Model output discussion - Post SSW - Will it turn cold?

[ukpaul]

4 minutes ago, MattStoke said:

Milder air into the far SW at the end of the GFS 6z. Game over ;-) 

Seriously though. Other than the cold arriving a tad later, the run is faultless.

My only concern is the system being squeezed by the high to the north. Any more of that and we get into cold but drier air. ECM toyed with that for a few runs and dropped it but it needs an eye being kept out for that.

[Frosty.]

13 minutes ago, Southender said:

.and then our only concern is about how rubbish the snow is for building as it's "too powdery" haha.

Yeah it could be the wrong kind of snow

The Gfs 6z wet bulb temps look encouraging for snow don't they..haha!!

 

[frosty ground]

12 minutes ago, Geordiesnow said:

I think the only concerns I have is the infamous shortwave development and whether the main instability airflow gets pushed too far southwards and into France and Spain. Remember cold uppers and warmish sea temps don't always mean full on convective snow showers, lapse rates are crucial also. I remember a case when i lived on Tyneside where on paper we had a nice easterly flow with -10 uppers but there was a lot of stratus cumulus cloud around with very minor hidden convection in it so its something to keep an eye on. It's why I rather have the easterly slightly further northwards initially rather than the current thinking of it sweeping through Germany/Holland/Southern England and into France as it gives more room for error that way.

All that said, really interesting output, in theory the easterly drift starts this week and we some chilly upper air temps mixed in at times so it's like the starter before the potential main course next week.

Lots of variations still to go though so be interesting what the final outcome will be.

How will a shortwave divert all that cold air southwards?

The jet is pushing everything west, any shortwave will get pushed along with it, the cold air will be pulled around and developing low on its northern flank, again it can't head south.

If the jet fails to push east to west then yes the cold may not make it but a shortwave at this point is not stopping the cold, all it will do is create lots of snow.

If anything the cold could push north west, dragging warmer air into the south east, but that also looks unlikely.

[Jimmyh]

can I ask a model related question here. when was genuinely the last time we saw the sub 528 dam air across the country like is forecast above??? we are reg showing 510-512 DAM air

I have been modelwatching for a few years but can only think that 1991 is comparable with this. Am I right

Edited February 20, 2018 by Jimmyh

[Frosty.]

Just looking at the Ecm 00z ensemble mean..now that's what I call a locked in very cold pattern...no sign of mild returning for a long time!!..coldies should relish this countdown to cold because it looks like being very special!

[Catacol]

Just to raise heads a bit from the short/medium term operational charts - SSW mean reversal now set to end around 27th Feb, a couple of days early than initially forecast

with not much scramble evident... so likely to be fairly accurate now. This will bring an end to 16 days of winds in reverse, with a downwelling response to follow. By 1st March ECM has a vortex showing a recovery to weak westerlies, but still a net easterly flow at 45/65 N

Longer term this vortex looks unlikely to me to recover sufficiently for a return to an atlantic westerly pattern of any strength. GLAAM is set to fall... but how low? Nino tendency beginning to look more and more of a factor, though increase in trades easterlies in the net 2 weeks may help pump up sub tropical high pressure belts and push the storm track a little further north once again. However next cycle of torques looks set to begin shortly, lag impacts for 10 - 15 March and this would assist in maintaining a meridional pattern at our latitude, especially when laid on top of a weak vortex and potential for neutral GLAAM.

End product? No automatic end of this cold pattern in sight. If the trades get a foothold then, as per MetO forecast I could see milder air at times nudging in to the SW... but otherwise this really could be a long and sustained spell to end winter. ECM monthly images in posts above not a surprise.

:-)

[Singularity]

A lot of easterlies messed up by shortwave lows were cases that had us looking to be near the western limits of a less extensive area of deep cold, with much less margin for error than we have on this occasion. 

Its like being sat on the train tracks instead of at the station, and so close to the train yard that even if it derails it will probably still crash into you.

Or something like that anyway!

For this reason it is a adjustment southward that I am wary of most - a rebuilding of the train line itself along a new trajectory. That 40% ECM cluster likely contains a fair few of those. There’s always something isn’t there? 

Edited February 20, 2018 by Singularity
T y p oh

[karlos1983]

6 minutes ago, Singularity said:

A lot of easterlies messed up by shortwave lows were cases that had us looking to be near the western limits of a less extensive area of deep cold, with much less margin for error than we have on this occasion. 

Its like being sat on the train tracks instead of at the station, and so close to the train yard that even if it details it will probably still crash into you.

Or something like that anyway!

