Model Output Discussion - 16th Jan 12z onwards - Smile While You Post!

[Sperrin]

Steve, how do you read the models for N Ireland? The reason I ask is your chart doesn't tally with the MetO.

We are under a yellow warning for 5-10cms of snow for Monday night/Tuesday morning

Curious to understand the difference of opinion?

Btw, always enjoy your posts, very helpful to a complete novice!

[Catacol]

 

 

The op has the US trough too deep and too cold compared to the mean. 

 

IDO - isnt that the point about the mean? An op solution will very rarely sit on the mean AND the reality of a pattern is also very unlikely to sit on the mean!! If I added up all the goals scored for and against during the Premier League yesterday I would come up with a mean score. But how many actual scores would match it?

 

The more examples you fit into a sample the more smoothed your mean. So to say that the op is wildly out of touch with reality because it is colder than the mean is a nonsense. Clustering is the only effective way to go... and in a volatile situation like this it is also a good idea to try and read the teleconnections. Rather than constantly picking charts and means out of the various runs and making statements about them, why not try and interpret them a bit using wider teleconnective understanding?

 

Bottom line is that we really dont know which way this is going to fall once the first slider passes through. In such a circumstance I would challenge the validity of the word "outlier" at all.

[SMU]

Steve, how do you read the models for N Ireland? The reason I ask is your chart doesn't tally with the MetO.

We are under a yellow warning for 5-10cms of snow for Monday night/Tuesday morning

Curious to understand the difference of opinion?

Btw, always enjoy your posts, very helpful to a complete novice!

 

HI Sperrin -

 

That 2nd image is really for the second event the first sliding event doesn't really effect the UK, Ireland set well on the first bout of energy ( especially NI) could see some decent falls especially at elevation in the NE of the region.....

 

S

[LomondSnowstorm]

I think the problematic forecast for Tuesday tonight shows that forecasting snow in this country is about as hard as it gets.! Latest thoughts from the models show a band of precip slowly moving in from the West on Tuesday and emphasis on slowly. As you would expect something a little milder moving in and if the models are correct, mainly a wintry mix on high ground over the west, cold rain for lowland areas. Dewpoints and 850,s are really not conducive for snow to fall especially on low ground.  Perhaps if that front moves further east and keeps itself togeather then ie east midlands may well see some snow, as it engages with some deeper cold. All up for grabs, but at the moment, a non event for snow come Tuesday for "most"    

 

Weird discrepancy between the Netwx MR model at 12Z and the GFS 18Zat the same timeframe:

The equivalent 18Z 5km NMM looks a bit colder at that timeframe than previously too (although still not widely sub 0C it's at least better for eastern areas):

front turning to snow as it moves east:

 

EURO4 out to 6pm Tuesday still has sub 0C DPs, although it tends to have a slight 'cold' bias:

Precipitation just starting to move in with air temperatures around 0C:

 

 

 

IDO - isnt that the point about the mean? An op solution will very rarely sit on the mean AND the reality of a pattern is also very unlikely to sit on the mean!! If I added up all the goals scored for and against during the Premier League yesterday I would come up with a mean score. But how many actual scores would match it?

 

The more examples you fit into a sample the more smoothed your mean. So to say that the op is wildly out of touch with reality because it is colder than the mean is a nonsense. Clustering is the only effective way to go... and in a volatile situation like this it is also a good idea to try and read the teleconnections. Rather than constantly picking charts and means out of the various runs and making statements about them, why not try and interpret them a bit using wider teleconnective understanding?

 

Bottom line is that we really dont know which way this is going to fall once the first slider passes through. In such a circumstance I would challenge the validity of the word "outlier" at all.

At D6+ large deviations from the climatological mean on the op will almost certainly be more diluted in the ensemble mean as you're always going to get some runs that go in a completely different direction. It possibly is overdone, but at the same time I wouldn't say it's notably an outlier given differences in other sectors.

Edited January 19, 2015 by LomondSnowstorm

[Trom]

It really depends , u can have a quick trop response almost immediately on occasion , the warming of jan 2013 saw a quick response of about 5/6 days , but I would normally say about 20+ days on avarage .

Thanks for that. So we're looking at that impacting on the charts most likely to be at the end of the range but something to be aware of in terms of cold in Feb. particularly interesting if we can get our current cold snap to extend which we've seen steps towards.

Really exciting model watching with short term fluctuations making big differences and interesting macro indicators moving. I leave Tamara and her torques to explain that. I've been working on understanding her posts and it's really interesting and I'm certainly getting a better understanding.  It's took a lot of reading and google searches mind!

