Model Output Discussion - 05/01/2016 18z onwards

[dragonfalls]

Hi is a under cut good for us is it cold pushing warm air away thanks still learning?

[Nick L]

Just now, northwestsnow said:

it pretty much is on the bottom set nickster, updated one

Admittedly I was looking at the wrong chart there. But still, not without some support. However, it's encouraging nonetheless. 

[Frosty.]

Looking at the Ecm 12z ensemble mean shows the cold spell digging in for longer and no push from the Atlantic, it's looking like we could be in for a longer cold spell which could evolve further.

[Unused sledge]

Do undercuts push or pull.. Please???

[bluearmy]

No idea on the clusters but the mean ECM 12z  could well have some heads being scratched in Exeter.

note that the control develops in a similar fashion to the UKMO but with the system to our South almost far enough north to be a classic channel low.  An Icelandic wedge ensures that the next two systems disrupt close to or over the sw of the UK.  

Interesting. 

[Rocheydub]

One thing for sure, this has been fascinating model watching! Nearly every time in the past where we had the shortwave drama or the will it slide debacle, we (SACRA and coldies members) have nearly always lost out. The UKMO has performed very well, and stuck to it's guns (assuming the un-thinkable doesn't occur) but I would suggest that while the UKMO has been rock solid in it's evolution, I would expect to see a halfway house between the superb alignment of UKMO, and the ECM at about 120/144 which will still be very good. The GFS has traditionally (in my memory anyway) being overly progressive with blowing away blocks. It's sometimes correct, but we'll know in about 5 days, how correct it is.

Remember until T72, in this volatile NWP output, it's not all done and dusted.

I expect another rogue run or two before this is signed sealed and delivered! As a weather enthusiast, 

[tight isobar]

On Sunday, January 10, 2016 at 4:59 PM, tight isobar said:

Just a quick one. I've picked the gfs showing frame' with the shunt of progression its eyeballing. 

It Again appears far to progressive and chucking up energy in over .

Before new data input gfs' the ecm far outweighed the gfs @3days+...qith the ecm only having data misfortune at precipitation issues ie wrong locate/and weaker pick up.id suggest on current gfs modelling' not much has changed via output  compare gfs/ecm. And strongly believe we are at the critical cross Roads as to where we are going. ..and I know which model either way I'll be putting my cash on!!!I don't know what makes me laugh more atm  del boy or the gfs....However I rekon the gfs is being a right "plonker"!!!

Miss model/divergance' coming Into reliable re-form.

And agaI.

Confused as to why Most of my posts pre-last 2hrs are GONE!!

[Weathizard]

If anyone is interested this from Ian F on Twitter re: ECM ensemble spread.

 

 

Edited January 12, 2016 by Weathizard

[Ali1977]

Ian Fs latest Twitter post ref ECMWF temp plot for Swindon shows the potential of the cold hanging around all next week. 

[nick sussex]

10 minutes ago, Unused sledge said:

Do undercuts push or pull.. Please???

The undercut we talk about here is when low pressure goes under a high pressure rather than over it.

This undercut supports the high to stay in place and not sink. Generally you'll see this with one large low pressure system to the west of the UK, the high to the ne is in a sense trying to keep it at bay, you'll know the high is winning if the low starts to weaken and then it ejects a smallish low pressure which we often refer to here as a shortwave se under the high.

Hope that's helps.

Edited January 12, 2016 by nick sussex

[cold snap]

But what is being chased here ?

Looks to me that if we do get a continuation of the cold,it will be as we are now .

models may want  keep us cold ,but those chasing Snow world ,Not happening with this pattern 

[Ali1977]

2 minutes ago, Mark wheeler said:

Right now I'm really confused only 4 hours ago Ian was saying only matter of timing with Atlantic return west wind shift but now this. Really is Shannon's time. Not a dig by any means just shows how interesting model watching has been this past couple of weeks . 

He's not saying it mild air won't return, just timings are hard to forecast - as shown by that chart.

[bryan629]

Hi , to Unused sledge and Dragonfalls

this is what generally happens when energy from a low pressure heading east bangs into a blocking high... in our location... 

The low gets squashed and `disrupts` ie changes shape.. it has to go somewhere and everyone on here wants/hopes the squashed low gets dragged under the blocking high, taking all its energy with it... just never stall where it is, as the energy will dissipate.. so we need a fairly strong stream to tug it under the blocking high... this will lead to a strong continental flow with bitterly cold air transferring over to our little island.. 

