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phil nw.

Model Output Discussion 01/09/17

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13 minutes ago, booferking said:

Can anyone tell me why the EC has no low going through midlands and GFS has 96hr..  And who is likely to be right massive differences here strange???

gfs-0-90.png

ECM1-96.gif

Seems like only ECMWF does this with UKMO and ARPEGE giving the GFS situation, huge difference for this time scale?

arpegeeur-0-96.png?0UW96-21.GIF?21-05

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I'd say around 250m which is a 10 minute walk away

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18 minutes ago, frosty ground said:

gfs-2-96.png?6
GFS sticking to its guns for Saturday morning NW of Birmingham has a chance of the white stuff.

gfs-1-96.png?6

This will sink away south East
 

Shortwave or what ever it is, needs to be further South for here, but yes NW of b'ham will see snow, dumping north above 300m

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162 gfs 6z..

Getting its act together.

Decent profile as a whole and is moving in line with yesterdays ec-12z..

Atlantic ridge strengthening!!!

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2 minutes ago, Jonan92 said:

Looking much better this run

00z

gfsnh-0-174_egq5.png

06z

gfsnh-0-168_uqr6.png

Some great WAA heading straight into the heart of Greenland!

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49 minutes ago, nick sussex said:

Not liking this mornings outputs which seem to be shifting things west .

The shortwave needs to run se and end up to the se of the UK not the sw as that pushes a ridge north ahead of it into the UK.

The UKMO is a shocker this morning both it and the GFS develop an even more west based set up. The latter eventually pushes the ridge to the se away but now we’re dealing with events well  outside of the reliable timeframe which means even more time for more variables to pop up.

ECM  holds onto it’s Amber warning, the GFS and UKMO are now moved to Red!

Yes, that upper shortwave/secondary low ejecting east over the N Atlantic from the upper trough over northern Canada late weekend and early next week could throw a spanner in the works with regards to how quickly it clears SE - which could scupper a second arctic reload next week after the brief cold NWly blast this weekend.

The EPS clusters quite widely spread over how quickly this shortwave trough clears through, some hold the trough back far enough west and long enough to prevent any deep cold from getting far south, though generally the guidance suggests it will get SE eventually to allow a reload form the north. Thankfully no dramas with regards to this feature from 06z GFS, which doesn't hold it back west.

If we can be confident the shortwave trough clears SE quickly as per GFS and ECM, more runs needed, we then need the block out west to hold to allow deep cold over northern Norway and Svalbard to get drawn this way next week. As although the synoptic evolution is working with help of blocking to the west, we are not really seeing any deep cold yet in the reliable timeframes. Though that's not to say we can't see some snow maybe overnight at lower levels, certainly high ground in the north and west is looking favourable from Friday.

Edited by Nick F

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Joker in the pack 6z.

Canadian lobe shunting things a tad east

Still plenty of time for exactions on this area.

Screenshot_2017-11-21-10-23-04.png

Edited by tight isobar

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11 minutes ago, I remember Atlantic 252 said:

Shortwave or what ever it is, needs to be further South for here, but yes NW of b'ham will see snow, dumping north above 300m

Not sure about that altitude just had a look at Alderley Edge which is 189m ASL

And it is forecasting heavy Snow.

C.S. 

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The problem with these sort of setups is they tend to degenerate to 12 hour topplers as the day nears:

gfs-0-174.png?6

Hoping I'm wrong.

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So from around 192hrs its atlantic waa -v- canandian migrating lobe and its army of shortwaves.

Can we get an' arm of decent advetion into greenland and further into the pole in time to disrupt the canadian eastward progression..and hold the ridge??

50/50 as thing are.

Its really is on the edge....

After the weekends cold shot!

 

Edited by tight isobar

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15 hours ago, swfc said:

 

 

Cracking 240hr mark there on the 6z.look at the jet profile and Atlantic ridge!!!!

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Just now, swfc said:
15 hours ago, swfc said:

 

 

Cracking 240hr mark there on the 6z.look at the jet profile and Atlantic ridge!!!!

sorry that post is for today

Cracker profile

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The GFS seems to be stuck in a loop of sending lows from the north west to the south east with a ridge of high pressure buing in the Mid atlantic after each pass.

Cool but not overly cold but a million miles away from the south westerlies that was meant to set up according to some on here on Friday. Maybe December isn't a right off then?

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12 minutes ago, tight isobar said:

So from around 192hrs its atlantic waa -v- canandian migrating lobe and its army of shortwaves.

Can we get an' arm of decent advetion into greenland and further into the pole in time to disrupt the canadian eastward progression..and hold the ridge??

50/50 as thing are.

Its really is on the edge....

After the weekends cold shot!

 

This the downside of not having a proper Greenland block in place next week, but relying on stout Atlantic ridging north instead. The GFS is trying to push the trop Polar Vortex over Canada further east toward Greenland while strengthening in the medium range - which puts pressure on the N Atlantic ridge to the west to flatten out. 

