Winter Model Discussion 18Z 13/1/13 onwards.

[NorthernRab]

It does seem to me people are picking up the 500hpa charts, seeing a massive deep area of blue coming our way and assuming this is going to be heavy snow blizzards.

What is actually happening is this is showing the pressure differences of a deep 968 low pressure coming our way which will pump atlantic warmth into our cold weather.

Given that it is already falling as rain/sleet in places and we are under the influence of supposedly cold weather, by the time this reaches us it will almost definatley be cold high winds, heavy rain

and dark grey skies.

No, I think they're seeing large bands of precipitation (carried initially by the deep areas of low pressure) crashing against a cold block set up over much of the UK. People aren't misreading the charts in this respect, somewhere in the UK is likely to get fairly hard this week, the question is where?

[MKN]

It does seem to me people are picking up the 500hpa charts, seeing a massive deep area of blue coming our way and assuming this is going to be heavy snow blizzards.

What is actually happening is this is showing the pressure differences of a deep 968 low pressure coming our way which will pump atlantic warmth into our cold weather.

Given that it is already falling as rain/sleet in places and we are under the influence of supposedly cold weather, by the time this reaches us it will almost definatley be cold high winds, heavy rain

and dark grey skies.

Many would infact get snow the surface winds would be off the continent pulling in sub zero dps. The UK would already have v cold surface temps. The 850s unlike yesterday would produce snow down to -2/3 rather than -5. Still until anythings set in stone not worth looking at them details. We all need to hope the ukmo is bang on the money then some serious snowfalls are likely

[TEITS]

Have to say im lacking some motivation to post this morning and that isn't because of poor charts, quiet the opposite. The reason simply being is the big guns i.e ECM/UKMO don't even agree at +72 although latest fax supports UKMO.

I can see many snow possibilities in the outputs but they all differ. The GFS suggests the initial approach from the W will be a classic stalling front across parts of the W bringing alot of snowfall but not making any progress further E than the W Midlands. This makes sense as I have seen this occur many times over the years. The UKMO/ECM all show huge snowfall potential and if the output continues then someone is going to see a blizzard. The word blizzard is often over used but this would be perfectly apt even for low lying areas.

Lets use the ECM at +144 and assume this is correct and then think of my location as an example. Now this chart shows a classic snow storm for anyone from the N Midlands, into N England. Now for my location this would be a rain event but the required shift S for this to be a snow event is so tiny synoptically speaking. The rain/snow dividing line would change in the output every 4hrs on the NAE and even on the day itself the system might be slightly further N or S. You then have the added complication of rain turning to snow on the W flank of the LP as it clears to the E as colder uppers move in.

Looking beyond this chaos and the overall trend from the models is very positive. Last time I checked the GEFS ensembles the mean rose to 0C but as you can see below this has dropped somewhat.

http://cdn.nwstatic.co.uk/ensimages/ens.20130115/00/t850Cambridgeshire.png

So in summary someone is going to get nailed this weekend into Monday. Based on the evidence so far the further S/W you are the more likely to see a brief return of less cold conditions with the N remaining cold. As for the snow potential and again the further N you are the greater the threat. Im not sure at this stage whether Scotland will see a snow storm because I feel LP will be too far S. So that leaves N England at greatest threat. Don't forget though the models bias to trend further S as +0 gets closer. Happens nearly every time in these situations!

Edited January 15, 2013 by THE EYE IN THE SKY

[Carlrg]

The BOM shows the jet pushing through for Saturday today, rather than sliding SSE as in yesterdays run.

http://www.meteociel...ode=5&archive=0

Edited January 15, 2013 by Carlrg

[metrosnow]

It does seem to me people are picking up the 500hpa charts, seeing a massive deep area of blue coming our way and assuming this is going to be heavy snow blizzards.

What is actually happening is this is showing the pressure differences of a deep 968 low pressure coming our way which will pump atlantic warmth into our cold weather.

Given that it is already falling as rain/sleet in places and we are under the influence of supposedly cold weather, by the time this reaches us it will almost definatley be cold high winds, heavy rain

and dark grey skies.

