Focussed Model Discussion

[knocker]

The 500mb and surface analysis for midnight

After the weekend a much better day today for most with less wind and plenty of sunshine. albeit quite cold. But around 1400 cloud and rain, sleet and snow will effect N. Ireland and western Scotland, courtesy of a stray occlusion, and move east through the rest of the afternoon and also start to effect western regions in England and Wales.

Through the evening and overnight the rain, sleet and snow showers will become more prevalent in the north west as a cold front encroaches and by the early hours light rain will be effecting south west Wales and England as a wave approaches from the west

Frequent wintry showers, many of snow will continue in the north on Tuesday but as the cold front tracks south east a more concentrated band of rain, sleet and snow will go with it. This is further complicated by rain across southern England as the aforementiod wave tracks east into northern France. A cold day, particularly north of the border

Through Tuesday evening the rain, which has turned increasingly to snow, will clear the south east as the wave continues to track east into Germany leaving most of the country dry, bright and cold with perhaps the odd wintry shower in the west.on Wednesday

Whilst all of this has been going on an upper low has tracked from NE America via the southern tip of Greenland to be mid Atlantic by midnight Thursday and twelve hours later a rather amorphous looking surface low is residing west of Ireland with the associated occlusion nudging into the west coast of same. So for the moment Britain is cold and dry but over the next 24 hours the low will track south east to be over the Bay of Biscay  and this movement will skew the occlusion across the UK. The problem here is how far north will any rain. sleet or snow on it get? For the moment I'll pass on that, So leaving this aside Thursday and Friday will be a couple of cold days

 

Edited January 28, 2019 by knocker

[knocker]

To continue briefly with the gfs. The main trough continues to track south east to be over Italy by 00 Monday but after a very brief ridge the next frontal system is impacting Britain by same time with more rain, sleet and snow. But to the west the subtropical high is ridging once more and is pushed east to over the country by midday Tuesday

[knocker]

This morning's fax updates have a vastly different interpretation of the low for midday Thursday. Far deeper and more organized and a much changed orientation of the occlusion which will effect the timing and distribution of the precipitation. Clearly this is causing a few problems

 

Edited January 28, 2019 by knocker

[knocker]

The ecm is actually pretty much spot on with that latest fax at midday It them moves the low ESE over the next 30 hours, all the same time readjusting the tilt so that the front tracks NE > NW

 

[knocker]

One has to say, that if you reside over on the Dark Side, this morning's ext EPS mean anomaly is pretty underwhelming It hasn't shifted that much over the last couple days towards establishing HLB,and  if anything it's nudging the other way with temps just a tad below average

 

[IDO]

The 12z op from GEFS yesterday was indeed an overdone suite, the mean anomalies are much more subdued on the 0z. As expected, the overreaction was due to the model spotting a change in the dynamics, ECM has cottoned on this morning and flattened the pattern. The ECM mean as we would expect less forceful. It may take till tomorrow for the models to get a grip of the new dynamic, Atlantic High -v- Canadian Vortex draining power struggle.

So we have lost that 3-4 days of stalemate where we had a slack set up in the Atlantic sector, the models deciding to move forward the speed of the HP systems breaking from the failed Pacific forcing. The difference between the ECM and GFS op is that when the second HP system hits the Atlantic sector, on the GFS it send some energy north whereas the ECM pushes the pattern east. That could be to do with phasing, but more likely early doors on a new dynamic so some entropy. 

With the lack of downwelling helping the NH profile as much as expected and the failure of the MJO signal to represent its composite we are seeing little-prolonged HLB'ing, having to rely on sliders in an NW-SE Atlantic pattern, better than nothing, but not what the SSW promised, Going forward without strong downwelling we may have to rely on cold shots like this in marginal situations for our snow fix...

 

[bluearmy]

22 minutes ago, knocker said:

One has to say, that if you reside over on the Dark Side, this morning's ext EPS mean anomaly is pretty underwhelming It hasn't shifted that much over the last couple days towards establishing HLB,and  if anything it's nudging the other way with temps just a tad below average

 

Yes, the eps AO predicted to go neutral ( almost positive)  as we head through week 2 (gefs stay quite neg) 

Edited January 28, 2019 by bluearmy

[Singularity]

EPS continue to insist that the MJO will stall in P6, which shuts down the generation of the positive frictional torques (+FTs) needed to further sustain a build of HLB (and help keep a negative AO in place for what it's worth). A big contrast to GEFS which see continued eastward MJO propagation and at high amplitude, so no surprise to see a better HLB and neg AO signal from them in the 8-16 day range.

