Model Output Discussion

[Jason T]

Well looking through all the comments this morning, i agree as i stated in this mornings old thread at 6.30 am that were my eyes playing tricks on me or have the models ALL gone through a time warp. Yesterdays sets just did not look of any interest at all, and as most are saying it seems todays models look awesome in comparison to recent displays.

If i remember yesterday most were saying time to give the models a break for now. Still as they say EXPECT THE UNEXPECTED.

Correct me if im wrong but these look alot worse than we had on the last cold spell models. Interesting times ahead for this coming week.

[J10]

I now I should know better, and please feel free to remove if slightly off topic.

But today's Country Tracks forecast was poor in terms of quality. In essence, cold to start, then milder for midweek then colder again before weekend, which does sum up the general pattern.

However my main concern relates to an occlusion moving down western areas on Thursday into Friday, the presenter (Laura Tobin) said rain for South Western areas, but the graphics showed snow, with temps of 8c. For frontal rain this would not be possible.

The warm sector can clearly be seen as can the expected precipitation, so a marginal event is possible, in fact we have seen two similar events this winter, 1 a mostly rain event (which had the the milder sector further east), with snow on the back edge, the second a mostly snow event (which had the the milder sector further east).

[Wayneywoo]

I am constantly reading everybody's opinion and expert analysis and enjoying all that is written. To take nothing away from those that are knowledgeable, are we now to expect something different from the output of all the models?

Seems to me that what we expect to happen should be left with the winters that have gone by. This winter has been different from the "norm" that we have gotten used to for so many reasons and now I see that what we expect to happen might not necessarily be what will happen.

Fascinating watching the models at the moment and to see how things are different in this winter! long may the differences continue. Seems the differences are what us cold lovers are needing!

edit: Just to clarify, I'm not talking about the models being wrong in the immediate timeframe, I'm talking more about FI and when the models disagree. Yesterday, everyone was expecting the typical short lived 24-48hr N'ly toppler. Now today, we see the N'ly lasting slightly longer. In winters gone by, you could pretty much guarantee that the earlier show of the N'ly is what would happen. Now the N'ly is getting closer and the models are closer to what they think will happen, things are different to what we expect.

This seems to be the theme for this winter, as an earlier poster said, Expect the Unexpected!

Edited January 24, 2010 by Wayneywoo

[Thundery wintry showers]

We won't be seeing anything like that. The GFS is synoptically highly unlikely; Low pressure would develop off S Greenland and topple the High. Many northerlies of this type over the years have seen maximas in the 7 to 9 range for coastal Southern areas particularly. I'm still favouring a quick toppling and a mild early Feb.

The maxima of 7 to 9C in the south only generally happen when the northerly doesn't sustain for more than 36 hours, meaning that the cold Arctic air fails to establish. The downgrade to a 36 hour toppler cannot be ruled out at this stage, I've seen the models show northerlies like this before only for them to be toned down dramatically near the time, and of course it's always been the form horse during the winters of the past 22 years or so.

However, that doesn't mean that it definitely will happen. The current pattern reminds me a bit of early January 1981, and although that month was mild overall and had just short-lived northerlies, there were three potent northerlies arriving one after another:

http://www.wetterzentrale.de/archive/ra/1981/Rrea00119810110.gif

http://www.wetterzentrale.de/archive/ra/1981/Rrea00119810113.gif

http://www.wetterzentrale.de/archive/ra/1981/Rrea00119810115.gif

I'm sure that if this chart was showing on the models many of us would be expecting a brief toppler due to relatively low heights over Greenland:

http://www.wetterzentrale.de/archive/ra/1999/Rrea00119990205.gif

...instead of this:

http://www.wetterzentrale.de/archive/ra/1999/Rrea00119990208.gif

So while I think it's too early for cold/snow lovers to get excited I am not sure about this possible downgrade to a feeble 36 hour northerly. Probably 50-50 either way, especially considering the relatively favourable teleconnections. Something similar to the northerly we had from 7-10 February 1999 is entirely realistic from the current situation.

[Tim Bland]

A complete 360 turnaround from the BBC. They have gone from showing cold easterlies with cold returning from the continent to showing the same map but with the warm to the west winning!

