General Model Output Discussion:

[snowfish]

Rather OTT if you don't mind me saying.

If members are expecting every run to show -15C E,lys then im afraid you're always going to be disappointed.

Lets jog our minds back to early Dec. Virtually all the runs were slightly different to each other as you would expect. However in saying this all the model runs had one thing in common and that was blocking to our N/NE/NW. Now some of the runs had bitter upper temps across the UK whereas other runs were less cold. However as we know the GFS was correct which is why we enjoyed the wonderful cold spell in mid Dec.

So what im basically saying is do not make snap judgements based on one run. Ask yourself is the GFS continuing with the trend of blocking and the answer is yes.

TEITS

Morning! Day off today so a quick post! Trends are good consecutive runs from the main three models have continued the cold trends the northerly occuring, with the easterly evolving albeit differently from run to run but there.... Delay would be a good word, but I agree with you in your thinking that it WILL happen, it's just a question of how soon?

[Guest North Sea Snow Convection]

to be fair CC thats far from nailed on.Its not just a couple of dodgy ops at all.ecm/ukmo AND gfs have backtracked this morning,actually ukmo didnt look great at 144h to me last night.

it could still happen but you could be setting up for a big fall if thats your position.

I think things look good as stated earlier for longer period, and as as Tom illustrated earlier, there is snow potential this weekend. But I agree that constantly making statements of certainty and ramping all the time about bitter cold is not being objective, as much as fretting over one output going wrong in the other direction is OTT as well.

I think that (the majority) of people who are trying to be objective about the output and pointing out what could go wrong (as well as right) is the happy medium and the way to go

Edited January 27, 2010 by North Sea Snow Convection

[nick sussex]

Interesting comments from NOAA regarding that all important shortwave in the USA.

LATER ON...THE 00Z ECMWF DEPARTS FROM

THE 12Z MULTI-MODEL ENSEMBLE MEMBERS IN MOVING A WEAKER SURFACE

LOW ON A MUCH MORE SOUTHERLY TRAJECTORY THROUGH THE MIDWEST RATHER

THAN THE NORTHERN PLAINS/GREAT LAKES/NORTHEAST.

As Steve M mentioned earlier this shortwave is crucial, also in terms of how deep it is this also from NOAA.

THE 00Z

GFS IS A REASONABLE ALTERNATIVE TO THE 00Z GEFS MEAN...THOUGH ITS

SURFACE LOW TRACKING ACROSS THE GREAT LAKES/NORTHEAST IS LIKELY

TOO WEAK.

If we remember last night the ECM 12hrs developed this low more and had it going with the general ensembles means of the ECM and GFS in the more northerly track, this had the effect of running ne towards the low near Greenland, they phased together which slowed the main troughs movement eastwards and allowed for a better pressure rise ne'wards.

It's amazing how this small feature has such an impact downstream. So basically if you're hoping for the easterly you want this low deeper and tracking further north.

Edited January 27, 2010 by nick sussex

[Frosty.]

Plenty of snow around this weekend before the bitter cold hits next week.

I must say CC that your confidence in next week is inspiring, as for the Easterly, I don't care how it evolves as long as it does evolve, it's always hugely difficult to get all the high's and lows's in the correct position to bring cold air to the uk but this winter is the glowing exception. An interesting N'ly coming up, a slower almost sluggish start as it will now be delayed by 24-36 hours but probably worth the wait with at least 4 days of sunshine and snow showers potential with frosty nights plus some trough features which should pep up the showers at times and merge them together.

[PB22]

The 06z GEFS ensemble suite as a whole isn't quite as good as the 00z set, the mean for T+168:

http://91.121.94.83/modeles/gens/run/gens-21-1-168.png?6

http://91.121.94.83/modeles/gens/run/gens-21-0-168.png?6

And the ensemble mean by T+216:

http://91.121.94.83/modeles/gens/run/gens-21-1-216.png?6

http://91.121.94.83/modeles/gens/run/gens-21-0-216.png?6

[TEITS]

An interesting N'ly coming up, a slower almost sluggish start as it will now be delayed by 24-36 hours but probably worth the wait with at least 4 days of sunshine and snow showers potential with frosty nights plus some trough features which should pep up the showers at times and merge them together.