The disrupted low will be pushing fronts into the cold air over our island laden with moisture which usually dump plenty of snow as they move through... it a scenario, i guess just about everyone on here love to see... we dont call it model porn for nothing ya know !! 

 

Edited January 12, 2016 by bryan629

[Vorticity0123]

It appears that parts of Western Europe are heading for a significant cold snap. Details still have to become clear, though. Yet, there is another remarkable player in the field which could have significant implications on our weather. And yes - this may well be a subtropical storm in January!

A subtropical storm in January?

The system I mention is located in the southwestern corner of the map below.

ECMWF 500 hPa heights (colours) and surface pressure (white lines) 12Z T+24.

As you can see, the system (designated 90L), has a core pressure of just below 1000 hPa. At first glance this system does not look like a remarkable system. And yet, this system may become a very special one. It appears that 90L may  turn into a subtropical storm, if it does so it would be named Alex. The NHC currently assesses the chances at about 50% that this system will become a subtropical cyclone. That would result in a very early start of the 2016 Atlantic hurricane season.

From NHC:

Quote

1. Cloudiness and thunderstorms have become a little more concentrated
and organized near the center of a non-tropical low pressure system
centered about 1100 miles southwest of the Azores.  The low is
producing winds to near 60 mph over the southern and eastern
portions of its circulation.  Although environmental conditions are
only marginally conducive for development, this system could become
a subtropical or tropical storm within the next day or so.  The
cyclone is expected to move eastward to northeastward over the
eastern subtropical Atlantic over the next couple of days.
Regardless of subtropical or tropical cyclone formation, this system
is expected to produce hazardous marine conditions over portions of
the eastern Atlantic for the next few days.  For additional
information, see High Seas Forecasts issued by the National Weather
Service and Meteo France.  The next Special Tropical Weather Outlook
on this system will be issued by 2 PM EST Wednesday.
* Formation chance through 48 hours...medium...50 percent
* Formation chance through 5 days...medium...50 percent

Towards the North Atlantic

One thing is certain - and that is that if Alex would develop, its lifetime will be relatively short. The models are insisting on moving 90L towards the north. The ECMWF shows this nicely:

 

ECMWF 500 hPa heights (colours) and surface pressure (white lines) 12Z T+24.

The system is denoted by the black circle. Along with its northward movement, the low pressure area is also taking a large swath of warm air along with it northward.

ECMWF 850 hPa temperature (white lines) 12Z T+24.

The red arrow indicates the movement of relatively warm air at 1500 m (about equal to the 850 hPa height) towards the north. The main question is of course: why would this be so important for our weather in the long term?

Boost to uncertainty?

Often, (sub-)tropical storms entering the extratropics tend to increase uncertainty in forecast in the extratropics. Such systems could (via interaction with other systems) cause wild swings in model output over extended timeframes.

Here, it seems that the system gets caught into a low pressure to the south of Greenland. Ahead of this system, warm air advection (seen by the yellow colours in the surface pressure and 500 hPa chart) is taking place. This could in this particular situation result in a formation of a ridge (a 500 hPa high pressure area) and associated surface high pressure area.

The bottom line is that as long as the fate of the system near the Azores remains uncertain, the system itself could aid in causing wild swings in the forecasts to follow. In which way these model swings will go remains to be seen. Nevertheless, this system could be an interesting player in the model forecasts to follow in the next few days.

 

EDIT: just as a point of interest: the 'undercut' of the low pressure area towards France under the high pressure area situated near Iceland (both at 500 hPa and at the surface) could well be linked to the ultimate fate of the low pressure area that I mention in the post above. Though the link is not a 1:1 relationship, it will definitely be linked in some kind or way.

Edited January 12, 2016 by Vorticity0123
Added some quick thougts on 'trough undercut'

[london-snow]

Well I'm back...

and a very happy new year to you all,

one or six words in brief - classic case of westward correction. 

Those that disbelive need not to look no further than into times gone by (archives),

what I expect : A blend between the ukmo and ecm, cold for a week then a battleground synario followed by a even colder plunge..

 

see you all on the cold side :-)

 

 

 

 

 

 

[ICETAB]

Perhaps new thread for the 18zs?

[Hodgheg]

This has by far been one of the strangest and nail biting periods out of all the years I've been following the model discussion net weather. Very enjoyable. One thing I've learned in the past year is the importance in probability in forecasting. Nothing is certain! 

