Model Output Discussion - 19th - 25th December

[phil nw.]

Current modelling continues with a Zonal outlook then but with the High never far away towards the south.

After a brief colder interlude tomorrow we return to South Westerly winds by Xmas weekend and unfortunately the fax for the day itself isn`t a very seasonal.

Into next week the High still there but differences apparent in the modelling of the High and byT168.

http://hw.nwstatic.c.../h850t850eu.png

http://hw.nwstatic.c...ecmt850.168.png

ECM shows the Euro High pulled further west to allow colder air to move south.

The ensembles going for a fairly average regime,maybe a slight downward trend later.

Both models then want to build the High over the UK which give a colder feel at the surface with night frosts,particularly if the ECM was to verify.

http://hw.nwstatic.c.../h850t850eu.png

http://hw.nwstatic.c...ecmt850.192.png

Those last 2 links being a week away are likely to change somewhat but they do illustrate that the current trend is not mild South Westerlies all the way.

Edited December 21, 2011 by phil n.warks.

[Bobby]

The GFS and ECM ensemble spreads show some uncertainty with the modelling near Iceland/Greenland at about +192

I guess this is because some ensembles try to build heights/high pressure near this area such as

This could lead to a possible Northerly ala

Maybe just a toppler but something to cling on to perhaps

[Frosty.]

I may well be wrong here but the change shown on models showing the warming are for 10 days time. Does it not take 8 plus days for this to then affect lower down. If so then the earliest impact would be from the 8th onwards, if indeed it does have an affect. Please feel free to correct if I am wrong as this is an area that I have little knowledge but I am trying to learn all the time.

That sounds about right although I think the model output is going to chop and change quite a lot more than usual beyond the T+144 / 168 hour range. Friday will be rather chilly with temps around 5-7c in the north with wintry showers, a band of more persistent rain will sweep southeast across southern britain and as the cold front clears, temps will drop a few degrees, a slight frost on friday night and xmas eve looks a bright and cool day with temps around 7c and then milder for the big day but with a lot of rain in scotland.

[Grimsby Snow Lover]

Well the forecasted NAO is looking a lot more promising as we end the year and start 2012. Perhaps the Atlantic will become more blocked as we enter the new year.

http://www.cpc.ncep....a/nao.sprd2.gif

The AO is also improving very slowly and for the first time in ages one run is well and truelly going negative.

http://www.cpc.ncep....ex/ao.sprd2.gif

It is worth remembering though that these change as often as the runs do so nothing set in stone yet, but if the Stratosphere is warming then the AO/NAO could go even more negative in time.

Edited December 21, 2011 by Grimsby Snow Lover

[Grimsby Snow Lover]

We are not far off from a regressing Atlantic high by next Thursday if the latest GFS run is to be believed. All we need now is for the high to position itself further west and we will be in business for a northerly plunge. More runs needed of course but support for a more blocked Altantic is beginning to show in the NAO forecast charts.

http://www.wetterzen...s/Rtavn1861.png

I know by the low resolution part of the run the hights are flattened by the relentless jet stream but something to keep an eye on. On a plus note the jet is quite a bit further south allowing the northern half of the UK to be on the cooler side of the jet compared with recent GFS runs by the same point. Hopefully a continuing trend here.

Edited December 21, 2011 by Grimsby Snow Lover

[Duane S.]

We are not far off from a regressing Atlantic high by next Thursday if the latest GFS run is to be believed. All we need now is for the high to position itself further west and we will be in business for a northerly plunge. More runs needed of course but support for a more blocked Altantic is beginning to show in the NAO forecast charts.

http://www.wetterzen...s/Rtavn1861.png

This has been showing up for a while now. It's a window for sure as troughing will aid WAA up towards more northerly climes around the 28th but I suspect it will be flattened out, a toppler the best outcome. BUT it's a break and I suspect shot 2 or 3 will work its magic going into early Jan.

[Grimsby Snow Lover]

This has been showing up for a while now. It's a window for sure as troughing will aid WAA up towards more northerly climes around the 28th but I suspect it will be flattened out, a toppler the best outcome. BUT it's a break and I suspect shot 2 or 3 will work its magic going into early Jan.

Really hope so, I am sure as the week goes on furture FI runs might brighten up things in this thread.

