Model Output Discussion - 14th Jan 12z Onwards

[Great Plum]

Early days but the 06z shows an increase in -10 uppers into Scotland...

http://www.wetterzentrale.de/pics/Rtavn962.gif

[SMU]

The overnight trending continues in the midterm 6z

At T96 the north sea low is further south elongating the northerly flow further - im sure I highlighted yesterday with the use of ptb 7 the chances of lower 850 s manifesting if this was to happen.

Well the op now has a pool of-10c air into scotland at 96 - it will continue to drift south.

The slider appears to be further SW as well.

The uptick in confidence on track & snow locale continues.

S

[Nick F]

That's encouraging. I think the slight worry around this morning is the raising of the 850s in the output this morning compared with last night. In my experience you need -7 at a bare minimum for lowland snow and -8 preferably. People says don't obsess over the 850s, but I've seen rain at -6C too many times to believe it.

 

T850s not always a reliable guide for forecasting snow/rain. But is a decent guide for Cold Air Advection and depth of cold.

 

If cold air is in place already at the surface with dew points at or below 0C - with little or no mixing, then T850s will be irrelevant (as long as below 0C). Even if T850s are only a couple of degrees below 0C, we can still see snow, if the layers below 850mb are cold enough and the dew points low enough.

 

Yes, it can rain with T850s as low as -6C, but, this is mainly due to the airmass below 850mb being mixed out or modified by 'warmer; air, such as long sea tracks over Atlantic.

 

I tend to rely more on partial thicknesses (1000-850mb) which takes in the lowest layer of the airmass and dew points for snow potential, rather than 850mb which is just one level at around 1000 odd metres up.

Edited January 15, 2015 by Nick F

[IDO]

Tuesday's snow potential as a front crosses is looking a Birmingham north event: 

 

Early days and time for changes but borderline uppers show how fragile this setup is for the snow starved areas.

[mulzy]

Am i hope-casting, but the 6z pushes the front way too quickly across the country  - I'm suggesting there is an eastern bias...

 

Dewpoints and uppers wrong side of marginal for most of the Midlands south...

 

[frosty ground]

Tuesday's snow potential as a front crosses is looking a Birmingham north event: gfs-2-126.png

 

Early days and time for changes but borderline uppers show how fragile this setup is for the snow starved areas.

With a small mild sector sneaking down the western flank,

The 0z had the same issue, but was on the milder side of the overall average for that time frame but not an outlier.........

[Polar Maritime]

Much better Heights over N/E Greenland on the 6z.

 

[SMU]

Again ignoring the slight eastward bias & energy seperation issues that the GFS generally has - the background signal in the model out to 144 indicated cold or very cold out to at least day 12 ( 288 )

S

[Captain Shortwave]

The GFS shows a real mix of rain, sleet and snow with that front for the south, probably a transition to rain, followed by a transition to snow again as the warm sector moves through.

Beyond that we do see the low drop to the south of us.

Heavy (perhaps thundery) showers into southern counties pushing in from the English channel, these also affect the south east, though precipitation looks more rain and hail again. Lets see how quick and effective any easterly is that follows. Eastern Scotland does show snow showers though at this point. It does start to turn much colder by day 7.

Edited January 15, 2015 by Captain shortwave

[chionomaniac]

Again ignoring the slight eastward bias & energy seperation issues that the GFS generally has - the background signal in the model out to 144 indicated cold or very cold out to at least day 12 ( 288 )

S

Steve, this is the new GFS so we need to reset any bias thoughts !

 

Though the trend is for slightly reinforced scandi blocking by day 7 so not bad - more in line with cumulative anomaly.

Edited January 15, 2015 by chionomaniac

[bluearmy]

Yes -  and 6-10 day cumulative GFS anomalies good

 

 

get_orig_img.gif

 

11-15 days do show an increase in the Azores high - but always with that NW/SE angulation to keep us below average - so not bad because pattern could repeat.

 

get_orig_img.gif

Ed - we're not beyond the possibility that the Siberian vortex could head towards Scandi due to the e greeny ridging and Alaskan ridging preventing the split vortices rejoining. certainly hasn't reduced in possibility over the past run or two.

[TEITS]

So from trumpets blowing and MetO/BBC saying coldest spell for 2 years to a 3-5 day marginal colder period?  Really is a funny thread this

 

 

BFTP

Lets be clear I did not say a 3-5 day marginal colder period is likely but remains a possibility as does a prolonged, very cold spell. The fact is we don't know how it will pan out with regards to an E,ly and neither do the models because lets be honest they are useless with the likely pattern coming up.

 

I am just trying to keep members feet on the ground to avoid some being disappointed.

 

Difference between 0Z/06Z highlights my point.

[A.J]

Tuesday's snow potential as a front crosses is looking a Birmingham north event: gfs-2-126.png

 

Early days and time for changes but borderline uppers show how fragile this setup is for the snow starved areas.

IDO, that's a little disingenuous......as mentioned ad nauseum yesterday, posting ppn type charts at future timescales like T126 and then commenting on where the 'snow line' will be is like playing a game of 'pin the tail on the donkey' only the tail and the donkey are missing......

