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Model Output Discussion 29th December - Into mid-Winter.


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Evening All For those of us who have been here for a long while there is times when you know you have to throw in the towel on chasing cold & times ( very rare ) when you 'just know' that the

Boom goodnight vienna

People being a bit harsh on Steve Murr, at least he has the balls to try and read and predict what may happen from his viewpoint rather than just posting what charts show.

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ECM did very well picking up the blocking theme holding back the atlantic this week, with GFS having none of it, but then showing the atlantic retreating, but ECM got it wrong with the northward extension of heights, instead they've ended up just to our SE. With little changing the overall pattern of recent weeks, no major forcings taking place to cause a sudden shift in things, I fully expect the ECM to continue to suggest scandi heights 7/8 day timeframe over coming runs. GFS show varying degrees of zonality sometimes with a major easterly push, sometimes holding back as the current GFS 18Z is showing, but the end result central core heights of the block being both sufficiently close to our shores to kick aside any significant zonal mobile westerly and also any cold continental air penetrating our way. So expect more of what we have had all winter so far for a bit more time yet... Feb holds chance of significant shift in things though, which way who knows...

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41 minutes ago, damianslaw said:

ECM did very well picking up the blocking theme holding back the atlantic this week, with GFS having none of it, but then showing the atlantic retreating, but ECM got it wrong with the northward extension of heights, instead they've ended up just to our SE. With little changing the overall pattern of recent weeks, no major forcings taking place to cause a sudden shift in things, I fully expect the ECM to continue to suggest scandi heights 7/8 day timeframe over coming runs. GFS show varying degrees of zonality sometimes with a major easterly push, sometimes holding back as the current GFS 18Z is showing, but the end result central core heights of the block being both sufficiently close to our shores to kick aside any significant zonal mobile westerly and also any cold continental air penetrating our way. So expect more of what we have had all winter so far for a bit more time yet... Feb holds chance of significant shift in things though, which way who knows...

An excellent wrap-up of developments i think. But it still strikes me as strange that ECM and GFS model so differently in a situation where there are, as you say, few major forcings taking place. In a relative quiet environment every model should be down to basic airo-, thermo- and other dynamic models..?

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1 hour ago, SN0WM4N said:

GFS actually taking steps towards the ECM solution but still flatter and further east it separates the low north sending less energy NE and keeps some back.

It's shown well in the jet stream forecast

Strong on a SW/NE axisgfs-5-186.png?12 

not as strong on the 18z with a curl back up by iceland. gfs-5-180.png?18

wont stop the atlantic onslaught but its a slowdown. 

I think it's always going to be difficult to get an easterly with the jet tracking north supressing the Scandinavian block southwards unless the jet tracks so far north it goes over the arctic like in 2004 or 2005 I think it was.

Most want rid of the UK High, but I have decided I would like it to stay. It is helping Europe to undergo repeated polar continental attacks so that there is even cold air entrenched way to our south. The best scenario for snow would in my view be for the UK High to stick around until the much mooted amplification that seems to be around allows the jet to align so that it approaches from the south-west. Even if the UK High is flabby and simply backs off to the east, this would still entail an approaching Low pressure system dragging in the cold air off the continent over the UK ahead of it. Normally you'd need a easterly/south-easterly flow, but with Spain and Portugal so cold by my reckoning even a straight southerly would suffice. It would then take a lot longer than normal for the atlantic air to override the cold air so a decent snowfall should spread north-eastwards across the UK before it turns milder. If the High holds firmer then a 1980s type battleground with fronts being pushed back would be possible.

This is probably an unlikely scenario, but I think I favour it to easterlies which have a high failure rate when consistently modelled and tend to promise 1987 or 1991, but usually deliver much less for one reason or another.

Edited by The Enforcer
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WINTER 2016/17 FULL REPORT No. 8 (PART 2) WITH JANUARY 16TH INPUT

Part 1 of my report was posted yesterday (on page 269 of this thread).

