GFS 06z charts discussion

[Stratos Ferric]

I suspect that the experts are going to struggle badly this coming week as this is an unusual situation for them. Normally we get nice easy topplers followed by mild but this is an entirely different situation with many wonderful possibilities that won't be nailed until the event is upon us. Some areas could see some mammoth snowfall depths.

If they struggle it will, I suspect, be nothing to do with the unusual nature of the event, so much as (and a few of us on here often make this point) the actual weather experienced hangs on a tenuous thread, the detail of which cannot be pined until much closer to the event. It's not desperately cold so any snow is marginal anyway; it then requires a particular alignment of fronts to inform considerations of which air mass dominates and how quickly fronts move, and of height given that temps will be bordlerline at the front.

Let's be clear, unfamiliarity os not the issue, it's ability to pick important detail at distance when the battleground is ill defined, marginal, and overhead.

[nick sussex]

Judging by the fax charts and the raw data it seems as if the ukmo have blended their own model with the ecm to reach a middle of the road view.

Heres the raw data from the ukmo 108hrs and the fax chart for the same time.

http://moe.met.fsu.edu/cgi-bin/ukmtc2.cgi?...&hour=108hr

http://85.214.49.20/wz/pics/brack3a.gif

Notice on the raw data the low near the sw as compared to the fax charts. So it looks like they have taken into account the ecm operational run but see enough in the ecm ensembles to suggest that the ecm is being too progressive.

[PersianPaladin]

The 06z show alot of accumultive snow through Thursday into Friday, in fact amounts that I find staggering, and to be quite honest can't really pick any holes in. The only things I would say is that as Thursday is over 90 hours away there should still be a little wariness to where this is going to go. Also it's worth mentioning that whether the snow is light/heavy or whether it simply changes to rain or occurs at all are subject to very small changes. However at the moment they have to be some of the best charts for snowfall I've ever seen inside 120 hours.

For the higher ground in the west maybe...but as it crosses eastwards over the pennines it is progged to either stall or become much lighter and patchier.

I'm not excited yet at all.

[Stratos Ferric]

Well you seem to have forgotten the snow that we had up here before the cold snap down south had pretty strange conditions. The 850 isotherm was around -1 or -2 and there was no 528dam line. But yet we still got snow.

500s are never more than a crude yardstick: you can get snow up to about 538 in the right conditions, and in the "wrong" ones still have rain at 522dm. The 850s are a much better gauge.

[BristolBlizzard]

Yes that is true, cornwall and devon have been known to see very deep snowdrifts from this type of scenario, I hope every single one of us wil see some lovely snowflakes in the week ahead.

I hope you're right but the ''Will it fall as rain?'' question comes into mind.

[mcweather]

Which 3 snowfalls were these and what level depths were recorded.

According to Dr Richard Wild of Weathernet. The top man in the UK when it comes to snowfall the top three falls Undrifted depth are.

Feb 15/16th 1929 200cm Dartmoor

9/13th March 1891 150cm Dartmoor

18/19 Jan 1881 150cm Dartmoor

[nick sussex]

And as we have some time to fill heres the latest ukmo 48hrs model and the corresponding output upto the same time from the 00hrs run.

UKMO 06hrs

http://moe.met.fsu.edu/cgi-bin/ukmtc2.cgi?...&hour=048hr

UKMO 00hrs

http://moe.met.fsu.edu/cgi-bin/ukmtc2.cgi?...&hour=054hr

The ukmo 06hrs has pressure slightly stronger to the north, its only a few millibars difference but this shows why I should get out more! As they say at a certain store, every little helps!

The ukmo run this extra 48hr model twice a day for 06hrs and 18hrs. Normally out around 11am and 11pm.

Edited February 4, 2007 by nick sussex

[Hairy Celt]

-6 air is now over Scotland with some good showers coming too!!

they are nothing more exciting than light rain showers.

[Thundery wintry showers]

The sypnotic comparisons to 47, 79 and the 80s are for once valid (a look at the archive charts can verify this for any doubters).

My only concern relates to how these sypnotics will pan out in 2007.