Such a relief to see the models have some agreement today and even more encouraging IMO is the agreement from the ensembles Some very uniquie clustering even past T+144. I still can't see anything to get excited about to be honest. A 4 day northerly starting Thursday with snow showers for exposed Eastern and northern areas. After this good agreement on a warm up from Mon 1st Feb until the 5th when we porbably see the same topler scenario again. Great if you live on the North York moors or in Aberdeen but just cold and dry periods for 95% of the poulation. I know we are being spoilt this year but everything is relative in life so unless there is widespread snow most are going to be dissapointed.

Can any experienced members advise if there is likely to be polar low formations in this northerly as this is the only way for most to see snow in the set up appart from the breakdown scenario (Rain preceeded by snow)

Edited January 24, 2010 by Tim Bland

[Duane S.]

It does now seem that this HP is going to be around in one guise or another for a while so we had better get used to it!

Beyond the impending Northerly and retrogression due to the PV split, there is (has been for a while) a signal for a flatter pattern coming out of the States, this will likely sink the Block a few degree's S and E back towards us especially if the PV regroups back towards GL. I struggle to see any sort of proper sustained retrogression, yet. The PV will soon be VERY nicely split and whilst that is the case things can change very quickly though.

One thing that does confuse me that maybe somebody could help me with, I'm amazed that the NAO doesn't want to go more negative under these circumstances. I would have thought looking at...

would translate into a strong -NAO?? As oppsosed to a neutral/slightly negative valuse that the NAO forecasts are showing?

[kold weather]

There is now a signal for high pressure in the atlantic along with a Scandi/euro trough to last, perhaps, for much of the first week of Feb. Assuming that verifies, then we have an extension of the cold pattern window, at the least, that didn't seem as possible previously. Beyond that, as you say, it is very uncertain. But quiet high pressure close by is a favourite (which would still give overnight frost) but with still the small chance of a cold pattern continuing with renewed northern blocking.

Anything can happen of course, but anything definitively mild keeps being put back further.

That sort of flow is probably one of my least enjoyable types IMO IF the upper trough isn't close enough to drag in an Arctic sourced northerly, otherwise you end up with a horrid cloudy anti-cyclonic flow and temps above average in the night and around average in the day...

No doubt this is a toppler, but it does seem to have a bit of bite about it and to be fair if anything this is upgrading all the time, not downgrading like previous events in the past.

What happens in the start of Feb looks very uncertain, the broad synoptics as Tamara says would be a HP to be close by, hopefully over the top rather then to the west or south and I suspect the ECM ensembles are quite keen on HP over the top of the UK from the looks of things.

Gotta admit that northerly is looking very interesting all of the sudden, starting to look like a proper thrust from the north rather then a little trickle.

[Frosty.]

Something similar to the northerly we had from 7-10 February 1999 is entirely realistic from the current situation.

Or perhaps the Northerly of late feb / early march 2006, always a risk of downgrades but never have I seen such model agreement fail to deliver in as little as 96 hours ahead, it's not as if we are looking at FI whimsy.

[January Snowstorm]

Quite a turnaround indeed today although last nights 18z had a certain flavour to it.

I suppose we are now looking at a set-up that could downgrade to leave nothing bar a fleeting Northerly, or upgrade to show us a full on Northerly spell.

If you want to look at the thing positively this Winter has been very different to date!

[Thundery wintry showers]

That's a good post Ian, we will have to see what the 12zs bring. It's difficult for me having defined the m.era, it can become too easy to expect the patterns to behave to certain parameters and of course we have already seen this winter how the 'rule book' can be torn up.

I don't think a 3-4 day northerly from this setup would be outside of the bounds of the so-called "modern winter"- after all, the winter of 1998/99 was in many ways a textbook "modern winter" with frequent westerlies interspersed with brief northerlies, but we did get that aforementioned northerly from 7-10 February 1999 which lasted 4 days. Since the teleconnections are hinting at a Nina type signal, maybe we might be headed for a February similar to 1999- generally mild with HP close to the south but with Scandinavian trough bringing occasional wintry outbreaks.

Or perhaps the Northerly of late feb / early march 2006, always a risk of downgrades but never have I seen such model agreement fail to deliver in as little as 96 hours ahead, it's not as if we are looking at FI whimsy.

The March 2006 northerly was supported by strong heights over Greenland rather than a mid-Atlantic high drifting up towards Greenland, so I don't think the current pattern supports a week-long northerly like we had back then.

