Model Output Discussion

[karyo]

Good to see the MJO coming closer to Phase 7. Let's hope it makes that extra step and prove the forecasts wrong once again!

However, the met Office update doesn't offer any excitement! In fact, it mentions the possibility for drier weather in the southeast towards the end of the forecast period which would indicate a ridge of high pressure over the continent - not what we want!

Karyo

Edited December 1, 2009 by karyo

[kold weather]

Thats suggestive of high pressure to our east...could be centered anywhere from the Med upto Russia itself but looking at the models I suspect they have a pattern where the UK really is in the middle of the two big forces at work and with a SE hint to the airflow and obviously higher pressure further east would both be suggestive of the SE being drier whilst the west could still be fairly wet if the lows are strong enough to push thier fronts in.

[MR EXTREMES]

I see where you're coming from, BB...BUT, wouldn't a massive, solid 'immovable' source of potential wintryness be better than a (more transient?) Scandi High - in the longterm?? :unsure:

yes it would but how many times this happened in the last 10years or more lol.

but its the blasted alantic coupled with el nino which is throwing so much energy up into the atmosphere.

as for the models i can very much understand why there are so many messy moments but its no different to most autumn winter moments thats why fantasy island is pointless looking at every year is the same.

i think this year is very much a typical nino pattern,

but this dont mean things cant change is just harder work to do so,

perhapes in the next 7-14 days we MIGHT have a clearer picture.

[Shunter]

Building blocks are coming together...

Teleconnections are looking favourable for NH blocking.

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.sprd2.gif

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.sprd2.gif

MJO possibly heading into Phase 7 soon

http://cawcr.gov.au/bmrc/clfor/cfstaff/matw/maproom/RMM/phase.Last40days.gif

[karyo]

Building blocks are coming together...

Teleconnections are looking favourable for NH blocking.

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.sprd2.gif

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.sprd2.gif

The AO forecast is really impressive!

Of course, the AO was strongly negative for much of October but it didn't result into anything cold for us. Maybe better luck this time!

Karyo

[Optimus Prime]

A negative AO doesn't always equal cold. If you look outside the box you would clearly see a negative AO is produsive of several different scenarios.

[nick sussex]

The AO forecast is really impressive!

Of course, the AO was strongly negative for much of October but it didn't result into anything cold for us. Maybe better luck this time!

Karyo

Yes these can be misleading and sometimes people see these going negative and think a cold spell is on the way but theres countless times the jet has amplified in the wrong place, to be honest with the current pattern we could easily end up with the trough anchored to the west throwing up southerlies on its eastern side, the pattern either needs to progress much further east with trough over scandi which is very unlikely or much further west with the atlantic trough far enough away to allow pressure to build westwards, then theres the added complication of how much energy goes into the southern arm of the jet, scandi highs sink without lower heights in the med.

This just highlights why it's so difficult to get a decent cold spell, what seems strange though is you hardly ever see the pattern stuck with trough over scandi it always seems stuck near the meridian!

IMO unless the pattern backs west then its looking like alot of rain and wind with temps average to mild, unless the jet dies down then its going to be very difficult to see the trough sinking southwards, although much has been made of building blocks for the future theres no guarantee these will deliver or that another variable pops up just at the wrong time, equally as we know the output can suddenly go in another direction. I'm not being unduly negative here just trying to be realistic looking at the current output.

[Methuselah]

Here's the chart from 24/12/1969...12C in Kent???

http://www.wetterzentrale.de/pics/archive/ra/1969/Rrea00119691224.gif

[snowmadchrisuk]

I can't remember ever seeing a setup like the one that is being shown recently , to have a high pressure so close to NE Uk and still be under complete control by low pressure in the Atlantic . I think there is a chance that by next weekend that high pressure might be showing to have more of an affect on us or at least the east of the country. I can't see us having pressures of 970-990 mb anyway and I think this is why the met office has been hinting that things might start to calm down in the south east.

[johnholmes]

Alert issued for snow

[Methuselah]

I can't remember ever seeing a setup like the one that is being shown recently , to have a high pressure so close to NE Uk and still be under complete control by low pressure in the Atlantic . I think there is a chance that by next weekend that high pressure might be showing to have more of an affect on us or at least the east of the country. I can't see us having pressures of 970-990 mb anyway and I think this is why the met office has been hinting that things might start to calm down in the south east.

That, SMC, is why I posted that innocuous-looking chart from December '69...By New Year, Kent was under snow with daytime maxes of -1C!

[nick sussex]

Given the upstream pattern the gfs looks quite plausible, the trough sits there, secondary lows form run into the uk and the spin back into the deep main low, these are charts we've all seen many times, then its a case of waiting and hoping the jet subsides and trough dissipates.

Then you hope that blocking is still strong to the ne to take advantage, what you dont want to see is pressure falling to the ne whilst you're waiting for the Atlantic trough to fill out, thats why the further west and south the trough the better chance of success at the end, how long this will take is uncertain. And theres no guarantee that the AO will remain negative or the upstream pattern will play ball, again I'm not being negative just trying to be realistic here, although we do see positive anomalies in the polar regions its still a difficult path to cold, but that really has always been the case in the UK.

Anyway we still have some uncertainties upstream and the matter of the unstable PV so we could still see some model changes.

Edited December 1, 2009 by nick sussex

[bluearmy]

the 12z paralell is odd very early on. (and later aswell - make sure you look at the NH plot).

Edited December 1, 2009 by bluearmy

[snowmadchrisuk]

That, SMC, is why I posted that innocuous-looking chart from December '69...By New Year, Kent was under snow with daytime maxes of -1C!

woohoo , Let's hope for a repeat of that then .

[kold weather]

Well the 12z model looks pretty much like what I'd expect, a -ve AO BUT not much true blocking but most of the blocking is due directly as a response of the strong LP in the Atlantic (much the same way as toppler highs) though the set-up is more stable with the jet still on a general NW-SE motion.

Eventually as I've said before if we keep getting this set-up we will get a slidder into Europe and the end result will be akin to the fantasy 12z GFS yesterday, just a case of if really!

Indeed Ian its not common synoptics, it could well evolve that way but another way it could eventually evolve in the longer term (we are talking a good 10-15 days ahead) is eventually the jet amplifies even more, we see a weak low split from the main vortex and dive SE, the main vortex then withdraws westwards and pressure tries to rise to the north as the slidder comes through. Its how we evolved into the Feb 2005 pattern and whilst it can mean there isn't as much cold in the circulation as other types of set-up its the safest way into a cold sustained set-up. We also saw it attempted in Feb 2007 but the jet was too strong in that instance and so whilst the slidder low ended up giving decent snowfall there wasn't nearly enough support from the north.

Edited December 1, 2009 by kold weather

[weather eater]

Fascinating model watching right now as the NWP wrestles with the various factors. It is unusual set-up for the christmas pudding, even though it will be average to mild over the coming week.

The plus points for cold fans are no PV and no monstrous Azores High looming. But for the period that the AO is likely to be negative, then the window for blocking to the North to 'benefit' the UK must be taken, because if it isn't then I would think that it is inevitable that we will see low pressure systems begin to make their way NE, and then that becomes very much a back to square one situation.

About as interesting as I've seen it over the last five years, What made me laugh about the 12z is the vast amount of cold to our east, but at no time does it make it to the UK. I would certainly call the blocking a trend now, but whether we can get past an implode and then get that cold over us stands on a knife edge and might well do for a while.

[Frosty.]

Alert issued for snow

According to the latest radar, there is plenty of sleet across much of scotland, cumbria & n. wales but no snow as yet.

The GFS 12z shows a very unsettled spell lasting another 7-10 days with a large depression to the west of the uk and high pressure to the northeast giving a strong SW'ly to SE'ly flow which will feel rather chilly despite temps actually being near average but never terribly mild. High Pressure then builds from the southeast later with cold but not bitter continental air and overnight frosts towards mid month but no sign at all of any snow in the outlook as we head towards christmas.

Edit..snow just appearing on the radar in scotland, this might be the last snow watch for 2-3 weeks!

Edited December 1, 2009 by Frosty039

[nick sussex]

Disappointing ukmo, pushes low pressure much further east And the azores high looking like it wants to make an appearance, also looks like developing deep trough to the west, hard to know what would happen after this.

http://www.meteociel.fr/modeles/ukmo2.php?nh=&ech=144&carte=1021

So already disagreements between the model output this evening, lets see what the ecm comes up with.

Edited December 1, 2009 by nick sussex

[Methuselah]

woohoo , Let's hope for a repeat of that then .

Well, I was in Royal Tunbridge Wells back then...I'm not saying it will happen, mate - only that it can??? So, please take note of KW's/NS's caveats? It could be (heaven forbid )that mild-mush reigns throughout! :unsure:

[phil nw.]

Fascinating model watching right now as the NWP wrestles with the various factors. It is unusual set-up for the christmas pudding, even though it will be average to mild over the coming week.

The plus points for cold fans are no PV and no monstrous Azores High looming. But for the period that the AO is likely to be negative, then the window for blocking to the North to 'benefit' the UK must be taken, because if it isn't then I would think that it is inevitable that we will see low pressure systems begin to make their way NE, and then that becomes very much a back to square one situation.

Hi Ian,

Yes a good summary of where we are.

It`s finally balanced and whilst the PV is fragmented and the jet further South this is the period we need to build those heights further North.

I think most of us are of the same opinion,no wild assumptions,just watching and hoping the energy stays South.

GFS12z is a decent start and keeps the status quo.

Edited December 1, 2009 by phil n.warks.

[Eugene]

UKMO 12Z an improvement over the GFS 12Z with a nice cool PM westerly, no nasty stubborn scandy/russian high to pull up warm southerlies.

http://www.wetterzentrale.de/pics/Rukm1441.gif

[Frosty.]

UKMO 12Z an improvement over the GFS 12Z with a nice cool PM westerly, no nasty stubborn scandy/russian high to pull up warm southerlies.

http://www.wetterzentrale.de/pics/Rukm1441.gif

There are no warm southerlies on the GFS 12z

[snowmadchrisuk]

There are no warm southerlies on the GFS 12z

Come on Frosty , this is warm for the time of year .

[phil nw.]

UKMO 12Z an improvement over the GFS 12Z with a nice cool PM westerly, no nasty stubborn scandy/russian high to pull up warm southerlies.

http://www.wetterzen...cs/Rukm1441.gif

Interestingly Eugene the GFS parallel does away with the Eastern block too.

http://www.meteociel...ode=0&runpara=1

A different way to an Easterly.Push the trough through and build from Iceland.

Model watching is not dull at the moment.

Edited December 1, 2009 by phil n.warks.

[bluearmy]

For cold fans, I'd would much rather see the southerlies than that UKMO chart. It is progressive and infers Low pressure piling through. Some of the great cold spells came after southerly spells.

there is nothing good about UKMO run tonight - unless you want a rdiging AH in about 10 days time with a resulting euro high. it might dry things up down here but it wont get us to cold.