Model output discussion pm 13/01/2016

[Polar Maritime]

Can we please keep radar and snow prospects for the regionals or the cold spell thread. Thanks.

[J10]

 

I have attached the above link giving the synoptic charts for the week ahead, based on the GFS 06Hz this morning, It also shows more detailed forecasts for the Alps.

[Snowyowl9]

UKMO was the first to show this,that slider low.

Now GFS 6z run showing a very interesting setup.http://www.wetterzentrale.de/pics/Rtavn481.html

http://www.wetterzentrale.de/pics/Rtavn961.html

 

 

[Tamara]

1 hour ago, Catacol said:

Amplification in the pacific evident at 7 days in the 06z

HP drifting to our East. Output now is indeed coming together, and disappointingly the transient northerly is turning out to be exactly that - transient. Gloomy Imbyism this morning suggesting no snow for lowland Somerset this week... :-(

But goggles on, chocks away - and good luck to those in central parts who look favoured to see snow in the next few days alongside an already snowy Scotland.

Looking further ahead if 1983 is indeed the template to follow, then we will see a milder blast from the atlantic at the back end of the week and then we wait to see how the amplified signal from the pacific will impact the atlantic. GP's AAM torpedo (!!) set to land in just over a week's time as we look to see more blocking establish itself. Any sign on the runs this morning? Yes there is. Almost bang on schedule a renewed push in our locale:

Will it push N, NW or NE? Way too far out to tell yet, but to my eye GP and Tamara's suggestions look good. I'll close my eyes to the disappointment of snow lovers in the SW regions this week, and keep my eyes firmly fixed on the last week of January. A ridge that is a bit stronger and a bit further west may deliver to the lowland SW yet.....

Medium term amplification signal in the Pacific is tied into the drop in relative atmospheric angular momentum from recent sky high total GLAMM values - with negative trending frictional torques an indicator of this - and associated lagged time for effects of this thereafter. The frictional torque as always, leading the mountain torque.

*Typo apology disclaimer: A previous post of mine suggested the GWO was in Phase 7 when it was in Phase 6.  I was speaking of the anticpated movement from Phase 6 to 7 and the upstream sub tropical energy expected as a consequence*

In the meantime however the Global Wind Oscillation Oscillation has entered Phase 7. *Further disclaimer wrt low AAM  forecast bias of GEFS product*

This has been the signal for the Pacific jet streak energy arriving from upstream, after what seems like an eternity in this recent model muddle, and highlights the attempts of the Atlantic to try and displace an increasingly impressive wall of cold air very close by to our north and east. Its going to be an enjoyable struggle especially in northern and eastern parts for this process to occur.   It is thereafter that the amplification arriving in the Pacific is most likely to send a little more downstream energy just ahead of it into the polar jet and provide a lull in the amplified Atlantic pattern.

However, what of the downward trend of atmospheric angular momentum (from a dizzy height in relative terms) and the future behaviour of the GWO as determinant of where the modelling heads from there?

Anticipated fresh westerly momentum across the Pacific, already well covered by GP, will send the GWO back to Phase 5 and yet another +AAM bubble. This will serve to create further poleward amplification in our parish and associated surge of WAA into the pole.   Guidance from the tropics (MJO) must be blended with the overall atmospheric signal rooted in the base Nino state, so caution required in terms of taking MJO signals and composites in isolation of the GWO.

In simple English this means that the shorter-medium term drop in relative AAM, as posted above, has a well underpinned suggested floor limit. What this in turn means synoptically, is that upstream flow (in tandem with some temporary tightening of the stratospheric vortex) is unlikely to favour the northern arm for long. As  we have already seen in recent modelling swings, there have been some wild over-estimations already in anticipation of -ve tendency in AAM and pre-cursor tightening of the vortex prior to stratospheric upper warming (yet to be fully estimated in its size)

So, the current cold amplified pattern only gradually receding to a milder (transitional) phase through this week before heading back to further amplification block possibilities. With January fast heading towards Feb, it will be very interesting to see how changing long wave patterns adjust a future cold blocking scenario. As cited over recent weeks, a next cold spell the closer and closer we get towards and then especially into Feb has good probability to have more teeth than this one, and with the southern stream showing greater willingness to back the greatest cold further west than we are set to see this week.