Yes based on the NAE we have to wait until Friday before we start pulling in the colder N,ly.

http://expert.weatheronline.co.uk/daten/proficharts/en/nae/2010/01/27/basis06/ukuk/pslv/10012906_2706.gif

Some S areas may actually start rather mild but these areas will become progressively colder as the system pulls away to the SE.

As for the weekend and i've learn't the hard way not to make too many assumptions. Prior to our last cold spell the Met O had my area targetted for heavy snowfalls. What actually occured is heavy snow affected the NW i.e Manchester and then we had that spell of heavy snow in the S. All I experienced was 10min snow showers. So my point is you just never know what may develop during this weekend. However in saying this I would love the 06Z to be right because thats a pretty impressive snow event for E Midlands/E Anglia during Sat night/Sun.

[Frosty.]

The 06z GEFS ensemble suite as a whole isn't quite as good as the 00z set, the mean for T+168:

http://91.121.94.83/modeles/gens/run/gens-21-1-168.png?6

http://91.121.94.83/modeles/gens/run/gens-21-0-168.png?6

And the ensemble mean by T+216:

http://91.121.94.83/modeles/gens/run/gens-21-1-216.png?6

http://91.121.94.83/modeles/gens/run/gens-21-0-216.png?6

Hi paul,

I'm sure there were some so-so gefs ensemble suites before the mega cold spell set in around mid december, I seem to remember some wobbles in the output back then before it all came together. We don't even know for sure how the N'ly will pan out so the E'ly is beyond the horizon right now.

Edited January 27, 2010 by Frosty039

[TEITS]

The ensemble mean at +300 is still very much towards blocking.

http://91.121.94.83/modeles/gens/run/gens-21-1-300.png?6

The difference between the 0Z/06Z really is tiny considering we looking at the mean of all members. The only difference at +240 is the centre of the HP is slightly further S.

[Glacier Point]

Have to say that more than half of me is very uncomfortable with the long range ensemble mean guidance on offer today.

For sure, GFS and GEM ensemble means are very bullish about a significant blocking structure centred over norther Siberia / Barents Sea to migrate eastwards towards Greenland.

Day 10 ensemble mean height anomalies depict about as strong a positive height anomaly as you could get at that range:

http://raleighwx.easternuswx.com/models/gfsensemble/00zGFSEnsembles500mbHeightAnomalyNH240.gif

http://raleighwx.easternuswx.com/models/cmcensemble/00zGGEMEnsembles500mbHeightAnomalyNH240.gif

For days 11-15, again solid cross model ensemble mean guidance:

http://raleighwx.easternuswx.com/models/gfsensemble/00zENS11-15day500mbHeightAnomalyNH.gif

http://raleighwx.easternuswx.com/models/cmcensemble/00zCMCENS11-15day500mbHeightAnomalyNH.gif

This may well be related to modelling of downwelling zonal wind anomalies from the jump in stratospheric temperatures and disruption of the polar vortex going on.

However, the Global Wind Oscillation composites, which are my main confidence-weakener, depict a likely evolution of the Scandinavina trough being more resiliant than modelled (this discussed several days ago and still there t120-144) towards a mean mid Atlantic ridge. Phase space composites for the more likely evolutions all suggest more energy going poleward than the model suites are programming.

Whether the evolution of blocking highs to the north-east are enough to shunt the jet equatorward is open to doubt given the unreliability of the modelling of the polar field. Therefore, some question marks for me beyond t168 and I would not be suprised to see the persistence of the core high pressure being west and north-west of the UK. That's still likely to deliver a cold 10-14 days but potentially not as severe as some model solutions of late.

A lot will depend here on how the developing ridge over the Arctic behaves and whether stratospheric propagation takes place within the medium to longer time frames.

