Model Output Discussion - 5th December - 11th December

[ANYWEATHER]

Steve Murr's opinion

Ian Brown's opinion

They both can't be right,

To Be Honest, all I can see is a very active "normal" regime for the time of year. Thursday and Fridays low seems to be intense, affecting the North more picticularly,as per normal, but looking at the broader outlook even the Southern half of the Uk will see some stormy conditions at times. As for Snow ,my thoughts is the Scottish Ski industry will benefit greatly from this set-up, marginal if non existent especially for the South on Low ground given the current synoptics, I expect The Mountains of Wales and the Fells and Peak district to have some white summits for a short time in the next few days. Any Thoughts anyone on perhaps some East Coast flooding with this Storm Coming Up? I will have to have a nose at the tide timetables!! :smilz38:

[Heisenberg]

Ok so forgive my ignorance as im learning as I go. But if the Jet tracks further south, then what does that mean for weather? Does it allow the low to get further south too?

[Duane S.]

I'd left the charts for a few days and having checked them last night and this morning one thing strikes me as significant, the jet stream is heading south. Plenty of scenarios to cold were being offered that involved it riding over the top of us, always plausible to get some cold to our shores that way but for proper cold to come to the south 19 out of 20 times (unless there is a very quiet Atlantic) we need the energy from the jet to be underneath us. Tentative but encouraging signs...

Back to the short term and WOW if you live in Scotland, this is the sort of chart you see the GFS progging up at 240 hr+ on the pub run. That is one serious looking depression for Thursday. The word blizzard often overused but some parts are going to be quite justifed in using the terms I think.

[ANYWEATHER]

Ok so forgive my ignorance as im learning as I go. But if the Jet tracks further south, then what does that mean for weather? Does it allow the low to get further south too?

Hi no worries, basically yes. and it also drags generally colder conditions over the Uk as the Jet moves South of The Uk......

[VillagePlank]

Models certainly still Atlantic dominated, looks like they are hinting at another attempt at a cold zonal shot this time next week, the ECM doesn't quite make it but the GFS does...will remain to be seen.

The big story however is that exceptional low...the NAE and GFS both suggests mean speeds getting into the 60-70kts range, gusts would probably locally go upto 90-100kts and that would cause in places extreme damage. Really can't overstate this storm enough at the moment, it looks dangerous.

Yes, batten down the hatches ....

[snow drift]

Yes, batten down the hatches ....

Places like Ayr, Oban etc could have av. wind speeds of 50 with gusts upto 95/ 100. This looks like it will be around for 6/9hrs. Surprised met have not gone at least orange for their warning on this.

[BLAST FROM THE PAST]

A very stormy and progresive outlook this morning, with a very brief Nwerley on Friday soon replaced by the next Atlantic system. Going forward we see the pressure rise to the South that I was talking about last night in repsonse to the persistant and burgeoning PV.

Ian

Apart from a brief ridge or two, what pressure rises? Are you suggesting the jet is moving north? It seems to my eye that it is moving more south and more conducive to cold zonality as well as the last week just gone.

Edited December 7, 2011 by BLAST FROM THE PAST

[Frosty.]

heavy snow and gales for hills in scotland tonight and tomorrow morning, then milder with rain and storm force winds, then snow again and NW'ly severe gales by tomorrow night, more snow and severe gales in the north on friday, friday night and saturday in scotland but wind speeds decreasing and then less cold but then colder again with more snow in scotland and hills further south, another stormy less cold spell on tuesday but then cold zonal again with more snow for hills and low ground in parts of the north and then maybe a milder interlude followed by more cold zonal.

[chionomaniac]

Ian

Apart from a brief ridge or two, what pressure rises? Are you suggesting the jet is moving north? It seems to my eye that it is moving more south and more conducive to cold zonality as well as the last week just gone.

I have to say that I would have expected the jet stream to take a different path than it has and I am quite encouraged by what I see.

Below I have marked the position where I would have expected the jet stream to take in this type of increased polar vortex set up.

But it hasn't. Now there are a number of issues that will dictate the position of the jet stream, the Atlantic trough and downstream events are just two.

But is it solely these that dictate the position and flow or is it other such as those that were highlighted in research this autumn.