For this reason it is a adjustment southward that I am wary of most - a rebuilding of the train line itself along a new trajectory. That 40% ECM cluster likely contains a fair few of those. There’s always something isn’t there? 

Thanks for that, good analogy! 

That southerly track though surely wouldn’t be a disaster though, as we would still be in the cold although just a lot drier... *for now* should it evolve like that? 

Or is that wrong?

TIA

Think I’m getting the pre cold spell jitters ?‍♂️

Edited February 20, 2018 by karlos1983

[Derecho]

7 minutes ago, Singularity said:

A lot of easterlies messed up by shortwave lows were cases that had us looking to be near the western limits of a less extensive area of deep cold, with much less margin for error than we have on this occasion. 

Its like being sat on the train tracks instead of at the station, and so close to the train yard that even if it derails it will probably still crash into you.

Or something like that anyway!

For this reason it is a adjustment southward that I am wary of most - a rebuilding of the train line itself along a new trajectory. That 40% ECM cluster likely contains a fair few of those. There’s always something isn’t there? 

Yup I'm concerned people are getting too carried away in here, that little low over Finland appeared again on the ECM at T72, it makes the westward flow of the Siberian cold pool less smooth, leaving the risk of pressure building over the UK instead with the really cold air on the other side of the channel. Remember the 00z yesterday?

Anyhow if its gone by this evening we should hopefully be able to rule that scenario out, though with the ECM showing that option represents 40% in the clusters it could very easily come to frution.

The 06z GFS didn't show the little Finland low however.

 

Sorry if I come across as a party pooper  but it was overlooked. Despite the little Finland low however the cold still made it!

Edited February 20, 2018 by Quicksilver1989

[ScottishSnowStorm]

So many people in here looking to when this cold spell is going to disapper from the models even while there is so much support for it through all aspects of the models.

Just sit back and enjoy the viewing and only look for things to derail when there is actually anything in the output to show that we will miss out because all we are seeing from now is things of beauty and nothing to suggest we will miss out 

[bluearmy]

27 minutes ago, Deep Snow please said:

A second year without summer. I know it's off topic but could an SSW have caused that?

funnily enough, I was wondering precisely the opposite yesterday. maybe a better summer is more likely off the back of a meandering jet due to a lack of deep arctic cold. for another discussion .....

 

2 minutes ago, Catacol said:

Just to raise heads a bit from the short/medium term operational charts - SSW mean reversal now set to end around 27th Feb, a couple of days early than initially forecast

with not much scramble evident... so likely to be fairly accurate now. This will bring an end to 16 days of winds in reverse, with a downwelling response to follow. By 1st March ECM has a vortex showing a recovery to weak westerlies, but still a net easterly flow at 45/65 N

Longer term this vortex looks unlikely to me to recover sufficiently for a return to an atlantic westerly pattern of any strength. GLAAM is set to fall... but how low? Nino tendency beginning to look more and more of a factor, though increase in trades easterlies in the net 2 weeks may help pump up sub tropical high pressure belts and push the storm track a little further north once again. However next cycle of torques looks set to begin shortly, lag impacts for 10 - 15 March and this would assist in maintaining a meridional pattern at our latitude, especially when laid on top of a weak vortex and potential for neutral GLAAM.

End product? No automatic end of this cold pattern in sight. If the trades get a foothold then, as per MetO forecast I could see milder air at times nudging in to the SW... but otherwise this really could be a long and sustained spell to end winter. ECM monthly images in posts above not a surprise.

:-)

indeed, the next downwelling wave is due by mid march so its possible we wouldn't see much of a return to normality ahead of another neg AO spell.  of course, any relaxation in the low uppers could allow surface temps and dp's to climb into strong thaw territory, given the time of year. that's why I think an attempt to break some march records could rely on widespread snowcover of a depth to cope with the strong solar input when it undoubtedly comes.

the rotation of the vortex from Canada around the pole looks brilliant on the NH profile. got to try and hold the greeny omega block in place to keep the push of the sceuro trough more to our east than west which would allow a west based -NAO to drive the souwester into Europe. 

btw, some wag mentioned a chunk of vortex having Brighton's name on the ticket a couple days ago ? looking at the ec op, its e Anglia and kent. seriously, that's a proper bonafide chunk of the vortex on the doorstep of s uk on that op. 

[Derecho]

5 minutes ago, ScottishSnowStorm said:

So many people in here looking to when this cold spell is going to disapper from the models even while there is so much support for it through all aspects of the models.

