Model Output Discussion - The Start Of Winter

[johnholmes]

Well, interesting comments above so my view using the anomaly charts.

For at least a couple of days now the ECMWF-GFS outputs, especially the ECMWF one have been a bit out of step with the NOAA 6-10, the latest from each is linked below.

Both ECMWF-GFS tend to make more of the troughing idea than does NOAA, and again when you look at the ECMWF version this is quite marked this morning. And it is a fairly good sequential change from its previous two outputs. Generally when there is a difference between the 3 I tend to back NOAA more than the other two. However the relative consistency on ECMWF to suggest a more north of west flow, with marked ridging west of the UK and the marked trough east of the UK (shown also on GFS and to some extent on the NOAA output), tend to make we wonder if ECMWF might not be nearer the mark in the predicted upper flow over the 6-10 day, maybe even 3-10 day period than the others. I also note the ideas out from Met suggesting it being westerly at the surface rather than n of west. Remember the anomaly charts are averages over the period they are relevant for, this means that on individual days the flow can be fairly different.

Certainly the overall temperature pattern at the surface seems more likely to be average to below than above, as a general idea through this period. Just how deep any surface system gets, thanks to the strongish jet and contrasting upper and surface temperature differences in NE N America is open to conjecture. 

An interesting week maybe even 2 weeks as to how this will play out so many will be glued to each frame of each run of each model. The detail at the surface obviously will come from the synoptic models not anomaly charts. Some folk on low ground and fairly well south COULD get to see some white stuff briefly before Christmas, something many have not seen for over 12 months.

links

 

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

 

http://www.cpc.noaa.gov/products/predictions/814day/500mb.php

 

Contour heights are somewhat lower as is often the case on the ECMWF-GFS version than NOAA, note also the 500mb 'thickness' lines on the Met O Fax charts off the eastern seaboard at times, showing some quite large changes over relatively short distances, a good indication of the marked temperature contrasts at the surface and in the upper air, hence the marked jet at times.

Fax link

http://www.weathercharts.org/ukmomslp.htm#t120

Edited December 6, 2014 by johnholmes

[Polar Maritime]

The Northerly looks a little stronger on the 6z for the 13th, With the low swinging a further South in turn taking the Jet with it. All in all a cool if not cold outlook, With plenty of Pm shots bringing snow to low levels from the Midlands North. With the Highlands sub-zero touching -14c..

 

Edited December 6, 2014 by Polar Maritime

[OldMetMan]

I guess it hardly needs saying, but the 06Z GFS portrays a serious snow situation, especially for the N Midlands northwards, perhaps even further south as the 528dm thickness value plunges down across the whole country.

The development of short-wave features looks, at this stage, highly plausible, given the proximity of the powerful jet and very strong baroclinic zone. A lot needs to happen first of course but it would be fascinating if such a pattern or something like it, were to happen.

Later runs should prove interesting.

[IDO]

IDO, you've used the 7am chart on Sunday, when the cold doesn't move in until the afternoon/evening. Monday is also looking like being the coldest day, and you've completely missed it out...image.jpg

Hi Barry was just marking the demarcation of the PM flow on each of the three shots. Of course they show colder air in the subsequent frames and I am not disputing that. The colder shots on the 06z are longer than the warm TM interludes. Too early to know about chances of snow but the two initial shots say no for south of Birmingham. Fridays PM flow will continue to change.

[BLAST FROM THE PAST]

Indeed pM air is the order of the day and 06z amplifies nicely again introducing some interesting little secondary troughs running through and if we get a holding pattern with trough to our east and ridge to our west these spawning trough features could bring some very interesting wintry weather.  MetO saying average to a little above is...well we'll see won't we. 

 

 

I think the ECM anomaly chart as JH has said makes more of the Atlantic amplified ridge and for me is more on the money,  The past 24hrs we have seen the models go for this more amplified outlook and I think there is more to come out of this as in any attempt to flatten out will be pushed back as we approach it. 

So below average temps coming [edit.. are here and more to come] and don't be surprised if some well below average temps start to show for mid December. 

 

BFTP

Edited December 6, 2014 by BLAST FROM THE PAST

[Chris K]

Hi Barry was just marking the demarcation of the PM flow on each of the three shots. Of course they show colder air in the subsequent frames and I am not disputing that. The colder shots on the 06z are longer than the warm TM interludes. Too early to know about chances of snow but the two initial shots say no for south of Birmingham. Fridays PM flow will continue to change.

