Model Output Discussion

[grab my graupel]

Secondary low further south on the 18z...good news for the north, not so good for the southwest:

http://91.121.94.83/modeles/gfs/run/gfs-0-132.png?18

Yes you are right, Paul, I think I need to have my eyes tested :lol: As others have said, the

track of this low is still very uncertain

[PB22]

Yes you are right Paul, I think I need to have my eyes tested :lol: As others have said, the

track of this low is still very uncertain

To be fair Brian it did start off further north and west before sinking a bit quicker. We can expect plenty of changes in the coming runs, especially with the three main models diverging greatly.

[PB22]

Worth mentioning that we could well be on for 15C somewhere tomorrow, it really does look like being a stunning late February day in the south and east:

http://www.wzkarten.de/pics/Rtavn2417.html

[damianslaw]

Worth mentioning that we could well be on for 15C somewhere tomorrow, it really does look like being a stunning late February day in the south and east:

http://www.wzkarten.de/pics/Rtavn2417.html

Ye 15 degrees is fairly noteworthy but nothing spectacular for the time of year, the feed of air isn't quite as warm as it could be... shame the azores high couldn't have waited a month later to show its face, its been wasted on february.. and for this reason a great irritation indeed, mind you they can whatever the time of year be notoriously cloudy.

[londonsnow]

pub run still going with that low, and associated 528 air. interesting stuff

[bluearmy]

new T120 FAX shows the kink in the flow on the raw output to be right between the 528/546 dam lines and headed where i wonder ????????

Edited February 26, 2009 by bluearmy

[Frosty.]

Oh well, which model will back down I wonder......hmmmmmm, the ECM 12z was an improvement on the 00z with cold air unlike the 00z which looked average. The ukmo is not buying it, more like the ecm 00z at T144 but will be interesting what the morning brings. I'm not expecting much though as we are about to enter march, any snow is only fleeting from now on.

[J10]

The temps on the GFS run would be the wrong side of marginal for Monday night into Tuesday, however this is one of the milder runs at that time, and many have it a few degrees colder.

However at this fairly short range you would rather have the main run on board rather than the ensembles as the main run has edged it at this range due to the better picking up of short waves and the like.

[NorthantsSnow]

Worth mentioning that we could well be on for 15C somewhere tomorrow, it really does look like being a stunning late February day in the south and east:

http://www.wzkarten.de/pics/Rtavn2417.html

Nice ramp but just checked the NMM high-res model on NW and skimmed through the hour by hour charts carefully and the highest temp anywhere tomorrow according to that is 13C in a few isolated spots around Kent/London/Essex. Now this model is fairly new but usually quite accurate so we'll see.

Allowing up to 1C margin of error we could see the odd localised 14C I suppose. But as for 15C, that doesn't seem especially likely.

Either way, this mild dross is on the way out now with a steady cooldown commencing by Sunday. A cold start to next week and indeed March now seems likely:

http://gfs.netweather.tv/gfs.20090226/18/81/ukmaxtemp.png

Not massively cold granted, but a bit more like it in my book. The only thing stunning about this current weather is how depressed it is making me feel.

[Eugene]

The week started depressing with mild feeling stagnant weather with light winds but since wednesday it has definately felt much cooler with cool dew points and a cool westerly breeze, i can't see anything that high today for most dewpoints still look cool and from tonight onwards we could be on for ground frosts/local air frosts every night.

I don't think next week is looking cold enough for low level snow but still higher ground anywhere could get a pasting and high routes in north midlands, northern england, wales and scotland could be dangerous.

Stil it will feel cold in those gusty winds with some nice convection by day likely, a great start to spring if you go on spring starting March 1st.

[Eugene]

Got to say ECM 00Z and GEM 00Z are looking fantastic this morning, after the windy cold unsettled spell slack LP`s move over us with northerly blocking, this would give lovely pleasant sunny days with some slow moving convective heavy showers inland in the afternoon (once daytime heating got to work) plummeting temperatures in the showers and cold frosty nights with patches of dense freezing fog, with lovely crisp clear polar air, just brilliant weather ahead B)

[dice48]

yea i agree cant wait ill be totally ragin if it dosnt come off!

[mountain shadow]

Still divergence in the models over the positioning of the low. A hundred miles can make all the difference as to whether we get rain/sleet/snow.