And this is the post of the day so far for me. Yes it's cold and yes there's been snow, but come on folks, time to get real. Five miles down the road it was raining yesterday afternoon, Not really much of a cold 'block' is it?

I'd love things to be 1947 all over again, but a kid blowing through a pea shooter on the Scilly Isles could probably blast this feeble effort away!!!

Edited January 15, 2013 by metrosnow

[lord stratus]

Hi,

After observing these forums for a while, one thing which becomes evident is that with snow, the forecasting is very volatile. It almost appears to change every ten minutes with new factors coming in to play and changing things.

Now when Met Office, BBC etc forecast, they will forecast and leave it for hours before making changes. Thus, does this mean when it comes to snow they will be inaccurate a lot of the time?

Also is there brief explanation as to the reason why snow forecasting is so difficult and is prone to change a lot?

Thanks

Your have observed correctly. Lets be

fair, the weather forecasters have struggled with the arrival of this cold spell, let alone any snow events, there are parts of the UK that will say "what cold spell". Convective snow from the North Sea and fronts from the east are less of a headache but can only be forecast at short notice some times.

This weeks snow event is probably there biggest nightmare as it really is down to the track of the incoming low. This will keep being corrected northwards/southwards during the next couple of days which will dictate where the snow is most likely.

[Gibby]

Good morning folks. Here is the report of the 00zs from GFS, UKMO, GEM and ECM for Tuesday January 15th 2013.

All models show a cold spell established over the UK for the next 4-5 days. For most there will be a lot of fine and frosty weather as a finger of High pressure ridges over the UK from High pressure out to the NE. A few wintry flurries could occur near the East and SE cast over the next few days. Later in the week pressure falls as Low pressure moves up against the cold block over the UK. The associated Low pressures under cut the Scandinavian High and eventually form Low pressure close to Southern England with a spell of sleet and snow, possibly disruptive late in the week and weekend, though it will turn to rain in Southern England later as milder air infiltrates NE from the SW.

GFS then shows cold conditions holding on in the North with further snowfall and strong East or SE winds. In the South skies will brighten somewhat with less cold weather and heavy rain showers early next week with possible thunder and hail near the coasts. Through FI a rinse and repeat pattern of a wintry North with further snowfall and somewhat less cold weather at times in the South persists with repeated spells of rain then thundery showers. It's not until the end of FI when the less cold weather spreads to all areas with the axis of Low pressure then further North with showers or longer spells of rain for all by then with just snow on Northern high ground in winds turning more West or SW everywhere.

The GFS Ensembles show a continuation of the cold weather in the South over the next three to four days before a moderation in the levels of cold occur from the weekend as unsettled weather moves in with precipitation at times. The members continue to be relative tight in the North with little spread. Uppers even out at around -3C to -5C in the South and close to -5C in the North. The operational is on the cold side of the pack in the North while in the South the operational isn't far from the average level for the run.

The Jet Stream shows a weak but Southward moving flow over the coming 48 hours or so before a strong surge of the Jet crosses the Atlantic South of the UK later this week as deep depressions on its Northern flank buffer up against the cold block to the NE.

UKMO for midnight on Monday shows Low pressure having moved gently NE into Southern England. After a cold and in places snowy weekend milder air will of filtered into Southern Britain with heavy and thundery rain showers here while Northern areas maintain the cold Easterly winds with further sleet or snow in places, especially over the hills.

GEM shows Low pressure too having moved a trough North over Britain with sleet and snow turning to rain before a complex Low structure moves into the UK and away slowly SE later. The weather would remain on the cold side for many with a lot of cold rain about but some wintry flurries around too at times, chiefly over the hills and towards the end of the period.

ECM shows a similar evolution to UKMO this morning, pulling Low pressure into Southern England next Monday with copious rain events following snowfall over the weekend as milder air gradually infiltrates North. As the Lows fill and move away ESE a renewed push from the Atlantic means a rinse and repeat pattern though with so much mixing of the air by then mostly rain will continue in the South while the North may continue to see periods of snow at times.