I think that is a fair assessment IDO....some decent cold shots from the NW/N with brief westerly interludes. However at the moment, the Azores/Atlantic high is being a bit of a pain, as it is repeatedly toppling cause the coldest uppers to water down and get shunted out of the way too quickly. It could eventually work in our favour though and is better than constant SW sourced winds.

Some areas in the north will see snow, but I think we need better amplification to allow that HP to nudge N before it risks getting pushed towards Europe or sit to the South of us....interesting times to see what happens next.

Edited December 6, 2014 by Chris K

[nick sussex]

An interesting set up shown on the GFS with that shortwave however it has a tendency to over do cold at that range and so its current precip projection of snow for especially central northern areas is unreliable.

 

The Pennines may well get some snow but on lower ground I certainly wouldn't be getting too excited especially as this shortwave may well disappear on future outputs. I think its best to not expect too much out of that and wait and see till nearer the time whether the cold advection does indeed get that far south.

 

It's overall pattern looks similar to this mornings ECM 00hrs run, the upstream pattern does undergo some temporary strong amplification over the eastern Pacific and western USA and because of this we might see some more changes upstream which might help to keep the high further north around that tiimeframe:

 

 

As you can see its a complex pattern with the jet all over the place in the Atlantic but upstream developing alot more amplification, this may well develop something more interesting towards the eastern USA which may in future outputs help the high.

 

We'll see over the coming days whether this happens.

Edited December 6, 2014 by nick sussex

[IDO]

 

 

 

 

I think the ECM anomaly chart as JH has said makes more of the Atlantic amplified ridge and for me is more on the money,  The past 24hrs we have seen the models go for this more amplified outlook and I think there is more to come out of this as in any attempt to flatten out will be pushed back as we approach it. 

So below average temps coming and don't be surprised if some well below average temps start to show for mid December. 

 

BFTP

 

 

Yes it does, and looking at its last 5 days height bias for D7 I would expect a more amplified ridge:

 

 

So if we assume that the bias is also on this morning's run then we can tone down the likely height anomaly at D7; and expect downgrades as we get to T-0.

[BLAST FROM THE PAST]

Yes it does, and looking at its last 5 days height bias for D7 I would expect a more amplified ridge:

 

NOAA_NWS_NCEP_WPC_MODEL_DIAGNOSTIC_-_INTERACTIVE_MODEL_BIAS_PAGE.jpg

 

So if we assume that the bias is also on this morning's run then we can tone down the likely height anomaly at D7; and expect downgrades as we get to T-0.

That's you expect downgrades as we get to T0?  I don't, I anticipate this amplification to be more pronounced as we go through to mid Dec.

 

 

Interesting projected Jetstream....in tatters over our neck of the woods...nice amplification in West NA. 

 

 

 

 

My favourite snapshot of the 06z run [just of the run not that it is spot on] is this little feature.....hope we have more showing up in subsequent runs......could develop nice for some

 

 

Has been pretty cold last few days here, very seasonal indeed, and near time this ain't a bad start to winter is it

 

 

 

BFTP

Edited December 6, 2014 by BLAST FROM THE PAST

[blizzard81]

What strikes me today is what a nice feeling it is to see cold charts for the forseeable with nothing mild in the offing whatsoever. Yes, we were spoilt in Dec 09 & 10 but believe me, there have not been many Decembers showing the current synoptics. Most Decembers are mild and south westerly driven.

[TonyH]

Yes it does, and looking at its last 5 days height bias for D7 I would expect a more amplified ridge:

 

NOAA_NWS_NCEP_WPC_MODEL_DIAGNOSTIC_-_INTERACTIVE_MODEL_BIAS_PAGE.jpg

 

So if we assume that the bias is also on this morning's run then we can tone down the likely height anomaly at D7; and expect downgrades as we get to T-0.

Is it bias though or just what it produces from the data it receives?

[Cloud 10]

The GFS 06z would provide 2 real pastings of snow within the next week if it verified,thanks to small southerly tracking lows that some have mentioned,the first of which affects parts of Scotland on Friday...

 

 

 

....and the second one the day after for parts of Northern England and Wales....