[TEITS]

I can't understand why you see celebratory smileys cropping up when people reference the very outer ranges of the GFS models, almost as if it's nailed-on to verify? It's almost like they enjoy the wrist-slitting - much like why a gambler gambles. Also, amuses me to see premature back-slapping. If 'epic' runs verify, then I'd be the first to shake a few peoples' hands, but there's no way I'm gonna congratulate someone just because one model run signals what they've suggested...in 7+ days time. No chance.

What I've noticed over the last few days (and countless runs now) is that yes we're trending towards a bit of a cold spell again. But am I going to go OTT in either direction, based on the output of one run? Hell no! I might be relatively new to model watching, but what I've quickly learnt is that it's just not worth taking notice of models suggesting the glaciers heading South again. Until proven otherwise, consider it a quirk - and concentrate on what the overall trend is. That's what I do, and it's saved me from many a smashed keyboard :lol:

I enjoy this thread, but do think the peaks and troughs tend to make it a bit of a 'murder mystery' at times. We all know that +300 is just a complete waste of time, so why do people still continue to post charts out in that range?? Baffles me, it really does.

No doubt this post will be moved/deleted - and this thread will continue unabated. C'est la vie.

Lets be correct about this.

Much of the excitement in the past 24hrs isn't due to one run neither is it at +300. What many are looking at is the prospect of blocking to become established between the +168/+240 timeframe and this has been shown consistently on many model runs especially the GFS.

I agree nothing is nailed on when we're referring to such a timeframe. However if the discussion on this thread was restricted to the reliable timeframe then the accuracy of this would result in little discussion.

[PB22]

Quite a big flip in the mid-longer term on the GFS ensembles:

http://www.wzkarten.de/pics/MT8_London_ens.png

http://www.wzkarten.de/pics/MT8_Manchester_ens.png

http://www.wzkarten.de/pics/MT8_Dublin_ens.png

http://www.wzkarten.de/pics/MT8_Aberdeen_ens.png

Also interesting to note the milder spikes now appearing over the next few days as various features get picked up.

[Weather-history]

In the short term , Friday looks more like it might be Snow again this morning . Although the Met Office have dismissed this idea.

Nothing in the models suggests this. NAE, GFS suggest a mainly rain event.

[Matt12]

Major downgrade on the GFS ensembles. Looks a lot less promising promising than last night, that's for sure. Still, the charts keep changing so no reason for them not to upgrade again this evening/tomorrow. We would need an upgrade on the GFS ensembles to get a decent cold spell imo.

Edited January 27, 2010 by Matt12

[TEITS]

Quite a big flip in the mid-longer term on the GFS ensembles:

http://www.wzkarten.de/pics/MT8_London_ens.png

http://www.wzkarten.de/pics/MT8_Manchester_ens.png

http://www.wzkarten.de/pics/MT8_Dublin_ens.png

http://www.wzkarten.de/pics/MT8_Aberdeen_ens.png

Also interesting to note the milder spikes now appearing over the next few days as various features get picked up.

Yes excellent to see the less cold peak suggesting the snow event during Sat night/Sun wasn't an outlier.

As for the medium-long range and blocking is becoming increasinly prevalant in the SLP ensembles.

http://charts.netweather.tv/ensimages/ens.20100127/06/prmslCambridgeshire.png

http://charts.netweather.tv/ensimages/ens.20100127/06/prmslOslo.png

http://charts.netweather.tv/ensimages/ens.20100127/06/prmslReyjavic.png

As I said in a previous post the positioning of the block can mean the difference between upper temps of 0C or -15C. Due to this we can expect vast changes in the 850hpa ensembles over the next few days.

Excellent update from the Met O suggesting the ECM OP didn't have much support from the ensembles.

