Model Output Discussion - 23rd Jan - 12z onwards

[Weather-history]

Lots of ramping this morning...but caution ! Lots of blues and purples shown however not a particularly cold source. No big freeze as yet.

Actually what is the situation regarding with thicknesses when you have very cold 500hpa ie deep blues and purples, aloft?

[IDO]

The three D10 means look very similar for that range:

 

  

 

Looks like the Atlantic block breaks around D11 for both the GEFS and GEM ensembles:

 

 

 

ECM is less progressive, that is taking the D10 mean at face value, but sometimes its suite follows the op blindly so I would have to see another run or two before that mean would be persuasive. 

 

Anyway good signs for the north at least for potential snow from later next week and even for the south a better chance than the winter so far.

[SMU]

Actually what is the situation regarding with thicknesses when you have very cold 500hpa ie deep blues and purples, aloft?

 

The thickness is related to the pressure contours so whilst the heights are lower ( ECM + GFS look around 512 ) once you calculate the fact thats along the 985 MB line- tthickness usually evens out to around the 524-528 line as we would expect.

 

Not much support for the ECM operational along the MEAN with a flatter pattern @ 240 over Greenland- so I suspect that will be the order of play- however not conclusive at this stage-

S

Edited January 24, 2015 by Steve Murr

[Eugene]

Lots of ramping this morning...but caution ! Lots of blues and purples shown however not a particularly cold source. No big freeze as yet.

 

There will be no big freeze this winter, the depth of cold needed over central europe is not there, still plenty of interest for cold weather fans, there are many of us that enjoy winter and any kind of cold weather not just the very rare and very elusive "Big Freeze".

[Liam J]

I remain cautious of the charts at this range as we have been let down many times before! Hopefully they'll continue to show the same even poss upgrade further into next week!  Am I right in thinking that given the very low thickness values the models are showing that the uppers wouldn't need to be desperately low for snowfall to occur? Haven't looked at the dew points yet but I imagine they will be fine from an Arctic source. 

[offerman]

I would say the charts have already downgraded somewhat compared to yesterday , some which I cautioned would most likely happen. The Azores high has been the driver this winter.

[SnOwFeSt]

These sort of set ups often look awesome but fail to live up to expectations as there is too much mild/ maritime air rotating around it.

Sure there will be a chance of snow, like we have seen in the past week, but looks like another wet snow event which quickly turns to slush.

The gfs shows the vortex spilling over the Atlantic high before any decent cold gets established. Based on the pattern so far this winter, I would not be surprised if it turned out something like this. The erm is more promising, with decent height rises promising something more prolonged, but I shant hold my breath until it's t+48!

I'd rather have nothing than that sort of snow!

[Weathizard]

I would say the charts have already downgraded somewhat compared to yesterday , some which I cautioned would most likely happen. The Azores high has been the driver this winter.

Nonsense. Could you please tell me exactly how they have downgraded?

If anything I would say the charts are better today

* we are a day closer to the 'cold spell'

* the general pattern looks as though it COULD be conducive towards not just a 'toppler' (more than this time yesterday)

*Thickness, Uppers & other factors still good for snow.

Let's get the cold sypnotics into a reliable timeframe (120/144) then look further down the line.

Edited January 24, 2015 by Weathizard

[mushymanrob]

There will be no big freeze this winter, the depth of cold needed over central europe is not there, still plenty of interest for cold weather fans, there are many of us that enjoy winter and any kind of cold weather not just the very rare and very elusive "Big Freeze".

 

you make a salient point actually. with no deep cold pool to tap into over europe then its unlikely we will get a big freeze.

but

was there a depth of cold over europe 2 years ago that delivered us a bloody awful march?

[sunnijim]

There will be no big freeze this winter, the depth of cold needed over central europe is not there, still plenty of interest for cold weather fans, there are many of us that enjoy winter and any kind of cold weather not just the very rare and very elusive "Big Freeze".

I'm not sure i follow your rational here,agreed there is no continental freeze at the moment but (A) we are not relying on a freeze from that direction,as a Northerly would bypass this and feed arctic air in as models seem to be firming up on and (B) the freezing temperatures would flood the continent from France up to the Russian steps later next week too,so a later East or Northeaterly would import that cold to our shores. Edited January 24, 2015 by sunnijim

[Snow Grain]

Another day of excellent charts coming up no doubt. All is looking great this morning but a word of caution. We have all been here many times before! I expect that when we get in closer range, everything will be shunted further east, leaving us under high pressure. So another non event on the horizon I feel.

[knocker]

The thickness is related to the pressure contours so whilst the heights are lower ( ECM + GFS look around 512 ) once you calculate the fact thats along the 985 MB line- tthickness usually evens out to around the 524-528 line as we would expect.

 

Not much support for the ECM operational along the MEAN with a flatter pattern @ 240 over Greenland- so I suspect that will be the order of play- however not conclusive at this stage-

S

 

I'm afraid I don't really understand that Steve,

 

The 500mb height is a function of temperature and is calculated from MSL to 500mb. The 1000-500mb thickness is also a function of temperature but calculated from 1000mb. Thus the 500mb height will be greater or less than the thickness depending on whether the 1000mb height is negative or positive which is dependent on the surface pressure. Less than a thousand negative and more than a thousand positive. The advantage of the thicknesses is that it gives the temp structure of individual layers such as 1000-850. 1000-700 etc.

