Winter Model Discussion 12Z 15/02/13 onwards.

[Dexter29]

Why are members following GFS ppn charts to a tee.

Don't even consider ppn rates and locations until at least Tuesday.

So that's another 14 GFS runs = 14 times the ppn amounts/locations will change!

[Severe Siberian icy blast]

Why are members following GFS ppn charts to a tee.

Don't even consider ppn rates and locations until at least Tuesday.

So that's another 14 GFS runs = 14 times the ppn amounts/locations will change!

Very good point . That's a lot of ups and downs to go for the members that look at shower distribution 170 hours away !!

[manutdmatt1986]

Latest from UKMO as far as Thurs sees little change to previous: in summary, "Risk of a few light wintry showers on exposed eastern coasts, increasing risk of loc moderate wintry showers in the S/SE by Thurs".

I like the sound of that! Thanks, Ian.

[Neilsouth]

Can anyone answer this question

Why doesn't the wind follow the isobars or vice versa?

[Liam J]

As if by magic in low resolution the GFS thinks hmmm something isn't right how can I remove this cold block as fast possible lol

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=264&mode=1

[Bristawl Si]

As if by magic in low resolution the GFS thinks hmmm something isn't right how can I remove this cold block as fast possible lol

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=264&mode=1

That is 4 days after the v cold and maybe snowy scenario is progged for, so to see a return to milder conditions by Feb 27th doesnt seem implausible for this time of the year.

Edited February 16, 2013 by Bristle boy

[johnholmes]

Can anyone answer this question

Why doesn't the wind follow the isobars or vice versa?

friction in the lowest layers

[shaky]

Nogaps is a beauty!!

[KTtom]

Not to much to get excited about from the overnight/morning runs. Cold - YES, Severe Cold - NO. Snow for some - YES. Nationwide - NO. Significant lack of cold pooling over Continental Europe. Expect further modification upwards of 850's and further downgrades. Advice - to follow the MET O on this one to avoid dissapointment.

Agreed, away from the SE and east coast (which is where the vast majority of members appear to live) I see very little of interest for 90% of the UK landmass now the SW threat has receded for next weekend.

A few in the SE are misleading some into thinking this will be a nationwide event, it won't. Anyone who dismisses the Met and talk up streamers and heavy snow will be throwing the toys out next weekend going by today's models as it just isn't going to happen.

[Liam J]

That is 4 days after the v cold and maybe snowy scenario is progged for, so to see a return to milder conditions by Feb 27th doesnt seem implausible for this time of the year.

I was using that as an example, if you follow the GFS into low res from T192 then the abrupt change is synoptics isn't so plausible IMO. At any stage of the winter you can experience a return of milder conditions following a cold snap, indeed the same could apply at any time of the year.

The chances of having sustained deep cold are greatly reduced as we enter March, thats to be expected given the ever longer days.

Edited February 16, 2013 by Liam J

[johnholmes]

Well I feel your answer just illustrates the problem with the BBC/Met O forecasts.

I have learn't that the models are useless when it comes to predicting convection and this is especially true with E,lys. If the output today remains unchanged then you don't even need to look at the projected precip charts from the models to know more than light snow showers will occur. The term light snow showers is only correct for Wed/Thurs but that isn't the case for the end of the week into the weekend when heavier showers would develop especially across E Anglia/SE.

Again just illustrates my point of over reliance on computer models these days. Remember a recent snowfall when you stated the SW was at greatest risk and I disagreed. Well the reality was the SW actually experienced mild temps whilst others enjoyed snowfall.

Just add im not having a go at you but I get frustrated at times because forecasting instinct has disappeared due to this over dependance on forecast models.

Dave, a word of caution, whatever your feelings about how much convection there MAY be note the word? Hard anayltical judgement by professionals is what they are paid for not to suggest snowmageddon IF the model outputs we see are correct. Remember they have a lot more data and also a lot more experience no matter how enthusiastic we may be on Net Wx?

You may be correct in the long run but caution this far out with ANY precipitation prediction is almost always proved correct-just think back to when/where/how much/when rainfall predictions in the summer? How many were spot on or even near the mark even at 48 hours out?

