General Model Output Discussion

[VillagePlank]

I'm amazed people think it will be dry. Which models shows that? The latest BBC forecasts presumably based on UKMO data have an extensive area of snow sitting over central and eastern England on Tuesday.

The cumulative precipitation forecast for the SE is 10mm for the week: at best that means 10cm's snow for the entire week. So, as I said, it will snow.

Best accumulations will be North East England where the show will stop - they will accumlate, at sea level, nearly a metre of snow this coming week, and Eastern Scotland will be very similar.

As for the CET area - Birmingham and Manchester worst affected with, at most, 16 cms of snow over seven days - yes, peeps, that's a whopping 10mm/day.

[tinybill]

Yep - Northern East Anglia, and Far East Kent.

off fine this for thuresday

[Optimus Prime]

worst affected with, at most, 16 cms of snow over seven days - yes, peeps, that's a whopping 10mm/day.

I make that 2.1MM a day. 1MM of rain=1cm of snow.

[Alex95]

The cumulative precipitation forecast for the SE is 10mm for the week: at best that means 10cm's snow for the entire week. So, as I said, it will snow.

Best accumulations will be North East England where the show will stop - they will accumlate, at sea level, nearly a metre of snow this coming week, and Eastern Scotland will be very similar.

As for the CET area - Birmingham and Manchester worst affected with, at most, 16 cms of snow over seven days - yes, peeps, that's a whopping 10mm/day.

I highly doubt we'll accumulate a metre! I know the NE is quite snowy compared to other areas of the country, but we're not Cairngorm. Similar situations have dumped 30-50cm up here, but then others have only given us 10-20cm, so we'll see.

[MR EXTREMES]

off fine this for thuresday

suggesting southern england aswell atlast.

is that from the sw or from the north?

[VillagePlank]

Thats quite easy to answer, the front represents the difference between -6/7C at 850hpa over the UK on Tuesdays and the -10/11C temps we see coming down on Wednesday. The set-up doesn't really favour our location VP but places in the Midlands look good for snowfall...I'd suspect our fun would come once that low has cleared to our south.

Also lets not forget the easterly last December was at this stage progged to be fairly dry, ended up giving a heck of a lot more precip then the models out at 144hrs could have dreamed off!

As I said, a weak front:

Isobars show a few kinks that would be badly modelled since they are within the scope of the gridded network, and they could produce the goodies. As I said above, it will snow, but it's hardly going to the be the end of the world that some are predicting, here! Reality check, and all that. Indeed, nothing more that has already been seen this winter!!

I think nowcasting will be the key, and there will be one or two serious snowfalss that really do create a serious situation. The main problem will be the extreme cold. If you have elderly neighbours, tomorrow is the day to offer to go shopping for them ...

[PB22]

Absolutely staggering model output again tonight, and I really do think we could be on the verge of seeing January 2010 go down in the history books.

For those of you worrying about snow amounts, how many times has it got to be said? There is no point worrying about it as various troughs and features won't be picked up until 24 hours beforehand. You only have to look at this weekend for examples of how snow can crop up unexpectedly.

Just relax everyone, the cold is getting established, the snow will follow.

[VillagePlank]

I highly doubt we'll accumulate a metre! I know the NE is quite snowy compared to other areas of the country, but we're not Cairngorm. Similar situations have dumped 30-50cm up here, but then others have only given us 10-20cm, so we'll see.

I am talking a weeks worth of snow, here - don't forget the sun will compress and melt a bit day by day. But, if measured, I think your location will see a metre of snow falling over the next seven days. Perfect location, and all that

Absolutely staggering model output again tonight, and I really do think we could be on the verge of seeing January 2010 go down in the history books.

For those of you worrying about snow amounts, how many times has it got to be said? There is no point worrying about it as various troughs and features won't be picked up until 24 hours beforehand. You only have to look at this weekend for examples of how snow can crop up unexpectedly.

Yep - nice and dry No worries, at all ...

[kold weather]

The cumulative precipitation forecast :

Whilst that is true you've got to remember 9 out of 10 times the models will vastly underdo convection and also for that matter are more likely to miss out on possible troughs/fronts at that range.

Today was a classic examply of how none of the models picked up on a first trough being quite a bit stronger then expected, and that was at just T6hrs...as John H has said many times, you may as well forget the precip forecasts from the models because they never handle such set-ups at all well.

FWIW I don't think Tuesday will be that bad here BUT there is some decent forcing going on in that front for a time on Tuesday looking at the models and therefore I'd imagine there would be a spell of probably moderate-at times heavy snow for a decent chunk of the north, the Midlands and Wales...though by the time it gets down there I think marginality will be popping up again...

However beyond that and look for the trend for the GFS to slowly up the precip amounts...I've seen enough times in the past the GFS do a very poor job with convection even at just 24-48hrs out...I'm so confident I'd make a punt and say most places will see some good snowfalls between now and the 14th, quite a few places getting at least 5-10cms...

[nick sussex]

The cumulative precipitation forecast for the SE is 10mm for the week: at best that means 10cm's snow for the entire week. So, as I said, it will snow.

Best accumulations will be North East England where the show will stop - they will accumlate, at sea level, nearly a metre of snow this coming week, and Eastern Scotland will be very similar.

As for the CET area - Birmingham and Manchester worst affected with, at most, 16 cms of snow over seven days - yes, peeps, that's a whopping 10mm/day.

Oh please tell me you're not using the gfs precip charts! they're always way out and for convective snowfall an utter waste of time. In terms of the possibilities the pattern is being driven by the major low over southern europe and high pressure to the nw, if the ecm verifies you're looking at basically a cyclonic east/ne flow for south eastern areas. Unstable flow with very cold upper air over a relatively warm north sea that is a recipe for major snowfall. At this range i'm not going to give snow amounts as it's just too far out but i'll repeat if the ecm verifies and i lived in the se i'd make sure i had a fully stocked fridge!

The ecm ensembles are just in for the Netherlands at least for over there the operational run is one of the warmest members for days 8-10.

http://www.knmi.nl/exp/pluim/Data/PLUIM_06260_NWT.png

[VillagePlank]

Yep I think folk have got your view point VP Time will tell.

Yup - OK let's look at the charts ... here's the ensembles which show very cold and dry weather for Kent:

There's certainly precipitation about - but, hey, it really ain't that much, huh? One would think I was making it all up for a laugh or something!

Go to the NetW charts and look up your location's ensembles - cold never means snows, it means it if it precipitates, it will snow (on the basis of the movement to an arctic maritime air mass)

Incidentally, I think that the 12z is far too dry, if it means anything. As the winds turn northerly then snow will be a defacto standard for a wide range of the country ...

[VillagePlank]

Whilst that is true you've got to remember 9 out of 10 times the models will vastly underdo convection and also for that matter are more likely to miss out on possible troughs/fronts at that range.

Perhaps in winter - but GFS vastly over-does the skew-t's when we're looking at thunderstorms in summer. How many times have you telephoned the missus on the basis of LI=-4, and CAPE>1000j/kg?

[TEITS]

What some have to realise about the precipitation is the models will never accurately predict the amount of convection that will occur. Take for example in the summer when thunderstorms are forecast, do the models accurately predict exactly where these will form. Now obviously the type of convection next week is due to the cold temps across the warm N sea. However the prinicipal remains the same and all the models can do is give you a rough guide. Even a high resolution model like the NMM can only give you a guide as to where convection will occur.

Look at this chart below and at the time very weak convection was suggested by the models.

http://www.wetterzentrale.de/archive/ra/2005/Rrea00120051227.gif

http://www.wetterzentrale.de/archive/ra/2005/Rrea00220051227.gif

I managed 10cm from that!

Having said all of this I remember back in the 1980's when the countryfile forecast would underestimate snowfall amounts during an E,ly. The week forecast often only used to mention scattered snow showers. However as the week progressed the forecast would change to prolonged heavy snow showers giving periods of snow. If the models continue the same then thats the kind of forecasts to expect in E areas.

[nick sussex]

NOW A MAN WHO TALKS SOME SENSE

Thanks. In these situations you have to use past experience as a guide aswell as the current output, i've seen enough easterlies to know what the ecm would bring but for obvious reasons i'm keeping quiet until nearer the time. The precip charts from the gefs ensembles are an utter waste of time, why does anyone bother with them.

[VillagePlank]

... as for the precip shown by VP in that gefs ensemble,how can i put this politely, it's a pile of tosh!

Probably true - but you can't use the negative as a basis for the positive, huh? ie GFS says it won't precipitate, therefore, it will .... I understand the notion that easterlies bring snow, but normally when there is a nice low, or something sitting over Belgium, or somewhere close, that acts as a conveyor. I don't see that. I don't see any deep low pressures. I don't see any convection. I don't see active PFJ's anywhere near north west europe.

I hope I am very wrong, and you are very right!!

[PB22]

Thanks. In these situations you have to use past experience as a guide aswell as the current output, i've seen enough easterlies to know what the ecm would bring but for obvious reasons i'm keeping quiet until nearer the time, as for the precip shown by VP in that gefs ensemble,how can i put this politely, it's a pile of tosh!

Absolutely, too many people here showing a clear misunderstanding of whats ahead. We'll just sit back and wait for events to unfurl, then we can watch people eat humble pie!

Anyway, ECM ensembles for Holland:

http://www.knmi.nl/exp/pluim/Data/PLUIM_06260_NWT.png

Cold cold cold, and barely any members rise above 0C over there in the next 10 days!

[Weather-history]

Has anyone saved the ensembles for January 2007? It will be interesting to compare with the current ones as one set was showing hardly a sniff of any cold weather whilst the other is hardly showing a sniff of mild weather!

[danm]

Whilst that is true you've got to remember 9 out of 10 times the models will vastly underdo convection and also for that matter are more likely to miss out on possible troughs/fronts at that range.

Today was a classic examply of how none of the models picked up on a first trough being quite a bit stronger then expected, and that was at just T6hrs...as John H has said many times, you may as well forget the precip forecasts from the models because they never handle such set-ups at all well.

FWIW I don't think Tuesday will be that bad here BUT there is some decent forcing going on in that front for a time on Tuesday looking at the models and therefore I'd imagine there would be a spell of probably moderate-at times heavy snow for a decent chunk of the north, the Midlands and Wales...though by the time it gets down there I think marginality will be popping up again...

However beyond that and look for the trend for the GFS to slowly up the precip amounts...I've seen enough times in the past the GFS do a very poor job with convection even at just 24-48hrs out...I'm so confident I'd make a punt and say most places will see some good snowfalls between now and the 14th, quite a few places getting at least 5-10cms...

Surely marginality wont be a factor by tuesday? i would of thought that by then any precipitation would only be snow.

[nick sussex]

Probably true - but you can't use the negative as a basis for the positive, huh? ie GFS says it won't precipitate, therefore, it will .... I understand the notion that easterlies bring snow, but normally when there is a nice low, or something sitting over Belgium, or somewhere close, that acts as a conveyor. I don't see that. I don't see any deep low pressures. I don't see any convection. I don't see active PFJ's anywhere near north west europe.

I hope I am very wrong, and you are very right!!

The reason i'm not giving possible snow amounts is we still don't know for sure how long the easterly will last and thats why i'm holding fire until we have a better idea, part of the uncertainty is exactly how much that southern european low deepens. In terms of the gfs i'm not just opposing its precip forecasts to be difficult! i've never trusted them and in convective scenarios they're even more out than in frontal precip situations.

[ChartViewer]

Some fantastic T24-T144 charts showing up for cold lovers bringing cold of between -3 to -8

on those charts.....However all models are now showing scatter for the period beyond and

I suspect a chance of Higher pressure to the South East/South.....Breakdown in 3rd week Jan and

then as GP said possible warmer temps for UK as colder Stratosphere, collapsing block meaning

Atlantic SW time....Most will welcome that I suspect after this cold spell a

[TEITS]

I understand the notion that easterlies bring snow, but normally when there is a nice low, or something sitting over Belgium, or somewhere close, that acts as a conveyor. I don't see that. I don't see any deep low pressures. I don't see any convection. europe.

I hope I am very wrong, and you are very right!!

You don't need any of those because its the interaction of the colder temps across the N sea that causes the instability. What we see here in the UK is no different to the lake effect snow they experience around the Great lakes. The only difference is the severity because they can experience lower upper temps. Sometimes those in the US can recieve nearly 1m of snowfall due to lake effect snow.

Feb 91 is a good example.

http://www.wetterzentrale.de/archive/ra/1991/Rrea00119910207.gif

Feb 2nd 2009.

http://www.wetterzentrale.de/archive/ra/2009/Rrea00120090202.gif

Trust me when I say if the models verify there will be convection. What members need to use is local knowledge in these circumstances.

Finally I will add that ideally what we want to see is a stronger flow. The stronger the E,ly the further inland the snow will penetrate.

[VillagePlank]

Ok guys - as others have said the week will play out, as it plays out. I am in no mood for a row. I see cold but generally dry for most of the uK, with favoured spots getting a hammering. There's no point in my opinion from hiding from the the fact that most people, by population, will not have disruptive snow.

Snow is hard to come by. Like thunderstorms, if one parameter is out, then it simply doesn't happen - hence the never ending frustration on this forum. It will be worse this time since the atmosphere is absolutely geared for snow - I'd be surprise if anyone reported rain from about 6am tomorrow morning.

I simply see the frequency of snow not as others see it. It will surely happen, but just not countrywide. As I said, I will be the first in queue to say I was wrong, if that occurs.

[grab my graupel]

As this is the model thread, can we get back to discussing the Models please?

Thank you

[VillagePlank]

Finally I will add that ideally what we want to see is a stronger flow.

Yes, any element of shear in these conditions will magnify any potential. But, once, again, I don't see it.

[nick sussex]

Ok guys - as others have said the week will play out, as it plays out. I am in no mood for a row. I see cold but generally dry for most of the uK, with favoured spots getting a hammering. There's no point in my opinion from hiding from the the fact that most people, by population, will not have disruptive snow.

Snow is hard to come by. Like thunderstorms, if one parameter is out, then it simply doesn't happen - hence the never ending frustration on this forum. It will be worse this time since the atmosphere is absolutely geared for snow - I'd be surprise if anyone reported rain from about 6am tomorrow morning.

I simply see the frequency of snow not as others see it. It will surely happen, but just not countrywide. As I said, I will be the first in queue to say I was wrong, if that occurs.

VP theres no problem in having a difference of opinion, i was more highighting the se as thats the area that would be most effected by any easterly, before that theres still snow chances for other areas, of course more eastern and ne areas would always be favoured with the current pattern but as an example of how surprises pop up, i was speaking to friends in Cornwall today who woke up to snow this morning.