Model Output Discussion 29th December - Into mid-Winter.

[winterof79]

Let's remember Ian talks for the West Country as well.....The further north you are the chances of colder N Westerlies improve.For some its getting interesting.

It may be offside nowadays to post 8-10 day charts but hey ho

 

Edited January 5, 2017 by winterof79

[Paul]

There've been a number of off topic posts in the last few hours. Usual rules apply in here - if it ain't about the models, then it's not suitable in this thread. The banter thread is the place for more random chat, ramps and the like

https://www.netweather.tv/forum/topic/86721-model-moans-ramps-and-banter/

 

[Blessed Weather]

I'm always interested in trying to understand why one run can vary so much from the previous run. So just for interest, here's why I believe there's such a huge difference between last night's GFS 18z and this morning's 0z. And it's largely down to how GFS handles a shortwave developing in the Atlantic on the 18z. This goes on to form a dartboard Low and pulls in the frigid northerly airstream as it pulls away to our east. In the 0z there is no such shortwave. Such a relatively minor development, but with huge implications. The 18z charts versus 0z:

T162 and near identical 18z  0z

T171 and 18z has shortwave developing 18z  0z

T186 and the dartboard Low develops  18z  0z

T216 Low moves east pulling in northerly  18z  0z

 

[Nick F]

1 hour ago, IDO said:

So we are looking at the last third of January for any pattern to swing to cold.

 

Really? Looking cold / below average on the daily GFS T2M anomalies from late next week if I'm not mistaken.

OK, a northwesterly flow is certainly not ideal for sustained deep cold and snow away from northern areas, but it's look progressively colder on GFS and EC this morning.

00z ECM shows increasing snow potential by day 8 across Scotland, particularly over hills but perhaps lower down too, also hills of northern England and Wales. Days 9-10 it even shows a snow threat down the eastern side of Britain, with a 1 day strong northerly flow direct from he arctic, though by then good chance it won't verify.

Certainly lots of wintry potential from tail end of next week from a NWly and perhaps briefly Nly direction showing, though obviously subject to downgrade this far off.

 

[Man With Beard]

1 hour ago, winterof79 said:

Let's remember Ian talks for the West Country as well.....The further north you are the chances of colder N Westerlies improve.For some its getting interesting.

It may be offside nowadays to post 8-10 day charts but hey ho

 

I see no problem posting D8-D10 charts as long as they are consistent, and today's ECM carries on from yesterday's - much colder by D8 with uppers generally below -5C. A vortex free Canada by D10 once again, too.

The only downgrade today is from the far-reaches of GFS 18Z - quite normal for that model of couse!

[Paul]

1 minute ago, Nick F said:

Really? Looking cold / below average on the daily GFS T2M anomalies from late next week if I'm not mistaken.

OK, a northwesterly flow is certainly not ideal for sustained deep cold and snow away from northern areas, but it's look progressively colder on GFS and EC this morning.

00z ECM shows increasing snow potential by day 8 across Scotland, particularly over hills but perhaps lower down too, also hills of northern England and Wales. Days 9-10 it even shows a snow threat down the eastern side of Britain, with a 1 day strong northerly flow direct from he arctic, though by then good chance it won't verify.

Certainly lots of wintry potential from tail end of next week from a NWly and perhaps briefly Nly direction showing, though obviously subject to downgrade this far off.

 

GEFS mean anomalies looking very similar too

  

[PompeyFC]

7 minutes ago, Blessed Weather said:

I'm always interested in trying to understand why one run can vary so much from the previous run. So just for interest, here's why I believe there's such a huge difference between last night's GFS 18z and this morning's 0z. And it's largely down to how GFS handles a shortwave developing in the Atlantic on the 18z. This goes on to form a dartboard Low and pulls in the frigid northerly airstream as it pulls away to our east. In the 0z there is no such shortwave. Such a relatively minor development, but with huge implications. The 18z charts versus 0z:

T162 and near identical 18z  0z

T171 and 18z has shortwave developing 18z  0z

T186 and the dartboard Low develops  18z  0z

T216 Low moves east pulling in northerly  18z  0z

 

 

Excellent post - makes it easy for the more novice of us here to understand how minor details can have huge impacts as they develop

[northwestsnow]

Excellent ukmo/ecm this morning ! Gfs falls off the wagon.

Still a bit far out to be confident but ecm brings in a cold north wester at 192 and seems to be in the process of kicking the PV off its Greenland perch by day 10.

day8

 

Edited January 5, 2017 by northwestsnow

[radiohead]

A good signal for cold air on the 0Z ECM ENS mean at T192.