Just sit back and enjoy the viewing and only look for things to derail when there is actually anything in the output to show that we will miss out because all we are seeing from now is things of beauty and nothing to suggest we will miss out 

Today is the final day I express caution. Just remember in early February 2009 all the GFS ensembles had T850s around -10C out to 384h except one rogue ensemble member.

It was that rogue ensemble member that got it spot on and the flip was around T72!, the rest of the month was mild

Edited February 20, 2018 by Quicksilver1989

[Polar Maritime]

That's some more post gone, So if yours is missing it's because it's not Model Output Discussion. During these up-coming v busy periods PLEASE keep on topic in here.

Thanks again, And on we go...

Edited February 20, 2018 by Polar Maritime

[Youcan'tbecirrus]

15 minutes ago, Catacol said:

Just to raise heads a bit from the short/medium term operational charts - SSW mean reversal now set to end around 27th Feb, a couple of days early than initially forecast

with not much scramble evident... so likely to be fairly accurate now. This will bring an end to 16 days of winds in reverse, with a downwelling response to follow. By 1st March ECM has a vortex showing a recovery to weak westerlies, but still a net easterly flow at 45/65 N

Longer term this vortex looks unlikely to me to recover sufficiently for a return to an atlantic westerly pattern of any strength. GLAAM is set to fall... but how low? Nino tendency beginning to look more and more of a factor, though increase in trades easterlies in the net 2 weeks may help pump up sub tropical high pressure belts and push the storm track a little further north once again. However next cycle of torques looks set to begin shortly, lag impacts for 10 - 15 March and this would assist in maintaining a meridional pattern at our latitude, especially when laid on top of a weak vortex and potential for neutral GLAAM.

End product? No automatic end of this cold pattern in sight. If the trades get a foothold then, as per MetO forecast I could see milder air at times nudging in to the SW... but otherwise this really could be a long and sustained spell to end winter. ECM monthly images in posts above not a surprise.

:-)

Based on the above, would you say that GFS model predictions indicating the cold spell could end by around 8th March is likely and therefore a 2 week cold spell is unlikely..   

[karlos1983]

Just now, Quicksilver1989 said:

Today is the final day I express caution. Just remember in early February 2009 all the GFS ensembles had T850s around -10C out to 384h except one rogue ensemble member.

It was that rogue ensemble member that got it spot on and the flip was around T72!

I think it’s wise! Until we can say with complete certainty this cold will arrive on Monday’ish and the models play with the idea of a shortwave drama, it should be discussed! All I’ll say is “ThatECM” 

(shudders and rolls eyes) 

[bluearmy]

5 minutes ago, Quicksilver1989 said:

Yup I'm concerned people are getting too carried away in here, that little low over Finland appeared again on the ECM at T72, it makes the westward flow of the Siberian cold pool less smooth, leaving the risk of pressure building over the UK instead with the really cold air on the other side of the channel. Remember the 00z yesterday?

Anyhow if its gone by this evening we should hopefully be able to rule that scenario out, though with the ECM showing that option represents 40% in the clusters it could very easily come to frution.

The 06z GFS didn't show the little Finland low however.

 

Sorry if I come across as a party pooper  but it was overlooked. Despite the little Finland low however the cold still made it!

you're most certainly not being a party pooper but realistic. there are so many shortwaves popping up in the flow - no surprise given its depth of cold and instability, that a deflection nw could easily throw a spanner in the works at this timescale. we should be a little reassured that since the last time we saw a reverse flow in process, the models have increased in resolution so should be better at picking these up.  this is why I gave Thursday's 00z run as being the point of lift off for the deep cold to be a hit/miss. in the meantime, plenty to drool over, as long as cluster two takes a hike !

[frosty ground]

9 minutes ago, Quicksilver1989 said:

Yup I'm concerned people are getting too carried away in here, that little low over Finland appeared again on the ECM at T72, it makes the westward flow of the Siberian cold pool less smooth, leaving the risk of pressure building over the UK instead with the really cold air on the other side of the channel. Remember the 00z yesterday?

Anyhow if its gone by this evening we should hopefully be able to rule that scenario out, though with the ECM showing that option represents 40% in the clusters it could very easily come to frution.

The 06z GFS didn't show the little Finland low however.

 

Sorry if I come across as a party pooper  but it was overlooked. Despite the little Finland low however the cold still made it!

So a little low over Finland is going to stop the retrogression of the upper high?

Delay and slightly divert the cold I can see but the pattern is backing west unless the jet takes a trip somewhere else.

[Paul]

Ok, we're in the lull before the 12z's roll, so time to lock this and get a new thread going: