Model Output Discussion - 23rd Jan - 12z onwards

[Paul_1978]

Someone earlier said that the models had "wishbone" written all over them in terms of precipitation for next week. They were right - for Sunday that's what the new warnings suggest - snow for much of Scotland but for England, mainly coasts only (for now).

Edited January 28, 2015 by Paul_1978

[Meggy]

Hi! Apologies because I'm not technically minded at all but I think I remember someone saying the GEFS have not been updated yet. does this mean they are still running with the bias of the old GFS or is the new GFS much better? sorry if this doesn't make sense, I don't usually venture outside the regional threads so please be gentle with me! 

[i luv snow]

Someone earlier said that the models had "wishbone" written all over them in terms of precipitation for next week. They were right - for Sunday that's what the new warnings suggest - snow for much of Scotland but for England, mainly coasts only (for now).

 

I think if troughs and disturbances (or even low pressure) forms in the bitterly cold northerly then ppn will be much more widespread than the warnings suggest. If they don't, you will very much see a wishbone effect with ppn sticking to Scotland and coastal areas only.

 

As these cannot be forecast until nearer the time, the met office will not be able to release any sort of warning at this stage - but can still be fairly confident for snow showers in these areas. Expect updates to the warnings, if/when troughs or developments take place for Sunday into early next week - but much nearer the time. Indeed, with snow you often see events take place which were never even forecast! That's the beauty of it!

[Banbury]

Hi! Apologies because I'm not technically minded at all but I think I remember someone saying the GEFS have not been updated yet. does this mean they are still running with the bias of the old GFS or is the new GFS much better? sorry if this doesn't make sense, I don't usually venture outside the regional threads so please be gentle with me! 

I don't think GEFS has been updated yet .

[chionomaniac]

The 6z ensembles continue to give me cause for concern re. next week, even more than the previous 8. I'm not sure how long this will be sustained before the op breaks and goes the way of the others? Perhaps it's on the right path but it would be good to see the many milder members head south to join their big brother:

 

Screen Shot 2015-01-28 at 12.47.06.png

I think that is fair enough - not that I would base any particular outlook on the GFS ensembles, but the trend for the ensembles is milder after day 6 over the last few runs, whereas the operational has hardly wavered.

 

I don't know whether I saw an answer to whether the ensembles upgraded at the same time as the operational - it would seem daft not to.

[Paul]

I don't know whether I saw an answer to whether the ensembles upgraded at the same time as the operational - it would seem daft not to.

 

They didn't, that upgrade is due later in the year.

[Jason H]

They didn't, that upgrade is due later in the year.

That makes the ensembles meaningless until then.

[chionomaniac]

They didn't, that upgrade is due later in the year.

Cheers Paul. 

 

Daft then . 

 

That would mean that I would take slightly less notice (don't disclude - but letting the Atlantic back in too soon was one of the old faves of the GFS ensembles) 

Stick with the operational and ECM ensembles.

Edited January 28, 2015 by chionomaniac

[frosty ground]

Cheers Paul. 

 

Daft then . 

 

That would mean that I would take slightly less notice (don't disclude - but letting the Atlantic back in too soon was one of the old faves of the GFS ensembles) 

Stick with the operational and ECM ensembles.

On the other hand the Ensembles picked up on this cold spell way before the operationals became solid on it....

[Mucka]

General summary of current snow prospects taking all the output and fax charts into account. (Open to change  )

 

Other than tonight/Thu looking good for some Northern and Western parts I think other major snow opportunities will come early next week.

 

Fri looks like many of the showers will be more of rain or sleet for many and still mainly in the N/NW and whereas Saturday will become gradually colder once more it is also likely to be the driest day in this spell with scattered sleet/snow showers. (on current evidence)

 

Sunday should see showers developing more widely along coastal areas and pushing inland, especially in the NE

Early next week it looks as though models have already picked up on likely instability in the strong Northerly flow so a more persistent band of snow may well push south Monday/Tuesday giving a widespread fall but of course that is along way out to forecast a snow event.