 

You can use either to denote warm or cold air providing you don't mix them up.

[picog]

BA , I think the term once bitten five times shy !!!! Lol.

I think BA might be having a mini ramp.

Ensembles for the whole county look like delivering a 5+ day cold spell.

[polarwind]

I would say the charts have already downgraded somewhat compared to yesterday , some which I cautioned would most likely happen. The Azores high has been the driver this winter.

Yes, but it's a driver every winter, although with different outcomes. This winter, it's tight and strong: It isn't big and flabby, as was the norm over the previous two or so decades, with accompanying mild SW winds in these parts. 

[winterof79]

I remain cautious of the charts at this range as we have been let down many times before! Hopefully they'll continue to show the same even poss upgrade further into next week!  Am I right in thinking that given the very low thickness values the models are showing that the uppers wouldn't need to be desperately low for snowfall to occur? Haven't looked at the dew points yet but I imagine they will be fine from an Arctic source. 

Not bad for short range too

 

850s for same time

 

 

 

Thats before we get a cold feed.

[TonyH]

you make a salient point actually. with no deep cold pool to tap into over europe then its unlikely we will get a big freeze.

but

was there a depth of cold over europe 2 years ago that delivered us a bloody awful march?

Yes it developed to our NE early March

In fact it had been there over Europe at times earlier in the Winter too:

Edited January 24, 2015 by TonyH

[Nouska]

Actually what is the situation regarding with thicknesses when you have very cold 500hpa ie deep blues and purples, aloft?

 

These IMO four panel charts illustrate this well as they show both values - the usual coloured contour lines and also the thickness. This is a quick comparison of ECM (left) and GFS (right). As usual, these are cached so need to change time stamps after all runs and change the hour for different steps.

 

http://brunnur.vedur.is/kort/ecm0125/2015/01/24/00/ecm0125_nat_gsm025_4panel2_2015012400_006.png

 

[polarwind]

There will be no big freeze this winter, the depth of cold needed over central europe is not there, still plenty of interest for cold weather fans, there are many of us that enjoy winter and any kind of cold weather not just the very rare and very elusive "Big Freeze".

Your claim is probably based on recent observations over the last couple of decades or so. Real cold can come from the north too - look at the charts from the 60's and the very strong and frequent ridging northwards into Greenland which resulted in very cold northerly outbreaks with associated polar lows. I can't recall a recent proper polar low - but I've not been really looking.

[winterof79]

The flow come weekend from a cold source make no mistake

 

[nick sussex]

Morning all

 

Not too much drama today thankfully with good support for a colder spell, the UKMO probably the pick of the bunch at T144hrs in terms of depth of cold.

 

In terms of the upstream pattern that's condusive to high pressure developing to the nw, not a proper Greenland block however, more centred further se.

 

The crucial time period is between T168 and T192hrs, a renewed surge of amplification is expected to occur to the eastern USA troughing, its at this point that we need to see the low upstream eject se'wards and its behind this that high pressure can establish to the nw.

 

The degree of amplification upstream and how far west that PV chunk can be pulled  at that time will determine where the high sets up.

 

The GFS 06hrs run has better WAA into Greenland related to a more amplified upstream low ejecting out of the ne USA.

 

A lovely run so far!

Edited January 24, 2015 by nick sussex

[Thinon]

Certainly a changeable spell of weather on the horizon, but I'm not convinced of any significant cold spell. A little bit hopeful particularly at this range.

[winterof79]

Morning all

 

Not too much drama today thankfully with good support for a colder spell, the UKMO probably the pick of the bunch at T144hrs in terms of depth of cold.

 

In terms of the upstream pattern that's condusive to high pressure developing to the nw, not a proper Greenland block however, more centred further se.

 

The crucial time period is between T168 and T192hrs, a renewed surge of amplification is expected to occur to the eastern USA troughing, its at this point that we need to see the low upstream eject se'wards and its behind this that high pressure can establish to the nw.

 

The degree of amplification upstream and how far west that PV chunk can be pulled  at that time will determine where the high sets up.

As they used to say on Mr Ben.........and then as if by magic

Edited January 24, 2015 by winterof79

[kev238]

Modelling blasts from the north / North west seems much easier for the models than from East/ North east.

Therefore there should be a high degree of confidence of a cold spell from the north . This will most likely be good for the north although in the south the weather could be sparkling with sunshine but largely dry ( in the main)

If these charts verify then the winter could creep into the good category for some northern part though they are unlikely to end the lying snow drought in the parts of the country that have not seen lying snow In the past 22 months .

[nick sussex]

As they used to say on Mr Ben.........and the as if by magic

Lol! next step is to cut off the high, the GFS now developing a shortwave at the base of the upstream troughing at T198hrs.

Edited January 24, 2015 by nick sussex

[winterof79]

If anyone had showed me this chart at the beginning of winter for the start of Feb i would have snogged them...

 

Just as we enter the usually quieter Atlantic period we have cut off the trough our side.Slack easterly feed off the snow making North sea.

Edited January 24, 2015 by winterof79