Dr Judah Cohen’s Latest Arctic Oscillation Report:

Judah Cohen’s has just published his latest AO report (at 2330 on January 17th). This includes his comments on the possible SSW.

Here is the link:

http://www.aer.com/science-research/climate-weather/arctic-oscillation

I copy his summary below:

...”Summary

The Arctic Oscillation (AO) is currently neutral and is predicted to remain slightly positive over the next two weeks.

The weakly positive AO is reflective of mostly negative pressure/geopotential height anomalies in the central Arctic and on the Eurasian side of the Arctic and mixed pressure/geopotential height anomalies in the mid-latitudes. With predicted increasing heights over Greenland and Iceland, the North Atlantic Oscillation (NAO) is predicted to be mostly negative this week.  However next week heights are predicted to fall near Greenland and Iceland, forcing the NAO in a slow positive trend.

Mid-tropospheric closed lows/negative geopotential height anomalies accompanied by cold surface temperatures will dominate the weather this week in Alaska, Europe and East Asia. In contrast ridging/positive geopotential height anomalies accompanied by mild surface temperatures will dominate the weather in Canada, the lower 48 United States (US), Northern Europe and Western Asia.

Starting next week a sudden stratospheric warming (SSW) /polar vortex (PV) weakening is predicted to begin, which will likely have a significant impact on the Northern Hemisphere (NH) tropospheric circulation in the coming weeks.

Strong poleward heat flux in the stratosphere over East Asia will both displace the stratospheric PV to the north slope of Asia and cause large height rises over Alaska and Northwest Canada.

The immediate response from the PV weakening will likely be increasing tropospheric ridging/positive geopotential height anomalies over northwestern North America directly under the stratospheric ridge and a deep tropospheric polar low under the displaced stratospheric PV over the north slope of Asia.

Rising heights over Alaska and Northwest Canada will help force troughing/ negative geopotential height anomalies accompanied by a cooling trend downstream over the Eastern US. Counterclockwise circulation around the polar low over the north slope of Siberia will transport North Atlantic maritime air into western Eurasia including Europe resulting in a trend to milder temperatures across the region.

East Asia tends to be cold leading up to SSW/PV weakenings with the cold weather easing post the SSW.  Therefore the next couple of weeks look to be cold across East Asia with a milder trend to follow.

I discuss below in more detail my expectations for the weather across the NH in the coming weeks within the framework of troposphere-stratosphere coupling...."

Here is part of his more detailed look at the “Impacts”:

….Impacts

Back in the fall and early winter, multiple times in this blog I offered the winter of 2009/10 as the best analog for what I expected for this winter in regards to the stratospheric PV.  In 2009/10 there was a SSW/PV weakening in November and then a second larger event that culminated in a major mid-winter warming in early February.  This winter there was a SSW/PV weakening in November and now all the weather models predict a second SSW/PV weakening to begin next week.  The PV weakening will continue to evolve past next week and will likely peak in early February but much uncertainty still exists.  But if the weather model forecasts verify then at least in regards to the stratospheric PV, the winter of 2009/10 will likely to turn out to be the best analog for winter 2016/17 in the observational record.  My expectations for the similarity in the stratospheric PV behavior were based on the similar snow advance index (SAI) values observed in October 2009 and 20016.  In contrast winter 2009/10 there was an El Niño and the quasi-biennial oscillation (QBO) was in an easterly phase.   This winter is a La Niña winter and the QBO is in a westerly phase.  But in spite of the similarities in the stratospheric circulation between the two winters, their have been important differences in the tropospheric circulation including a much more negative AO so far in winter 2009/10.