At the moment Tim Polar Low formation looks unlikely and what is being progged is quite a 'straight' northerly which brings a kind of wishbone effect so that the showers affect Northern Scotland but only coastal areas (East and West) further South. Of course the output could change to bring a tilt in the wind direction which could bring showers/little troughs inland.

The breakdown scenario from the NW is unlikely to bring snow other than to the very highest ground as in this set-up mixing out of the cold air tends to get ahead of the PPN.

A pretty fair assessment, and again the northerly of February 1999 was a good example- the breakdown afterwards was a non-event. There was a trough on the 8th which brought snowfalls to much of central, western and southern Britain, but other than that it was mainly sunny and cold with snow showers for the usual areas (NE Scotland, Norfolk, N Wales, some east coast counties of England). If the northerly lasts for a few days, though, troughs will probably appear at some stage during its stay.

[J10]

At the moment Tim Polar Low formation looks unlikely and what is being progged is quite a 'straight' northerly which brings a kind of wishbone effect so that the showers affect Northern Scotland but only coastal areas (East and West) further South. Of course the output could change to bring a tilt in the wind direction which could bring showers/little troughs inland.

The breakdown scenario from the NW is unlikely to bring snow other than to the very highest ground as in this set-up mixing out of the cold air tends to get ahead of the PPN.

I tend to agree with all of that.

I don't think a 3-4 day northerly from this setup would be outside of the bounds of the so-called "modern winter"- after all, the winter of 1998/99 was in many ways a textbook "modern winter" with frequent westerlies interspersed with brief northerlies, but we did get that aforementioned northerly from 7-10 February 1999 which lasted 4 days. Since the teleconnections are hinting at a Nina type signal, maybe we might be headed for a February similar to 1999- generally mild with HP close to the south but with Scandinavian trough bringing occasional wintry outbreaks.

The March 2006 northerly was supported by strong heights over Greenland rather than a mid-Atlantic high drifting up towards Greenland, so I don't think the current pattern supports a week-long northerly like we had back then.

A pretty fair assessment, and again the northerly of February 1999 was a good example- the breakdown afterwards was a non-event. There was a trough on the 8th which brought snowfalls to much of central, western and southern Britain, but other than that it was mainly sunny and cold with snow showers for the usual areas (NE Scotland, Norfolk, N Wales, some east coast counties of England). If the northerly lasts for a few days, though, troughs will probably appear at some stage during its stay.

I certainly would welcome a repeat of Feb 1999, going by my records, there were 4 overnight topups of snow here, giving up to 4-6 inches in the shade, which admittedly did thaw quickly in the sun.

[Geordiesnow]

Good too see the models upgrading the initial Northerly and they have all continued the trend of bring the Northerly which was predicted to hit all of the North Sea towards us now for Thursday.

With the 2nd shot, this has also been upgraded and it would just be nice too see the return of some decent sunny spells and night time frosts. Hopefully if the airflow is northerly is enough, snow showers can affect both eastern and western coasts aswell as Northern Scotland which could see quite a bit of snowfall if the current models come off.

[Frosty.]

The March 2006 northerly was supported by strong heights over Greenland rather than a mid-Atlantic high drifting up towards Greenland, so I don't think the current pattern supports a week-long northerly like we had back then.

Spot on Tws,

I was in shetland back then and we had over a foot of level snow and 6 foot drifts, even a 72 hour blast of similar intensity would deliver deep snow cover for exposed northern and eastern areas and a generally very cold, arctic feeling cold snap for all areas. We do have some milder air pushing into scotland by tuesday but still rather cold further south and then turning much colder in the far north during thursday...hopefully.

[Guest North Sea Snow Convection]

That sort of flow is probably one of my least enjoyable types IMO IF the upper trough isn't close enough to drag in an Arctic sourced northerly, otherwise you end up with a horrid cloudy anti-cyclonic flow and temps above average in the night and around average in the day...

No doubt this is a toppler, but it does seem to have a bit of bite about it and to be fair if anything this is upgrading all the time, not downgrading like previous events in the past.

What happens in the start of Feb looks very uncertain, the broad synoptics as Tamara says would be a HP to be close by, hopefully over the top rather then to the west or south and I suspect the ECM ensembles are quite keen on HP over the top of the UK from the looks of things.

Gotta admit that northerly is looking very interesting all of the sudden, starting to look like a proper thrust from the north rather then a little trickle.

Yes, quite a potent northerly possible!