This is colder than the GEFS mean despite having more than double the ENS members watering down that mean.

[northwestsnow]

Yes the ecm mean looks good for Pm incursions.

It should be noted that the ecm/ukmo are probs not promoting a winterwonderland across the whole of the UK, initially high ground in NW Britain looks favoured in the PM flow..hoping ecm is seeing some kind

of vortex displacement ala day 10..

Edited January 5, 2017 by northwestsnow

[johnholmes]

The colder outlook on GFS is supported by the anomaly charts, they have been suggesting a colder burst as a probability for several days in the time scale shown by GFS now.

links below

last evening from NOAA, less than the ECMWF below but the pattern certainly allows for deep cold incursions as being shown by GFS at times.

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

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

not able spend much time this morning, trying to get my heating sorted, would occur when -2 C outside. Got more clothes on than when walking!

Edited January 5, 2017 by johnholmes

[Summer Sun]

Cold ens from ECM as we approach the halfway point of winter

[BLAST FROM THE PAST]

I am still liking the ecm and ukmo. 18z GFS although the deep FI I liked the look of the evolution, for me the deep trigger LP came too soon.  I think the ECM the way it is loaded at t240 would head similar and timing closer.  But who knows really, still too far ahead to avoid a spoiler popping up

 

BFTP 

[knocker]

The ext EPS continues with the transition upstream with LP in the NE Pacific/Alaska and still an active Canadian vortex. Downstream still the trough to the east tending to a positive tilt but not that close the UK in the SE. Thus tending towards a more zonal upper flow with weak ridging to the SW and temps remaining below average. No sign of this changing to temps significantly below average thankfully.

Edited January 5, 2017 by knocker

[jvenge]

GEFS showing the AO and NAO mildly negative from mid month, with few going for positive. I think the GFS had leftover sherry though, as it is keen to send both strongly negative. The GFS has been doing this for a few days now, but a skeptical person would rightly point out it keeps bumping it back a few days as well.

ECM neutral for both and slightly negative in the EPS. Canadian GEPS more in line with ECM thinking.

 

 

[TEITS]

Even for my location im pleased with the model output today. Worth mentioning for our members in Scotland is the risk of a relatively small but deep secondary low pressure system developing at the base of the low pressure that is located further N. This could occur from the 12th Jan to 14th Jan.

 

 

[fromey]

i ve seen this posted 

"Models are indicating a stratospheric ridge to build in over Europe during the late 11-15d period."

what does this mean and how would this effect us here on our small little island.

also the zonal winds are indicated to drop, i assume this is taken into account in the models

Be gentle, trying to learn

 

fromey

[carinthian]

17 hours ago, carinthian said:

Well the snow arrived exactly on time. Our fine mesh snow model last evening forecast snow to start at 1500 hours local time,in fact it was 15 mins too late !! It forecasts a 24 hour snowfall with 19cm by 1200 local tomorrow. Forecast temp of -14c at 2200m. Tomorrow night -25c in the valley. The  forecast model is 2kx2k range for my location. Mountain top locations will see higher snow rates and values. Getting exited now, time for a walk in the stuff and celebrate this much needed snowfall in the pub!

C

Morning, just up date you with the latest over here. We currently have 16 cm of fresh snowfall in my location. The fine mesh model we used predicted 19cm at 1200 local today, so it will be mighty close to that mark and again very impressive tool for our planning. The main cold front is passing  with a pronounced cold flow in its wake. -12c here in resort and -16 c at 2000m with a added wind chill . The same system brought snow to Stockholm yesterday and low temps. This picture sent by my daughter on her way to work this morning in the city centre, -11c. The models continue to show a very cold picture in Central Europe for the next 48 hours with further snowfall in the coming 24 hours. Should turn less cold over the coming weekend but no snow melt.

[tight isobar]

Some v-decent output again this morning ukmo/ecm..

Gfs goes on a-tad of a wobble' and after yesterday's eye watering performance' it's obviously muscle tired after flexing. 

Although I think most know it was pretty keen on evolving some stunning synoptics im confident that cross model will begin a morepplausible set of runs/evolution s in todays suites..

Also worthy of note are the ens..that overall show a keen move towards a colder outlook from around mid/next week. 

All in all some very promising signs available! 