In Summary this morning despite a complex pattern there is quite a bit of agreement on the course of events in the coming week or two. This week looks like being essentially dry with just a few wintry flurries in the East. Frosts will be sharp and severe with some freezing fog possible. The next phase of the weather will be over the end of the week and weekend as milder air tries to displace the cold pool over the UK with a messy period of snow and sleet moving steadily NE over the UK. How much snow and for how long remains an open for debate question this morning as the models can sometimes overplay the speed at which cold air in Winter can be displaced but as shown this morning most areas of Southern England and Wales will be into less cold and showery conditions early next week while the North hangs on to colder easterly winds and the threat of further snowfall. In the longer term the weather remains complex and shows that the cold, though modified remains stubborn and could return back South on occasion though with a strong Atlantic it does look this morning that a gradual advantage to the milder air out to the SW will succeed. However, having said all this there is plenty of time for the models to change and for the milder conditions to be held back more than is currently shown which could have major implications down the line.

[Severe Siberian icy blast]

A few tweets from Matt leading on from his last post, sounds good!

Matthew Hugo â€@MattHugo81

00z EC ENS mean is cold and with lows from the Atlantic never moving E or NE, generally having a NW to SE movement, with a SE'ly

Matthew Hugo â€@MattHugo81

00Z EC ENS far more bullish for a front to move into the UK during Fri...Snow would be possible from the W, details highly uncertain though.

Very interesting this because he said earlier he eagerly awaited the ens , this is interesting , so the ECM is also going for sliders , the ukmo has been absolutely rock solid , when they first rolled out with these charts several days ago it looked very dubious , and I for one was very sceptical , infact the charts look more like something you see from gfs in deep fi , but no , these are very reall possibilities and 4days away , for me the ukmo is leading the way by a country mile at the minute.

[TEITS]

And this is the post of the day so far for me. Yes it's cold and yes there's been snow, but come on folks, time to get real. Five miles down the road it was raining yesterday afternoon, Not really much of a cold 'block' is it?

Sorry but yesterday has nothing to do with this weekend. During yesterday parts of the S did see rain instead of snow but this was expected due to the warmer sector.

During the rest of this week we're going to see mins drops as low as -10C in places and -6C quiet widely. The max temps will struggle to get above 0C and remain below in some locations.

[UV-RAY]

Wow it's a bit feisty in here this morning, I am in the Net Weather Model Output Thread and not some " come and have a go if you think your hard enough" forum.

Anyway a quick check and it appears I'm in the right forum After viewing this mornings output all I can say is who would want to be a forecaster, so I'll offer up my best guess at what may or may not happen this weekend and beyond. The low out West IMO will probably only effect SW areas of the country, I don't see it making much progress beyond, hopefully it will on a purely selfish note but going off past events similar to this, then this is generally what happens in such set ups. The block out East really is putting up a fight, one which we haven't seen for quite a long while, we could well be looking at a major snow event for the SW and parts of Wales, one which could be on par with 78. Thereafter lord knows as it all depends on the angle of attack from this low, but with the Atlantic in attack mode and the block in defensive mode I suspect lots of fun and games, unless your a forecaster that is.

[IDO]

Very interesting this because he said earlier he eagerly awaited the ens , this is interesting , so the ECM is also going for sliders , the ukmo has been absolutely rock solid , when they first rolled out with these charts several days ago it looked very dubious , and I for one was very sceptical , infact the charts look more like something you see from gfs in deep fi , but no , these are very reall possibilities and 4days away , for me the ukmo is leading the way by a country mile at the minute.

The latest UKMO fax:

Looks like it may stall over the Atlantic on that chart. Its all about opinions at the moment, the pros are unsure as are the models and all the members on here are highlighting the divergence. We should see some interesting runs in the next 24 hours when hopefully it will become clearer.

[karlos1983]

Wow it's a bit feisty in here this morning, I am in the Net Weather Model Output Thread and not some " come and have a go if you think your hard enough" forum.

Anyway a quick check and it appears I'm in the right forum After viewing this mornings output all I can say is who would want to be a forecaster, so I'll offer up my best guess at what may or may not happen this weekend and beyond. The low out West IMO will probably only effect SW areas of the country, I don't see it making much progress beyond, hopefully it will on a purely selfish note but going off past events similar to this, then this is generally what happens in such set ups. The block out East really is putting up a fight, one which we haven't seen for quite a long while, we could well be looking at a major snow event for the SW and parts of Wales, one which could be on par with 78. Thereafter lord knows as it all depends on the angle of attack from this low, but with the Atlantic in attack mode and the block in defensive mode I suspect lots of fun and games, unless your a forecaster that is.