Since late December I have discussed our experimental PV forecast model that was predicting a PV weakening for the second half of January.  That forecast was at least two weeks ahead of the Global Forecast System (GFS) model forecast of a PV weakening.  The PV forecast model predicts that the stratospheric PV will be generally weak through mid-February.  If the model is qualitatively correct then the upcoming PV weakening could be a prolonged event, which in my opinion complicates the forecast.  If the predicted poleward heat flux for next week immediately resulted in a major mid-winter warming (MMW where the winds reverse from westerly to easterly at 60°N and 10 hPa) then the forecast should be relatively easier.  Changes in the atmospheric circulation associated with the MMW would propagate to the surface within two weeks and likely last through the end of winter.  However at least for now that is not what I am anticipating.  As we saw last winter even if the PV weakens, the poleward heat flux can remain active leading to warm episodes at the surface even if the PV weakening results in short-lived colder weather.

The near term forecast related to the SSW/PV weakening does look straightforward.  A pulse of poleward heat transport next week is predicted to displace the stratospheric PV from the North Pole towards the north slope of Siberia next week. The poleward heat flux is also predicted to warm the stratosphere over the western Arctic (closer to Eastern Siberia and Alaska) leading to ridging/positive geopotential height anomalies over Alaska and Northwest Canada.  This is a similar stratospheric PV pattern that was observed at the end of November though this time the ridging is predicted to be of greater amplitude and more extensive than back in November.  In November the downstream cooling from the ridging was focused in western North America.  However I expect any downstream cooling from the upcoming ridging to be focused in the Eastern US.

Back in November the displacement of the PV towards northern Eurasia resulted in very cold temperatures in Western Asia due to strong troughing across the region.  This may yet occur but at least initially the weather models are predicting increasingly westerly flow across western Eurasia.  For much of the winter, ridging across and to the east and west of Northern Europe has blocked maritime air from penetrating into Western and Northern Asia resulting in a cold winter so far.  However with the stratospheric PV predicted to be displaced towards northwestern Eurasia, geopotential heights are predicted to fall across the region.  Lower heights across northwestern Eurasia and predicted rising heights across southwest Eurasia will result in strengthening westerlies across the region.   This will allow mild maritime air to overspread Europe and Western Asia.  I do think that this pattern is transitory and I discuss below in the Longer Term section my expectations for how the pattern across both continents may evolve…..”

..."Longer term The near term the impact of the predicted troposphere-stratosphere coupling should be relatively straightforward.  Across eastern North America, as often is the case, the increase in WAFz/poleward heat transport will coincide with a relatively mild period.  However the resultant SSW and ridge building over northwestern North America will favor increasing troughing and colder temperatures over the Eastern US with time.  For reasons that I don’t understand even though it often turns milder across eastern North America during periods of active WAFz/poleward heat transport, across East Asia it often turns colder.  More Arctic outbreaks are predicted for East Asia for next week and the cold weather should continue until the SSW peaks and then I would expect it to turn milder in East Asia.  However on the western side of Eurasia, including Europe, the initial impact from the SSW/weakening PV will be a turn to milder weather.  Because the PV is near the north slope of Siberia, the counterclockwise flow around the PV is westerly.  This favors enhanced westerlies across Europe and a turn to milder weather...."

If a more prolonged SSW....

..."For Europe, the immediate impact of the SSW/weak PV is for the weather to turn milder.  However if there are subsequent pulses of WAFz/poleward heat transport this should further weaken the stratospheric PV and nudge it closer to Europe.  This could either turn the winds more northerly across Europe or even force the stratospheric PV into Europe.  Both of these scenarios would reverse the weather once again across Europe and result in much colder temperatures.

Over the next few weeks I will be looking for one of three possible outcomes.  The first, my personal favorite, is a PV split, which I believe favors snowstorms.  No sign of it yet in the weather models but multiple WAFz/poleward heat transport pulses would make this scenario increasingly likely.  The second possible outcome is for the stratospheric PV to be bodily displaced into Europe.  This would likely focus the largest negative temperature departures across western Eurasia including Europe. The third possible outcome is for the PV to be displaced into the northern North Atlantic.  This would likely result in strong cross polar flow into eastern North America and focus the largest negative temperature departures across eastern Canada and the Eastern US...."