For example, in the eighties usually an 850 isotherm of around -5C or -6C aloft was pretty much guaranteed to deliver an event - today that is on the worse side of marginal with even -7C and -8C 850s often accompanying cold rain.

So maybe our snowless problem is twofold these days

1) We dont get the right set ups as often

2) When we do it has to be super cold because they don't deliver at the same temp as they used to

I'd love to be proved wrong (not least to reign in some of the GW rampers) however I don't hold out much hope for my own Central London location

I reckon that it's the SSTs that are the main issue here- more airmass modification at low levels, thus the 850's have to be that little bit lower.

[Stu_London]

The ukmo 06hrs has pressure slightly stronger to the north, its only a few millibars difference but this shows why I should get out more!

The ukmo run this extra 48hr model twice a day for 06hrs and 18hrs. Normally out around 11am and 11pm.

Certainly worth a look as the UKMO has performed very well through this.

Even the JMA solution of a couple of days ago may end up closer to reality than its more heavyweight rivals ECM and GFS which is remarkable as at the time I thought the model had programmed the earth to be spinning in the opposite direction for that particular output

[grab my graupel]

Sorry posted in wrong thread

Edited February 4, 2007 by grab my graupels

[Stu_London]

500s are never more than a crude yardstick: you can get snow up to about 538 in the right conditions, and in the "wrong" ones still have rain at 522dm. The 850s are a much better gauge.

Feb 2005, Clerkenwell

850s -11C

Thickness c. 519dam

Rain!

Although it did produce about 3cm of lying snow in the Regents Park area less then 3km away.

[The PIT]

Country File was a good forecast. Getting the Shovel out here just in case.

Question is can this High be like Highs of old and hang around for a bit or will it be two pushes from the Atlantic and it's all over folks.

[Thundery wintry showers]

Certainly worth a look as the UKMO has performed very well through this.

Even the JMA solution of a couple of days ago may end up closer to reality than its more heavyweight rivals ECM and GFS which is remarkable as at the time I thought the model had programmed the earth to be spinning in the opposite direction for that particular output

I picked up on that also. The JMA in its easterly scenarios had a low moving south down the North Sea pulling in a NE'ly behind it, and the GFS 06Z shows a lesser version of that very scenario- after the heavyweight models had all gone for a very temporary NNW'ly followed by a slack high-pressure area.

I agree re. the UKMO- it's consistently progged two to three days of northerlies, which at the moment looks most likely to happen.

[paul tall]

According to Dr Richard Wild of Weathernet. The top man in the UK when it comes to snowfall the top three falls Undrifted depth are.

Feb 15/16th 1929 200cm Dartmoor

9/13th March 1891 150cm Dartmoor

18/19 Jan 1881 150cm Dartmoor

A tad more than a dusting then

But there is a humungous difference between what Dartmoor gets and what the SW generally gets.

[Rustynailer]

I reckon that it's the SSTs that are the main issue here- more airmass modification at low levels, thus the 850's have to be that little bit lower.

Its whether or not the precipitation falls at night or not aswell IMO.

Also I remember in the 70s and 80s after dinner at school if it was snowing you were very lucky, usually it had turned to rain by then.

Russ.

[Snowyowl9]

Very fascinating Ian. This scenario has Feb 1978 written all over it to me. The last chart on the CF forecast was a dead ringer for Feb 18/19 1978.

On that occassion here in Dorset we got 18 inches of level snow blwon into 25 foot drifts !!

Ive only waited 29 years to see another chart with that sort of potential.

I don`t remember that occasion the snow never made it this far north perhaps.

http://www.wetterzentrale.de/archive/ra/19...00119780219.gif

It won`t be nothing like feb 1978 now feb 1996 looks more likely though and the upper air wasn`t that low either it snowed here anyway,the last battleground I saw before last March,the last major snowfall I saw in feb though with 8 inches on that day

http://www.wetterzentrale.de/archive/ra/19...00119960206.gif

http://www.wetterzentrale.de/archive/ra/19...00219960206.gif

This looks even better than that with a better angle of approach and colder upper air temps.

http://85.214.49.20/wz/pics/Rtavn1081.png

http://85.214.49.20/wz/pics/Rtavn1082.png

[January Snowstorm]

Well I'm off to watch the rugby and I recommend everyone does the same.

It should be a cracker and for all you betting larks I have Ireland to score over 25pts or more

[mcweather]

Interesting to note that whilst we are all wrapped up in the end of the week scenario that 0600 also progs a similar scenario in the longer term as well.

FI I know interesting and worth keeping an eye on as well.

[johnholmes]

Judging by the fax charts and the raw data it seems as if the ukmo have blended their own model with the ecm to reach a middle of the road view.

Heres the raw data from the ukmo 108hrs and the fax chart for the same time.

http://moe.met.fsu.edu/cgi-bin/ukmtc2.cgi?...&hour=108hr

http://85.214.49.20/wz/pics/brack3a.gif

Notice on the raw data the low near the sw as compared to the fax charts. So it looks like they have taken into account the ecm operational run but see enough in the ecm ensembles to suggest that the ecm is being too progressive.

much of the ability to be a 'good' forecaster, now as before the advent of computers, is to be able to sift all the data available and come to a rational and reasonable judgement of what seems likely to happen.

Its for certain that Met O Operational HQ will be an absolute hive of activity onwards. Looking at all the data from all the models and trying to decide which one is giving the best guidance as each run comes out. I almost wish I was back in the thick of it, but I'll content myself with 'playing' at forecasting from here.

Its probably the best looking set up at T+96 than for many a long day. Possibly back to Xmas 2005, probably more so as that was never more than scattered snow showers or the prob of a trough in the northerly enhancing shower activity.

This does have the potential, early days yet, but the potential, to deliver something not seen for quite a while.

I note the very sensible provisio by TWS, and possibly others, on the effect of SST's at the moment. That is likely to play a substantial part in the final decision on will it/won't it/whether and how much.

John

Edited February 4, 2007 by johnholmes

[nick sussex]

much of the ability to be a 'good' forecaster, now as before the advent of computers, is to be able to sift all the data available and come to a rational and reasonable judgement of what seems likely to happen.

Its for certain that Met O Operational HQ will be an absolute hive of activity onwards. Looking at all the data from all the models and trying to decide which one is giving the best guidance as each run comes out. I almost wish I was back in the thick of it, but I'll content myself with 'playing' at forecasting from here.

Its probably the best looking set up at T+96 than for many a long day. Possibly back to Xmas 2005, probably more so as that was never more than scattered snow showers or the prob of a trough in the northerly enhancing shower activity.

This does have the potential, early days yet, but the potential, to deliver something not seen for quite a while.

I note the very sensible provisio by TWS, and possibly others, on the effect of SST's at the moment. That is likely to play a substantial part in the final decision on will it/won't it/whether and how much.

John

Afternoon John do I detect even a little ramp from yourself! I don't envy the ukmo at all this week as it looks a real nightmare to forecast. I must say though that the ukmo 120hrs raw data is a great chart its a shame that the ukmo have edged away from that in their fax charts. Lots of fun model watching though even though its a real thriller.

Edited February 4, 2007 by nick sussex

[andy_leics22]

Impressive 06z for the battle ground scenario I was talking about Each run seems to get better in terms of it pulling off, especially if the PPN comes to most areas after dark, thats when the best chance would be, still 4 days off yet though and things will change. Looks decent though so far

[Harsh Climate]

I don`t remember that occasion the snow never made it this far north perhaps.

http://www.wetterzentrale.de/archive/ra/19...00119780219.gif

It won`t be nothing like feb 1978 now feb 1996 looks more likely though and the upper air wasn`t that low either it snowed here anyway,the last battleground I saw before last March,the last major snowfall I saw in feb though with 8 inches on that day

http://www.wetterzentrale.de/archive/ra/19...00119960206.gif

http://www.wetterzentrale.de/archive/ra/19...00219960206.gif

This looks even better than that with a better angle of approach and colder upper air temps.

http://85.214.49.20/wz/pics/Rtavn1081.png

http://85.214.49.20/wz/pics/Rtavn1082.png

wow, the charts now are looking better than them (although subject to changes.) We got 10inches one night dureing that set-up.