Edited February 16, 2013 by johnholmes

[Gibby]

Good morning folks. Slight OT I know but just a quick apology for no report from me last night or this morning. A 24hr bug got hold of me yesterday morning but I am feeling much better today so should be back for the 12zs.

[Frosty.]

This upcoming cold spell looks like it will persist until well beyond T+240 hours according to the GEFS 00z mean & ECM 00z ensemble mean, the Scandinavian High looks like becoming a very strong feature, there is even a suggestion of a ridge extending down from Greenland further on, the general pattern is very wintry with a mix of snow showers, severe frosts and freezing fog further north where winds are lighter being closer to the core of the high, cold air starts pushing into east anglia as early as tomorrow night, now compare this to what the GEFS mean was indicating around midweek, 2 weeks of swly winds and rain, things have changed dramatically.

Edited February 16, 2013 by Frosty039

[bluearmy]

Agreed, away from the SE and east coast (which is where the vast majority of members appear to live) I see very little of interest for 90% of the UK landmass now the SW threat has receded for next weekend.

A few in the SE are misleading some into thinking this will be a nationwide event, it won't. Anyone who dismisses the Met and talk up streamers and heavy snow will be throwing the toys out next weekend going by today's models as it just isn't going to happen.

I would wait to see the day 5 faxes for friday and the weekend before dismissing this upcoming spell for northern uk. Scotland does look too close to the block but then the block may not be positioned like that come verification. As far as northern england is concerned, i'd be thinking that looks to be bang in line for convective stuff come the end of the week.

Ian's info re the meto thinking for thursday seems pretty reasoned. Friday could be a tad different if the day 6 chart comes to pass.

[mushymanrob]

I think Steve'e chart would produce snow showers for Derby. Not everywhere though - certainly not the far NW of England, N Ireland or much of Scotland.

hi... trust me, ive NEVER had snow showers (or rain for that matter) here in derby off a straight run of winds south of east, without an embedded feature or a close by low, when theres a static high feeding it. im about level with the top of norfolk, so any winds south of that have a short sea crossing and a long land one before it gets here. we are very prone however to showers from a direction north of east. that has a much longer sea crossing and much shorter land crossing...

Can anyone answer this question

Why doesn't the wind follow the isobars or vice versa?

because air flows out from a high pressure and into an area of low, not directly, but in a shallow spiral close to the line of isobar.

snow showers?... likely judging by this mornings outputs, but just how big will these be? march 98 saw a spell of snow showers (locally), they were quite frequent, but light, didnt settle. so showers might not always lead to a covering.

Edited February 16, 2013 by mushymanrob

[dixonoid]

I think the easterly this time is going to be a lot different and the block is going to be stubborn to shift, as the Vortex is on the move a more European position than Canadian, so it's going to be third time lucky by the looks of it and we are going to actually get a cold easterly or Beasterly!! :-) The pattern this year has been a Siberian high with undercutting lows and not much in the way of -Nao, which every one has been looking for! Hopefully we get a Negative Nao soon or i feel we may have another write off summer with the Northern blocking we have been looking for!

PV more Canada based

Pv Moving into more european position :-)

I think this cold snap is going to have a nasty sting to it :-)

[pyrotech]

Hi John. Regarding your question about isobars. Which i am sure you know answer too. Im on phone so struggling to read today. Anyway i am going to answer it and you can then correct if i am out abit and miss anything. I believe a few factors play in firstly coronial effect and secondly high and low pressure is trying to equal. With high pressure attemting to move towards low to equalise. I believe friction comes into play also but first two are main players. The isobars only show lines of equal pressure not wind direction but due to the above you can work out direction and it is few degrees off so you can use as rough guide only the direction of isobars. Also direction runs inwards in low and out on high from isobar direction. Im confused why u asked as i know your experienced forecaster so assume someone has confused isobar and exact wind direction. Im not expert so any correction to my limited model analysis is always appreciated. From samsung galaxy so sorry for any mistakes

[Snowman.]

Agreed, away from the SE and east coast (which is where the vast majority of members appear to live) I see very little of interest for 90% of the UK landmass now the SW threat has receded for next weekend.

A few in the SE are misleading some into thinking this will be a nationwide event, it won't. Anyone who dismisses the Met and talk up streamers and heavy snow will be throwing the toys out next weekend going by today's models as it just isn't going to happen.