Edited January 19, 2015 by Trom

[ANYWEATHER]

Weird discrepancy between the Netwx MR model at 12Z and the GFS 18Zat the same timeframe:

The equivalent 18Z 5km NMM looks a bit colder at that timeframe than previously too (although still not widely sub 0C it's at least better for eastern areas):

front turning to snow as it moves east:

 

EURO4 out to 6pm Tuesday still has sub 0C DPs, although it tends to have a slight 'cold' bias:

Precipitation just starting to move in with air temperatures around 0C:

 

 

 

At D6+ large deviations from the climatological mean on the op will almost certainly be more diluted in the ensemble mean as you're always going to get some runs that go in a completely different direction. It possibly is overdone, but at the same time I wouldn't say it's notably an outlier given differences in other sectors.

Just be very careful from the models

[Catacol]

Last thought before bed.... linked to my focus on the gradually creeping Russian high. GFS at T90 tonight: 

 

 

If you run the sequence you will see that at T90 we get to 1040mb and all the while it is nudging to the west. At around T120 the model starts to return to the westerly progression of all elements, something we have seen many times before over the years when it tries to get a grasp of a blocking high.

 

I am seriously beginning to wonder whether by the end of the week this high might not be nudging out into the North Sea, and with an increasingly split flow supportive of the southerly tracking jet. I have nothing more than years of observation to back this up, but there will come a tipping point where the vortex will - instead of pushing the high back SE will actually deflect over the top of this feature and squeeze it back west. Chio mentioned it earlier and I did allude to this myself a day or three ago.

 

Any supportive evidence? - models undercook HP resilience - in my eyes always. MJO is toying with a spin back to phase 6 from phase 7/8 and that is no bad thing. Glosea and JMA have it slightly differently over the next week, but sufficient doubt in this that MJO might follow the ECM and support high pressure more to the north. Vortex energy out west is definitely moving away across the pole to Siberia. Solar flux has fallen in the last 10 days. Final chart offering of the night - 120h strat forecast at 70hpa from yesterday. Note support for the pacific ridge, vortex primarly sat over Siberia, and ongoing signal for troughing over Europe.

 

 

 

Very interesting indeed. My spidey sense is starting to tingle a bit. All eyes on this Russian/Scandy high....

[A.J]

please remember this is not the 'will it snow in xxxx' thread. For those kind of posts please use the cold spell discussion thread found in the general weather discussion area and the regional threads. Unfortunately a few posts have been removed because of this

 

Steve has been kind enough to post his thoughts and charts based on his experience and current model outputs, so I'd recommend using them as a point of reference in making your own decisions on whether or not any one locale will receive snowfall rather than requesting specific 'snow forecasts'....This will help in keeping the thread clear for model discussion

 

Many thanks

[Trom]

On the strat's implication on the troposphere I found this model hugely illuminating in terms of the direction of cause and effect.

 

 

Source: Recretos 

Edited January 19, 2015 by Trom

[The Enforcer]

Well for every forecast showing rain, there's another one showing snow. According to the latest NMM, http://www.meteociel.fr/modeles/wrfnmm.php?ech=54&mode=1&map=0 there is some snow in southern areas between 2am and 2pm on Tuesday and to a more limited extent between 5pm and 12am and then more significantly from 7am Weds until 12pm Thurs, which is the end of the run. This will inevitably change, but it at least demonstrates that snowfall is an option.

 

 

GFS high res show nicely how after the front initially pushed through from west to east we start to get a pull back as the low starts to "reshape" and becomes a cut off low and drags in a south easterly flow with the ppn moving back West. This is a feature that needs watching closely IMO. There would certainly be a higher chance of some decent snowfall for some from this type of evolution.It was tentatively mentioned in the Countryfile forecast as well.........

 

GFS has plenty of PPN around from +48 through to +72 though at that range the details will change, but the cut off Low scenario is worth watching!!

The 18z NMM http://www.meteociel.fr/modeles/wrfnmm.php?ech=3&mode=1&map=5 is similar to its 12z output for the timeframes mentioned above. You can see the precipitation pivot and move back eastwards during late weds/early thurs.

Edited January 19, 2015 by The Enforcer

[-uksnow-]

Just to add my 2 pence to Catcol above: 

 

Take a look at the GEFS 18z panel - this saga is far from resolved yet. For example, choosing a random point at 168 hours away i count exactly 10 ensembles leaving us in an easterly flow with developed heights to the NW or disrupting troughs over us and down into Europe

 

Similarly the control run introduces a similar theme right up to 192 hrs (Haven't bothered looking past that - i see very little point)

 

The spreads at 192 also back this up; 

 

 

Huge spread over Scandinavia. Im far from saying this is going to go in a guaranteed direction, but its not over until the fat lady sings.. 