Stepping backward in range now; the FAX for Thu shows the key feature with respect to any snow of note falling in the south;

That triple point has enough of a disturbance associated with it to distort the flow, diverting the warm sector away into N. France while keeping a cold continental flow in place across S England. Question is whether this feature develops enough to 'buckle' the occluded front, holding it up and also causing it to mix out faster... this of course leads to a loss of precipitation intensity before long, but it can be very heavy during the initial stall. So I can see the potential for a narrow swathe of England to see some impressive totals in a short space of time. Where exactly, well that's the millionaire question!

 

Also briefly on Tue - I see the 06z GFS shifted slightly northwest with the LP system but it's still not enough to hold the occluded front up much away from the far SE. It's a very sensitive situation to small adjustments though; any increase in the SSE/SE flow coming up against the occluded front will not only slow it down but pep it up a bit too. Not only that but every hour slower takes it further into the night when settling is more likely... so it's a forecaster's nightmare alright - but that being said, I feel it will be hard going to get more than a cm or two from it at low levels away from the SE corner of England.

The unstable flow with sub-zero dew points on Weds might be another matter for the SW, however.

[Singularity]

Became more than expected so posting here too;

 

The eastern flank disturbance is a little stronger on the 06z - a step toward the Euros and the reason the front has a bit more trouble moving NNE. It also distorts the surface flow  into England sufficiently that it remains easterly enough to keep drawing from a frigid Germany through midnight Friday, before turning back more easterly during Friday morning.

    

The main inhibitor to snow is then the dew points;

Interesting how some negative DP air is wrapped into the LP circulation on this run, setting up a new boundary that develops further through Friday with snow widely across Wales and western England. The 00z ECM had similar developments but didn't develop the boundary as much and had more of a NE angle to the flow, which was less effective for the southwest.

[knocker]

34 minutes ago, Singularity said:

EPS continue to insist that the MJO will stall in P6, which shuts down the generation of the positive frictional torques (+FTs) needed to further sustain a build of HLB (and help keep a negative AO in place for what it's worth). A big contrast to GEFS which see continued eastward MJO propagation and at high amplitude, so no surprise to see a better HLB and neg AO signal from them in the 8-16 day range.

 

Yes indeed but considering the ecm upgrade in June did to some extent address this area

Quote

improves forecast quality in the tropics, enabling better predictions in the extended range in Europe and elsewhere, notably at weeks three and four

and the gfs is awaiting the upgrade, one tends to put more faith in the former. Or to be more precise, I do.

https://www.ecmwf.int/en/about/media-centre/news/2018/ifs-upgrade-improves-extended-range-weather-forecasts

Edited January 28, 2019 by knocker

[bluearmy]

The extended clusters look a bit binary .....wouldn’t say they preclude HLB ....

[IDO]

1 hour ago, Singularity said:

EPS continue to insist that the MJO will stall in P6, which shuts down the generation of the positive frictional torques (+FTs) needed to further sustain a build of HLB (and help keep a negative AO in place for what it's worth). A big contrast to GEFS which see continued eastward MJO propagation and at high amplitude, so no surprise to see a better HLB and neg AO signal from them in the 8-16 day range.

 

 

I have to disagree, the negative AO on the GFS is down to a wedge of heights running through the region and peaking on Feb 1 before the -AO weakens and heads back to neutral, as that wedge slips off the Arctic region:

I do not believe this is a direct result of the MJO forecast to go into phase 7 in early Feb as that wedge has already initiated. This -AO is just a transient feature, not a sustained signature from say a static Pacific Rossby wave. 

From last year a Pacific wave in full glory:

Looking at the current extended GFS for Pacific forcing:

We can see the failure of the yellow warmer 500hPa, subdued by the troughing of the upstream pattern, preventing strong forcing to the Pacific pattern. The PNA index^^^ is rather muted highlighting the lack of Pacific forcing.

TBH the MJO has not for me been a driver of the NH pattern this year and I am wary of taking much notice of it going forward due to the clear interference.

[knocker]

The clusters at T240 are supportive of the det run with trough pressurizing the ridge but after that I'll call a friend

Edited January 28, 2019 by knocker

[Dean E]

1 hour ago, Singularity said:

EPS continue to insist that the MJO will stall in P6, which shuts down the generation of the positive frictional torques (+FTs) needed to further sustain a build of HLB (and help keep a negative AO in place for what it's worth). A big contrast to GEFS which see continued eastward MJO propagation and at high amplitude, so no surprise to see a better HLB and neg AO signal from them in the 8-16 day range.

