heat storage across the tropical oceans in general, aside from the sauna like Pacific SST anomalies.

 

Relative to the anomalous peaking heat of the 3.4 Nino zone, this is still sufficient to destructively interfere with the end matured stage of this massive Nino event, manifested as a slow erosion commencing east of the dateline. With Indian Ocean convection on going, easterly trades are finally picking up and with momentum transport, being added to the sub tropics there is easing of the strong westerly winds across the Pacific, despite the strength of the event.

 

The consequence is to to force torques downwards and add a -ve tendency to Atmospheric Angular Momentum. Such an atmosphere/ocean disconnect set to eclipse with change the one in Winter 87 that has cropped up in analogue forecasts this year - and featured a much more modest Nino than this one. 

 

The Global Wind Oscillation is set to complete a fast orbit through high AAM Phase 6 into Phase 8/0 in the short term as an initial response to falling momentum. This is consistent with, and fully advertises the strong upstream amplification heading from upstream into the Atlantic to provide the cold northerly this weekend.

 

The MJO  forecasts have proved quite chaotic thus far, but still point to the convection which has progressed to the East Indian Ocean to grind to a halt and retrogress back westwards. The implication of this is a further fall in AAM as implicated by GEFS forecasts into a low amplitude Nina-esque Phase 1,2,3 which, if verifying accordingly,will rubber stamp that unprecedented disconnect as discussed above.

 

The problem is that this is not a distinctive and organised MJO wave that moves seamlessly from east to west. It is the case that Nino phases usually don't feature regular MJO activity of any note, but this unprecedented hybrid event features such widespread anomalous warmth, that the spotted convection evident is too sporadic, unreliable and elusive to forecast pinpoint.

 

Adding all this together makes it extra hard to predict far ahead at all. Aside from the tropical and extra tropical messy interactions and uncertainties as described, we have a burgeoning Siberian High responding to good albedo feedback from early snow cover. On the other hand to this, we also have an ominously growing spiral of stone cold vorticity waiting to spin its way down the stratospheric layers to fire up the tropospheric westerlies big time, if it isn't challenged by the tropospheric pathway in some form or other, and, crucially, if the atmospheric circulation as discussed above starts messing for too long with established and expected Nino poleward amplification feedbacks.

 

Many who have written LRF's are depending on such key assumptions to verify.

 

I don't write or attempt to compile LRF's. But for purposes of this post I am going to be more conservative than usual within the 15 day-ish time period that my summaries usually cover.

 

It is seemingly increasingly likely that support is growing for the ridging in the Atlantic to play quite a part through this period. The longevity and discussion of the cold snap is well covered already in this thread, but allowing for band-with of a few days, one way or the other, there is at this stage reasonable support for the amplified ridge to flatten out, and, consistent with the falling AAM momentum theme, there is credence to some additional energy being switched into the polar jet resulting in erosion of heights from the NW. Southern parts of the UK may hold on to some fine and crisp weather under a possible inversion in this scenario - although in general temperatues heading back to near normal. Not at this stage, to the likes of the noteworthy mildness of recent weeks that will make the upcoming cold shot seem all the more marked than it normally would do.

 

It gets very tricky from there. Taking into account a probable last kelvin wave across the Pacific to add the last heat touches to the central basin heat total, it is likely that a further increase in westerly wind additions will increase frictional torques and AAM will bounce back. Frictional torques always lead Mountain Torques - and this is where it gets interesting in terms of Siberian High feedbacks. It is important that a bounce back in AAM has oomph to push the Global Wind Oscillation far into Stage 4 to make a Phase 5 landfall, and initiate that +MT. This has positive consequences for stratospheric wave breaking, We cannot take some of the more illuminating FI results of this in modelling for granted. There is at least as much that can go wrong, as might go right.

 

In this sense we will want the niggling tropical signal in the Indian Ocean to, in popular parlance 'do one'. The ENSO cycle is peaking and turning, and atmospheric forcing is going to become less Nino esque, despite there being a long way from a high peak to cool in the pacific, but nonetheless we do not want the ocean/atmospheric relationship to scupper the future existence of Siberian High feedback and SSW potential. Furthermore, we do not want Nina-esque jet stream tendencies playing into the hands of a stratospheric vortex which is not going to need much encouragement at all to run riot this winter.

 

Please forgive my lack of links here. I have typed this post whilst eating a yummy fish and chips takeaway! :wink:

 

 

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When you see high pressure stretching from Greenland to Africa in mid November it really is something!!

Fantastic charts for coldies at the moment and far from the drivel served up last year.

The 18z upgrades the cold a nudge. It really will feel bitter by Saturday

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Upgrade on potency on GFS 18z a parcel of -11C 850's over the heart of Scotland very cold air indeed.

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That's a very cold day for Saturday - and one tasty low rolling down the North Sea hot on its heels. There will be many white scenes during the day and following evening, I would expect. And getting closer to T0 all the time. Looks like ECM wasn't over-amplifying a few days ago after all...

 

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The most pleasing thing so far on the 18z is the fact that the Siberian High reverts to being aligned more favourably again

 

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That's a very cold day for Saturday - and one tasty low rolling down the North Sea hot on its heels. There will be many white scenes during the day and following evening, I would expect. And getting closer to T0 all the time. Looks like ECM wasn't over-amplifying a few days ago after all...

 

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Polar low? :)

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The 18z gfs has the max winds tomorrow swinging very quickly across Ireland and England during late PM and evening.

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