Edited January 5, 2017 by tight isobar

[bluearmy]

6 minutes ago, carinthian said:

Morning, just up date you with the latest over here. We currently have 16 cm of fresh snowfall in my location. The fine mesh model we used predicted 19cm at 1200 local today, so it will be mighty close to that mark and again very impressive tool for our planning. The main cold front is passing  with a pronounced cold flow in its wake. -12c here in resort and -16 c at 2000m with a added wind chill . The same system brought snow to Stockholm yesterday and low temps. This picture sent by my daughter on her way to work this morning in the city centre, -11c. The models continue to show a very cold picture in Central Europe for the next 48 hours with further snowfall in the coming 24 hours. Should turn less cold over the coming weekend but no snow melt.

Just so everyone realises, this is the upper trough we should be under if the returning jet hadn't shoved the Azores trough nw and sunk the ridge se !

fine margins !

[frosty ground]

Just now, bluearmy said:

Just so everyone realises, this is the upper trough we should be under if the returning jet hadn't shoved the Azores trough nw and sunk the ridge se !

fine margins !

Which is exactly what @knocker said could happen and unfortunately did happen.

 

[BLAST FROM THE PAST]

31 minutes ago, TEITS said:

Even for my location im pleased with the model output today. Worth mentioning for our members in Scotland is the risk of a relatively small but deep secondary low pressure system developing at the base of the low pressure that is located further N. This could occur from the 12th Jan to 14th Jan.

 

 

Indeed TEITS although main concern for me is 14-18. If the AZH doesn't ridge back in could be a very impactual period developing

 

BFTP

[Alekos]

25 minutes ago, frosty ground said:

Which is exactly what @knocker said could happen and unfortunately did happen.

 

Yes Northern jet is so powerful these days !

[Singularity]

 

GFS on the left and ECM on the right, both at +144 hours.

There's a major difference with the pattern over the U.S. and as a result developments in the western N. Atlantic; ECM has a much sharper and better defined trough over the U.S. which supports a larger and stronger ridge in the far-W. Atlantic going forward.

  

As a consequence, whereas GFS has the ridge failing to link up with the Azores ridge and pull it west while trapping any disturbances SW of the Azores in place, ECM is all for it.

So in future runs I believe that trough over the U.S. developing in the 120-144 hour range will be a key feature to watch. Alas I can't see much evidence of it on the 06z GFS as of +126 hours. It looks to be a classic case of whether cold air will dig far south enough to facilitate low pressure development over the central U.S. which then leads to amplification of the pattern right across the Atlantic. Tricky features to nail down so no wonder the Met Office are hedging their bets.

 

Edit: I should have included UKMO which really goes for the pull-west of the ridge and produces a 1050 mb high just off Newfounland which is a rare sight. GEM has the sharp U.S. trough and so still manages to retract the ridge despite more interference with the connection process between it and the one exiting Canada.

 

So we have a case of ECM, UKMO and GEM vs. GFS with the upstream pattern. A three to one vote for a setup conducive to a major trough digging well south while east or at least just east of the UK. Question is, will the cold air import be clean enough or, if not, feature a secondary low that's favourably placed (e.g. running along The Channel if you live in the south) for once?

My main worry even if we get full model agreement on the strong retracting ridge will be the scope for a secondary low to form near S. Greenland and then hang back there a bit - which scuppered a nice northerly opportunity last winter I seem to recall.

At the moment I'm 'playing' for a cold spell lasting 2-3 days. Something longer seems feasible IF the MJO plays ball but so far this winter it's not been kindly inclined, just teasing a bit of favourable activity here and there - such as what helped to set up our current short run of chillier days and cold nights. So I'm not raising the bar very high at all right now. 

I have a niggling feeling the stratospheric developments, proving rather sluggish as they are in their travels toward something that could lead to notable vortex disruption, may encourage this winter to drag out a bit, which will be a right pain in Feb unless something dramatic happens. Oops, my optimistic hat fell off for a moment there 

 

Edited January 5, 2017 by Singularity
More is More

[Evening thunder]

11 hours ago, ghoneym said:

Been meaning to ask this for a while, why are the previous runs on the GFS not available at +237 & +240 ?

Cheers

Couldn't see this answered but I think it's because when the previous run came out 6 hours before those time-slots would have been +243 and +246, which don't exist (the chart viewer 'shifts' things forward 6 hours so we're comparing at the same forecast hour).

I guess it's the same reason that the T+384 chart doesn't change from T+372 for previous runs on the Netweather viewer

Edited January 5, 2017 by Evening thunder