It's pretty hard to get a cold spell that delivers to the whole of the UK and gets sustained. January was actually a good event for 90% of the country with fronts approaching the west on Friday then Sunday had a front run up the side of the UK.

But as always the Further North and West you are with easterlies its harder to get the precip but lets hope the brakedown gives everyone some good stuff but first we need to get into the cold spell before we see anything.

[johnholmes]

The Coriolis effect is linked to the Gradient wind and the question was why the surface wind is not the same as the isobars or the reverse.

You are making it too complex, the reason the surface wind is different to the isobars, which are governed by the balance between the Pressure Gradient Force and Coriolis is simply friction nothing else. This explains why there is much less change to ship wind reports in terms of the isobar direction than over land there is far less friction over the sea than the land.

honest

[legritter]

Well im very happy with this mornings charts .after next wednesday a chance of some snow coming into eastern parts and perhaps if favourable conditions [synoptics ] are ok pushing further west .some good hard frosts around and a possibility of an atlantic frontal event .also something could develope to our east and drift our way .Met office faxes will give us more clues as we go through the week .i dont expect anything meaty to show up on the charts till monday ,but worth waiting for if it does .if we can get some good cold air to our east with good 850S things can pop up at short notice .ok sea temp are colder now than say dec but sun getting stronger so all to play for in my book ,cheers neighbours are cutting the grass .

[claret047]

This is a very good looking Easterly on the Gfs 06z, quite a lot of snow showers coming well inland, exciting times ahead next week.

Yes I agree the charts this morning look absolutely brilliant, but if I was TEITS I would be a little concerned as there appears to be a "hole" in the precipitation charts you posted right over the top of his house!

Before anyone chastises me for my comment on a precip chart that far ahead I was joking and I realise that this could all change with fine tuning of the location of the various components that make up weather in our neck of the woods. It is what makes the whole thing so interested and has kept me engrossed since when I was a youngster during the 1962/63 winter.

On a personal note I feel that this time there is more likelihood of things going to the general themes shown over the last three or so models (12z, 18z 0Z & 06Z) and we are for a very cold lengthy spell of weather with notable snowfall to be expected in some areas from next weekend onwards. As has been stated elsewhere the favoured spots under such a regime' will always be eastern, southeastern and northeastern districts, depending on wind direction as well as more southern counties if we experience a channel low developing.

I am really looking forward to seeing future model output to see how it is all expected to develop.

Kind Regards

Dave

[Paul_1978]

Recalling Ian McCaskill's famous Feb '91 forecast and those words "there is a low moving up from France". That's what I'm going to be looking for in the next week!

[Frosty.]

Latest from UKMO as far as Thurs sees little change to previous: in summary, "Risk of a few light wintry showers on exposed eastern coasts, increasing risk of loc moderate wintry showers in the S/SE by Thurs".

I suppose that is based on the ukmo model since the gfs shows widespread snow showers later next week, which is historically how this type of easterly would evolve.

[bradymk]

I suppose that is based on the ukmo model since the gfs shows widespread snow showers later next week, which is historically how this type of easterly would evolve.

If you want to use GFS precip which are normally useless at this range anyway then use the GFS 0.5 here http://www.meteociel.fr/modeles/gfs/precipitations/3h.htm Not accurate at all but little bit more accurate than the normal GFS precip charts some post. Does not show showers moving much inland until Friday but most of the models we see are not great in handling convective showers, especially at this range.

[johnholmes]

Hi John. Regarding your question about isobars. Which i am sure you know answer too. Im on phone so struggling to read today. Anyway i am going to answer it and you can then correct if i am out abit and miss anything. I believe a few factors play in firstly coronial effect and secondly high and low pressure is trying to equal. With high pressure attemting to move towards low to equalise. I believe friction comes into play also but first two are main players. The isobars only show lines of equal pressure not wind direction but due to the above you can work out direction and it is few degrees off so you can use as rough guide only the direction of isobars. Also direction runs inwards in low and out on high from isobar direction. Im confused why u asked as i know your experienced forecaster so assume someone has confused isobar and exact wind direction. Im not expert so any correction to my limited model analysis is always appreciated. From samsung galaxy so sorry for any mistakes

See my full answer but I did not ask the question another poster did, I simply answered 'friction in the lowest layers' !