[shedhead]

Good to see some hope appearing in the longer term, especially in regard to the potential strat warming, but in the meantime mild/very mild conditions look set to predominate. 13, 14 or even a localised 15c looks very possible at times between now and next Weds, with the latest runs showing 850hpa temps quite often above 5c. As ever we don't have to like it, but as far as the bulk of the next 6 or 7 days is concerned we do have to accept it.

[Kent Clipper]

We are not far off from a regressing Atlantic high by next Thursday if the latest GFS run is to be believed. All we need now is for the high to position itself further west and we will be in business for a northerly plunge. More runs needed of course but support for a more blocked Altantic is beginning to show in the NAO forecast charts.

http://www.wetterzen...s/Rtavn1861.png

I know by the low resolution part of the run the hights are flattened by the relentless jet stream but something to keep an eye on. On a plus note the jet is quite a bit further south allowing the northern half of the UK to be on the cooler side of the jet compared with recent GFS runs by the same point. Hopefully a continuing trend here.

It's certainly something worth keeping an eye on. The ECM were showing a surprisingly cold NNE'ly flow on the 0z earlier and this received some support from a few of the GEFS ensembles and DE Bilt too.

http://www.wetterzentrale.de/pics/Recm1922.gif

The northern crank of the jet stream will no doubt topple the block pre new year but its encouraging that such a cold chunk of air can still move quickly south even in such a zonal and flat pattern.

Should the SSW event propogate downwards and then manages to to shift the PV to Scandinavia in the longer term it will be an interesting start to 2012.

Lots to keep an eye on at the moment.

[Grimsby Snow Lover]

Good to see some hope appearing in the longer term, especially in regard to the potential strat warming, but in the meantime mild/very mild conditions look set to predominate. 13, 14 or even a localised 15c looks very possible at times between now and next Weds, with the latest runs showing 850hpa temps quite often above 5c. As ever we don't have to like it, but as far as the bulk of the next 6 or 7 days is concerned we do have to accept it.

Quite rightly put there Shedhead. Thats the beauty of our climate and mild days like you have suggested are perfectly 'normal' for British winters as are days when we see below average conditions. If we had a continental climate then things would be very different. I don't think the mild conditions will last much more than a week though.

[igloo]

first signs of the atlantic slowing with possible blocking.it may be the models are starting pickup the slow change in our atmosphere but we do need a few more runs but

[NorthernRab]

Good to see some hope appearing in the longer term, especially in regard to the potential strat warming, but in the meantime mild/very mild conditions look set to predominate. 13, 14 or even a localised 15c looks very possible at times between now and next Weds, with the latest runs showing 850hpa temps quite often above 5c. As ever we don't have to like it, but as far as the bulk of the next 6 or 7 days is concerned we do have to accept it.

I'd rather you specified who "we" is referring to - there will be a fairly cold zonal blast for some around the 23rd / 24th so it's not all mild for the next week.

A period of zonal and very changeable weather coming up for the next 5 days or so, especially over Scotland / N.Ireland and parts of North England, where the weather will alternate between really quite blustery, damp, fairly mild weather (although feeling a lot colder in the wind) and colder weather with sleet and snow showers (feeling cold in any wind). More settled towards the SE of England, although temperatures could be supressed at night where there is little wind.

Thereafter, very much anyone's guess at the moment, very little agreement. Keep an eye on the 28 / 29th for a possible Northerly, far too far out for now though.

[shedhead]

I'd rather you specified who "we" is referring to - there will be a fairly cold zonal blast for some around the 23rd / 24th so it's not all mild for the next week.

A period of zonal and very changeable weather coming up for the next 5 days or so, especially over Scotland / N.Ireland and parts of North England, where the weather will alternate between really quite blustery, damp, fairly mild weather (although feeling a lot colder in the wind) and colder weather with sleet and snow showers (feeling cold in any wind). More settled towards the SE of England, although temperatures could be supressed at night where there is little wind.

Thereafter, very much anyone's guess at the moment, very little agreement. Keep an eye on the 28 / 29th for a possible Northerly, far too far out for now though.

I didn't say it will be mild all next week NR, I said.... Good to see some hope appearing in the longer term, especially in regard to the potential strat warming, but in the meantime mild/very mild conditions look set to predominate. 13, 14 or even a localised 15c looks very possible at times between now and next Weds, with the latest runs showing 850hpa temps quite often above 5c. As ever we don't have to like it, but as far as the bulk of the next 6 or 7 days is concerned we do have to accept it.