Cold with overnight frost and ice throughout, but a good deal of dry and bright weather for many parts of the UK by day. However, wintry showers are likely for exposed northeastern parts throughout the period, with a risk of more persistent sleet or snow for some eastern areas at times on Monday. Rain, maybe hill snow, might reach the northwest on Tuesday. Wintry showers may spread further inland towards the end of the week as winds become more northeasterly. The mainly dry weather with frost, ice and possibly fog, is likely to continue for much of the rest of the period, with temperatures mostly below normal. However, wintry showers or more persistent snow could affect eastern and southern areas towards the end of the period.

Edited January 27, 2010 by THE EYE IN THE SKY

[Cecil Hogmanay Melchett]

Yes excellent to see the less cold peak suggesting the snow event during Sat night/Sun wasn't an outlier.

As for the medium-long range and blocking is becoming increasinly prevalant in the SLP ensembles.

http://charts.netweather.tv/ensimages/ens.20100127/06/prmslCambridgeshire.png

http://charts.netweather.tv/ensimages/ens.20100127/06/prmslOslo.png

http://charts.netweather.tv/ensimages/ens.20100127/06/prmslReyjavic.png

As I said in a previous post the positioning of the block can mean the difference between upper temps of 0C or -15C. Due to this we can expect vast changes in the 850hpa ensembles over the next few days.

Excellent update from the Met O suggesting the ECM OP didn't have much support from the ensembles.

Cold with overnight frost and ice throughout, but a good deal of dry and bright weather for many parts of the UK by day. However, wintry showers are likely for exposed northeastern parts throughout the period, with a risk of more persistent sleet or snow for some eastern areas at times on Monday. Rain, maybe hill snow, might reach the northwest on Tuesday. Wintry showers may spread further inland towards the end of the week as winds become more northeasterly. The mainly dry weather with frost, ice and possibly fog, is likely to continue for much of the rest of the period, with temperatures mostly below normal. However, wintry showers or more persistent snow could affect eastern and southern areas towards the end of the period.

thats a very good update dave.

The question is is it based on todays models or yesterdays?

[PB22]

thats a very good update dave.

The question is is it based on todays models or yesterdays?

I'd say yesterday's. I know a lot of people don't agree, but I am 99% sure those updates are based on the previous days models because they nearly always reflect the previous days output.

[Frosty.]

Major downgrade on the GFS ensembles. Looks a lot less promising promising than last night, that's for sure. Still, the charts keep changing so no reason for them not to upgrade again this evening/tomorrow. We would need an upgrade on the GFS ensembles to get a decent cold spell imo.

Well the meto update is a huge upgrade despite the gefs ensembles downgrade so something is wrong somewhere!! thankfully the ecm 00z op run was a mild outlier in FI with plenty of much colder solutions.

Edited January 27, 2010 by Frosty039

[aien aristeuein]

Yes excellent to see the less cold peak suggesting the snow event during Sat night/Sun wasn't an outlier.

As for the medium-long range and blocking is becoming increasinly prevalant in the SLP ensembles.

http://charts.netwea...bridgeshire.png

http://charts.netwea...6/prmslOslo.png

http://charts.netwea...mslReyjavic.png

As I said in a previous post the positioning of the block can mean the difference between upper temps of 0C or -15C. Due to this we can expect vast changes in the 850hpa ensembles over the next few days.

Excellent update from the Met O suggesting the ECM OP didn't have much support from the ensembles.

Cold with overnight frost and ice throughout, but a good deal of dry and bright weather for many parts of the UK by day. However, wintry showers are likely for exposed northeastern parts throughout the period, with a risk of more persistent sleet or snow for some eastern areas at times on Monday. Rain, maybe hill snow, might reach the northwest on Tuesday. Wintry showers may spread further inland towards the end of the week as winds become more northeasterly. The mainly dry weather with frost, ice and possibly fog, is likely to continue for much of the rest of the period, with temperatures mostly below normal. However, wintry showers or more persistent snow could affect eastern and southern areas towards the end of the period.

A question from a new forum members to a respected and often read old timer

the precipitation on Thursday into Friday modelled on the GFS is coinciding with temperatures close to zero down the east of england. Is this clearly a wet weather event or perhaps a surprise snow event. I am unsure of what the predicted dewpoints are? As a three counties person I am intrigued at the modelling of the period Saturday into Sunday because at the moment is says very snowy.

