Model Output Discussion - Stormy Period Inbound...

[IDO]

Hi IDO,

Right I'm with you but I don't see any potential for a ridge within the 10 day time-frame within GFS, only more prominent warm sectors which is why ECM is the better run IMO. GFS just delays the transfer and so has low pressure forming further West causing more of SW/NE gradient to the flow and bringing the Azores high more into play.

 

Yes unfortunately as you say the most likely scenario is a weak pressure rise in the Atlantic. Even with better phasing on the GFS around D8-10 there is still too much energy coming from the Canadian vortex to make the Atlantic ridge anything more than a brief affair. However it marks the pattern change, with draining of that vortex, so further height rises *could* be more successful. 

[Captain Shortwave]

Hence my post was for many,and backed up by the 850s which would not relate to above average for many Midlands northward.

Surely people must understand that in summer London is several degrees warmer but in winter the opposite.As shown here for e.g.  http://modeles.meteociel.fr/modeles/gens/run/gensnh-0-4-168.png?6

Actually even more northern areas see near or above normal temperatures for the next week or so. 

For example Glasgow - 10C, 6C, 8C, 6C, 6C, 8C, 5C with few if any night time frosts. (BBC forecasts)

Just because the 850s are cold, in a maritime based flow the temperatures are greatly modified so even a -6/-7C north westerly can often bring temperatures in the range of 5-7C which on the face of it isn't that cold. Add to that the days where a milder source of air is shown and the above average weekly anomaly is pretty much clear cut. 

Edited January 7, 2015 by Captain shortwave

[Mucka]

Yes unfortunately as you say the most likely scenario is a weak pressure rise in the Atlantic. Even with better phasing on the GFS around D8-10 there is still too much energy coming from the Canadian vortex to make the Atlantic ridge anything more than a brief affair. However it marks the pattern change, with draining of that vortex, so further height rises *could* be more successful. 

 

Yes but that is day 10 (+) and ECM is very much in line with potential ridge then so better the PV remain organised as shifts IMO so that any secondary lows form further East and track further South limiting warm sectors until then.

We see that the 06z runs were a little better in this regard than the 00z (GFS) and hence we end up with more snow possibilities - not quite as good as ECM/UKMO but getting there compared to the 00z.

Of course this is only relevant to transient snow possibilities in a typically zonal flow out to day 10 but I still think the ECM way of doing business would hold more promise down the line as well as it is likely to leave less residual PV energy around West of Greenland as shown in your anomaly maps.

 

Thanks for the explanation.

Edited January 7, 2015 by Mucka

[nick sussex]

If we just take the starting point of whats likely to verify versus whats uncertain then we're really only left with a solid signal to displace the Azores high further west at T240hrs.

 

That in itself is likely to lead to some drop in temperatures however the amplitude of the pattern upstream is uncertain which will dictate the level of that drop.

 

Because of the mixed signal re the MJO then theres a variety of solutions on offer, the Azores high displacement looks like a longer term trend if you're looking at the ECM ensembles but whether that ridges further nw/n or whether we get the topple ridge towards Scandi are all uncertain.

 

If the MJO actually manages to go into phase 7 and 8 then that would of course be a background signal that would signify a better chance of some deeper cold.

 

At this point I'd rule nothing in or out, it might just be some colder PM shots with a touch more potency than normal or a more direct Arctic sourced flow.

[MR EXTREMES]

To my eyes the models suggest colder milder spells and this has been the theme across all models for the time being.

2inches of snow in the south if it happens bank and a smile on my face to be honest one snow shower would brighten up my winter.

There's a lot of enriched cold from our nw and Scotland northern England look likely to have some fantastic snowfall very wintry all things considered.

And there's no question most likely a relaxation of the zonal train towards months end and in my life time I've seen some classic winter weather here on the costa del south coast in feb in fact other than 2009/10 most snowfall has been back end of winter late jan and feb here in the south.

[winterof79]

Actually even more northern areas see near or above normal temperatures for the next week or so. 