[shedhead]

Ian

Apart from a brief ridge or two, what pressure rises? Are you suggesting the jet is moving north? It seems to my eye that it is moving more south and more conducive to cold zonality as well as the last week just gone.

Tend to agree with you here BFTP... shock, horror!! Things are definately not shaping up as I expected them too, the Jet is farther south and it's angle means we are getting far more Pm air than I envisaged. That's not to say

the vast majority of the populus will see meaningful snow anytime soon and the outlook nationally is far from cold, but a slow inexorable shift south, rather than north is clearly starting to emerge.

Good call.

Edited December 7, 2011 by shedhead

[I remember Atlantic 252]

06Z shows snow for central England for sunday evening, no way will that come off

I would have thought the jet moving south would be bad news for the south? more rain rather than dry

Edited December 7, 2011 by snow? norfolk n chance

[aggy]

Places like Ayr, Oban etc could have av. wind speeds of 50 with gusts upto 95/ 100. This looks like it will be around for 6/9hrs. Surprised met have not gone at least orange for their warning on this.

oh oh thats where i live lol

[Paul White.]

06Z shows snow for central England for sunday evening, no way will that come off

I would have thought the jet moving south would be bad news for the south? more rain rather than dry

Hi could you explain please why you don't think it will come off. It does seem to me that as the jet is slipping further south more and more pm air is being circulated through the uk to bring snow to many areas. That's my take anyway

Paul

[snowking]

06Z shows snow for central England for sunday evening, no way will that come off

I would have thought the jet moving south would be bad news for the south? more rain rather than dry

Yes difficult to expect off the back of just one run - but it's one of the possible surprises that Steve was referring to earlier:

http://hw.nwstatic.co.uk/gfsimages/gfs.20111207/06/108/airpressure.png

http://hw.nwstatic.co.uk/gfsimages/gfs.20111207/06/111/airpressure.png

http://hw.nwstatic.co.uk/gfsimages/gfs.20111207/06/114/airpressure.png

You can see the kink in the isobars passing along the southern half of the UK, indicating some sort of shortwave disturbance. Although given the marginality at the time, it would likely be a rain to something wintry event, though of course above 2-300m or so snow seems more probable. Being overnight would help lower levels to a certain extent too.

Unfortunately I'm sure we all expect it to disappear come the 12z, but just an example of what can happen in such an unstable flow

SK

[Zakos]

06Z shows snow for central England for sunday evening, no way will that come off

I would have thought the jet moving south would be bad news for the south? more rain rather than dry

the chance of a downgrade is a high as its such a marginal event, but it's certainly far from no chance! Speaking in general terms, a southerly jet is better for us in terms of cold and snow. There are exceptions though.

[Frosty.]

I would have thought the jet moving south would be bad news for the south? more rain rather than dry

No it's great news, the southeast has a drought so all rain will be welcomed by the water authorities at least.

[weathe20]

So again after this storm has passed through we are just 'as you were'. Still looks just cool zonal to me with a mess of shortwaves.

[BLAST FROM THE PAST]

I have to say that I would have expected the jet stream to take a different path than it has and I am quite encouraged by what I see.

Below I have marked the position where I would have expected the jet stream to take in this type of increased polar vortex set up.

But it hasn't. Now there are a number of issues that will dictate the position of the jet stream, the Atlantic trough and downstream events are just two.

But is it solely these that dictate the position and flow or is it other such as those that were highlighted in research this autumn.

Hi Ed

Agree with this, solely looking at strong PV + cold stratos that is what I would expect. Yep I would suggest that something else is dictating the positioning of trough/s

BFTP

Tend to agree with you here BFTP... shock, horror!! Things are definately not shaping up as I expected them too, the Jet is farther south and it's angle means we are getting far more Pm air than I envisaged. That's not to say

the vast majority of the populus will see meaningful snow anytime soon and the outlook nationally is far from cold, but a slow inexorable shift south, rather than north is clearly starting to emerge.

Good call.

Agree with the no meaningful snow bit generally speaking and yes cold for some and cool to average for many generally.

Got to say, very interesting weather and pattern at the moment, I think so anyway.

BFTP

Tend to agree with you here BFTP... shock, horror!!

But let this be the last time!!!!!