[mcweather]

much of the ability to be a 'good' forecaster, now as before the advent of computers, is to be able to sift all the data available and come to a rational and reasonable judgement of what seems likely to happen.

Its for certain that Met O Operational HQ will be an absolute hive of activity onwards. Looking at all the data from all the models and trying to decide which one is giving the best guidance as each run comes out. I almost wish I was back in the thick of it, but I'll content myself with 'playing' at forecasting from here.

Its probably the best looking set up at T+96 than for many a long day. Possibly back to Xmas 2005, probably more so as that was never more than scattered snow showers or the prob of a trough in the northerly enhancing shower activity.

This does have the potential, early days yet, but the potential, to deliver something not seen for quite a while.

I note the very sensible provisio by TWS, and possibly others, on the effect of SST's at the moment. That is likely to play a substantial part in the final decision on will it/won't it/whether and how much.

John

Have to agree with you there John. It is early days but the best set up we've seen in the reliable timeframe for many a long year. There is huge potential especially if the low progged to be out near Rockall on thurs decides to slide SE wards down the edge of the block as in days of old.

A nightmare to call knowing the how ignorant the media reaction that will follow if the forecasters go small and it comes big and conversely if they go big and it doesnt go big in the south east.

[West is Best]

The sypnotic comparisons to 47, 79 and the 80s are for once valid (a look at the archive charts can verify this for any doubters).

My only concern relates to how these sypnotics will pan out in 2007.

For example, in the eighties usually an 850 isotherm of around -5C or -6C aloft was pretty much guaranteed to deliver an event - today that is on the worse side of marginal with even -7C and -8C 850s often accompanying cold rain.

So maybe our snowless problem is twofold these days

1) We dont get the right set ups as often

2) When we do it has to be super cold because they don't deliver at the same temp as they used to

I'd love to be proved wrong (not least to reign in some of the GW rampers) however I don't hold out much hope for my own Central London location

A rare incursion by me into this thread, but wanted to respond to your very sensible post Stu. It's nice to see that sort of post amidst talk of shovels and record snow depths - do some people never learn?!

Although synoptically there may appear a similarity with '47, 79 and the 80's I really think the comparisons are fraught with danger. Those winters had deep, deep, cold pooling ahead of advancing fronts. I know this from memory (except '47) as well as factually by the CET. Even the much-trumpeted mild start to '47 was anything but (why does this error continually get repeated?) compared to this year's near record warmth in the UK and in much of western and northern Europe.

Secondly, the orientation is very important. When fronts stalled in those classic set ups they sometimes did so with front edge easterlies - pulling really cold air in from an already cold continent. This time, at the moment, the orientation looks much more south-easterly and perhaps southerly, and without such a cold pool draw.

As it happens, these events were frequently over-ramped by forecasters in the 80's, normally by the low pressure centres tracking slightly further north at the last minute. They were usually marginal set-ups even then, with all the cold and synoptic conditions I have just mentioned. This time looks precarious in the extreme to me, and unless things change I'm not mindful to think anywhere south of, say, Northamptonshire is likely to get more than the briefiest of initial flurries before the rain kicks in. On the high ground to the north it may be a different story, but I'm really saying that just so as not to appear a party-pooper (which I'm not).

By the way, the famous blizzard of February 1978 (seldom mentioned on here) which cut off the south-west peninsular was from memory largely unforecast: it took all by surprise. 25 foot drifts on the M5 and 30cm of level snow in Exeter, with 100cm of level snow on Dartmoor. Now that's the real deal! I fear very much for disappointment this time, especially with the rampometre now broken through the roof!

By the way, not all stalling is good. You need an undercut. I can recall several instances of stalling fronts simply fizzling out with generally rising temps. When the ppn eventually did arrive it was in the form of rain. OK, I'll bugger off back to the in-depth thread!