For example Glasgow - 10C, 6C, 8C, 6C, 6C, 8C, 5C with few if any night time frosts. (BBC forecasts)

Just because the 850s are cold, in a maritime based flow the temperatures are greatly modified so even a -6/-7C north westerly can often bring temperatures in the range of 5-7C which on the face of it isn't that cold. Add to that the days where a milder source of air is shown and the above average weekly anomaly is pretty much clear cut. 

Last comment on this.We do not all live in city centers and frosts are predominantly harsher in rural areas of which vastly exceeds city center areas.The METO medium range forecast has wintry showers to low levels in the North and above average temps would not fit with this which is what Knocker was showing.BBC 5 day forecasts are city based and not reliable in my mind.I usually stick with 850s and find they relate to how cold it feels.Here is the GFS which generally over cooks temps

http://www.wetterzentrale.de/pics/Rtavn10217.gif

 

 http://www.wetterzentrale.de/pics/Rtavn16817.gif

http://www.wetterzentrale.de/pics/Rtavn19217.gif

 it could be wrong too i appreciate.

[Captain Shortwave]

Last comment on this.We do not all live in city centers and frosts are predominantly harsher in rural areas of which vastly exceeds city center areas.The METO medium range forecast has wintry showers to low levels in the North and above average temps would not fit with this which is what Knocker was showing.BBC 5 day forecasts are city based and not reliable in my mind.I usually stick with 850s and find they relate to how cold it feels.Here is the GFS which generally over cooks temps

http://www.wetterzentrale.de/pics/Rtavn10217.gif

 

 http://www.wetterzentrale.de/pics/Rtavn16817.gif

http://www.wetterzentrale.de/pics/Rtavn19217.gif

 it could be wrong too i appreciate.

I checked other stations in Scotland, same story(urban or rural). 850s and surface temperatures do not always correlate, especially so in winter. A continental flow will be much colder than a maritime one at this time of year. Hence in an easterly we may just need 850s to be just below 0C for precipitation to turn to snow, whilst in a westerly you need -7/8C for snow to fall to low levels.

Knocker's 8 day anomaly chart looks pretty good to me, the coldest weather being in areas where the cold can hold on more effectively (For example the Highlands). Rest of the UK looks above normal. You also have to remember that the anomalies are for an average including day and night, given the strength of the winds even the colder spells will struggle to bring a widespread frost.

Anyway this feels like groundhog day as the same discussions were used around this time last month. The CET figure at mid-month will pretty much answer this discussion (currently running at 1.9C above average to this point).

Edited January 7, 2015 by Captain shortwave

[frosty ground]

Actually even more northern areas see near or above normal temperatures for the next week or so. 

For example Glasgow - 10C, 6C, 8C, 6C, 6C, 8C, 5C with few if any night time frosts. (BBC forecasts)

Just because the 850s are cold, in a maritime based flow the temperatures are greatly modified so even a -6/-7C north westerly can often bring temperatures in the range of 5-7C which on the face of it isn't that cold. Add to that the days where a milder source of air is shown and the above average weekly anomaly is pretty much clear cut. 

Is Glasgow the best place to use thou for this set up?

[IDO]

Last comment on this.We do not all live in city centers and frosts are predominantly harsher in rural areas of which vastly exceeds city center areas.The METO medium range forecast has wintry showers to low levels in the North and above average temps would not fit with this which is what Knocker was showing.BBC 5 day forecasts are city based and not reliable in my mind.I usually stick with 850s and find they relate to how cold it feels.Here is the GFS which generally over cooks temps

http://www.wetterzentrale.de/pics/Rtavn10217.gif

 

 http://www.wetterzentrale.de/pics/Rtavn16817.gif

http://www.wetterzentrale.de/pics/Rtavn19217.gif

 it could be wrong too i appreciate.

 

Hi Winter. Not saying you are wrong, in fact quite the opposite. Anyone in rural areas especially with a good ASL will be experiencing a better seasonal feel than us urbanites. However 82% (*) of the UK population reside within an urban environment (source) so I believe that when we mention temps it is fairer and more helpful for us to use Cities. Also that is why I use the CET as it is between the obviously milder south and colder north.