Quite rightly put there Shedhead. Thats the beauty of our climate and mild days like you have suggested are perfectly 'normal' for British winters as are days when we see below average conditions. If we had a continental climate then things would be very different. I don't think the mild conditions will last much more than a week though.

Agreed GS - the latest GFS suggests the height rises later next week get flattened again rather quickly, but hopefully future runs will build the HP and further weaken the Jet, which in tandem with a weakening of the PV should hopefully deliver much better prospects for cold towards week two of Jan.

[Glacier Point]

The last two GFS operationals (didn't see the 18z) have come up with attempted cut off lows in the Atlantic (t168 and again around t300) as a result of an amplification in the longwave pattern over North America. The 00z GFS ensemble suite picked these as well and generally trend the mean ridge back further west and north-west with a resulting better organised trough digging to our east.

Make that the last three now, plus the first of these modelled by UKMO t144.

Angular momentum plots appear to suggest that the westerly wind anomaly across 50-60N is coming to any end and GFS operational starting to develop some amplification in the extended range. I wonder, is the 'tank empty' warming light on the polar westerlies flashing away on the dashboard ?

[Backtrack]

Make that the last three now, plus the first of these modelled by UKMO t144.

Angular momentum plots appear to suggest that the westerly wind anomaly across 50-60N is coming to any end and GFS operational starting to develop some amplification in the extended range. I wonder, is the 'tank empty' warming light on the polar westerlies flashing away on the dashboard ?

I've quite enjoyed the Polar Westerlies.

When you say that the tank is empty, you're suggesting that they are now likely to be few and far between am I correct?

What would you say the next trend would be? E.G December has so far has been dominated by NW'erlys, and I recall a post a few weeks back from yourself suggesting Easterly winds becoming a feature on the GFS' runs.

Is this still the case, or have things changed since then?

Thanks.

Edited December 21, 2011 by Backtrack

[Cloud 10]

Make that the last three now, plus the first of these modelled by UKMO t144.

Angular momentum plots appear to suggest that the westerly wind anomaly across 50-60N is coming to any end and GFS operational starting to develop some amplification in the extended range. I wonder, is the 'tank empty' warming light on the polar westerlies flashing away on the dashboard ?

The BOM has a good example as well. http://176.31.229.22...nh-0-144.png?12

[NorthernRab]

I didn't say it will be mild all next week NR

I know you didn't, I was just filling in the gaps of what you chose to leave out for you

Any potentially cold certainly looks like coming from the north rather than the east at the moment (I find a good way of checking this is by comparing the Highlands GEFS T850s to the Aberdeenshire GEFS T850s), but there's a period of changeable and unsettled weather to come, especially for Scotland where it will switch between quite cold and really rather mild.

[nick sussex]

This low pressure at 168hrs is beginning to look interesting for the UK.

The cold air is quite far south into the Atlantic and theres a chance of some snow as this clears away if we can get a sufficient undercut of colder air.

We do though need to see the high further north initially and we need this to topple se'wards forcing the low more into the Channel, rather than the Low Countries, certainly something to keep an eye on in future outputs.

I should add this is in relation to the ECM, the GFS does have a low but the high is orientated unfavourably for that snow chance.

Edited December 21, 2011 by nick sussex

[Cloud 10]

Yes,an interesting ECM at 168hrs showing more amplication in the jet which GP mentioned.

Looks like a snowy chart for Northern Scotland if it came off.

[chionomaniac]

Make that the last three now, plus the first of these modelled by UKMO t144.

Angular momentum plots appear to suggest that the westerly wind anomaly across 50-60N is coming to any end and GFS operational starting to develop some amplification in the extended range. I wonder, is the 'tank empty' warming light on the polar westerlies flashing away on the dashboard ?

I think that that would fit in well with the mean zonal mean wind anomaly chart that I posted yesterday in the strat thread. That certainly looked like the propagating westerlies were reducing and perhaps we are seeing the first signs of this on the ground as it were.

[snowingman]

oh dear....no snow !! for atleast 2 weeks 12z, less heating i guess

[phil nw.]

This low pressure at 168hrs is beginning to look interesting for the UK.

