Spring Model Discussion 18Z 6/3/13 onwards....

[mushymanrob]

I might be wrong and I have had a bit of stick from a few knowledgeable people on here tonight which is fine, everybody to their own viewpoint but I still maintain that cloud cover is being underestimated by many on here in the convective snow potential next week with cold weather a certainty but disruptive snowfall a definite non certainty the more likely end result.

the bbc graphics out to tuesday support you, our east mids 5 dayer has cloud cover all the way with only a temp range of +3c to 0c even under -10 uppers.... the bbc have also stated there will be 'no disruptive snow' in the period for their forecast (anywhere).

however.... wouldnt this feature, embedded in sub 528 produce snow? (fax @ 120)

http://www.wetterzen...n/fsfaxsem.html

I feel sorry for those working outside, rather like mushy and for market gardeners trying to keep their stock

its not working outside thats the problem john, its not working outside!

Edited March 8, 2013 by mushymanrob

[johnholmes]

Whilst I understand the models can change over night , I'm a bit confused to be honest because , to me , every signal is pointing toward a very snowy few days , but I don't know much about how these dry caps work , I remember a lot of talk on this during the last spell , and to hear this dry lid at roughly 850hpa (1500mts) again is alarming because it was fairly accurate last time, so it's quite a confusing post because it seems to contradict people's thoughts this morning , any explanation from one in the know please explain ?! Thanks

If I get chance I will try and explain via a pdf in about 1 hour unless someone else does it before.

[Radiating Dendrite]

the bbc graphics out to tuesday support you, our east mids 5 dayer has cloud cover all the way with only a temp range of +3c to 0c even under -10 uppers.... the bbc have also stated there will be 'no disruptive snow' in the period for their forecast (anywhere).

however.... wouldnt this feature, embedded in sub 528 produce snow? (fax @ 120)

http://www.wetterzen...n/fsfaxsem.html

its not working outside thats the problem john, its not working outside!

They stated "at the present time" on the bbc.

To be far their graphics are about as much use as a chocolate teapot.

[Paul]

This not being the BBC forecast thread, can we stick to what the models show rather than what the presenter may or may not have said on the latest tv forecast?

[Average Joe]

Whilst I understand the models can change over night , I'm a bit confused to be honest because , to me , every signal is pointing toward a very snowy few days , but I don't know much about how these dry caps work , I remember a lot of talk on this during the last spell , and to hear this dry lid at roughly 850hpa (1500mts) again is alarming because it was fairly accurate last time, so it's quite a confusing post because it seems to contradict people's thoughts this morning , any explanation from one in the know please explain ?! Thanks

Hi.....I'm going to nervously hold my hand up and say that I am as well....and I put this down to me simply being nowhere near as knowledgeable as the vast majority of posters on here.

I say that because reading most of the comments since last nights runs, they are suggesting that pretty much everywhere, including my area in the SE, is likely to get what I would term a reasonable amount of snow. I say that given that people are getting very excited, and that there's talk of sledges etc etc...maybe not here, but certainly in the SE Regional Board.

BUT, when I read the latest Met Office forecast, both the symbolic one which I'm led to believe is model generated, and also the text forecast which is regularly updated by 'hand', as well as looking at this morning's video forecasts on the Beeb, who I'm led to believe get their info from the Met, then there's no alarm bells ringing at the moment, or talk of anything significant. I'm not sure if they're hedging their bets, or if they're simply in possession of additional information which those on here aren't?

[FrenchScotPilot1]

The North Sea is pretty cold at the moment (about 5 degrees). See http://ghrsst-pp.metoffice.com/pages/latest_analysis/sst_monitor/ostia/index.html?i=34&j=2

But the 850 hPa air forecast to cross it is expected to be around -15 degrees.

My question is: what value of temperature gradient (SST-850 hPa) do you use for effective convection? This is about 20 degrees in this case.

Obviously, it also needs moisture for showers.

Many thanks for some pointers,

Stephane

[Purga]

Certainly looking very good for the south overall and particularly the South Downs & Coast coast on Monday

Not to mention the wind

Excellent stuff!!

[nick sussex]

A really interesting scenario playing out in todays models.

It's one of those types of set ups that can produce some big snow totals,however the timing of the front moving south is likely to chop and change.

