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Model output discussion - here comes the beast!


Message added by Paul

Please only post model discussion in this thread 

For more general chat and banter, or moans and ramps loosely around the models, please head to the banter thread:
https://www.netweather.tv/forum/topic/86721-model-moans-ramps-and-banter/

For general weather chat including about the snow/cold chances around the country, please go to the regional threads:
https://www.netweather.tv/forum/forum/142-regional-discussions/

We also have a special post SSW cold spell discussion open here:
https://www.netweather.tv/forum/topic/89358-ssw-related-cold-spell-will-it-wont-it/

Thank you!

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Early guidance forewarning of next weeks weather was issued earlier on, and this has been further enhanced with extended outlooks in bulletins. AFAIK (comms not being my area) public agencies and majo

Come on those looking for the breadown before the major cold and snow has begun You will be very lucky if that is the correct word to see this in ANY winter in the rest of your lives I would sugg

Microscale detail absorbing an awful lot of attention on here, when in reality it is a waste of emotion. The macroscale pattern is now fixed - it will not change significantly now for the start of nex

Posted Images

Day 6 from the GFS

gfs-0-144.png?12

GFS probably good enough with the low stalling just short of the UK and starting crawl east along the English channel, whilst 850s lift out it is still good enough for snow.

UKMO

UW144-21.GIF?24-17

This does bring a more maritime feed into the south though a spell of heavy snow is likely with it turning back to rain on the back edge, not overally mild behind, just less cold. We may get the colder air back south again though with that cold air extending east.

GEM

gem-0-144.png?12

SImilar, heavy snow turning back to rain on the back edge, never overly mild afterwards with the cold air never far away in the south and never really leaving the north.

The theme is similar in terms of the broad trend, but the placement of the pattern by a couple of hundred miles north or south is crucial in determining cold and snowy conditions on milder conditions. Plenty of precipitation moving across the UK given the set up which could easily turn to snow the further north you are.

 

Edited by Captain Shortwave
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12 minutes ago, Nick123 said:

Silly question alert. If that was to verify.... it looks very snowy for the north? Or am I reading it wrong?

Yes but look at UKMO and GEM, both of which would blanket the north over Thursday and Friday rather than a few inches.

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UKMO and GEM don't look to dissimilar so I'd assume the temperature profile would be similar for both.

Anyway the game for the south is real simple with this, if 850hpa stays below 0C, it'll snow due to the cold surface...above and it depends on how deep the mild layer air is, rain or perhaps freezing rain (which maybe the MOST dangerous of all solutions, how often do we get freezing rain?)

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Just now, kold weather said:

Very close run thing for the south on the 12z GFS, probably another 20-30 miles south and an all snow event for everyone.

As it happens, GFS goes for a big snow event west of say a line from Portsmouth north and a freezing rain event further east in the SE. Back to snow later.

BETTER run than the 06z GFS for sure but still mighty close either way!!

Yep agree with that. Very tight margins here indeed. Its not so much how far north the low gets rather that we want it slightly further east to keep us on the colder side. The main risk is to the SE (after a whole lot of snow). I think further west its just a straightforward blizzard given the set up. Better 12z run that's for sure though.

 

 

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1 minute ago, kold weather said:

UKMO and GEM don't look to dissimilar so I'd assume the temperature profile would be similar for both.

Anyway the game for the south is real simple with this, if 850hpa stays below 0C, it'll snow due to the cold surface...above and it depends on how deep the mild layer air is, rain or perhaps freezing rain (which maybe the MOST dangerous of all solutions, how often do we get freezing rain?)

No, the dewpoints are more important, above zero rain, below zero at least falling as snow.

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1 minute ago, ukpaul said:

No, the dewpoints are more important, above zero rain, below zero at least falling as snow.

The airmass is so cold the dewpoints and 850hpa temps will probably be almost identical, so they are probably telling the same story, at least for the initial thrust of snow from the south. As time goes by things change.

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3 minutes ago, PerfectStorm said:

GEM's solution.... :O 

gem-2-132.png?12

That looks like a good dump!  Many of the runs this afternoon look like giving us the best of both worlds.  Heavy snow from the system moving up from the South and then a continuation of the cold as it fills and moves East into the Low Countries.

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So, the GFS is keeping the cold for the north and midlands, still too energetic maybe?

gfs-1-192.png?12

And what do we make of this in the wings???

gfs-0-192.png?12

No it's going balls up again,  it at least it tried this time.

Edited by Mike Poole
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Appears the GFS 12z is starting to correct this low *slowly* southwards.

FDFD.thumb.png.01ba7a5da5877e960ea912f9b961b895.png

From over the years, forecasting any low from the South is difficult as it's against the norm. As @Steve Murr and others have stated, a move towards the Euro's take on the track is looking more likely right now.

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2 minutes ago, kold weather said:

The airmass is so cold the dewpoints and 850hpa temps will probably be almost identical, so they are probably telling the same story, at least for the initial thrust of snow from the south. As time goes by things change.

The south has DPs over zero from Friday lunch until Saturday (at least GFS says so), so about four or five degrees higher than any 850s.

156-101UK_wex9.GIF

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3 minutes ago, ukpaul said:

The south has DPs over zero from Friday lunch until Saturday (at least GFS says so), so about four or five degrees higher than any 850s.

156-101UK_wex9.GIF

Ireland looks well placed. With dewpoints below zero and heavy ppn it could close the country

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There's a mass of very cold air just waiting to keep the easterly flow going if we can get over the hurdle of those low pressure systems trending too far north. Swing them south over France and we could be extending things for quite a while.

gfs-0-192_hxb5.png  gfs-1-192_gra3.png

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Just now, January Snowstorm said:

Ireland looks well placed. With dewpoints below zero and heavy ppn it could close the country

Definitely, although it's way too far out and it could change hundreds of miles either way. This one has Ireland, the Welsh/English border and around the Severn Estuary in its sights before it calms down.

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