The AO has been 'trying' to go more positive of late but the signal to me looks like another period of -AO coming up with the vortex displaced. That should underpin this being more than the classic toppler associated with a +AO arrangement. As described before, the jet pattern should be conduisive to the atlantic high moving back north westwards after the passage of any lows that track SE from the Greenland area.

I think with the suggestion of the recent westerly positive zonal winds slowing down, once the Scandi trough signal breaks down there is every chance that high pressure will stay at a high enough latitude to keeps things cold over the UK - with more settled conditions and frost.

There is even the small chance that the -AO pattern will reload if angular momentum patterns allow once more and this could reload real high pressure over Greenalnd once more like in early Jan. This looked quite a big outsider previously, but has perhaps become something to watch through the first part of Feb.

Edited January 24, 2010 by North Sea Snow Convection

[Thundery wintry showers]

From a selfish perspective I would also welcome a repeat of 7-10 February 1999 as snow showers hit Norfolk and parts of east Suffolk throughout, resulting in 7 mornings of snow lying at nearby Lowestoft, and I imagine Norwich must have had at least five or six such mornings. At Cleadon, where I was at the time, showers mostly stayed out at sea on the 7th and 8th but came inland at times on the 9th and 10th, giving 3 mornings with over 50% cover.

However the "wishbone effect" is a very real issue with the low strength of the sun at this time of year, so if we're to see more widespread snowfalls then we will probably need troughs to swing the wind to the NW and/or NE at some stage. By late February/early March the sun tends to be strong enough to generate some homegrown convection (e.g. 1993, 2001, 2004, 2006) but I can't remember this happening in a late January or early February northerly.

Tonight's models will be key to see whether there is much chance of a significant downgrade. I think if we get complete model agreement on something potent again, then we'll be unlikely to see any major downgrades from there. But if one or two of the models go for something weaker and shorter-lived then we may need to counsel some caution.

[Jason T]

I think tonights models will if anything be even more interesting. This mornings models were and are the biggest change and sign in days.

[Neilsouth]

That's a good post Ian, we will have to see what the 12zs bring. It's difficult for me having defined the m.era, it can become too easy to expect the patterns to behave to certain parameters and of course we have already seen this winter how the 'rule book' can be torn up.

And last winter

I don't think the last few years of weather have followed any set pattern

[Cecil Hogmanay Melchett]

And last winter

I don't think the last few years of weather have followed any set pattern

lol neil yes last winter was cold and this winter has been very very cold.

not sure this is entirely releveant but can anyone say when we last saw two cold winters on the bounce?

[Jason T]

Edited January 24, 2010 by silver line

[reef]

From a selfish perspective I would also welcome a repeat of 7-10 February 1999 as snow showers hit Norfolk and parts of east Suffolk throughout, resulting in 7 mornings of snow lying at nearby Lowestoft, and I imagine Norwich must have had at least five or six such mornings. At Cleadon, where I was at the time, showers mostly stayed out at sea on the 7th and 8th but came inland at times on the 9th and 10th, giving 3 mornings with over 50% cover.

However the "wishbone effect" is a very real issue with the low strength of the sun at this time of year, so if we're to see more widespread snowfalls then we will probably need troughs to swing the wind to the NW and/or NE at some stage. By late February/early March the sun tends to be strong enough to generate some homegrown convection (e.g. 1993, 2001, 2004, 2006) but I can't remember this happening in a late January or early February northerly.

Tonight's models will be key to see whether there is much chance of a significant downgrade. I think if we get complete model agreement on something potent again, then we'll be unlikely to see any major downgrades from there. But if one or two of the models go for something weaker and shorter-lived then we may need to counsel some caution.

Id find it very welcome too. Some of the deepest snowfalls in the last 10 years here (though not necessarily lasting very long) have come from setups similar to whats shown on the GFS. Northerlies remain the best source of snow here, as moderation by above average North SSTs has had a massive effect in recent years. So much so that anything east of NNE and the flow has to be extremely potent to negate the effects and guarantee snow.

Theres a definite chance we could see the cold spell downgraded into a 36-48 hour event though. The end of this cold snap is still in the T+168 range which is very prone to change this far out. To be honest, even if the flow turned NNW and we missed out on the snow showers, Id just be happy to see some winter sunshine. It has been very dull in the last couple of weeks.

lol neil yes last winter was cold and this winter has been very very cold.

not sure this is entirely releveant but can anyone say when we last saw two cold winters on the bounce?