 

 

 

Way to far out for any specifics,but there is the potential for heavy snowfall over parts of the UK within the next week or so,and that's not counting Sunday night/Monday morning which could spring some surprises.

 

 

 

[IDO]

Is it bias though or just what it produces from the data it receives?

 

That's what NOAA calls it, "bias", who am I to argue with the experts?

 

You can see from the London Snow risk that the op is probably another extreme. That is the lowest snow risk for the last few days:

 

 

As you can see from temps 3 of the days will be about 2c above average and 3-4 below average. Ties in with the UKMO update of around average temps for the south. The further north, as you would expect from a NW'ly, should feel a bit cooler. 

[Penrith Snow]

Regarding temperatures over the coming 10 days I would expect given the strong WNW flow ranging from well below average in NW Scotland to above average in SE England due to it's longer exposure to warm sectors.

This kind of cool zonality often results in near or even above average temperatures in Central England as the mild sectors can push temperatures above 10c for a short time even though temperatures are fairly low for long periods.

The very snowy zonal spell of January 1984 is a classic point as monthly temperatures were near normal in Northern England despite frequent and heavy snowfalls and 15+ days with lying snow!

This is the reason for the MetO prediction of mean temperatures a tad above normal.

Andy

[Summer Sun]

Pity no scale on that SS

 

Awaiting GFS P returning on Monday afternoon then we'll be able to see the snow depth's more clearly

 

Will be interesting to see if this develops any further over the coming days

 

 

The temperatures are perfect for it to fall as snow across large parts

 

 

Just a shame GFS P isn't available atm otherwise we'd be able to see how much would fall

 

[johnholmes]

Regarding temperatures over the coming 10 days I would expect given the strong WNW flow ranging from well below average in NW Scotland to above average in SE England due to it's longer exposure to warm sectors.

This kind of cool zonality often results in near or even above average temperatures in Central England as the mild sectors can push temperatures above 10c for a short time even though temperatures are fairly low for long periods.

The very snowy zonal spell of January 1984 is a classic point as monthly temperatures were near normal in Northern England despite frequent and heavy snowfalls and 15+ days with lying snow!

This is the reason for the MetO prediction of mean temperatures a tad above normal.

Andy

 

just a technical point the actual temperature has not too much connection to the wind speed but one feels the cold much more in widny contitons with the same temperature. Thus perhaps a forecast should have something like, about average temperatures but feeling much colder in the wind?

[Gael_Force]

Not to worry, Gavin - other tools at our disposal.

 

Instant weather maps have a great range of parameters. Snow depth accumulated by 192 on the 06 GFS.

 

http://www.instantweathermaps.com/GFS-php/showmap-eurosfc.php?run=2014120606&time=INSTANT&var=SNOD&hour=003

 

[AWD]

With the focus significant, long term cold weather, I think there will still be plenty of transient, wintry weather in the short term, mainly but not exclusively for northern areas.

As the weekend progresses, colder crisper air will sweep down from the NW behind the current cold front leaving the UK. For the south this will introduce crisp, winter sunshine and a notable air frost tonight.

For the North, especially NW facing coasts such as Northern Ireland and Western Scotland, snow showers will start to usher inland, initially over high ground only but as the colder air further entrenches and the WBFL falls, so will the isotherm level and sleet/snow could start to fall to lower levels too, especially across Scotland;

Leading to some modest accumulations in said areas;

Obviously the more elevated you are te better the accumulative snowfall but I do think some low lying areas could see some settling, transient snowfall too.

A cold feel to the weather for all of us though;

With a cold upper air Pm flow;

And as I said earlier, where skies clear, some sharp air frosts are likely over the next few nights;

The upper airflow modifies as we enter the new working week and our next focal point looks like being a possible, notable storm depression midweek next week. All models favour the centre of the depression to pass to the north of mainland UK;

Obviously the track and intensity of the storm is subject to change at this range still, but the NWP output do merge together to favour the windiest weather over Scotland, where storm force winds are possible;

Very windy everywhere, just Scotland and Ireland bearing the brunt of the winds. I won't post PPN charts up yet as, IMO, it's too early to expect detail for that regard.

Something to watch, away from the "snow hunting" nevertheless.

Back to "snow hunting" now anyway, and the 06z GFS Op throws up and interesting scenario for next weekend, this time bringing the south into play too.