This period is also complicated by the shortwave trough that will slide SE through Monday - the track and development of this feature has given the models a real problem and it has been modelled to behave in all manner of ways.

The current likelihood is that it will track either just W or through Ireland and head into the continent but very much open to change and how much it develops will  be key. The more it develops the further East rather than South its path is likely to be.

Given we will likely benefit from the very cold unstable air from the North anyway and that hoping for a big snow event from it is fraught with danger of introducing milder air and cutting off that cold flow, then my hope is it doesn't develop too much and tack across the South of the UK.

Of course the perfect scenario is for it to develop once South of the UK and track East as  a channel low giving the South a good dumping - indeed the South is at risk of two separate decent snowfall events early next week but neither is by any means certain to materialise. 

I do expect early next week to have the most snow interest for the country though.

 

Thus far the ensembles be it ECM or GFS have not been keen to put us in an Easterly flow but other than this mornings dubuious GFS 06z suite the general theme has been to lengthen this cold spell out the 4th/5th which is what ECM London ensembles show.

 

 

We can see that a small cluster want to extend the cold out further still but they predominantly go for a warm up from around the 5th.

If the ops hold steadfast in the further cold outlook and the ensembles improve this evening I will be a little more excited about a long lasting cold spell but also worth noting that the ECM Op and GFS op have different routes to an extension of the cold which is good in that it means there are possibilities available but bad in that there is no coherent signal.

Edited January 28, 2015 by Mucka

[carinthian]

Yes, the snow chase starts today. As soon as the cold flow become entrenched ,The Met 25Km Model ( snow prediction computer ), similar to what we use here in the Alps for snow prediction with-in a specified area, provides significant detail for the forecaster, however, it is important for local knowledge input be be added. Daily fax updates should now show areas/ regions of potential snowfall over the come days. There is always a surprise element, so accurate prediction will never occur. Finally, check the precipitation radar on here and have fun chasing and wishing snow in your direction and remember the surprise can be an added bonus. Enjoy the cold and snow, you lot really deserve it !

C

I think at this stage of the developing cold/possibly snowy spell there will still be some uncertainty regarding snowfall predictions by the Met Office. Currently, tonight the North West and particularly on higher ground will see some heavy snow showers. This will be the main area of concentration and concerns. Other regions could see some snow , but not likely to accumulate to much. Tomorrow and into the weekend and beyond all new data will be analysed but no rash predictions can be expected. Always be prepared for the unexpected. Tomorrow , I will try and extract the latest snow thoughts for the UK from our experts. In the meantime, I am sure the UKMO will monitor the situation closely and act accordingly when the probability factor increases as shown by their snow model as described in the above post.

[The Enforcer]

Surprised this hasn't been picked up on this thread.

 

Area of snow moving SE tomorrow night across Wales, Midlands towards the SE.

 

http://www.wetterzentrale.de/pics/Rmgfs453.gif

 

Another band of snow moving S across much of the UK.on Monday night.

 

http://www.wetterzentrale.de/pics/Rmgfs1443.gif

 

Subject to change but just highlighting the snowfall potential is for much of the UK.

 

You are right to highlight these, but I must issue a *CLUMPY* alert to recognise the fact that GFS is notorious in exaggerating snowfall. Time will tell.

 

For comparison for the small hours of Friday, NMM hi-res chart: http://www.meteociel.fr/modeles/wrfnmm.php?ech=3&mode=1&map=5 - too much rain attached to that area of precipitation for my liking. Also rain for Friday evening, which was to be expected.

Edited January 28, 2015 by The Enforcer

[weather eater]

Which rather supports the idea that the operational is considered far more important and trusted even without the support of the ensembles. Sometimes they are a guide and sometimes not and frankly they are subject to as many vagaries as the operationals. They are run from the same data as the operational but tweaked. Subsequently if an operational run differs quickly and substantially from the previous run because of big data changes from the previous run then its ensembles will also reflect a big change from the earlier runs ensembles. In other words an ensemble set is only relevant to its operational or at least only to the point of divergence between operational runs.