Post of the day for me, and i only had to read it once. ;-)

[MisfitDog3]

I think block holding is, marginally, favoured at the moment. It wouldn't take much to stack the weighting into Atlantic Breakthrough BUT I'm not convinced any AB would last very long and the block would re-establish itself. It's all very interesting and a few grumpy heads on here should chiiiilllllll! It's not 10 degrees and raining....so it's at least 4 to 5 days of something much colder and potentially something very special!

[chris55]

I done a little chart yesterday for those newbies learning about the models in the South West thread, I thought I'd pop it in here as well,

A south east wind is crucial and very helpful when looking to get snow out of a situation where milder air is coming up against a cold block. Yesterdays non event (for the West) moved in from the north west which is a totally different kettle of fish to what is being hinted at for Friday.

Having the wind in from the south east means the milder/moister Atlantic air picks up the much drier cold air off the continent, this means dew points are lower and 850s can be higher and snow still fall, so as long as your ahead of the frontal boundary snow is much more of a risk.

[stainesbloke]

Hi Steelermark I am from the south so not quite true, I just see the 'improvement' overall and the slowing down of the Atlantic as each run/day passes and the shifting south of the jetstream.

If this trend continues whether 1st attempt 2nd or 3rd snow will be had by most. Temps in south looking to be 0c daytime MAXIMA come Thurs / Fri. Bring on the fronts.

BFTP

Yes, some great charts churning out for the end of the week. It does look IMHO that the block will hold with increasingly cold temperatures across much of the UK. Good to see daytime maxima not progged to rise above freezing....that's really important and reminds me of many of the snowy spells in the 80s. I remember temps in those cold spells stayed sub zero for days, even in London. Awaiting further charts/info with interest!

[Dublin Novice]

I get the impression that despite some quite mouthwatering charts for you guys across the water that we on the East coast of Ireland are somewhat too far westerly to see some snow action.

Would any of the more experienced and learned among you see any possibility of the battleground scenario delivering for us?

Cheers.

[steelermark]

And this is the post of the day so far for me. Yes it's cold and yes there's been snow, but come on folks, time to get real. Five miles down the road it was raining yesterday afternoon, Not really much of a cold 'block' is it?

I'd love things to be 1947 all over again, but a kid blowing through a pea shooter on the Scilly Isles could probably blast this feeble effort away!!!

But that's completely untrue isn't it?. The block is only just getting established over the British Isles. Yesterday was always going to be marginal for some because of the warm sector, anybody that believed anything else clearly wasn't reading what was in front of them.

Temperatures are going to continue to fall away as the week goes on, by the time the fronts arrive the cold air will be fully entrenched over pretty much everybody. It won't get blown away like you say at all. Somebody, somewhere will have some fun this weekend but it won't be everybody, it hardly ever is in situations like this.

[Carlrg]

The 2m charts show a rise in temp from Sunday onwards.

http://www.meteociel.fr/modeles/bome_cartes.php?ech=6&code=0&carte=0&mode=8&archive=0

[swfc]

The 2m charts show a rise in temp from Sunday onwards.

http://www.meteociel...ode=8&archive=0

thats the bom chart.not saying it wont be close but doubtfull

[Troubleatmill]

Have to say im lacking some motivation to post this morning and that isn't because of poor charts, quiet the opposite. The reason simply being is the big guns i.e ECM/UKMO don't even agree at +72 although latest fax supports UKMO.

I can see many snow possibilities in the outputs but they all differ. The GFS suggests the initial approach from the W will be a classic stalling front across parts of the W bringing alot of snowfall but not making any progress further E than the W Midlands. This makes sense as I have seen this occur many times over the years. The UKMO/ECM all show huge snowfall potential and if the output continues then someone is going to see a blizzard. The word blizzard is often over used but this would be perfectly apt even for low lying areas.