A cut off cold pool straddles the UK, after another sharp Pm flow takes hold once the midweek storm exits UK airspace. I will just show the basic charts here as no doubt the situation will change in future output, plus at the time of writing this post, the 06z ensemble data wasn't out so how much support this evolution has is unknown to me currently. (Not that I'm expecting too much ensemble support yet which doesn't mean we should dismiss it as I would expect Op runs to be more accurate in detailed evolutions like this).

Anyway, the 06z GFS Op shows wintry PPN spreading much further South, albeit transient as we would expect currently;

With an ever lowering WBFL;

This demonstrates the possibility of snowfall when other values are favourable and not necessarily requiring the -5c 850hpa temp most search for. Not saying for one minute this will happen mind you, just discussing the model output in the model output discussion thread.

So plenty of weather happening in the next 10 days or so. I posted a week or so back that I reckon the majority of the UK will struggle to see average/above average temps for the first 2 weeks of December and that still very much looks the case, with colder, seasonal weather the form horse for the foreseeable. Many areas at risk of some wet sleet/snow sometime over the next 10 days;

Scotland very much at the focal point of this, with the Scottish hills and mountains possibly seeing some significant falls/accumulations.

In my lifetime, meaningful snowfall before Christmas is rare IMBY, with January and February always the far more favourable months for wintry weather so the pattern we have for the foreseeable is actually one of the more interesting patterns in recent years for December (with some obvious exceptions) and definetly one of the more seasonal IMBY.

I did mention at the beginning of my post that I wasn't as optimistic as some in regards to further, perhaps more significant wintry weather developing over the Xmas period. The Meto outlook and the latest EC ens really not changing my view either;

A recovery in temperatures and a return to a more mobile westerly pattern definetly evident based solely on those in the longer term. I, however, am not going to pretend i know what the longer term outlook holds for us, for now, I'm going to enjoy the seasonal, below average weather for the next 10 days or so with some good air frosts likely in the period and perhaps, yes just maybe, some transient wet snowfall for me even, way down South.

You northerners have even more to hope for and look forward too and hopefully, come January, the more favourable winter month for us southerners IMO, we can all look forward to building snowmen.

EDIT: a few charts have posted in the wrong order, however, I'm sure you get the gist.

Edited December 6, 2014 by AWD

[Summer Sun]

Not to worry, Gavin - other tools at our disposal.

 

Instant weather maps have a great range of parameters. Snow depth accumulated by 192 on the 06 GFS.

 

http://www.instantweathermaps.com/GFS-php/showmap-eurosfc.php?run=2014120606&time=INSTANT&var=SNOD&hour=003

 

 

Thanks for the link, going by that most parts of the UK should at least see a dusting of snow by this time next week

 

Edited December 6, 2014 by Summer Sun

[knocker]

I think the evolution of secondary low on the 06z run quite interesting.

Charts weatherbell.

 

[Paul]

The NetWx-SR model going for some quite sizeable accumulations of snow over the next 48 hours..

 

 

 

[J10]

Latest Ski Forecast with Synoptic Charts from the 06Hz run for each of the next 7 days.

 

https://forum.netweather.tv/blog/189/entry-4851-alps-weather-forecast-6-december-2014/

[Skyraker]

http://en.m.wikipedia.org/wiki/Polar_low

It's sometimes worth remembering that polar lows can develop at very short notice.

The models can fail to predict such features and first warning comes from satellite observations.

[Polar Maritime]

Yes we would need -40c or lower at 500hpa for Polar Lows, With such an unstable airmass who knows..

 

Edited December 6, 2014 by Polar Maritime

[Paul]

This isn't due to go live on the site until tomorrow, but since I just finished the main part of it I thought I'd share in here. 

 

We've now got free viewers for the NetWx-SR and NetWx-MR models (were the NMM's) - our in house hi-res models. The SR is a short range (48 hour) 4km model for the UK, with the MR running out to 7 days at 12km resolution.

 

SR:

http://www.netweather.tv/index.cgi?action=netwx-sr;sess=

 

MR

http://www.netweather.tv/index.cgi?action=netwx-mr;sess=

 

I hope you like them

 

Ps - For Netweather Extra (and Extra Lite) subscribers these pages will automatically take you to the subscriber versions of these charts rather than the free one if you're logged in.

 

Just thought I'd repost this, as it's all live and properly linked up on the site now.