Model Output Discussion

[TEITS]

"this is more likely towards the end of next week into next weekend."

That seems to have been a reoccurring theme for those waiting for a snow event from this particular cold spell (and away from Kent of course!). Always just over the metaphorical horizon!

Like I say on Tues there is a risk of rain turning to snow as the front moves E. Check out the latest +84 fax chart.

http://www.wetterzentrale.de/pics/brack2a.gif

I know it seems frustrating when I say we might have to wait. However I just don't believe this LP tracking S will bring widespread snowfall to many low lying areas especially S England. We need to pull in a colder N/NE flow with a disturbance to the S clashing with this colder air to bring a widespread snow event. Those who are saying widespread heavy snow next week are being misleading.

[keithlucky]

I more interested whats happening behind the front looks more interesting for snow,there seems to be a pretty strong nnwest flow, which gives us a better chance of heavy wintry showers in western uk.

[karyo]

As I said yesterday, take those local forecasts with a huge pinch of salt. Its a type of scenario that gives unexpected snowfalls and rainfall when one expects snowfalls.

When I saw yesterday's local forecast I thought they should have mentioned the possibility of something wintry. However, today although their forecast was unchanged, it looked more on the money as the upper air temperatures for early next week look wrong side of marginal. 24 hours ago, things looked colder!

Karyo

[Frosty.]

Those who are saying widespread heavy snow next week are being misleading.

I mentioned there is a good chance of heavy snow developing across scotland during next week, especially further north and that seems a fair assessment based on the 00z models, for us further south though it looks wet with sleet mixed with the heavier rain and snow on high ground only.

[D KARLSON]

i think the chaos theory applies here,and sorry JH for my aside on your unintentionally funny will it snow next week post.

With the low wobbling around in situ over britain ,temps marginal it will end up boiling down to how heavy the precipitation is and if the heavier precipitation coincides with the night time period.

as for after this who knows, but it always seems likely that Scotland will hang on to something of an easterly flow as high pressure continues to influence fro the north, as a result i think Scotland could well be snowed in over the coming weeks

Edited February 12, 2010 by D KARLSON

[snowmadchrisuk]

Like I say on Tues there is a risk of rain turning to snow as the front moves E. Check out the latest +84 fax chart.

http://www.wetterzentrale.de/pics/brack2a.gif

I know it seems frustrating when I say we might have to wait. However I just don't believe this LP tracking S will bring widespread snowfall to many low lying areas especially S England. We need to pull in a colder N/NE flow with a disturbance to the S clashing with this colder air to bring a widespread snow event. Those who are saying widespread heavy snow next week are being misleading.

Based on yesterday's 6z , I think we can for once use the term "Downgrade" with some truth . You have got to get the Cold uppers and the precipitation at the same time in February . Also -10 850's are needed really . We can get away with -5 in December and January in the right conditions but in Feb day time temps rise to high .

Snow events can still happen though and we just need to wait for the perfect setup . To be honest it is raining quite heavy in Leicester right now and looking at the models I would have forecast Snow at least at first . The NAE isn't perfect though as it says it should be rain everywhere and it is Snowing in many Southern counties this morning.

[TEITS]

I mentioned there is a good chance of heavy snow developing across scotland during next week, especially further north and that seems a fair assessment based on the 00z models, for us further south though it looks wet with sleet mixed with the heavier rain and snow on high ground only.

I wasn't referring to you Frosty as I said with the exception of Scotland/ higher ground of N England.

[Guest]

I wasn't referring to you Frosty as I said with the exception of Scotland/ higher ground of N England.

Even then I think lowland Scotland may struggle to see widespread snow. Anything over approx. 300m should get a pasting up here, but I'm not fancying how marginal the models look for snow lower down. It could just be a horrible sleety mess all over the UK.

[locneverstop]

It does look as though we are going to have a general lack of snow Tuesday, as a couple of people have said the upper air just isn't cold enough.

It is interesting I think that FI is slowly having the SW systems pushed further ahead in time with each subsequent run. Looks like it could be quite cold for some time to come?

[snowmadchrisuk]

It does look as though we are going to have a general lack of snow Tuesday, as a couple of people have said the upper air just isn't cold enough.

It is interesting I think that FI is slowly having the SW systems pushed further ahead in time with each subsequent run. Looks like it could be quite cold for some time to come?

To be honest mate I'd rather have 12 degrees and Sunshine than Cold rain . A few surprises next week still can not be ruled out as there is some quite heavy precipitation going to be developing .

[The PIT]

Evaporative cooling comes to mind and this may be the key. Light prec rain next Tuesday heavy rain then temps may fall enough to bring snow down to lower levels. Pity the low got all the milder air wrapped up in.

[Duane S.]

Right, now I know I have wheeled out this old nugget before but I think it is worth reminding people that 850 uppers are not the be all end all of whether it will snow or not.

I know this was different in that the line of attack was different so I am not drawing any sort of direct comparison but... taking this chart at face value who would have thought 30 hours of non snow on the south coast would occur? But it did. Further inland received up to 90 cm and rural towns were cut off for days (even Weymouth was severed from the outside world for nearly 3 days)

[MisfitDog3]

Pity the low got all the milder air wrapped up in.