Judah continues with his usual look at the near term, the next few weeks and further ahead. This part contains many maps, charts and diagrams and is far too long for me to reproduce here.

Brief Comment:

For us, Judah indicates, colder this week, milder next week. Longer term, possible impacts from the SSW but not necessarily good news for coldies - initially milder in western Europe. Later impacts might bring northerlies to Europe and possibly much colder conditions but this could change.

***IMPORTANT NOTICE***

This will be the last time that I will provide my full coverage of Judah Cohen’s weekly updates. I allowed myself to become pretty obsessed with his reports even when I had started to become more critical of them. I previously stated that I felt that many of Judah’s tweets were publicity grabbing with one liners in response to a single model’s output and the next tweet frequently showed the opposite. Even his more balanced and better considered weekly updates have often become an over-reaction to current output and seem to have become increasingly inconsistent. By passing on some of Judah’s comments I might become guilty of ramping up what might already be a ramp - he is also a coldie.

I still have considerable respect for Judah’s research into the extent of Asian snow cover in October and its impacts on early winter conditions. There does seem to be a strong correlation in most winters. I feel that his own model becomes less reliable as the impacts wear off in the second half of winter.

So, from now on, I may occasionally provide a link in my full weekly reports when I consider something worth reporting on. Perhaps someone else might wish to take up the mantle.

Next full report due this Sunday.

 

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32 minutes ago, Man With Beard said:

GFS 18Z ensembles 100% mild by D10. ECM ensembles for London about 90% mild

That's just it though,day 10,it was early next week.Wonder how far they keep pushing it back?.

Interesting.

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Looks like the models may be about to shift back to a colder outlook again. ECM looks very interesting. In the same way that we lost our easterly for this week, and then had zonality looking quite certain, now this seems to be getting pushed back further and further and is not so certain any more, a very interesting trend. Might we now eventually get our easterly later next Week, it does now look possible.  Wednesdays model runs will be very interesting, and I would not be surprised to see increasing support for an easterly for later next Week!                                        

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14 minutes ago, northwestsnow said:

Well the only positive i can find from GFS 0z is that its mainly dry out to lala land.The NH profile is not pretty though.

The PV seems reluctant to leave its perch..

Not pretty and no way the ECM will atick with its last run, still the SSW is there and moving ever closer so fingers crossed that gives us a good chance in Feb - with our luck though I'd imagine the US will turn v cold, as it looks like doing late next week onwards before any SSW trop response.

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13 minutes ago, Ali1977 said:

Not pretty and no way the ECM will atick with its last run, still the SSW is there and moving ever closer so fingers crossed that gives us a good chance in Feb - with our luck though I'd imagine the US will turn v cold, as it looks like doing late next week onwards before any SSW trop response.

No i don't think for one minute ECM will look much like last night.

Rukm1441.gif

UKMO looks mainly dry and cold,esp at night i would have thought but its hard to see a route to cold uppers and a snowy set up from the chart above.

Must admit all my eggs are in the Strat warming now, tbh im feeling a bit tired now of chasing the rainbow, half a day of snowcover in Dec and Jan is actually on a par with last years write off so although its been drier for most (thank goodness) its still been another sorry effort for snow fans.

So, a drier cold week or so looks odds on with a slide into a more unsettled regime,hopefully a brief one..

GEM is absolutely awful good job its cannon fodder..

Edited by northwestsnow
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The praise for the ECM is misleading as it had three runs with a frigid easterly from a Scandi high, when in fact we ended with a Euro high and a Continental feed for the SE. When you are chasing snow that is very disappointing. Of course last night's 12z was ECM at it again, rarely do their verification's hit 0.1 but it has been close two times recently and the model is pretty useless at D10 at times. Its spread from last night shows it is clueless. ECM D16 spread>>

EEM1-240.gif

The current SE flow means cold nights but the days are not bad with some sun and it hit 6.7c max in my area yesterday, so close to the average.