 

They didn't, that upgrade is due later in the year.

[Nouska]

On the other hand the Ensembles picked up on this cold spell way before the operationals became solid on it....

 

The one thing the old GFS was good at was picking out a northerly plunge, at long range - likewise its ensembles which we are currently viewing. The fact the ensembles got this and the last cold spell right is no guarantee that they are correctly modelling the future well; especially if there is to be an easterly component to the weather.

[carinthian]

Nice clearance of the cold front. I know its a bit off topic but there is cloud bulge developing over the Southwest. This is not convective, seems more frontal. Don't think it will cause any problems but just goes to show the unpredictability of forecasting in cold flow. Just worth keeping an eye on if anything develops on the radar.

C

[Captain Shortwave]

Well first key point coming up, day 4

GFS

Keen to send that low over the ridge and towards the south of the UK. Cold over the UK with the -8C isotherm covering the majority of the country, snow showers around northern/western and eastern coasts.

 

UKMO

 

Very similar

 

Day 5

GFS

The low just misses and goes into France. Again the main focus is the wave following on from Iceland. Which in this run turns into a significant snow event.

 

UKMO

Similar set up with that low, going into the Bay of Biscay. Another area of snow moving south through Scotland at this time.

Edited January 28, 2015 by Captain shortwave

[frosty ground]

The one thing the old GFS was good at was picking out a northerly plunge, at long range - likewise its ensembles which we are currently viewing. The fact the ensembles got this and the last cold spell right is no guarantee that they are correctly modelling the future well; especially if there is to be an easterly component to the weather.

Of course you are 100% correct........

We should also expect a wide set of outcomes at the time frame we are discussing anyway

Edited January 28, 2015 by frosty ground

[Day 10]

Snow moving south?

 

[Met4Cast]

Can't believe how quiet this forum is. We're about to go into the coldest spell of the season, where is everybody?

 

UKMO and GFS at 120 similar with the "almost channel low", UKMO looks better long term with more amplification of the high

 

UKMO 

 

 

GFS

 

 

GFS goes onto produce a shortwave feature running down the Eastern side of the country

 

 

[Day 10]

The ukmo and gfs 144

 

 

[nick sussex]

Nice to see the models not making any dramas over that shortwave, both the GFS and UKMO clear this se. The latter though is more favourable going forward in terms of developing a colder east/ne as the ridge is likely to topple towards Scandi.

 

The UKMO looks to bring in 850's around -10 on its T144hrs output.

[weather eater]

Can't believe how quiet this forum is. We're about to go into the coldest spell of the season, where is everybody?

 

 

 

It's always the same Daniel as soon as the cold begins to bite everyone leaves for the regional's, which rather proves the point that in winter this thread is just a snow chasing one and very few are that interested in synoptic models unless snow is in the mix. Nothing really wrong with that I guess and I suppose (and I include myself here) we just hate to admit we are still all little kids at heart and snow brings that out in us.

 

Mean while in model land we have some of the best continuity I have seen for a cold spell modelled by the operational runs since 2010. The only disappointment for those of us who want to see a really prolonged and bitter cold spell is that we cannot seem to get the ops to do more than give some faint hints at possible heights to our NW.

Edited January 28, 2015 by weather eater

[Smiler1709]

Out to t204 well out of realistic timeframe but the high is dropping South shutting off the cold feed, something the ensembles are hinting at

[TEITS]

Snow risk continues on the 12Z with disturbances tracking S early next week on the cold N,ly flow.

 

http://www.wetterzentrale.de/pics/Rtavn1444.gif

 

Excellent UKMO as beyond the +144 chart the winds would begin to veer NNE then NE/E,ly.

 

http://www.meteociel.fr/ukmo/runs/2015012812/UN144-21.GIF?28-17

 

 

Just add the channel low everyone is mentioning is only likely at this stage to possibly hit the extreme SW. This is not your typical channel low that tracks W-E as this is suggested to track SE.

Edited January 28, 2015 by TEITS

[Eugene]

Is that the "Murr Sausage" i see at T+210hrs.