ECM has the low centered over Donegal

http://91.121.93.17/pics/Recm1441.gif

GFS a couple of hundred miles further east in the North Sea

http://91.121.93.17/pics/Rtavn1441.png

With the METO much different with it centered away up towards the Faeroe's

http://91.121.93.17/pics/Rukm1441.gif

[johnholmes]

the position of the centre is still open to change as all 3 models deal with it in a rather different way.

Certainly a headache for any forecaster as they try and grapple with what warnings may be needed. Wind is an obvious one but just where?

At least from Monday we can follow its actual progress as it exits north America just south of Newfoundland which should give a better 'old fashioned' empirical way, assuming the 3 models are then still having trouble deciding where it will track.

Edited February 27, 2009 by johnholmes

[mushymanrob]

Nice ramp but just checked the NMM high-res model on NW and skimmed through the hour by hour charts carefully and the highest temp anywhere tomorrow according to that is 13C in a few isolated spots around Kent/London/Essex. Now this model is fairly new but usually quite accurate so we'll see.

Allowing up to 1C margin of error we could see the odd localised 14C I suppose. But as for 15C, that doesn't seem especially likely.

Either way, this mild dross is on the way out now with a steady cooldown commencing by Sunday. A cold start to next week and indeed March now seems likely:

disputing a degree or so is rather pedantic mate B) , 15c could be reached in a few favoured areas IF the sun breaks through....

odd isnt it, this weather depresses you but uplifts me! maybe ive had more sunashine...

with some slow moving convective heavy showers inland in the afternoon (once daytime heating got to work) plummeting temperatures in the showers and cold frosty nights with patches of dense freezing fog, with lovely crisp clear polar air,

that doesnt add up... crisp clean air with dense freezing fog at night? foggy air is anything but 'crisp and clean'...

im not so sure the models are getting this one anything like right. the fax seems the most plausable which is suggesting a more mobile atlantic driven pm regime rather then the ecm's slack areas of low pressure. however, in the sunshine it will feel most pleasant in what still is 'normal' early spring weather.

[nick sussex]

Some interesting output from the ecm this morning with pressure building in from the east over the top of the slack low pressure, the ecm actually resembles the gem from a few days ago . Unfortunately as we head into March theres not as much cold pooling to the east and its hard to say whether this would produce anything wintry as we're not sure of the upper air temps here.

Overall the models fill the low out with the jet running quite south but not far enough and overall although it will turn colder theres not really any model output which draws on a really cold source of air, for the ecm to deliver you would need everything coming together perfectly and the PV dropping the cold air into Russia with the right orientation of high so at the moment I think its a longshot.

At this time of year I'd rather look to the north if you want some exciting convective snow showers and sunshine in between and this can deliver some exciting weather but again you need a true Arctic flow that hangs around for a few days.

So for those bored by the recent dull mild weather at least there will be a change and there should be more sunshine and some heavy squally showers perhaps wintry over high ground in the north but if you're looking for a proper reminder of winter then its hard to see where this could come from, that is unless of course the ecm can stick with its pattern and everything goes right for a change! B)

[Yeti]

ECM uppers only really conducive to hill snow

http://en.vedur.is/photos/atlant_evr_hitas...27_0000_132.png

Some interesting output from the ecm this morning with pressure building in from the east over the top of the slack low pressure, the ecm actually resembles the gem from a few days ago . Unfortunately as we head into March theres not as much cold pooling to the east and its hard to say whether this would produce anything wintry as we're not sure of the upper air temps here.

Overall the models fill the low out with the jet running quite south but not far enough and overall although it will turn colder theres not really any model output which draws on a really cold source of air, for the ecm to deliver you would need everything coming together perfectly and the PV dropping the cold air into Russia with the right orientation of high so at the moment I think its a longshot.

At this time of year I'd rather look to the north if you want some exciting convective snow showers and sunshine in between and this can deliver some exciting weather but again you need a true Arctic flow that hangs around for a few days.

So for those bored by the recent dull mild weather at least there will be a change and there should be more sunshine and some heavy squally showers perhaps wintry over high ground in the north but if you're looking for a proper reminder of winter then its hard to see where this could come from, that is unless of course the ecm can stick with its pattern and everything goes right for a change!