The cold air is quite far south into the Atlantic and theres a chance of some snow as this clears away if we can get a sufficient undercut of colder air.

We do though need to see the high further north initially and we need this to topple se'wards forcing the low more into the Channel, rather than the Low Countries, certainly something to keep an eye on in future outputs.

Certainly signs of somethings afoot with the energy looking to split off Newfoundland at T144hrs. showing that cut off low.

http://www.wetterzentrale.de/pics/Rtavn14415.png

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

http://www.wetterzentrale.de/pics/Recm1441.gif

underlining GP`s view that the Atlantic train is slowing.

Interesting developments around T168,especially on the ECM as you pointed out Nick

http://www.wetterzentrale.de/pics/Recm1682.gif

Cold air wrapped around the north of the low would likely bring a snowfall in Scotland.

However the pattern flattens out again after a brief ridge gives way under pressure from the west and the jet returns north.

Signs though that the main core of the vortex energy starts to seep towards the Scandinavian side of the Arctic with a trough development there later.

http://www.wetterzentrale.de/pics/Recm1921.gif

http://www.wetterzentrale.de/pics/Rtavn1921.png

The pattern overall has some hints of readjusting but is still looks too flat overall and with the Heights to the south never far away it limits any lasting cold incursions for now.

[nick sussex]

Certainly signs of somethings afoot with the energy looking to split off Newfoundland at T144hrs. showing that cut off low.

http://www.wetterzen.../Rtavn14415.png

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

http://www.wetterzen...cs/Recm1441.gif

underlining GP`s view that the Atlantic train is slowing.

Interesting developments around T168,especially on the ECM as you pointed out Nick

http://www.wetterzen...cs/Recm1682.gif

Cold air wrapped around the north of the low would likely bring a snowfall in Scotland.

However the pattern flattens out again after a brief ridge gives way under pressure from the west and the jet returns north.

Signs though that the main core of the vortex energy starts to seep towards the Scandinavian side of the Arctic with a trough development there later.

http://www.wetterzen...cs/Recm1921.gif

http://www.wetterzen...s/Rtavn1921.png

The pattern overall has some hints of readjusting but is still looks too flat overall and with the Heights to the south never far away it limits any lasting cold incursions for now.

Thanks Phil a good summary of things.

I'm not going to overplay the chances of snow off that low in case it causes a stampede to the nearest sledge shop! For the timebeing it's a small chance but given some of the rather underwhelming output recently at least it gives us something to talk about.

As everyone knows I've been droning on about favourable and unfavourable topples in recent days, we need to see the topple in such a way that the low heads se through the spine of the UK rather than more ese into the continent.

Whatever happens as you mentioned the jet will probably flatten the ridge again but I think any snow would be welcome to many regardless of how long it stays around for.

We'll have to see what the models do over the coming days, it's a rather complicated set up and at 168hrs too far ahead to have alot of confidence in.

Edited December 21, 2011 by nick sussex

[Frosty.]

Latest models this evening show a coldish day on friday but then turning mild until the middle of next week, at that point the gfs pulls down a brief arctic northerly but it only lasts around 12-18 hours before the ridge to the west topples southeast but the Ecm not buying the arctic northerly idea so a lot depends on whether the low develops and it's track but then into FI the gfs returns the uk to a cool, occasionally cold zonal pattern for the north at least. There is a peak time for the high to the south of the BI to get closer as it travels slowly east and the southeast looks like having the best of the weather early next week, on the flipside, scotland looks like having a very wet and windy christmas weekend and wet and windy at times througout next week with temps near average.

[mcweather]

Make that the last three now, plus the first of these modelled by UKMO t144.

Angular momentum plots appear to suggest that the westerly wind anomaly across 50-60N is coming to any end and GFS operational starting to develop some amplification in the extended range. I wonder, is the 'tank empty' warming light on the polar westerlies flashing away on the dashboard ?

I note GP'S cautious post regarding the polar westerlies gradually running out of juice so to speak with interest.

The CFS extreme range model that starts at 364 and heads on out to 1092 hours which has been showing endless westerlies and very much a mild rinse and repeat scenario for ages now has suddenly switched to repeated northerly and easterly outbreaks from about mid Jan onwards ( worth a peak if only from a chart porn point of view) which fits in very nicely with GPS's own winter forecast and that of RJS as well

Possibly the first stirings of a change down the line perhaps