Hang on a mo, you're talking in the past about something in the future which doesn't even exist yet!

Let us see how this rolls on across the models during the next 36 hours or so. Track is all important!

[lukemc]

Hi,

Just asking a question regarding next weeks low pressure system? Why would it seem that rain rather than snow would be likely for most of the country (except high ground) as we seem to have most or if not all of the building blocks in place for a cold and wintry spell of weather, we have a negative NAO that is negative (and trending deeply negative), a jet stream that is way way south of us over North Africa (surely this should allow the cold air build), a cold continent still and the retrogression of the high pressure system towards Greenland, in essence a Greenland High. And also you have got to remember that we are still Mid February, not April - the days are still quite short and as an example a few years ago we got the biggest snowfall of the winter in many areas (including mine in Liverpool!) in March (2006) - which was almost a full month on from the time we are now in the winter. So what puzzles me is why this event is looking light a non event in many areas as far as snow is concerned taking into account those factors just asking for a logical explanation also why do you think over the last two weeks or so the models have trended to downgrade cold/snowy weather as we get closer to the reliable timeframe, is it something to do with the programming of the various systems?

Luke

[Tom D]

Right, now I know I have wheeled out this old nugget before but I think it is worth reminding people that 850 uppers are not the be all end all of whether it will snow or not.

I know this was different in that the line of attack was different so I am not drawing any sort of direct comparison but... taking this chart at face value who would have thought 30 hours of non snow on the south coast would occur? But it did. Further inland received up to 90 cm and rural towns were cut off for days (even Weymouth was severed from the outside world for nearly 3 days)

On the other hand, it's just rained here in Leicester and according to the models, 850hpa temps are -6/7 but as surface temperatures are around 3/4c it is rain at the surface.

[full_frontal_occlusion]

Looking at todays output, I'm not convinced that the evolutions offered are showing the final outcome and not simply by how much the patterns have changed since last weekend from widespread snow to cold damp squibs and everything in between.

The Meto adding the widespread snow warning for next Tuesday sounds like an insurance for the possibility of an event. Too long range to be accurate given the current state of the models - better to be downgraded/removed than be caught out with all the ramificatios that would entail re' their credibility.

ffO

[MKN]

On the other hand, it's just rained here in Leicester and according to the models, 850hpa temps are -6/7 but as surface temperatures are around 3/4c it is rain at the surface.

On the other hand to that though, i heard places further south have had snow this morning and thats probably down to the fact there within the 528 dam line whereas we will be out of it now. Next week we will be fine with the 528 line covering most of the uk.

[mountain shadow]

Hi,

Just asking a question regarding next weeks low pressure system? Why would it seem that rain rather than snow would be likely for most of the country (except high ground) as we seem to have most or if not all of the building blocks in place for a cold and wintry spell of weather, we have a negative NAO that is negative (and trending deeply negative), a jet stream that is way way south of us over North Africa (surely this should allow the cold air build), a cold continent still and the retrogression of the high pressure system towards Greenland, in essence a Greenland High. And also you have got to remember that we are still Mid February, not April - the days are still quite short and as an example a few years ago we got the biggest snowfall of the winter in many areas (including mine in Liverpool!) in March (2006) - which was almost a full month on from the time we are now in the winter. So what puzzles me is why this event is looking light a non event in many areas as far as snow is concerned taking into account those factors just asking for a logical explanation also why do you think over the last two weeks or so the models have trended to downgrade cold/snowy weather as we get closer to the reliable timeframe, is it something to do with the programming of the various systems?

Luke

Beacuse although cold, it won't be cold enough for many.

The particular issue is the upper air temperatures at around 5000 feet are only around -5oC, and you really need temps around -7oC - -10oC. This can be overridden buy other factors such as the rate of rainfall/snowfall etc.

It is a very complicated and marginal position and it really will be a case of looking out the window and seeing whats falling from the sky.

For Northern Ireland it is even more marginal despite being closer to the colder air source, we have the trough sitting just about over us moderating the temperature. Where as this part of the world looked best for snow three days ago, it's now in one of the worst although the higher inland hills will still do well.

[TEITS]

The Meto adding the widespread snow warning for next Tuesday sounds like an insurance for the possibility of an event. Too long range to be accurate given the current state of the models - better to be downgraded/removed than be caught out with all the ramificatios that would entail re' their credibility.

ffO

The Met O advisory is simply due to the fax chart at +84.

http://www.wetterzentrale.de/pics/brack2a.gif

As the front moves E it could turn to snow during Tues. However at this range I would be amazed if the fax chart for Tues remains unchanged.

[Hammer]

Looking at todays output, I'm not convinced that the evolutions offered are showing the final outcome and not simply by how much the patterns have changed since last weekend from widespread snow to cold damp squibs and everything in between.