Because of where the front starts it can hopefully deposit snow to more areas, then as it slips south the areas much further north that might have missed out can get some snow showers.

Another positive here is that it does eventually have to clear into France so that those waiting in the far south should still see some snow.

Lots more happening after that with a chance of more snow as fronts head south from the north past T96hrs but that could be a bit more marginal and also whether theres an occlusion and how far west that is.

Regarding any convection any cloud shield will hinder that hence for those areas that might miss out on frontal snow its important the cloud shield clears.

Edited March 8, 2013 by nick sussex

[fergieweather]

Based on latest NAE and amalgamation with 00z GM, we see dynamic snow accumulations of 5-10cm through Midlands later Sunday. Exeter have re-modelled this, factoring-in diurnal influence and depth temperature. Settling will be intensity-dependent and current prognosis is catering for 5-10cm above 300m; 1-3cm lower levels. It's outside warning criteria (impact-based) for now. However, accumulations in far S / SW overnight into early Monday look a tad more concerning and are being closely watched in output.

[Roger J Smith]

5-6 C not a bad water temp for snow squall development, Lake Huron is almost always in that range in its maximum production and the uppers of -12 to -15 fit the bill also. Granted the North Sea is a bit wider (from Denmark to Yorkshire anyway) than Lake Huron but not really that much in a full northerly that can arrive with 50 cm at the south end of the lake, so in this situation, I would not be too surprised if some heavy snow developed. The dynamics are better than last month's near-miss in the southeast, at least for Sunday night and Monday morning, and the Irish Sea also looks in play.

This low coming in from the southwest appears capable of lifting a degree or two (it's at 47 N now) and I don't think it will weaken.

The whole scenario is coming together very fast like Jan 1987 did, and needs to be treated as volatile, not steady-state. Things are going to happen fast and winds could become very gusty as a result (maximum gust potential for gradient in other words).

Strap in and hold on.

[BLAST FROM THE PAST]

Yes as has been suggested this low to our SW the other day was getting shunted further south as it entered France, it now has been adjusted closer to us and could be a real problem if it edges a tad further north.

I also think that the original suggestion of snow showers not being that intense off the north sea could be wrong and may well be far more lively and organised. Already we see that midlands even at low level are at risk of snow on Sat/Sunday, this is an upgrade and although the Beeb forecast has just said that no snow anywhere is anticipated to be problematic [that goes against what Fergie is suggesting 'could' be the case now] I suspect we coud see some neartime upgrades.

BFTP

[johnholmes]

Hi.....I'm going to nervously hold my hand up and say that I am as well....and I put this down to me simply being nowhere near as knowledgeable as the vast majority of posters on here.

I say that because reading most of the comments since last nights runs, they are suggesting that pretty much everywhere, including my area in the SE, is likely to get what I would term a reasonable amount of snow. I say that given that people are getting very excited, and that there's talk of sledges etc etc...maybe not here, but certainly in the SE Regional Board.

BUT, when I read the latest Met Office forecast, both the symbolic one which I'm led to believe is model generated, and also the text forecast which is regularly updated by 'hand', as well as looking at this morning's video forecasts on the Beeb, who I'm led to believe get their info from the Met, then there's no alarm bells ringing at the moment, or talk of anything significant. I'm not sure if they're hedging their bets, or if they're simply in possession of additional information which those on here aren't?

best you stick with the current professional advice which will if necessary be updated rather than the hype or hopecasting that does occur from some posters. Not easy I know but in my view no one can say with any degree of confidence just what will fall out of the sky for LOW lying areas in the south or how much. For hills even well south then several cm's is POSSIBLE based on current outputs.

read the inputs from Ian F who is a weather presenter in the SW and has access to most of the UK output including talking with the senior man.

Edited March 8, 2013 by johnholmes

[ANYWEATHER]

Looks as there will be some brutal cold for this time of year encroaching from the NorthEast as we move through the next two days. Amounts of snow at this point are virtually impossible to call, but with any precip falling from the sky it will be of snow, even in coastal areas as this time of year will see less in the way of thermal warming as the ssts are about the lowest at this time of year. The difference in the last cold spell to this one is quite stark to be honest, the high pressure core is way off towards Iceland leaving the Uk in a much more disturbed flow with much less capping. Anyway, this chart below shows where the high pressure core was generally during the last cold spell showing a much more capped airflow which Ive highlighted in black. There will be some very interesting weather coming up which wont be forecastable right down to the wire......