Stepping backward in range now; the FAX for Thu shows the key feature with respect to any snow of note falling in the south;

That triple point has enough of a disturbance associated with it to distort the flow, diverting the warm sector away into N. France while keeping a cold continental flow in place across S England. Question is whether this feature develops enough to 'buckle' the occluded front, holding it up and also causing it to mix out faster... this of course leads to a loss of precipitation intensity before long, but it can be very heavy during the initial stall. So I can see the potential for a narrow swathe of England to see some impressive totals in a short space of time. Where exactly, well that's the millionaire question!

 

Also briefly on Tue - I see the 06z GFS shifted slightly northwest with the LP system but it's still not enough to hold the occluded front up much away from the far SE. It's a very sensitive situation to small adjustments though; any increase in the SSE/SE flow coming up against the occluded front will not only slow it down but pep it up a bit too. Not only that but every hour slower takes it further into the night when settling is more likely... so it's a forecaster's nightmare alright - but that being said, I feel it will be hard going to get more than a cm or two from it at low levels away from the SE corner of England.

The unstable flow with sub-zero dew points on Weds might be another matter for the SW, however.

The trend over the last 24 hours or so is for Thursdays system to increasingly stall somewhere over the UK and then run along Southern areas during Friday and exit on Saturday, so some westward shifting going on, especially by the GFS (nothing new there). Indeed there is some good consensus with the GFS and EC in regards to Friday...

GFS 06z                                                           EC 0z

  

But as you said, wind direction looks like being a key for developments regarding Thursday. SE'lys delivered south of the M4 (like during Jan 2013), so an interesting time ahead.

[Man With Beard]

30 minutes ago, knocker said:

The clusters at T240 are supportive of the det run with trough pressurizing the ridge but after that I'll call a friend

Yes I think with that trough anomaly in that position, it's hard to see anything other than a southerly source to our weather by about the 7th February (just possible that a euro ridge will keep the atlantic at bay enough to allow continental flow but bit of a long shot)

As Knocker says a bit of mash-up beyond that - on cluster 1, beware interpreting the heights anomaly to the NE as a nailed-on cold factory, since without low heights over Europe, this might be result in a Sceuro high rather than a Scandi one

IMO, the wise money right now is on an end to the cold early next week, at least for a week or so - perhaps Scandi heights may bring the cold back by mid-month but that's pure guesswork.

[bluearmy]

14 minutes ago, Man With Beard said:

Yes I think with that trough anomaly in that position, it's hard to see anything other than a southerly source to our weather by about the 7th February (just possible that a euro ridge will keep the atlantic at bay enough to allow continental flow but bit of a long shot)

As Knocker says a bit of mash-up beyond that - on cluster 1, beware interpreting the heights anomaly to the NE as a nailed-on cold factory, since without low heights over Europe, this might be result in a Sceuro high rather than a Scandi one

IMO, the wise money right now is on an end to the cold early next week, at least for a week or so - perhaps Scandi heights may bring the cold back by mid-month but that's pure guesswork.

I think the eps model is ‘adjusting’ and you need to give it a couple of runs to find the possible routes forward .... sounds very unscientific I know 

Tonight’s 46 could be a questionable run ...

[stodge]

Afternoon all

Before the 12z toy-throwing starts elsewhere, a thought or two on the medium to longer term evolution.

The picture for next week and beyond is still being resolved at this time (naturally) but the signal for a shift to a more anticyclonic pattern seems to be strengthening. The 6Z Parallel brings in some very cold air next week as the Azores HP ridges cleanly into Scandinavia. The OP doesn't make the transfer cleanly while the Control looks promising until a spoiler LP drops down the British Isles and the ridge is broken.

Interestingly, the 00Z GEM brings back my little mid-Atlantic LP from last week which pushes NE and brings heights to the east of the British Isles.

I'm also noting a hint of another Wave 1 warming from the Eurasian side which we emphatically don't want or need.

The 06Z GEFS look very anticyclonic in far FI but where the core and orientation of the HP will be is still to be resolved.

 

[knocker]

There is currently a batch of wintry showers effecting western Scotland. a few down the east coast and these parts as well, In the former area these showers will become more frequent during this evening and over night and spread further afield as they become increasingly of snow so that by morning maybe some accumulations but also very icy in the very cold ground temps. Elsewhere a widespread frost as well if not as cold.

Edited January 28, 2019 by knocker

[Singularity]

The main event next week is an ejection of the deep cold completely from the eastern U.S. into the N. Atlantic. 

In typical fashion, the model response to this is to start developing large, vigorous troughs with a lot of eastward 'shove' to them - but as recent history has shown us, this often proves to be too efficient a response, with the actual result less organised, maybe featuring a very intense system but not necessarily one moving strongly E or NE.

Given that there's also a strong signal for height rises generally between a little SW of the UK to somewhere north of Scandinavia, it seems reasonable to anticipate a settling down of the UK's weather with surface temps dependent on how much maritime air becomes entrained into the circulation during the transition out of the UK-Euro trough stage.

A possible wildcard is the MJO if it has enough eastward propagation and downstream influence, but I'm becoming sceptical of that possibility as GEFS may still be very amplified but are slowing down the propagation, and it's that which really counts when looking to sustain a +AAM regime sufficient for blocking to establish N/NE of the UK. That then leaves us with the settled conditions as a holding pattern until any SSW-driven impacts arriving by mid-Feb.

Not a very exciting prognosis I know - but it seems that after delivering last month only for the stratosphere to counter it, the MJO's not in the mood to do what we'd like this time around, despite the stratosphere being in a more co-operative stage. Figures! Usual caveats apply though - I might be reading too much into today's adjustments!

[knocker]

Just to note, en passant, that the 100mb analyses has a very 500mb look about it at T192

[knocker]

Pretty good agreement between the fax and the ecm this evening for 12 Thursday

Over the next 24 hours the ecm swivels the low on it's axis as shifts it south east with main center in Biscay. Thus the weakening front tracks up through southern England into the Midlands with some patchy rain. sleet and snow.

Over the next three days this trough is forced south over the Mediterranean by the combined forces of the strong east European block and a renewed Azores high ridging from the south west which also thwarts the next thrust of energy from the west until eventually fronts break through late Monday

Edited January 28, 2019 by knocker

[Sky Full]

3 hours ago, knocker said:

There is currently a batch of wintry showers effecting western Scotland. a few down the east coast and these parts as well, In the former area these showers will become more frequent during this evening and over night and spread further afield as they become increasingly of snow so that by morning maybe some accumulations but also very icy in the very cold ground temps. Elsewhere a widespread frost as well if not as cold.

Hi Knocker - do you have any current or very recent satellite images you could post?  I find it very interesting and helpful to compare the current charts and fax charts to the photographic satellite images you share with us from time to time.  Understanding how the weather develops over the next few days would be a lot easier if I could see what it looks like from above!

[knocker]

35 minutes ago, Sky Full said:

Hi Knocker - do you have any current or very recent satellite images you could post?  I find it very interesting and helpful to compare the current charts and fax charts to the photographic satellite images you share with us from time to time.  Understanding how the weather develops over the next few days would be a lot easier if I could see what it looks like from above!

This is the 1800 geostationary WV image showing the showers over Scotland and the low to the south west/ If their are any decent images tomorrow Ill post them

[knocker]

Comparing the EPS mean anomaly over two days is indicative of a retrograde step vis HLB, And there is not a lot of cold air around

Edited January 28, 2019 by knocker

[Catacol]

12 hours ago, knocker said:

...One has to say, that if you reside over on the Dark Side, this morning's ext EPS mean anomaly is pretty underwhelming It hasn't shifted that much over the last couple days towards establishing HLB,and  if anything it's nudging the other way with temps just a tad below average

 

It is grim. Clearly the Jedi have returned in force. There are all kinds of theories out there at the moment as to why we have repeatedly failed to see any HLB. They are all interesting, and in the dreadful months of summer heat while we hide from burning, sweating and heat-induced lethargy we can examine them with a sharp eye and clear head (assuming air con....) Right now I’m still looking at a set of signals that should be creating a different hemispheric long wave....but are not. Masiello has admitted to a bit of a bust in the current phase, Furtado looks on shaky ground and GP has disappeared. And underpinning it for me is a frustration - if we cannot develop our handbook with any accuracy and place a degree of trust in the signals we are seeing then we really are only “hope casting” as some describe, and that sticks in the craw. We want to be better than that.

We have an approximate two week window to see whether any hint of the winter forecast can be saved. If we get to mid month with no cold block and no strong suggestion from the ENS of one just around the corner then 2018/19 will have to go down as one almighty bust. Sidney can then leave his nuts in warm storage for another 12 months.