Edited January 19, 2015 by -uksnow-

[West is Best]

 

Beyond potential snowfall this week and I still cannot see a return of milder weather infact so far the 18Z remains cold especially towards the E.

 

Good morning all.

 

First things first, the later outlook. All three models have a return to mild next weekend so whilst this may not be the case we should be open about it (edit, see Emotional Rollercoaster's post above which I've just seen: quite right). These are the respective T144 charts, so not exactly FI and note unanimity between GFS and UKMO, and almost identical ECM:

 

UKMO

GFS

ECM

 

Secondly, we've been hearing about westward progression of this low for some days now. Here's an example of how the upper air temps have moved significantly east: identical ECM charts from yesterday's 12z to the overnight 0z:

 

Yesterday

Today

 

So, for this coming week. I've never seen such a stand-off before between the BBC / Met Office (with whom I agree) and some on here / GFS / Steve. It shows how borderline this coming event is. The BBC forecasters are currently going for wintry mix, mainly sleet and rain for southern Britain whilst Steve's snow map and the GFS snow type charts are showing significant snowfall. What to make of this?

 

The reason I side with the current Exeter thinking on this remains the frontal attack line. Because the fronts are progressing west to east there is little or no extreme undercut. The first front would therefore most likely both fizzle out and drizzle out. By this time, without undercut, the 850 hPa temps and dew points are rising so that the second front pushes through, again straight west to east, as rain. The frontal attack west to east shows up on the latest Fax charts:

 

What we would have wanted to see is the centre of the low forced west, pulling the front into a 90 degree axis straddling from 270 to 90 degrees. This is the best snow scenario for southern Britain as exemplified in a channel low: the front pushes in hits the cold, easterly driven, air ahead leading to an easterly or north-easterly flow and huge undercut. The current set up is completely different with the frontal attack line axis almost running from 0 to 180 degrees as the fronts themselves push through from west to east. See below:

 

 

The best hope actually probably resides with the kink, which leads to an undercut, which you can see here on yesterday's fax chart and which Steve has occasionally mentioned. We await to see if this is still showing in today's update. I fear, to be frank, that it won't and that this is chasing phantoms, but there we go:

https://forum.netweather.tv/gallery/image/20666-/

 

I'm not trying to be party pooper. The GFS still shows widespread snow. I think this is questionable and at the moment for the reasons above I think it's falling the wet side of the fence. I earnestly hope that's completely wrong.

Edited January 19, 2015 by West is Best

[TEITS]

Morning Richard.

 

I must admit the promising signs yesterday morning of the cold spell continuing has largely disappeared with all models keen on bringing a spell of W,lys. How long these will last is questionable though.

 

As for this weeks potential snowfall and its worth mentioning that the Met O are forecasting snow for the Midlands/E Anglia on their regional forecasts. It is only the SE/SW/S England that it suggests rain/snow. Looking at the Euro4 and to me it looks as though the heaviest snowfall will be across the Midlands/parts of N England with this moving slowly SE. However how far SE this snow extends is uncertain and in my opinion this is ,more likely to fall as rain across London and extreme S counties.

[Gustywind]

Good morning all.

 

First things first, the later outlook. All three models have a return to mild next weekend so whilst this may not be the case we should be open about it (edit, see Emotional Rollercoaster's post above which I've just seen: quite right). These are the respective T144 charts, so not exactly FI and note unanimity between GFS and UKMO, and almost identical ECM:

 

UKMO

GFS

ECM

 

Secondly, we've been hearing about westward progression of this low for some days now. Here's an example of how the upper air temps have moved significantly east: identical ECM charts from yesterday's 12z to the overnight 0z:

 

Yesterday

Today

 

So, for this coming week. I've never seen such a stand-off before between the BBC / Met Office (with whom I agree) and some on here / GFS / Steve. It shows how borderline this coming event is. The BBC forecasters are currently going for wintry mix, mainly sleet and rain for southern Britain whilst Steve's snow map and the GFS snow type charts are showing significant snowfall. What to make of this?

 

The reason I side with the current Exeter thinking on this remains the frontal attack line. Because the fronts are progressing west to east there is little or no extreme undercut. The first front would therefore most likely both fizzle out and drizzle out. By this time, without undercut, the 850 hPa temps and dew points are rising so that the second front pushes through, again straight west to east, as rain. The frontal attack west to east shows up on the latest Fax charts:

 

The best hope actually probably resides with the kink, which leads to an undercut, which you can see here on yesterday's fax chart and which Steve has occasionally mentioned. We await to see if this is still showing in today's update. I fear, to be frank, that it won't and that this is chasing phantoms, but there we go:

 

I'm not trying to be party pooper. The GFS still shows widespread snow. I think this is questionable and at the moment for the reasons above I think it's falling the wet side of the fence. I earnestly hope that's completely wrong.