[Ali1977]

The Easterly is forming well at day 7, however the heights towards Scandy could do with being a few hundred miles North of this if it's longevity of the cold and East winds your after...

[chionomaniac]

Ed - we're not beyond the possibility that the Siberian vortex could head towards Scandi due to the e greeny ridging and Alaskan ridging preventing the split vortices rejoining. certainly hasn't reduced in possibility over the past run or two.

That possibility hasn't escaped me - in fact it is more than that- depends on how the EPO ridge makes inroads into the Arctic- currently models suggesting slight lowering of heights to our NW days 11-15 - but this could be just as easy setting up for the reload you mention by month's end. Would like another little nudge from the MJO and strat though.

Edited January 15, 2015 by chionomaniac

[SMU]

Steve, this is the new GFS so we need to reset any bias thoughts !

 

Though the trend is for slightly reinforced scandi blocking by day 7 so not bad - more in line with cumulative anomaly.

Well thus far its exhibiting the same typical trending to the euros ( mainly ukmo )

Which is

* reduced eastward progression over atlantic features when there are scandi heights present -

* depleted 850 temps from northerly / easterly flows as the real time event draws closer.

My track & trajectory forecast at this stage wouldnt have the front reaching EA or lincs At the moment GFS has it in the north sea..... (120)

S

[West is Best]

Much better 06z GFS compared to the 0z (I know I know) for the position of the slider low. Because it's further west and south-west to T150 the uppers are correspondingly much lower for a larger proportion of the country: the Cotswolds northwards but taking in Norfolk and Lincolnshire.

 

For lots of snow situations in Britain it's always going to be slightly marginal. These are usually the best snowfall setups of all though, when they come off. It's a cliche but you can't make an omelette without breaking some eggs so if we want to get snow here, we have to go through this dicing. This 6z looks good though. Very good.

Edited January 15, 2015 by West is Best

[Polar Maritime]

The Easterly Flow looks a little cleaner. Some bitter -10 uppers to pull in from the N/E..

 

Edited January 15, 2015 by Polar Maritime

[West is Best]

IDO, that's a little disingenuous......as mentioned ad nauseum yesterday, posting ppn type charts at future timescales like T126 and then commenting on where the 'snow line' will be is like playing a game of 'pin the tail on the donkey' only the tail and the donkey are missing......

 

Haha, best post I've seen for a long time. Take heed everyone.

[chionomaniac]

Well thus far its exhibiting the same typical trending to the euros ( mainly ukmo )

Which is

* reduced eastward progression over atlantic features when there are scandi heights present -

* depleted 850 temps from northerly / easterly flows as the real time event draws closer.

My track & trajectory forecast at this stage wouldnt have the front reaching EA or lincs At the moment GFS has it in the north sea..... (120)

S

I remember quite clearly a slider event two years ago when the models played out the same and only in the last 24-36 hours did the models all converge on the warm zone being as large as the GFS originally suggested so I am wary. What followed on was notable though.

[IDO]

IDO, that's a little disingenuous......as mentioned ad nauseum yesterday, posting ppn type charts at future timescales like T126 and then commenting on where the 'snow line' will be is like playing a game of 'pin the tail on the donkey' only the tail and the donkey are missing......

 

Just commentating on that chart at that time. This ties in with the 0z take and is a possibility. I did say that at the time that it was just one run. Surely we are just commentating on the current output and I don't see a problem in that, otherwise we wouldn't have much to say. Though I suspect if I said it showed a snow fest for the whole UK you would not have brought this up?

 

Showers battering the east coast around D8+:  

Edited January 15, 2015 by i'm dreaming of...

[Nick F]

That's a seriously frigid cold pool dropping south across NE Scandinavia and NW Russia, if only we could tap into that. Well, if we could get the block to the north and NE to orientate in the right way ... i.e. not extending too far into NE Europe and Russia then sinking south.

 

With regards to the slider low early next week, it starts off as a deep low coming out of NE Canada on Sunday, just hope it fills quickly before it slides SE towards the UK as, I think Nick Sussex mentioned, we don't want it too deep or it'll drag too much mild air north ahead of it.

[Ali1977]

This set up would be better for those in the East and SE, Thames streamers and showers penetrating East to West would all be of snow, and probably make it all the way towards Wales and the far SW.

[Stormyking]

The GFS 06z looks better to me than the 12z, with a stronger blocked over Scandi, and a stronger or longer looking cold easterly, which to me looks like it would bring snow showers (Thames Streamer style) to East coast, South East and the South (including coasts), not doom and gloom this morning i don't think, still some very decent signs indeed!

 

 

Edited January 15, 2015 by Stormyking

[Neilsouth]

That's encouraging. I think the slight worry around this morning is the raising of the 850s in the output this morning compared with last night. In my experience you need -7 at a bare minimum for lowland snow and -8 preferably. People says don't obsess over the 850s, but I've seen rain at -6C too many times to believe it.

 

Which is what I said would happen, it happens time and time again! Why I don't know

 

This is looking like another mid/northern affair, I feel for you southerners