1995/96 and 1996/97.

Bear in mind though last winter was only really cold from the Midlands southwards (plus the NW) :

http://www.metoffice.gov.uk/climate/uk/anomacts/2009/16/2009_16_MeanTemp_Anomaly_1971-2000.gif

This one is generally cold everywhere and overall far more snowy. Last winter was exceptionally poor here with just 3 days of lying snow, this one so far has managed 18 days.

Edited January 24, 2010 by reef
Posted correct link

[yamkin]

Silver line, I would like to add the GME 00Z to your collection Can't wait for the GME 12Z

UK Outlook for Friday 29 Jan 2010 to Sunday 7 Feb 2010:

On Friday (29th) and Saturday (30th) it is expected to be rather cold and windy with a mixture of sunny or clear spells and wintry showers. The highest risk of significant snow is likely to be across eastern areas. Widespread overnight frosts may be locally severe. From Sunday (31st) and to start the following week the weather is most likely to remain similar with sunny or clear spells and showers, with the highest risk of snow over Scottish mountains. Temperatures are likely to be near normal but it will feel cold in the wind with overnight frosts continuing inland. There is low confidence through the rest of the week and into the weekend (6th/7th) with the strongest trend for a similar pattern of weather to continue.

Updated: 1135 on Sun 24 Jan 2010

Edited January 24, 2010 by yamkin

[andymusic]

I now I should know better, and please feel free to remove if slightly off topic.

But today's Country Tracks forecast was poor in terms of quality. In essence, cold to start, then milder for midweek then colder again before weekend, which does sum up the general pattern.

However my main concern relates to an occlusion moving down western areas on Thursday into Friday, the presenter (Laura Tobin) said rain for South Western areas, but the graphics showed snow, with temps of 8c. For frontal rain this would not be possible.

The warm sector can clearly be seen as can the expected precipitation, so a marginal event is possible, in fact we have seen two similar events this winter, 1 a mostly rain event (which had the the milder sector further east), with snow on the back edge, the second a mostly snow event (which had the the milder sector further east).

totally agree with you - felt like the end of the forecast was rushed and 8 degrees and snow really don't mix - may be the model changes today have caught them off guard and hasty changes had to be made!

[Jason T]

Silver line, I would like to add the GME 00Z to your collection Can't wait for the GME 12Z

UK Outlook for Friday 29 Jan 2010 to Sunday 7 Feb 2010:

On Friday (29th) and Saturday (30th) it is expected to be rather cold and windy with a mixture of sunny or clear spells and wintry showers. The highest risk of significant snow is likely to be across eastern areas. Widespread overnight frosts may be locally severe. From Sunday (31st) and to start the following week the weather is most likely to remain similar with sunny or clear spells and showers, with the highest risk of snow over Scottish mountains. Temperatures are likely to be near normal but it will feel cold in the wind with overnight frosts continuing inland. There is low confidence through the rest of the week and into the weekend (6th/7th) with the strongest trend for a similar pattern of weather to continue.

Updated: 1135 on Sun 24 Jan 2010

Many thanks yamkin.GME 12Z is going to be the one.

Edited January 24, 2010 by silver line

[Snowyowl9]

GFS 6z run doesn`t hardly give the mild a chance to penetrate as such not in the S/SE.

http://91.121.93.17/pics/Rtavn8417.png

Then the -5c uppers come crashing in same time.

http://91.121.93.17/pics/Rtavn842.png

http://91.121.93.17/pics/Rtavn9017.png

Edited January 24, 2010 by Snowyowl9

[Duane S.]

totally agree with you - felt like the end of the forecast was rushed and 8 degrees and snow really don't mix - may be the model changes today have caught them off guard and hasty changes had to be made!

Without a doubt it was embarrassing to watch. No wonder they are looking for a new Service Provider other than the MET!

I know it's O/T but I think the MET have been found out. Too many years relying on the weather to behave in a certin way, which it mostly did. Then some sort of pattern shift appears to have taken place (I accept this is up for debate)and they are all over the place!

Sorry, back on topic. Tonight's charts will be of increased interest after this morning's. I don't think we are looking at further upgrades today (not major ones anyway), just as long as we can keep the Northerly like it is for the next couple of days showing on the charts then that will do me. Baring in mind that from a IMBY perspective they are rarely a lot of cop.

Today's AO and NAO looking good...

Compare with yesterday's (which was itself an upgrade)...