The atmospheric circulation feedbacks will do their work for those looking for further cold pattern, based on the anticipated guidance and expectations - the proviso is that the stratospheric vortex plays ball with its temporary tightening, and then suggested displacement back across to the 'right' side of pole. In this sense we are back to trusting the amount of latent meridionality available to 'duff up' the vortex *lady-like description*, such as has been the mantra for the current cold spell

NWP modelling is still very much focussed on the tightening vortex phase, and therefore evolvement of the tropical/extra tropical forcing pattern will be disguised somewhat - and this in turn means that renewed Atlantic amplification of the pattern in the medium to longer term is unlikely to be a seamless model watching experience. Is it ever? But don't let some less palatable model output as we head increasingly through this week, detract from the very distinct and credible possibilities thereafter.

In the meantime though, plenty to keep an eye on in the few days ahead with short term snowfall potential anyway

 

[Mucka]

The models and ensembles are now solidly behind a slow messy breakdown with slow erosion of the surface cold from the West from around midweek, perhaps staying cold throughout next week in the East with a very gradual lifting of temperatures.

However, there has been some small but interesting movement in the output this morning toward reinforcing the idea that we won't have to suffer any milder weather for too long. How so?

If you look at ECM out to 120 you will notice the second attempt at a breakdown manages a little undercut and although it subsequently sends all the energy NE and flattens the pattern that is interesting because previously it has not attempted sending any energy SE on the second attempted breakdown.

Below are today's 00z and yesterday's compared with the 12z alongside that to sjow how ECM has made no attempt to send energy SE in previous output for this time-frame and that could be quite significant if it is a new trend.

UKMO the other day actually sent a low SE rather than just disrupt energy a little energy which was quite surprising but it immediately dropped it in subsequent runs and no other model repeated the dose so I dropped the idea but today the signal for more undercut has reappeared although UKMO itself doesn't go with it and nor does GFS operational output but ECM op and within GFS ensembles, although solidly behind the breakdown, is shown more inclination to disrupt energy SE on the second attempt by the Atlantic to push in.

If it does happen we will see a more significant ridge build to our East and a deeper European trough which would be better for overall cold chances returning relatively quickly, perhaps even before months end. Something to watch for this evening anyhow.

Those who get snow, enjoy, enjoy, enjoy!

[Weather Observer]

Quote "the atmospheric feed backs will do their work for those looking for further cold pattern, based on anticipated guidance and expectations"

That is not a world away from my gut instinct that the UKMO had called this cold spell correctly and that it would last longer than the models had at first suggested. I also feel a second more severe cold period will follow .Despite coming from different ends of the spectrum, the old and the new, we are both on the same page and long may there be room for both of us Right or wrong!

Edited January 16, 2016 by Weathervane

[bluearmy]

The higher res charts on meteociel are a while behind but far more revealing re precip(GFS0.25 o)

 

 

[IDO]

The low on Monday stalls further west on the GFS 12z so the main precipitation remains in the SW, initially as rain but could turn to a wintry mix Monday night:

So dry for the east Monday and a strip down the middle of the UK will see some light snow (maybe). So the SW on this run could get some white stuff. Of course subject to change still.

[Iceberg]

I rather like the changes in the gfs up to t80. Just to clarify I am talking about the med/Spanish area and the lessening of the Azores high. Pressure generally lower, sometimes 5mb lower. It doesn't seem much but at that  is a good trend in that timeframe. 

[Cloud 10]

UKMO 12z 120 hrs.

 

 

From hero to zero!

[Eskimo]

The lack of posts says it all really. Breakdown of the cold now inevitable with the UKMO bringing in raging SW winds. We can talk about the 'niggles' between now and next Thursday, but it's evident that the Jet Stream will position itself in it's normal position by later next week. Apart from tonight's snow and possibly mondays snizzle, we now need to start looking for bigger and better come late January and February. 

[shaky]

Jheez didnt expect the ukmo to look that bad!!thats a huuuge change from.this morning!!!

[IDO]

^^^ Yes no change from this morning and as usual UKMO comes on board a day or so later than GEM, ECM and GFS. These three have been consistent with that wave from the Azores around that time for a day or so, and the UKMO been all over the place, last nights T144 for example:

Anyway as expected a holding pattern after D6 as the PV regroups and the NH mid and high latitude blocks sink. How long that will be is the next question.

[Hammer]

So if at 120h it shows snow it won't happen if it shows milder it will happen. I felt earlier in runs things looked like they were suggestive of stronger block.

[Frosty.]

5 minutes ago, shaky said:

Jheez didnt expect the ukmo to look that bad!!thats a huuuge change from.this morning!!!

It's nothing like the latest met office update. The writing is not on the wall for this current cold spell yet!  

[ukpaul]

Most people are likely in regional forums or, gasp, actually out in the open air! It's beautiful and cold out there. Better than seeking out the worst chart that comes out and so far out not to be likely in the first place.

 

3 minutes ago, PerfectStorm said:

The lack of posts says it all really. Breakdown of the cold now inevitable with the UKMO bringing in raging SW winds. We can talk about the 'niggles' between now and next Thursday, but it's evident that the Jet Stream will position itself in it's normal position by later next week. Apart from tonight's snow and possibly mondays snizzle, we now need to start looking for bigger and better come late January and February. 

 

[Liam J]

Given the flip flop nature of the outputs nothing is set in stone, the UKMO held firm while GFS & ECM wanted to bring in the Atlantic sooner, if the GFS had been correct a day or two ago then we'd be looking at SW'ly winds for the end of this weekend! Was very late to the party, epic fail... Cold been extended well into next week, not worth worrying about charts 5+ days away as they will likely change.... 

[Kentish Snowman in Yorks]

9 minutes ago, IDO said:

^^^ Yes no change from this morning and as usual UKMO comes on board a day or so later than GEM, ECM and GFS. These three have been consistent with that wave from the Azores around that time for a day or so, and the UKMO been all over the place, last nights T144 for example:

Anyway as expected a holding pattern after D6 as the PV regroups and the NH mid and high latitude blocks sink. How long that will be is the next question.

That post is completely misleading!

UKMO has been leading the way up until the last day or two with the other models, particularly GFS being dire and playing catch up!

Also, how can a chart 120 hours all of a sudden be correct when the output is wildly different from yesterday and at odds with the METO forecast?

Just a completely bizarre post if you ask me!

[igloo]

On 1/15/2016 at 4:15 PM, karlos1983 said:

 

well only comfort i can give is from the GEM which is miles away in FL. the GFS on the other hand is a real horror show you never no a week or so things may look a bit better chins up

[Iceberg]

Yep both gem and gfs have temp even on Thursday of 0-4c for most of the country (baring sw and coasts etc)

every model is allowed to have a bad run. The truth is that every model tried to bring the breakdown far to quickly. Meto though was the best of a bad bunch. 

[Frosty.]

2 minutes ago, Kentish Snowman said:

That post is completely misleading!

UKMO has been leading the way up until the last day or two with the other models, particularly GFS being dire and playing catch up!

Also, how can a chart 120 hours all of a sudden be correct when the output is wildly different from yesterday and at odds with the METO forecast?

Just a completely bizarre post if you ask me!

I agree there is a lot of uncertainty beyond the week ahead and the form horse is still for cold weather to continue until next weekend at least with a fair chance it could last longer...the mild Atlantic mush is being pushed back day after day and 1 ukmo op run doesn't change anything.

[phil nw.]

It should be no surprise really that ukmo is now the villain as the change to mild is now within range of the charts we see.It is now showing the same trend as the others at that time frame.

The current cold spell's approx duration of around 7/9 days has been well forecasted in the ens.This still looks about right.

Meanwhile some snow is falling around the country with a chance of some more in places over the next couple of days.

[Hammer]

Per Fergie.

@James1uk we're hopeful of clearer story by end of Sun; models will have assimilated the 2 key dictating factors (in US & SE Europe) for us

[The Enforcer]

Enough uncertainty remains not to take the T+120 UKMO as gospel, judging by the 12z charts available so far:

Zonal:

 

Blocked:

[Iceberg]

Just going through the gefs at t48 for my area and I find pressure is all over the place. 1000-1015 even at t48 and obviously various amounts of energy going under the block.