Lets use the ECM at +144 and assume this is correct and then think of my location as an example. Now this chart shows a classic snow storm for anyone from the N Midlands, into N England. Now for my location this would be a rain event but the required shift S for this to be a snow event is so tiny synoptically speaking. The rain/snow dividing line would change in the output every 4hrs on the NAE and even on the day itself the system might be slightly further N or S. You then have the added complication of rain turning to snow on the W flank of the LP as it clears to the E as colder uppers move in.

Looking beyond this chaos and the overall trend from the models is very positive. Last time I checked the GEFS ensembles the mean rose to 0C but as you can see below this has dropped somewhat.

http://cdn.nwstatic....bridgeshire.png

So in summary someone is going to get nailed this weekend into Monday. Based on the evidence so far the further S/W you are the more likely to see a brief return of less cold conditions with the N remaining cold. As for the snow potential and again the further N you are the greater the threat. Im not sure at this stage whether Scotland will see a snow storm because I feel LP will be too far S. So that leaves N England at greatest threat. Don't forget though the models bias to trend further S as +0 gets closer. Happens nearly every time in these situations!

Really well put Dave

Experience also tells us that lp's in this situation dont end up as far North as initially shown, so would not be at all suprised to see the Precipitation making it as far North as say Cheshire across to Mansfield and Skegness but not much further, and all areas south of this Seeing heavy snow and indeed blizzards in some spots.

Will all come to light in future runs, but great looking charts this morning!

[mulzy]

Sorry but yesterday has nothing to do with this weekend. During yesterday parts of the S did see rain instead of snow but this was expected due to the warmer sector.

During the rest of this week we're going to see mins drops as low as -10C in places and -6C quiet widely. The max temps will struggle to get above 0C and remain below in some locations.

Agree TEITS - the upcoming scenarios (undercutting lows) is totally different to what happened yesterday.

How many times have the models overplayed the Atlantic influence and underplayed the block? I firmly believe this is what is happening at the moment. Folk in the south should not be dis-heartened by the outputs today.

UKMO leading the way...

Edited January 15, 2013 by mulzy

[Paul]

Seeing quite a few posts where members are having a dig at others for 'not being able to read the charts', which isn't really on. If someone has misread a chart or is barking up the wrong tree a bit, rather than shouting at them, please offer your opinion in a more reasonable, friendly way. This forum is open to all, not everyone is an expert and no-one is going to learn if the only feedback they get is negative, condescending and non-constructive.

[WhiteFox]

Really well put Dave

Experience also tells us that lp's in this situation dont end up as far North as initially shown, so would not be at all suprised to see the Precipitation making it as far North as say Cheshire across to Mansfield and Skegness but not much further, and all areas south of this Seeing heavy snow and indeed blizzards in some spots.

Will all come to light in future runs, but great looking charts this morning!

Yes, it is a case, once again, of people taking model output at face value. I know there is always the argument of "This is the model thread and we are discussing what they show", but if anyone has been watching the models over the past week, the one thing they do show is systems tracking further south and west; this is clear.

WRT snow v rain, there's not much to add other than that which has already been pointed out by many posters: in these situations you will not see the cold mixing out until the frontal boundary crosses;where the winds backs to West of South you see the changeover to rain. So long as the wind stays east of south the PPN generally stays frozen.

Quite often, even when the Atlantic does break through, you can get two fronts pushing up against the block, with the first staying as all snow and the second eventually succeeds in pushing mild air through. If the cold air remains firm then the first front gives all snow and the second front never makes it, something which some charts are showing.

As for "yesterday had rain so there won't be any snow when the Atlantic pushes in", it is important to bear in mind that we have much colder upper air temperatures now and this is now feeding through to surface temperatures. By the mind we get to any Atlantic attack we will have cold surface temperatures, and a circulation around any Atalntic systems drawing cold air from the continent.

Yesterday the cold air hadn't really entrenched so the wamer air mixed into the system raised temperatures through the day; I saw a temperature of 5oC on the drive home around 6.30 last night (going by the car thermometer!) which was the warmest for the whole day.

[Snowly does it]

06z has the cold air further east by T66 with only EA and parts of the south and midlands in under -5 air, however lets see what sort of fight back it mounts from here

[swfc]

things slightly further east on the 6z at 72 hours and pressure to the north east slightly lower.