Not sure what stand off are you referring to, the Met has my locale (which is Southern Britain) down for heavy snow late Tue and Wednesday, or do you mean Southern England?

Charts look quite progressive this morning, especially ECM which brings the Azores/mild sw in by Friday.

[TEITS]

Also worth pointing out that when it comes to marginal snowfall the timing is also important. If you look at the +48 Euro 4 you will see much of the snow arriving in the Midlands occurs during late evening and continue into the overnight period.

 

http://expert-images.weatheronline.co.uk/daten/proficharts/en/euro4/2015/01/19/basis00/ukuk/prty/15012100_1900.gif

 

So the real question for my location and others nearby is how far SE will this snow extend?

[Eugene]

Not sure what stand off are you referring to, the Met has my locale (which is Southern Britain) down for heavy snow late Tue and Wednesday, or do you mean Southern England?

Charts look quite progressive this morning, especially ECM which brings the Azores/mild sw in by Friday.

 

 

No it doesn't, GFS and ECM 00Z both pop up a ridge at the weekend keeping it chilly, the warm up isn't until next Monday, a whole week away, plenty of time for changes.

[Long haul to mild]

Good morning all.

 

First things first, the later outlook. All three models have a return to mild next weekend so whilst this may not be the case we should be open about it (edit, see Emotional Rollercoaster's post above which I've just seen: quite right). These are the respective T144 charts, so not exactly FI and note unanimity between GFS and UKMO, and almost identical ECM:

 

UKMO

GFS

ECM

Morning WIB.

Certainly good agreement in the models for the synoptic setup next weekend but temperatures barely struggle to get above freezing in some places so I would disagree that it will be mild, away from the extreme West.

Regards

[Captain Shortwave]

Apart from the micro-detail about the coming occluded front, the models actually are in good agreement to the end of next weekend really. Looks like the front of Friday will signal a return to a more westerly orientated pattern.

Next weekend still looks pretty cold still under a polar maritime influence so it will only be until next week when temperatures will start to properly rise as the usual variation of TM and PM airmasses starts to begin.

Unfortunately at this juncture it's a question of when and not if the milder air returns given the westerly theme establishing. The heights to our east never really get any influence over us except for the brief easterly of Thursday. Lets hope many wil see some snow over the coming week, though at this moment there is nothing particularly significant in accumulations forecast.

[Gustywind]

No it doesn't, GFS and ECM 00Z both pop up a ridge at the weekend keeping it chilly, the warm up isn't until next Monday, a whole week away, plenty of time for changes.

Not sure how to post images on an iPhone, but the 96h chart clearly shows sw/Azores ridge into most of western uk for Friday?

[SMU]

Richard your not comparing the same on Meteociel charts mate your comparing 1300:z V 01:00 Z. ( your loaded up both 72 hr charts but the 00z is only 12 hours past the last 12z- so they are 12 hours apart...

if you load the 84 hour chart which is 13 PM thurs which is when they are the same time

=http://en.vedur.is/photos/atlant_evr_hitaspa/150119_0000_84.png

Theres no movement east mate.- just a tiny correction west but negligible

in terms of slider location-

Weds 06z am seems to be the time when PPN its at its most widespread although the amounts have decreased overnight

http://en.vedur.is/photos/atlant_evr_urkomuspa/150119_0000_54.png

S

Edited January 19, 2015 by DiagonalRedLine
Image versions of the charts included - DRL

[shaky]

Richard your not comparing the same charts mate your comparing 1300:z V 01:00 Z.

 

Theres no movement east mate.

hi steve!after looking at all the charts the snow line seems to be in the same place as the the chart 2 you posted last night! ! Therss been no downgrade at all!latest euro 4 has heavy snowfall for the midlands! !! And then high pressure seems to come im after that giving us very cold days ans nights till at least start if next week!! Don't see a rapid thaw!! Another thing ive notice is ecm backs the flow slightly south south east at 48 hours compared to euro4 and gfs!! Do you think that will help bring in colder dew points!!

[SMU]

hi steve!after looking at all the charts the snow line seems to be in the same place as the the chart 2 you posted last night! ! Therss been no downgrade at all!latest euro 4 has heavy snowfall for the midlands! !! And then high pressure seems to come im after that giving us very cold days ans nights till at least start if next week!! Don't see a rapid thaw!! Another thing ive notice is ecm backs the flow slightly south south east at 48 hours compared to euro4 and gfs!! Do you think that will help bring in colder dew points!!

 

Yes seen the Euro 4 looks good at 48

thats 6 hours behind the ECM 54 I posted above

 

In terms of moderation I think the sweet spot max is now 8-10CM...

 

 

Gotta go-

S

[MR EXTREMES]

Richard your not comparing the same on Meteociel charts mate your comparing 1300:z V 01:00 Z. ( your loaded up both 72 hr charts but the 00z is only 12 hours past the last 12z- so they are 12 hours apart...

 

if you load the 84 hour chart which is 13 PM thurs which is when they are the same time

=http://en.vedur.is/photos/atlant_evr_hitaspa/150119_0000_84.png

 

Theres no movement east mate.- just a tiny correction west but negligible

 

in terms of slider location-

 

Weds 06z am seems to be the time when PPN its at its most widespread although the amounts have decreased overnight

http://en.vedur.is/photos/atlant_evr_urkomuspa/150119_0000_54.png

 

 

S

indeed steve snow line has not changed but certainly a shame we could not get a deep channel low heading futher into europe to draw a better easterly this has turned out horrid and of coarse as stated some of us still await a flake of snow.

 

very dissapointed and even more dissapointed to see such a longterm model outlook 

and from these charts i see nothing but the same like we have had since december although this pattern still may favour the northern areas still.

all in all cross model agreement as stated by the bbc 5 dayer lastnight the forecaster was extremely confident of this pattern winning out.

so its safe to suggest that we await to see if something far more confident pops up before feb for another cold spell.

[IDO]

Well it looks like, as others have said, that the cold spell will last to the weekend, front clearing Friday and a brief ridge followed by the Atlantic at D8. Then from the current NH profile it looks like the PV over Siberia will drain back to our NW (NE Canada). It looks a slow process and the mobility does not really promote any chance of HLB'ing. By around the 2nd Feb the PV is re-organised, control and op:

 

 

 

What happens after then may determine the Feb flow. Of course that is based on this run and it may change. Has about 50% support from the ensembles, so by far the largest cluster, but several more runs needed to see if it has spotted the next trend.

 

ECM and GEM also back to the Atlantic from around D8. All the models suggesting the Russian high is pushed back east after D8 so some sort of push west by that high now looks to have missed the boat.

 

So the main question is can some in the south get a spell of snow  this Wednesday? The London ensembles have been consistent around 40% for several runs, so there is still a chance for some in the south:

 

 

(Note the op and control are the coldest runs Friday-Sunday with the majority bringing in the milder air on Sunday.)

 

According to the hi-res WRF the first front slows as it travels east and stalls by T50 and the second front catches it by T56:

 

 

So spine of the UK. Afterwards the satellite low gives the SE a chance of some snow:

 

 

 

So promising 

Edited January 19, 2015 by i'm dreaming of...

[Severe Siberian icy blast]

Apart from the micro-detail about the coming occluded front, the models actually are in good agreement to the end of next weekend really. Looks like the front of Friday will signal a return to a more westerly orientated pattern.

Next weekend still looks pretty cold still under a polar maritime influence so it will only be until next week when temperatures will start to properly rise as the usual variation of TM and PM airmasses starts to begin.

Unfortunately at this juncture it's a question of when and not if the milder air returns given the westerly theme establishing. The heights to our east never really get any influence over us except for the brief easterly of Thursday. Lets hope many wil see some snow over the coming week, though at this moment there is nothing particularly significant in accumulations forecast.

Considering the changes at anything post 4/5 days at the minute i find it hard to see how you can gain confidence from charts at t144 , "it's not if its when " has to be the most misleading post of the year I'm afraid . Yes the models have picked up an apparent eastward movement following Fridays low but given its 5 days away I'm not worried just yet, remeber the models done this several days ago with regards to tue front , only to backtrack .

Particuarly given the MJO signal to keep things amplified , along with the split vortex , and yes another warming looking more and more likely , with decent wave one coming in from about day 6 onwards which will only put more pressure on the vortex , then given all this , also with Tamara's excellent posts over the last few days on where we'r going moving forward , raging southwesterlies don't really tie in too well at all to be honest and rather than allowing one run of the models to make my mind up I think il continue to sit quietly and try to look at the bigger picture with regards to background drivers, il be very surprised if these charts verify . They may of picked up on a push , but as they normally do they'll most likely be over reacting to a signal , only to fall back in line over the coming few days .