[nick sussex]

The big variable here which is why Ian F mentioned that concern for the far south/sw is what happens to that low pressure in northern Biscay.

The models handle this differently, the ECM deepens it more than the UKMO,this can pump more energy into any frontal zone and its how far north that is that will determine just how much snow falls.

Its a very complex set up,and certainly won't be sorted out till very close to the time.

Theres still also the chance that the models move the boundary further south and any intensification happens further into the Channel, its really a total nightmare to forecast.

Edited March 8, 2013 by nick sussex

[johnholmes]

A really interesting scenario playing out in todays models.

Regarding any convection any cloud shield will hinder that hence for those areas that might miss out on frontal snow its important the cloud shield clears.

not necessarily Nick as the cold air is/will undercut the moist frontal zone above it creating some instability to around 6000ft, looking at the predict for Doncaster. Just how this will impact on what is likely to be still falling from medium levels is far from clear.

predicting amounts from the sky at any time of the year as I often say beyond even T+24 let alone 48 hours is a mugs game!

[nick sussex]

not necessarily Nick as the cold air is/will undercut the moist frontal zone above it creating some instability to around 6000ft, looking at the predict for Doncaster. Just how this will impact on what is likely to be still falling from medium levels is far from clear.

predicting amounts from the sky at any time of the year as I often say beyond even T+24 let alone 48 hours is a mugs game!

Yes but I've never seen decent convection with a veil of high cloud,as for the frontal zone that's a different matter.

[chionomaniac]

best you stick with the current professional advice which will if necessary be updated rather than the hype or hopecasting that does occur from some posters. Not easy I know but in my view no one can say with any degree of confidence just what will fall out of the sky for LOW lying areas in the south or how much. For hills even well south then several cm's is POSSIBLE based on current outputs.

read the inputs from Ian F who is a weather presenter in the SW and has access to most of the UK output including talking with the senior man.

I think it is fair to say also though John that the met office hold responsibility and will not be swayed by interrun variance, and have time on their sides before Monday to wait until details become clearer. Half the fun on here is to see a stonking run, as it is released, and comment on what that particular run would bring if it was correct. We don't have that same professional responsibilty to hold back on commenting on dream synoptics when they come out. Of course seeing dream synoptics that suggest a lot of snow for three days hence and receiving said snow are two different things - which is why the met office don't overplay things. Could you imagine it if they said a snow hurricane was on the way and it failed to materialise?

Edited March 8, 2013 by chionomaniac

[Average Joe]

best you stick with the current professional advice which will if necessary be updated rather than the hype or hopecasting that does occur from some posters. Not easy I know but in my view no one can say with any degree of confidence just what will fall out of the sky for LOW lying areas in the south or how much. For hills even well south then several cm's is POSSIBLE based on current outputs.

read the inputs from Ian F who is a weather presenter in the SW and has access to most of the UK output including talking with the senior man.

Thank you John....very much appreciated.

[shaky]

Latest NAE has rain turning to snow through parts of Northern England moving into the midlands on Saturday so GFS has really led the way on this. Met Office forecast now mentions the possibility of rain turning to snow in some areas as well.

GFS looking good until a shortwave spoiler appears and cuts off the cold feed but a good chance that is not being modelled correctly at that range. The ensembles will tell us more.

The midlands looks like the place to be tomorrow!!

[johnholmes]

re my offer to explain the skew-t, I am not ducking the issue but it is very complex woth warm moist air being undercut by colder unstable air. To anyone not familiar with these diagrams it will be very confusing so best left for the time being to a very simple explanation.

The colder air you will see moving south by late Sunday, for this area for example, will still have the frontal cloud shield at higher levels but the colder and unstable air beneath it. This will, in theory, allow convection to develop in that colder air. The top of any clouds will be limited by the inversion to give it its correct terminology, CAP as used by some. As time goes on the upper cloud shield will move south allowing the colder air to extend higher up, perhaps as high as 8-10,000ft. This would obviously with a freezing level at or near the surface allow fairly hefty showers to develop, and most likely they would be of snow.

I hope this helps answer the question. I do urge you to take time and read the Net Wx Guide on skew-t diagrams, it seems very popular with 60k or more of hits. If you have any questions after reading this please send me a pm and I will do my best to answer you-I am away Monday-Friday next week though.

John

I think it is fair to say also though John that the met office hold responsibility and will not be swayed by interrun variance, and have time on their sides before Monday to wait until details become clearer. Half the fun on here is to see a stonking run, as it is released, and comment on what that particular run would bring if it was correct. We don't have that same professional responsibilty to hold back on commenting on dream synoptics when they come out. Of course seeing dream synoptics that suggest a lot of snow for three days hence and receiving said snow are two different things - which is why the met office don't overplay things. Could you imagine it if they said a snow hurricane was on the way and it failed to materialise?

I was simply attempting to suggest the most sensible way to someone new and who was saying they were confused. Of course I understand the differences between the excitement on here and the more measured outputs from the Met office

Yes but I've never seen decent convection with a veil of high cloud,as for the frontal zone that's a different matter.

Oh but in 40 years or so Nick I have seen lots of such examples. Not to say that this event will be one but they are not unusual believe me.

Edited March 8, 2013 by johnholmes

[johnholmes]

The North Sea is pretty cold at the moment (about 5 degrees). See http://ghrsst-pp.met...x.html?i=34&j=2

But the 850 hPa air forecast to cross it is expected to be around -15 degrees.

My question is: what value of temperature gradient (SST-850 hPa) do you use for effective convection? This is about 20 degrees in this case.

Obviously, it also needs moisture for showers.

Many thanks for some pointers,

Stephane

have a look at the skew-t diagrams for the area you are interested in is my suggestion-honestly never used rule of thumb for convection as I have always had access to either t-phi's or skew-t diagrams

hope that helps?

[FrenchScotPilot1]

have a look at the skew-t diagrams for the area you are interested in is my suggestion-honestly never used rule of thumb for convection as I have always had access to either t-phi's or skew-t diagrams

hope that helps?

Will do. Thanks for the wealth of knowledge John.

[BLAST FROM THE PAST]

I think it is fair to say also though John that the met office hold responsibility and will not be swayed by interrun variance, and have time on their sides before Monday to wait until details become clearer. Half the fun on here is to see a stonking run, as it is released, and comment on what that particular run would bring if it was correct. We don't have that same professional responsibilty to hold back on commenting on dream synoptics when they come out. Of course seeing dream synoptics that suggest a lot of snow for three days hence and receiving said snow are two different things - which is why the met office don't overplay things. Could you imagine it if they said a snow hurricane was on the way and it failed to materialise?

That's fair enough Ed but I think many on here have witnessed many short term change arounds by the forecasters [particularly upgrades to snow, cold longevity etc] which I find rather odd sometimes as so many people see it happening well beofre the change forecasts are made. Responsibilty also lies in informing people of potential issues. Sometimes the veil of 'responsibilty' is used to cover poor forecasting IMO. Reason I say this is that I have followed different forecasters on the regional news bulletins and some say and speak of the potential way ahead of others. I find the inconsistency very odd at times.

BFTP

[johnholmes]

That's fair enough Ed but I think many on here have witnessed many short term change arounds by the forecasters [particularly upgrades to snow, cold longevity etc] which I find rather odd sometimes as so many people see it happening well beofre the change forecasts are made. Responsibilty also lies in informing people of potential issues. Sometimes the veil of 'responsibilty' is used to cover poor forecasting IMO. Reason I say this is that I have followed different forecasters on the regional news bulletins and some say and speak of the potential way ahead of others. I find the inconsistency very odd at times.

BFTP

probably because they are, like Ian F, NOT employed by the Met Office but the BBC. That applies to a number of Met trained forecasters, Paul Hudson Look North is just one example.

[chris55]

The mean on the GEFS has moved quite a bit this morning with the initial dip now not quite so cold, this is all to do with the track of the low to the south west and although the very cold uppers are moderated somewhat, the snow risk increases significantly. The dividing line between the cold and less cold air was down over northern France over the past few days and we have seen a trend from all models to shift this north. That puts places in southern England and Wales at higher risk of potential frontal snowfalls.

The northward extent of any associated ppn is unknown at this stage and slight changes in track and intensity will need watching closely over subsequent runs.

Plus we have the front dropping south on Sunday, and convective potential from the east with showers driving inland. Overall an exciting period of weather coming up.