Certainly the Atlantic ridge slackens in the extended EPS, but still with a Euro trough anomaly, so could be we revert back to NWly flow eventually after another arctic reload next week. The caveat is that the models may not be handling the blocking over the Atlantic and PV over Canada too well, so we may end up seeing more protracted blocking. Indeed 06z GFS FI teases us with further amplification upstream, with ridge building back over the top of troughing sliding SE into Europe and the UK gets an Ely.

Edited by Nick F

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GFS takes Saturdays low further North whilst the APERGE sees a more Southerly track and as a result, the snow risk is further South too.

winteroverview_102.thumb.jpg.8a327712e9c74491126292adbac58aaf.jpg

Now, given the GFS's love of tracking low pressure systems too far North in these situations I think the APERGE will probably be closer to the mark bringing the risk into Southern England, rather than the North Midlands.

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Lots if uncertainty as we head into Friday if indeed a developing low heads our way  I said yesterday I prefer if this stI'll did not develop as I much rather see the brighter showery weather to move in instead and I'll still stand by that as most areas would see rain with higher ground would see snowfall. The GFS admittedly does increase the potential of more lower levels seeing some snowfall but I think it may have a slight cold bias as it always has lower upper air temp than the ukmo and ECM but Im fairness we never know just how full on accurate those 850 temp are. 

Wednesday into Thursday looks slightly concerning for rainfall amounts in Cumbria it got to be said, one to keep an eye on for sure.

Further afield, well I would not worry too much about another west based NAO developing just yet but I do see the models are showing the same old problems of if it's more east based we are struggling to get a proper Greenland high and instead it just remains an Atlantic high.

Edited by Geordiesnow

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1 hour ago, cheshire snow said:

GFS showing up to 4 inches of snow over higher ground of the North Midlands on

Saturday,looks like the sweet spot is around the Buxton/Glossop Area.

C.S. 

2

Looks more like Yorkshire Dales and North Pennines to me

108-780UK.thumb.GIF.6cc654c7aa89fef68d6726c5caa44a3c.GIF

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Looking at the ensembles  most show a potential snow event anywhere from the north all the way down to the Midlands.  At this range its very difficult to pinpoint the actual position regarding the low.  It looks like most will at least see some of the white stuff failing from the sky.  Ive also noticed the Aperage is also showing this low for Friday into Saturday .  And depending on which run you look at  Last nights run or this mornings  the main band of snow is again anywhere from the North to the Midlands    Interesting   

Also see attached Short ensembles for Brum  Opp very close to the mean

Edited by weirpig

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Thankfully the GFS 06 hrs run has a better shortwave track. It might be a case of rinse and repeat with another one heading se later.

The key is to get low heights into Central Europe which hold there. As long as the PV over northern Canada remains stalled there with low heights over Europe that keeps the door firmly shut on any milder conditions .

In terms of the possible snow earlier on I remember reading that the Met Office does take note of the Arpege model.

Edited by nick sussex

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1 hour ago, Nick F said:

Yes, that upper shortwave/secondary low ejecting east over the N Atlantic from the upper trough over northern Canada late weekend and early next week could throw a spanner in the works with regards to how quickly it clears SE - which could scupper a second arctic reload next week after the brief cold NWly blast this weekend.

The EPS clusters quite widely spread over how quickly this shortwave trough clears through, some hold the trough back far enough west and long enough to prevent any deep cold from getting far south, though generally the guidance suggests it will get SE eventually to allow a reload form the north. Thankfully no dramas with regards to this feature from 06z GFS, which doesn't hold it back west.

If we can be confident the shortwave trough clears SE quickly as per GFS and ECM, more runs needed, we then need the block out west to hold to allow deep cold over northern Norway and Svalbard to get drawn this way next week. As although the synoptic evolution is working with help of blocking to the west, we are not really seeing any deep cold yet in the reliable timeframes. Though that's not to say we can't see some snow maybe overnight at lower levels, certainly high ground in the north and west is looking favourable from Friday.

As far as I can see the 06 gfs tracks the trough  in a very similar manner to the morning's ecm and at T156 has it phased in the with the main positively tilted trough over the UK. The main difference at this time is that the European high has rested the colder air sinking south over Europe unlike the ecm

But this it quickly corrects facilitated by strong ridging in eastern Europe and low and behold with the route now established to the Canadian vortex lobe we now have two possible energy feeds, one from the north west and even one from the north :shok:

Of course this is subject to revision at 12

gfs_z500a_natl_27.thumb.png.1f18ae41cb939fc203f8592b911267d3.pnggfs_z500a_natl_39.thumb.png.4cca254b29ecdc9f7aa7ba1c201664e9.png

Edited by knocker

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I’d be a bit dubious of the GFS and that shortwave deepening that much. This is a known bias of it.

These set ups are notoriously difficult to forecast accurately in terms of snow versus rain . 

The track will be effected by the depth of the low, so if you’re in the south you want a shallower feature in the north something a bit deeper as this will take it further ne.

It’s a marginal set up regardless.

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