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Paul

Winter Model Discussion - Cold Hunting - 20th Dec

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New thread for the 12z's - please take a moment before posting to make sure you're using the relevant thread - a lot of the posts in the previous thread during today would have been much more suited to the mayhem thread (linked below).

Current Model Related Threads:

The winter / cold model output discussion thread (this one) - busy, fast moving, sometimes a bit of a rollercoaster, generally cold orientated, with views from a wide range of people with differing interests, biases and levels of knowledge.

In depth model discussion, analysis and summaries - slower moving, sometimes more technical, straight down the line type model analysis, info and discussion:

http://forum.netweat...-and-summaries/

Model mayhem - all the emotion from looking at the models, rants, ramps, hopes etc

http://forum.netweat...n-ramp-go-nuts/

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First post is nothing to do with the models, awesome... Please, have some consideration for the rest of the community who want to use this thread to read about and discuss the models - we've got other threads for rants, moans, wishes etc.

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If you're hoping for a little snow then we must see some more amplification upstream.

This may help draw the Azores high westwards, the ECM 00hrs had a developing low running ne out of the southern states around 168hrs up to the eastern USA.

We need an inland runner towards western Greenland, this might allow a lull in the constant stream of low pressures and allow some retrogression of the Azores high.

It might just be a one off ECM operational run but its realistically the best chance within the current NH set up for cold air to dig further south into the UK.

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Well, on balance, the models did a pretty good job this week, by and large they all showed northeast scotland getting an undercut of cold air from scandinavia and it turns out it's correct, the far northeast of scotland looks cold in the next few days or so with max temps of around 4c with spells of heavy rain turning to sleet and wet snow over hills but mostly rain down at sea level. For most of the uk, tomorrow is a window of drier and brighter weather before more bands of heavy rain sweep north and east for sat/sun and christmas eve, again the far northeast clinging on to colder air but probably being mixed out by the 24th, temps closer to average elsewhere but xmas day and boxing day perhaps colder and more showery with overnight frosts and ice.

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slighly better at 69h better hieghts over scandi and LP further east but still dont see an undercut coming offh500slp.png

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gfs up to 63hrs looks like the low pressure aproaching the sw is push the ne ridge up there could be an undercut on the early stages of the gfs.

no it looks like the heights to our east by 69hrs is finally losing its grip good i say lets move on lol.

low heights are getting to far northeast i think its going to be the heights to the nw which will be our friend hopefully infact ive seen enough to say that its the gfs thats backing down now.

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gfs up to 63hrs looks like the low pressure aproaching the sw is push the ne ridge up there could be an undercut on the early stages of the gfs.

no it looks like the heights to our east by 69hrs is finally losing its grip good i say lets move on lol.

we would have a much better chance if that shortwave doesnt appear between greenland and norway

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So the low at 87hrs is further west and north over Scotland than the 06z, which is better IMO as this can help bring us the cold faster when the low moves west. h500slp.png

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we might see an upgrade on the northerly in this run the LP making better tracks northeast in this run so should help open things up from the north.

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we would have a much better chance if that shortwave doesnt appear between greenland and norway

nice early pressure build nw over greenland at 87hrs could be good news after all.

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Differences between the 12z and 06z, as you can see we are in a much better position as the low is further west, along with the Russian high

post-17320-0-32687700-1356019400_thumb.p

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h500slp.png

h500slp.png

At 96 hours, compared to the 06z

> depression north of the UK considerably further east

>Better ridging in the Atlantic

>Arctic high stronger

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nice early pressure build nw over greenland at 87hrs could be good news after all.

yeah well lets hope we can have some real success with greenland cos it looks like if we fail there then its gonna be a really long road back to anything that might resemble a long cold spell

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Are heights over W greenland as good as E? With the PV to the east of the heights surely it will just be a stalemate? And end up moving away towards central canada?

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yeah well lets hope we can have some real success with greenland cos it looks like if we fail there then its gonna be a really long road back to anything that might resemble a long cold spell

if we want a northerly though we need heights to our east to back east enough for us to get a northerly.

is this another so close moment coming up.

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good chance of some christmas snow of some sort on this runh850t850eu.png

could be nice greenland pressure build aswell between 1045 and 1050mb

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could be nice greenland pressure build aswell between 1045 and 1050mb

Be careful there, its a surface high, the high we are all looking for consists of greens and yellows in that area and not blue/purple.

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that LP just wants to hang around north of scotland and keep the cold uppers out for christmas day

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At least Xmas isn't looking like the barbecue it was a few days back, a chance of some snow in the north but take into account the GFS 850's with this sort of pattern often show a cold bias.

We do need to see some changes upstream to deliver something that can last more than 24 hours.

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that LP just wants to hang around north of scotland and keep the cold uppers out for christmas day

I dont think its a problem as its this low 'anchored' by Scotland which is driving the cold towards the south.

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post-12276-0-25958300-1356020107_thumb.p

Heavy snow/sleet moving into Scotland and Northern Ireland on christmas night, plentiful snow shrs for Scotland, Northern Ireland and NW England (mostly high ground) on Boxing day as well.

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Be careful there, its a surface high, the high we are all looking for consists of greens and yellows in that area and not blue/purple.

Surely, in order to achieve a SLP of 1060mb requires nothing more (or less) than a certain amount of air, in a column - in this case, a lot of air?

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