Of course if you're desperate then you could look at the WMC Moscow for some deep cold air off the Atlantic:

http://91.121.94.83/modeles/wmc/run/wmc-1-120.png

B)

[Paul]

For those wanting to compare the current modelling for the low pressure system next week, can I recommend our model comparison page - all 4 major models are shown in the same place:

http://www.netweather.tv/index.cgi?action=modelcomp;sess=

[SussexmarkyMark]

So for those bored by the recent dull mild weather at least there will be a change and there should be more sunshine and some heavy squally showers perhaps wintry over high ground in the north but if you're looking for a proper reminder of winter then its hard to see where this could come from, that is unless of course the ecm can stick with its pattern and everything goes right for a change!

Nick. If you were still living in Sussex you would know that we have not had long periods of dull weather here. The weather has varied considerably from location to location across the UK. Last Saturday was stunning in Brighton with almost unbroken sunshine and light breezes. Whilst some days have been overcast, others have not. Today has begun with cloudless skies and temperatures of 8c and a forecast high of 13c. Tomorrow looks equally good.

As for the models for next week, it looks like it will turn unsettled. Not much in the way of snow except in hillier northern areas, but certainly turning more unpleasant with cool, wet and windy periods B)

The week started depressing with mild feeling stagnant weather with light winds but since wednesday it has definately felt much cooler with cool dew points and a cool westerly breeze, i can't see anything that high today for most dewpoints still look cool and from tonight onwards we could be on for ground frosts/local air frosts every night.

The GFS goes for highs of 11 to 13c quite widely today

[Eugene]

Looks like to me going by the models this morning the jet could be weakening after the first week of March with blocked conditions taking over, whether that equates to cold, average or mild we`ll have to see but i feel an average to cold blocking period ahead mid to late March which of course can still give pleasant sunny days with day temps 10C to 13C in between the cold spells, greater diurnal temperature ranges will increase from now on.

[ANYWEATHER]

In the short term still not much changing ie from now to Monday, some rain in the northwest but thats it, but if the models are correct for the bulk of next week it will feel completely different from recent days. Turning very unsettled, ,very windy for some [something to look out for] and much colder with some appreciable snow on some northern and western mountains ie scotland ,lakeland fells and Snowdonia. Some heavy squally showers as well so lots going on next week,!

[johnholmes]

For those wanting to compare the current modelling for the low pressure system next week, can I recommend our model comparison page - all 4 major models are shown in the same place:

http://www.netweather.tv/index.cgi?action=modelcomp;sess=

if we compare how the 2 models out to 240 deal with the low for next Tue-Wed; very different end result.

ECMWF makes it the major part with a cyclonic type of weather for the Uk whilst GFS builds the surface high from the south west/west to make the weather anticyclonic.

which leaves the forecaster with a problem beyond 5-6 days, which to believe!

Edited February 27, 2009 by johnholmes

[MAF]

if we compare how the 2 models out to 240 deal with the low for next Tue-Wed; very different end result. ECMWF makes it the major part with a cyclonic type of weather for the Uk whilst GFS builds the surface high from the south west/west to make the weather anticyclonic. which leaves the forecaster with a problem beyond 5-6 days, which to believe!

so in situations like this John, is there a "middle ground" where a forecast can be made to try and cover all possibilities?? or is just a case of giving a "best guess" and either getting a pat on the back for guessing right or scorned for getting it wrong?

[Snowaddict]

Shamless ramping from me considering that there is great uncertainty past T+120 at the moment, but anyway, if we are to view the medium term ECMWF charts:

Starting at T+168 right through to T+240, the British Isles is under -5 850mb temperatures, with -10's scattered widely in the T+192 and T+216 timeframe.

At T+240, we can see that a cold easterly is setting up....

If only...

[johnholmes]

so in situations like this John, is there a "middle ground" where a forecast can be made to try and cover all possibilities?? or is just a case of giving a "best guess" and either getting a pat on the back for guessing right or scorned for getting it wrong?

it can be either

sometimes one model appears to be a better guide than another and at other times, and this is not uncommon, the 'middle' ground can be used.

In this set up that might be difficult so its a case of wait and see for a day or two.

The middle term drivers, AO and NAO both suggest a colder rather than a milder spell is likely. Also the 500mb anomaly charts, from whichever centre, also suggest a 500mb flow north of west, again suggesting cold rather than mild. Contour values are being suggested of about 534DM, over the middle of the UK,rather below the early March average.

Edited February 27, 2009 by johnholmes