The Meto adding the widespread snow warning for next Tuesday sounds like an insurance for the possibility of an event. Too long range to be accurate given the current state of the models - better to be downgraded/removed than be caught out with all the ramificatios that would entail re' their credibility.

ffO

I disagree. Meto clearly see the risk, hence issuing this well in advance, lets be honest, they could have left it to Saturday or even Sunday.

If anything if the risk is very low then issuing an advisory and then removing it, would probably not look to great either.

In many ways I like the confidence of issuing an advisory now, showing once again human input comes in to play, rather than leaving it to a computer.

[Guest North Sea Snow Convection]

Right, now I know I have wheeled out this old nugget before but I think it is worth reminding people that 850 uppers are not the be all end all of whether it will snow or not.

I know this was different in that the line of attack was different so I am not drawing any sort of direct comparison but... taking this chart at face value who would have thought 30 hours of non snow on the south coast would occur? But it did. Further inland received up to 90 cm and rural towns were cut off for days (even Weymouth was severed from the outside world for nearly 3 days)

Next week we would need a sustained source of cold air and low dewpoints from the continent, much as gave rise to the snow in the example you have given' to keep any ppn as snow beyond Tuesday. It looks a temporary event to me.

After Tues it looks, on current suggestions by the models in general anyway, that the air over and around the UK is basically just cyclonic and the air just gets mixed out and dewpoints rise - neither is going to be very conduisive at all for snowfalls beyond Tuesday apart form higher hills further north.

The position and orientation of the low has to change in the modelling to keep us on the right side of the polar front rather than the constant suggestions of the low phasing with other low pressure to the south and west and preventing the low sinking away with the cold air to the north of the lows following back south over the UK.

For the Uk as a whole it is a frustrating pattern in terms of what could be with blocking to the north and reverse zonal winds. The hope is that the low complex gets forced south and/or east of the UK and an easterly or northerly can follow with a fresh source of decently cold upper 850 temps and lower dewpoints. But there is little sign of that in the models atm.

Edited February 12, 2010 by North Sea Snow Convection

[Weathizard]

Could that pocket of cold air over France come into play?

[Guest North Sea Snow Convection]

Could that pocket of cold air over France come into play?

Initially yes - as I was just saying, the residual surface cold and a draw of air from France will be condusive for the snow that is suggested for Tuesday. Unfortuantely after that the pattern is just cyclonic and temps and dewpoints will go just the wrong side of marginal for many places, most especially in the south, without a fresh source of upper cold air to draw on.

[SP1986]

Initially yes - as I was just saying, the residual surface cold and a draw of air from France will be condusive for the snow that is suggested for Tuesday. Unfortuantely after that the pattern is just cyclonic and temps and dewpoints will go just the wrong side of marginal for many places, most especially in the south, without a fresh source of upper cold air to draw on.

That pattern could last quite a while too, there doesn't seem to be any signals suggesting either a return to wortwhile cold or mild. This pattern sort of reminds me of the pattern we had to endure in summer 2008, albeit from a slightly different set of circumstances.

In my opinion I would take mild and drizzle any day over the pattern that's programmed currently.. let's hope it changes somewhat to either one with a higher chance of snow, or one to a chance of some 'Spring'' warmth.

[MR EXTREMES]

Next week we would need a sustained source of cold air and low dewpoints from the continent, much as gave rise to the snow in the example you have given' to keep any ppn as snow beyond Tuesday. It looks a temporary event to me.

After Tues it looks, on current suggestions by the models in general anyway, that the air over and around the UK is basically just cyclonic and the air just gets mixed out and dewpoints rise - neither is going to be very conduisive at all for snowfalls beyond Tuesday apart form higher hills further north.

The position and orientation of the low has to change in the modelling to keep us on the right side of the polar front rather than the constant suggestions of the low phasing with other low pressure to the south and west and preventing the low sinking away with the cold air to the north of the lows following back south over the UK.

For the Uk as a whole it is a frustrating pattern in terms of what could be with blocking to the north and reverse zonal winds. The hope is that the low complex gets forced south and or east of the UK and an easterly or northerly can follow with a fresh source of decently cold upper 850 temps and lower dewpoints. But there is little sign of that in the models atm.

your words have not fallen of deaf ears my friend,the models seem very keen to take this system sw its not a good way to go if cold is to follow the mixing was and is always a concern,

with nice blocking and this happens what a shame i still think we have a little time yet for developments but not from the system causing the problems.

once if this moves away far enough it may well open the door mid month its a long shot but very possible depending on whether we can hold blocks in position,although this could well dwindle away.

its a dissapointment whats happened but it looks like being the over all trend,

i dont think anyone can deny that this is very marginal even for the north and even worse for the south sw and east unless theres a dramatic shift,

ive waited for days for a shift east its never really looked likely with always 1 model throwing up hope,

this hope has pretty much gone.

but thats not to say mid next week another trend towards cold cant build,

but its getting towards the end of our winter season with less cold floating around and a building heat source.

i cant see the models making a shift so i cant see this as being a major event apart from maybe the north of scotland and on the highest hills in wales with cumbria being the boundry point.:unsure: