Model output discussion - deep cold inbound?

[weirpig]

Another sombraro on the Gem

[kold weather]

16 minutes ago, TSNWK said:

do we think -5/-6 uppers on the 144 will introduce a rain risk - thiking on the -7 and rain streamer early January?

All will depend on the exact wind orientation on Monday.

Should we keep a ESE/SE flow as the LP introduces any warm sector (far from certain either!) then it won't be an issue.

Should the winds come from the north-sea, as per the 00z ECM, then we'd probably be looking at a period of sleet and maybe very wet snow on Monday before it scoots out of the way again.

[Drifter]

GEM actually doing the opposite of trying to bring low pressure in and instead a ridge of high pressure comes across us.

That could give some very frosty nights - plus if we can get hp established over us for a while it could then set up round 2 (pure speculation).

[Kentspur]

Even at 162hrs the GEM is considerably colder than the 0z run -1c uppers over SW Ireland replaced by -5c to -6c!! And minus 12c uppers over more of the East&Kent

Edited February 3, 2021 by Kentspur

[weirpig]

MMM  lets hope  its going off on one here

[Cloud 10]

UKMO 144 hrs,a massive reversal of zonal winds.

 

[Timmytour]

30 minutes ago, winterof79 said:

Stunner for the North that bad boy with a long fetch frigid  Easterly running o'er a warmer North Sea

 

Not sure the North Sea is going to stay warmer for too long under that!  

[MJB]

41 minutes ago, kold weather said:

All will depend on the exact wind orientation on Monday.

Should we keep a ESE/SE flow as the LP introduces any warm sector (far from certain either!) then it won't be an issue.

Should the winds come from the north-sea, as per the 00z ECM, then we'd probably be looking at a period of sleet and maybe very wet snow on Monday before it scoots out of the way again.

Hmmm really? I had 10cm of snow from -5 850's a couple of weeks ago I am surprised you  aren't saying snow Darren 

Edited February 3, 2021 by MJB

[ITSY]

Just a flag - and apologies if recent posts have come across negative because these synoptics are legitimately brilliant for the majority of us - but there seems to be a not insignificant chance of some quite heavy rainfall across the South in advance of any potential snow  on Sunday/Monday and thereafter. Initially that could be a real pain for those of us in marginal circs...

[swebby]

11 minutes ago, Singularity said:

Worthy of note that GFS has also increased the amount of high pressure to the north of the UK.

Even its classic dartboard low is struggling to make inroads.

I tend to have a view the GFS dartboard lows are that model knowing roughly where the energy will be in regards to cyclogenesis but not knowing how to resolve it into a complex pattern of separate low pressures that eventually do manifest in that model in shorter time frame.  So it takes the simple option of dumping the cyclogenesis onto a single point.

In this instance, with that high pressure to the north, i would assume (probably naively) that if it is a complex system of lows, it would be in the form of disruption - with a train of lows being ejected and heading SE (sliding) under the block?

[Djdazzle]

1 minute ago, ITSY said:

Just a flag - and apologies if recent posts have come across negative because these synoptics are legitimately brilliant for the majority of us - but there seems to be a not insignificant chance of some quite heavy rainfall across the South in advance of any potential snow  on Sunday/Monday and thereafter. Initially that could be a real pain for those of us in marginal circs...

I think it's a small risk, and only for the very extreme south.

[Paul_1978]

33 minutes ago, Frosty Winter said:

Beautiful UKMO 12z at t144. Looks like it could be trying to set up a more sustained cold spell here!

I hope you're right - but we need to keep an eye on the low following behind. Whilst the GFS slid it under the block on the 0z, it didn't on the 6z or the 12z. Be interesting to see what the ECM does with it. Sunday to Wednesday look great for coldies - Thurs onwards is the next hurdle to keep an eye on if we want longevity out of this!

[sheikhy]

I still think we can upgrade from here as hard as it is to imagine!!!

[Drifter]

Amazing to think that only *yesterday* morning, GFS was progging this for Monday morning.

Shows how far we've come!

[Chrisover93]

1 minute ago, Djdazzle said:

I think it's a small risk, and only for the very extreme south.

Define exstream south

Edited February 3, 2021 by Chrisover93

[Singularity]

2 minutes ago, swebby said:

I tend to have a view the GFS dartboard lows are that model knowing roughly where the energy will be in regards to cyclogenesis but not knowing how to resolve it into a complex pattern of separate low pressures that eventually do manifest in that model in shorter time frame.  So it takes the simple option of dumping the cyclogenesis onto a single point.

In this instance, with that high pressure to the north, i would assume (probably naively) that if it is a complex system of lows, it would be in the form of disruption - with a train of lows being ejected and heading SE (sliding) under the block?

Short answer, yes .

To be fair to the model, I've seen others do it plenty of times too - just not quite so often. ECM does it more these days than it used to in past versions.

[AdrianHull]

1 minute ago, MJB said:

Hmmm really? I had 10cm of snow from -5 850's a couple of weeks ago I am surprised you  are saying snow Darren 

Yes you did. But I think people want  snow from the continent with low uppers. Not a wet 10cm snow /slush 

[Tim Bland]

If you look at the cold across the pond it’s no wonder the jet stream is going into over drive. The block is strong but with a jet like that it’s no match unfortunately.   Long cold spells usually occur when the jet / Atlantic is quiet and this is difficult with that much cold over northern USA. Still a chance that we can get an extra day or so out it and the first shot could slide and give snow , but I don’t think we can sustain our cold for long.
Still 5-6 days with widespread snow cover is significant! ️ 

[nick sussex]

The outputs show a range of options in terms of depth of cold and slightly different evolutions .

I know which one I’d be cheering on if I was still living in Sussex but I signed the NW pledge for neutrality ! 

Seeing as I’m an impartial observer here and won’t be doing any IMBYISM I’m hoping this spell can deliver for everyone .

[Djdazzle]

1 minute ago, Chrisover93 said:

Define exstream south

South coast, maybe Hampshire. (sorry @Alderc!

[BarnetBlizzard]

Am i the only one thinking GFS 12z and the ensembles are looking a bit iffy for those further south? 

[Neilsouth]

2 minutes ago, Tim Bland said:

If you look at the cold across the pond it’s no wonder the jet stream is going into over drive. The block is strong but with a jet like that it’s no match unfortunately.   Long cold spells usually occur when the jet / Atlantic is quiet and this is difficult with that much cold over northern USA. Still a chance that we can get an extra day or so out it and the first shot could slide and give snow , but I don’t think we can sustain our cold for long.
Still 5-6 days with widespread snow cover is significant! ️ 

 

Yes but equally it could force low pressure systems into France, with a number of channel low's

[Chrisover93]

2 minutes ago, Djdazzle said:

South coast, maybe Hampshire. (sorry @Alderc!

Its not a real BFTE if hampshire doesnt

[kold weather]

3 minutes ago, MJB said:

Hmmm really? I had 10cm of snow from -5 850's a couple of weeks ago I am surprised you  are saying snow Darren 

All depends on the wind direction and plenty of other factors.

The GFS 12z has other factors that are more than good enough. For example a SE wind which allows for slightly lower dew points and a good feed of lower thicknesses into the region to compensate. 

00z ECM turned it to rain for the SE as the wind direction was too much ENE which meant the dew points and other factors also were too high, before it turned back to snow for most as the warm sector filled in and cooled down.

I think we will be ok down here, but I've gotta keep people aware of the downside, especially as this place becomes a cold hivemind ay times, then they all get surprised when things dont go as expected for some.

 

 

[Jason H]

11 minutes ago, kold weather said:

All will depend on the exact wind orientation on Monday.

Should we keep a ESE/SE flow as the LP introduces any warm sector (far from certain either!) then it won't be an issue.

Should the winds come from the north-sea, as per the 00z ECM, then we'd probably be looking at a period of sleet and maybe very wet snow on Monday before it scoots out of the way again.

That's very much a worse case scenario. All I can see is snow from that set up.