BFTP

[tinybill]

looking at the models looking a bit wild , will be keeping a eye on the storm surge coing down the north sea

[shedhead]

Hi Ed

Agree with this, solely looking at strong PV + cold stratos that is what I would expect. Yep I would suggest that something else is dictating the positioning of trough/s

BFTP

Agree with the no meaningful snow bit generally speaking and yes cold for some and cool to average for many generally.

Got to say, very interesting weather and pattern at the moment, I think so anyway.

BFTP

But let this be the last time!!!!!

BFTP

Unlikely, as I have absolutely no problem in admitting I get it wrong at times. This is weather after all and no one has all the answers... well apart from you know who of course! That goes without saying...

[SMU]

Just a quick post as regard to Ians reply-

I would say that all the while we get small shortwaves developing off the polar jet they are going to run NW>SE along the jet axis- because the low at ariound 160 looks like taking a more southerly track then it stands to reason that any shortwave will follow a similar southerly track along that axis- (NB as long as the main low is close to the Meridian line or east of it)

Ians pressure rises to the south will be encouraged by shortwaves developing along the Sub tropical jet which is also very active as well, running east out of texas + the southern states & swinging north in the central atlantic-

These systems will develop when the clash along the polar front (because of the strong thermal gradient) & because of their SW>NE trajectory no matter how well orientated SE the Polar jet is any STY systems will not recurve South- they will also have height rises to their east-

the 06z shows exactly this- A main low at 160 getting to the East of Scotland & a few clipper shortwaves running close to the south over the UK before eventually a break in the atlantic ridging allows a system to develop to the SW-

This cycle has been going for the last week & looks like continuing-

Not that exciting unles you live in the North at elevation, however at times can bring periods of wet snow to the Midlands- those in the SE will have nothing really to shout about unless we get very lucky & the winds get more Northerly & the shortwaves stay very shallow not pumping any WAA ahead of them-

As for the SST's around the UK they are going to take a hit this week due to very consistent upwelling.....

S

Edited December 7, 2011 by Steve Murr

[JamesC]

Can't believe no one has mentioned the storm out near the southern tip of Greenland.

http://hw.nwstatic.co.uk/gfsimages/gfs.20111207/06/63/airpressure.png

That is one hell of a low pressure......more powerful than the one hitting Scotland over Thursday night.

[Frosty.]

Apart from some mushy mild weather on the Gfs 06z beyond T+250 hours, it looks like a generally cold zonal pattern for the next 7-10 days at least, occasionally cool zonal but cold at times with some snow for many parts of the uk although most of it on hills and more generally further north so excellent news for the scottish ski industry after a largely snowless november. I am concerned that the run up to christmas could be dominated by mild dross and sw'ly winds but I guess that's the price to pay for this upcoming spell.

Edited December 7, 2011 by Polar_ Low

[WhiteFox]

Agree with the no meaningful snow bit generally speaking and yes cold for some and cool to average for many generally.

Got to say, very interesting weather and pattern at the moment, I think so anyway.

BFTP

I concur. I think people need to be clear that when zonality is mentioned it does not simply mean a SW airmass, but can best West or North Westerly. To me, zonality implies a pattern of generally rising temperatures from south to north at a point in time; exactly what we see right now. A strong jet delivers far more interest than blocking close to the UK (if it is too far East or South); whilst I do not enjoy damaging storms, I do relish the prospect of generally unsettled weather, something which we have seen far too little down in the South this year so far. It's much more interesting to see developing shortwaves and Atlantic storms than seeing high pressure over Europe causing systems to stall over the Atlantic.

The one question I have is how long it will be before the Siberian high starts to sneak westwards and we start seeing the endless posts on whether it will reach our shores? Usually it starts to show its hand around the end of January into February; towards the end of winter last year it kept pretending to drift west without ever coming close.

In the current setup, if the jet shifts farther south, there is the potential for height rises to the North East, but these setups are the equivalent of a 1000 piece jigsaw puzzle, and one piece is often missing having been hoovered up by a reinvigorated jetstream. Setups such as that we saw last year are safer, but we will see...

[Weathizard]

I know its Fi but most of the gfs ensembles seem to take a dive right at the end of the run, I'm no expert on stratospheric conditions ect so I was wondering how likely does colder weather towards the final third of december look according to other more complicated stuff