AA

[TEITS]

thats a very good update dave.

The question is is it based on todays models or yesterdays?

I would say the 3-5 day forecasts are based on last nights +96/+120 fax charts which is why these updates often appear around 3am. However the 6-15 day updates must be based on this mornings ECM/ensembles. To suggest otherwise is absurd because why would you make a forecast using data from yesterday evening when you can use this mornings. This is why the updates come out around lunchtime.

[andymusic]

Major downgrade on the GFS ensembles. Looks a lot less promising promising than last night, that's for sure. Still, the charts keep changing so no reason for them not to upgrade again this evening/tomorrow. We would need an upgrade on the GFS ensembles to get a decent cold spell imo.

Don't forget the GFS has a tendency to provide us with a "trend" out in FI - then it backs away - then it brings it back again - so just keep an eye on things - it's already played with this idea a few times - I think it's onto something!

[Cecil Hogmanay Melchett]

I'd say yesterday's. I know a lot of people don't agree, but I am 99% sure those updates are based on the previous days models because they nearly always reflect the previous days output.

i would tend to agree paul.it was not long ago the beeb were talking about bitter e winds when we all knew it wasnt going to happen looking at the models.quite a few people think the updates reflect the models the day before.

although as teits says it sounds a bit absurd that the 15dayer would be from yesterdays runs,doesnt it?

Edited January 27, 2010 by happy days

[PB22]

I would say the 3-5 day forecasts are based on last nights +96/+120 fax charts which is why these updates often appear around 3am. However the 6-15 day updates must be based on this mornings ECM/ensembles. To suggest otherwise is absurd because why would you make a forecast using data from yesterday evening when you can use this mornings. This is why the updates come out around lunchtime.

I have just been reliably informed from a trusted contact that the 6-15 day updates are based on the previous day's 12z models Dave. Don't ask me why its done like this, but for some reason it is. :lol:

Edited January 27, 2010 by Paul B

[Frosty.]

I'd say yesterday's. I know a lot of people don't agree, but I am 99% sure those updates are based on the previous days models because they nearly always reflect the previous days output.

Seems stupid to use old out of date information when we are in such a dynamic constantly changing weather pattern, why would they use obsolete data when the 00z model runs are early morning and the update comes out 6 hours or more later.

[TEITS]

A question from a new forum members to a respected and often read old timer

the precipitation on Thursday into Friday modelled on the GFS is coinciding with temperatures close to zero down the east of england. Is this clearly a wet weather event or perhaps a surprise snow event. I am unsure of what the predicted dewpoints are? As a three counties person I am intrigued at the modelling of the period Saturday into Sunday because at the moment is says very snowy.

AA

At the moment based on the models the Thurs/Friday looks a rain event for most with DP above freezing. However if the 06Z verified for Saturday night then this would bring a decent snow event for E Anglia/E Midlands and locations just N of London. The DP with this event are suggested to be below freezing in the areas I mention.

http://www.wetterzentrale.de/pics/Rmgfs908.gif

http://www.wetterzentrale.de/pics/Rmgfs968.gif

If the 06Z verified then the locations I mention could see snowfall amounts of around 10cm.

However the track of the SW is perfect for my location but its worth keeping an eye to see if this changes.

http://www.wetterzentrale.de/pics/Rmgfs931.gif

I have just been reliably informed from a trusted contact that the 6-15 day updates are based on the previous day's 12z models Dave. Don't ask me why its done like this, but for some reason it is. :lol:

I think your contact is telling you porkies mate.

If this is true then why isn't the 6-15 forecast updated at the same time as the 3-5 day forecast. Seems strange that the 6-15 day forecast is updated around 8hrs later!

[Frosty.]

You'd think different if you knew who my contact was! :lol: Like I said, don't ask me why its done like this.

That explains why their updates are always wrong