 

Anyway a cooling down is evident from D10 for all and hopefully that may develop into something for the south.

 

(*) London's population for instance is 60% (3m) higher than Yorkshire and Humberside combined.

Edited January 7, 2015 by i'm dreaming of...

[LomondSnowstorm]

It's very much dependent on exact location as to whether you'd get better results with a similar setup, but for eastern Scotland temperatures are usually a touch lower in a westerly compared to the same uppers in an easterly because coastal modification is far less of a factor. The main issue with westerlies is the wind speed is usually higher, which causes a lot of mixing. For Saturday into Sunday this is the main reason we struggle to get temperatures widely below about 1-2C for most of Saturday evening. When the winds on Saturday night do eventually die down temperatures on the GFS P (which I've found to be pretty reliable so far) get down to levels which would allow for low level snow:

However, while temperatures before this point are likely to stop lying snow the uppers mean that we're still likely to see showers falling as sleet or snow even with temperatures of 3-4C. I doubt we'll see enough to give more than a dusting below 200m as temperatures rise again through the day on Sunday, but higher up should certainly see some decent accumulations.

More promising at the moment is Tuesday, when wind speeds look relatively weak (10-15mph sustained for most):

Uppers sustained generally below -6C (although with a potential warmer/windier period Tuesday evening):

 

As a result temperatures could end up much lower, and if it comes off as modelled by the GFS P you'd expect lying snow down to low levels: 

 

So yes, it is tough to get particularly cold temperatures even for Scotland in a strong westerly, but in a slacker flow you can definitely get conditions cold enough for low level snowfalls and even air frosts away from the immediate west coast. Just some of the setups that have delivered at least some lying snow to low levels:

     

All pretty marginal mind you and there's probably more misses than hits when the uppers downgrade or the wind speeds upgrade, but -6C uppers can be good enough in the right setup for westerly/northwesterly snow.

[meathead]

So what happened to all the positive chat that was going on in here last night? Have the models turned mild again?

[knocker]

So what happened to all the positive chat that was going on in here last night? Have the models turned mild again?

 

I think what is required is something akin to a 192hour temp anomaly so you get an average positive or negative index. I can see it being quite useful.

Edited January 7, 2015 by knocker

[Mucka]

So what happened to all the positive chat that was going on in here last night? Have the models turned mild again?

 

Nope

 

[Nick F]

However, while temperatures before this point are likely to stop lying snow the uppers mean that we're still likely to see showers falling as sleet or snow even with temperatures of 3-4C. I doubt we'll see enough to give more than a dusting below 200m as temperatures rise again through the day on Sunday, but higher up should certainly see some decent accumulations.

More promising at the moment is Tuesday, when wind speeds look relatively weak (10-15mph sustained for most):

All pretty marginal mind you and there's probably more misses than hits when the uppers downgrade or the wind speeds upgrade, but -6C uppers can be good enough in the right setup for westerly/northwesterly snow.

 

Other key parameters that signal whether snow will fall to lower levels are dew point (ideally needs to be 0C or below) and partial thickness between 1000mb and 850mb, which takes in the surface airmass (boundary layer) and is probably a better tool than  the 850mb temp (which doesn't always reflect surface conditions) of whether snow will fall at lower levels in long-fetch maritime flows that are well-modified in the boundary layer from the Atlantic SSTs.

 

 

The dew point progged by 12z GFS fits the bill for most of the UK by Saturday evening. Partial thickness ideally needs to be below 129 gpdm for snow. Obviously these parameters may change nearer the time, though remarkably GFS has remained consistent with the timing and depth of cold.

 

Temps may looks high, as you suggest, from GFS progs, but will drop during the showers as precip and convective downdrafts cool the air. Showers along coasts more likely of rain/sleet given the warming from SSTs.

 

As some others, I think may have mentioned, although GFS may show parts of Scotland and just west facing coasts elsewhere seeing the sleet/snow showers, the model doesn't show the Cheshire Gap shower streamer that often occurs in these northwesterly flows and can penetrate well inland, even as far as London/Home counties occasionally.

 

A brief blink and you'll miss it window for wintry potential over the weekend, basically Sat afternoon/early evening through Sun morning before it warms up too much from the west Sun afternoon.

Edited January 7, 2015 by Nick F

[Eugene]

Nope

 

 

You should know Mucka only the deepest sourced siberian blast matters to many, PM shots don't count. :smiliz19:

[Stormyking]

Still a rather unsettled period indeed on the latest 12z, and into next week aswell again, it doesn't actually look particularly mild either, with some snow in some parts of the UK, especially further North! 

[IDO]

Poor GFS Op after D10, very flat with more TM than the 06z: 

 

 

 

 

[Captain Shortwave]

Day 7

GFS (P)

GFS OP

Not a trend we want to see to be honest, it does look like we will see the polar vortex leave a gap in the Atlantic sector which will allow heights to ease northwards, just don't create the gap around this time, the approaching low is then forced to track north east which brings the Azores high back into Europe again. No surprise that GFS low resolution is poor and the GFS (P) shows no cold interests to day 9 so far.

Edited January 7, 2015 by Captain shortwave

[Mucka]

You should know Mucka only the deepest sourced siberian blast matters to many, PM shots don't count. :smiliz19:

 

LOL yeah and I'm one of 'em!

Sometimes though we have to make the most of what we have and if we can squeeze some snow out of this zonal phase then it might just get those with thinning patience through till something better shows.

 

(Just keep them away from GFS 12z op  ) 

 

UKMO somewhat better than GFS for dragging in some colder upper air in run up to mid month.

 

Edited January 7, 2015 by Mucka

[Nick F]

Long long way off, but like yesterday's 18z, todays 00z and 06z GFS the 12z has a depression come out of NE Canada and deepens the low further mid-Altantic, before sweeping it NE as intense depression between Scotland and Iceland by mid- next week. Amazing it's consistency with this low at that range.

 

06z had back edge snow for all UK as sharp cold front moves SE:

 

12z has back edge snow just for the north as the front moves SE:

 

But 12z quite snowy for Scotland Weds night!

 

This is not a forecast of course ... at this range these charts are Eye Candy only!

 

But shows we may get some proper cold zonality later next week and perhaps not just for the north. Cold zonality across northern Britain through much of next week on 12z, with every day having snow potential across parts of Scotland, particularly, but not exclusively, the central belt north.

Edited January 7, 2015 by Nick F

[geordiekev]

I think what is required is something akin to a 192hour temp anomaly so you get an average positive or negative index. I can see it being quite useful.

 

The problem I find with anomaly charts and mean charts is that if you have a mean chart of say 365 days then it would indicate that we have no Winters or Summers which would be untrue. So IMO in the extreme seasons such as Winter and Summer long term mean charts do not represent the extremities that often occur within an average pattern, so each day needs to be taken at face value if you are looking for extremities which many are, as most should know that longer spells of Sunshine or Snow are rare in the UK and what makes our weather quite unique.

[Frosty.]

GFS 12z op run, as with the 6z, looks cold and wintry for much of next week, especially in the north west. Some parts of the UK will see a covering, perhaps significant falls of snow next week once wet and windy weather clears SE early next week.

[Biggin]

The Beeb are making noises re the 2 LPs forcast  for Fri and the weekend, particularly Scotland, do the models support their worries ??

[IDO]

At least the GFS P tries for something synoptically more useful in FI, but again it is way out to D15 before we see some potential:

 

 

 

That also keeps with the D10 toppler scenario so is more in keeping with the recent output. Maybe the op was an outlier (hopefully). So the first wave of heights now unlikely to be anything but transient ridging. There are reloads as the PV loses its energy to our NW so maybe eventually or maybe not. Certainly a hard road to cold this January...

 

 

[mulzy]

Tease in deep FI on the GFSP.

 

 

However as far as the reliable/medium term is concerned, more of the same - zonal (predominantly mild and stormy at times).  GFS Op can be summed up with the much used term on here "flat as a pancake".  Still waiting for signs of a pattern change...

Edited January 7, 2015 by mulzy