My ramblings are because the GEM, GFS and GEFS all 100% support a Euro high replenished from D5 by another Azores wave with the PV lobe moving to the north of us preventing anything other than a MLB. This has been the vane of our Winter so a bit puzzled why members would want this delay to a zonal spurt, as I am pretty sure the zonality will be for only the short term? This setup is horrid for snow or cold uppers, the next 2 weeks basically poor; London ens:

graphe6_1000_306_141___Londres (14).gif

As for the MJO, its been a bit player this Winter and I am not going to suddenly hang my hat on that until I see it actually being instructive. It is clear other factors are driving the NH weather, as a weak PV is primed for a trop forcing but all we have had to date was a weak Pacific Ridge that gave us a very transient NW'ly-N'ly. The Azores and the mobility of the PV has been the best guide to the UK pattern and we await the zonal spell to disconnect that and hope there is a reset once that is completed. Unlike others I am not interested in this Euro high delaying further developments and it hanging on like this just means the chance of snow remains nominal.

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16 minutes ago, northwestsnow said:

Looks to me like an ECM climb down , just too much energy in the Atlantic for a change...

 

 

It looks like it's heading the same way to me..

 

ECH1-192.gif.png

Edited by D.V.R
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2 minutes ago, D.V.R said:

It's looks like it's heading the same way to me..

 

 

ECH1-192.gif.png

Yeah it looks amplified again, and that's quite a sharp trough that looks like shutting the Atlantic off...strange but is it true! No support at all for last nights run; that's all we know for now.

Edit - 216 isn't going for an Easterly though with the cold again heading for Eastern Europe - they've had a very cold run this year.

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2 minutes ago, Ali1977 said:

Yeah it looks amplified again, and that's quite a sharp trough that looks like shutting the Atlantic off...strange but is it true! No support at all for last nights run; that's all we know for now.

Edit - 216 isn't going for an Easterly though with the cold again heading for Eastern Europe - they've had a very cold run this year.

Seems to me like more of a variation on a theme rather than a full climbdown. Yesterdays solution was more "extreme" yes but still a broadly similar evolution. GFS still on a different path. Ensembles will be interesting. 

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gefsens850London0.png

Ensemble agreement is probably as good as it has been for a while for the next 7/8 days. After this the expected spread of outcomes, but looking quiet for the next week at least. Pretty dry until the end of the month.

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Morning everyone, I've just been having a look at the 'weeks 1 to week 4 anomalies charts' from the CFS, and after this week of anti cyclonic gloom, it does look as though the zonal train is going to be much more of an influence to our weather. 
... Yes I know, its the CFS, and yes I know it can change at the drop of a hat, but I can only comment on what I'm seeing... And I'm also sorry if this isn't what people want to see or hear. :mellow:
 

wk1.wk2_20170116.z500.gif

wk3.wk4_20170116.z500.gif

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3 minutes ago, Dangerous55019 said:

Morning everyone, I've just been having a look at the 'weeks 1 to week 4 anomalies charts' from the CFS, and after this week of anti cyclonic gloom, it does look as though the zonal train is going to be much more of an influence to our weather. 
... Yes I know, its the CFS, and yes I know it can change at the drop of a hat, but I can only comment on what I'm seeing... And I'm also sorry if this isn't what people want to see or hear. :mellow:
 

wk1.wk2_20170116.z500.gif

wk3.wk4_20170116.z500.gif

The cfs has been atrocious all winter. Long may it last :)

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Looking at this mornings ECM 00z at T192 compared to yesterdays 00z at T216 & high pressure looks to be staying in control of the majority of the UK barring the far North west of Scotland, hoping it is a trend that continues. We can only hope that last nights 12z was on to something but if the rule of thumb of the ECM over amplifying and GFS of under amplifying is true in this case, we would probably end up somewhere in the middle.

Even though cold on the whole as been lacking this season we haven't had much in the way of 'default zonality' so if we get a couple of weeks of it then so be it. we are British and we're ard!

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