[snowbob]

Well what an amazing week of model watching.

still learning after five years but this last week has been difficult for us learners and the more seasoned model watcher, ( as well as the met )

had a feeling that the ukmo may be on to something and thought any day now this could be salvageable as long as Steve posts about his westward corrections from both the ecm and the gfs.

spot on once again from Steve. Which I could not see this morning.

the experienced posters on here are really great at what they do and are not scared of sticking their neck out.

gfs 18z gonna be a big pub run

as is the 0z

[johnholmes]

Good to see an upturn in mood this evening. It really is funny reading some posts over the last few days.

To me there has never been any doubt that the cold would arrive into England during today with Scotland already in the cold air over the past weekend, at least for many areas.

I tend to look 6 days or more ahead so the showing today of the possible Tropical Storm is something that was mooted several days ago. What effect if it does become one is hard to predict, especially so at this time of the year. Almost unknown I would think.

What effect this will have on the anomaly charts I follow is also hard to predict, that is other than confusion! Currently the NOAA output seems to be suggesting that somewhere between day6 and 14 the 'cold' ridge will have given way to a more mobile Atlantic type of flow. From past experience I would suggest later rather than sooner in that time scale. Interestingly the 8-14 shows some signal of rising +ve values in the entrance to the western English Channel, with the ridge still there, east of the UK now, and also the trough down into Europe. It does appear as if the Atlantic will win out but as to how long for I have no idea. I will leave that to others more aufait with later teleconnections.

So cold for a week to 10 days becoming increasingly dry after whatever happens tomorrow into Thursday for some areas. That looks interesting and I suspect changes will occur in will it snow or not for any particular low lying area right up to T+6 hours.

links

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

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

the 12z run shows GFS reinventing ridging from the Azores area. How 'real' this will turn out to be remains to be seen

[peborant]

I can confirm that in Scotland cold air is already in place, with a clear trend downwards and a nice pasting that fell overnight and into the morning on the Ochil Hills (lying to about 300-400m. Expecting the fourth air frost tonight, how well we do is entirely up to clear skies as the -4 upper will arrive shortly and that guarantees some frost if nothing else. 

Looking ahead i don't think IMBY we do great snow-wise although I guess with the whole volatility of the situation I am in for a surprise or two. 

 

*** what I expect : A blend between the ukmo and ecm, cold for a week then a battleground synario followed by a even colder plunge..

 

That sentence sums up the whole feeling that I have got going on about this sit...let's see how events unfold! Fascinating times though

 

[chrisbell-nottheweatherman]

Weatherweb seem to be siding with the GFS, at least in this video analysing the Jet Stream charts and 500 mb output.  Their thinking seems to be that a strong Jet streak will move out of Canada at the weekend,  giving a short-lived battleground set-up early next week before the Jet heads north, setting-up on a SW-NE flow axis again - very similar to December.  They do mention the possibility of the Jet heading south again as heights develop close to the UK, but expect a resurgent vortex to flatten those heights, returning the UK to full zonality later in the month:

 

 

 

My suspicion is that this video is rather one-sided, given that it relies purely on one model (GFS), and therefore ought not be taken as some kind of "proof" that the block will be demolished easily.  We've seen since last night's ECM just how difficult it is for operational runs at present to work-out the effects of a possible 'rebound' of the AO, in addition to the influence of the subtropical system described in an earlier post.  To my (still inexperienced) eyes, the GFS charts discussed in the video seem to reverting to that models' usual tendency to overdo the strength of the Jet and underplay the resilience of the block, especially given that more knowledgeable posters than I have explained that, the longer a cold block remains in place, the harder it usualy is to dislodge.

[Ali1977]

Subtle differences at T84 on the latest GFS, nostep in any direction and closely sticking to the last run.

[booferking]

5 minutes ago, Ali1977 said:

Subtle differences at T84 on the latest GFS, nostep in any direction and closely sticking to the last run.

High slightly stronger @ 96hr low also further west of the tip Greenland @108hr.

Edited January 12, 2016 by booferking

[bobbydog]

the frosts dont even seem too harsh anywhere. the south west seems to escape any frost at all!

would be nice to get a few frost days to kill off the pesky insects and reset nature.

"the daffs are safe for now"

Edited January 12, 2016 by bobbydog

[The Enforcer]

Not only has GFS been a bit out on a limb with the westwards progression of atlantic air, but it also seems to have some glaring errors in the detail. Take next Monday, when the 12z is predicting a transitional snow event:

Mostly rain over my location, yet snow over France. However, when you look at the 850's:

The -5C isotherm is over my location and the mass of snow over France is above 0C. It certainly doesn't inspire confidence. And of course, the ensembles show that the operational is one of a handful of milder runs on 18th: