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Captain Shortwave

Model Output Discussion - The final stretch to Christmas

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ooh, nasty!!!!  http://www.meteociel.fr/modeles/gfse_cartes.php?ech=132&code=0&mode=0

 

North Sea storm surge here I'd imagine. Wouldn't want to be living on the coast in parts of EA if this happens. Ridging further north with a small discrete high pressure cell forming. More evidence of a tendency to northern blocking? 

Would this sort of chart produce any snow and can you explain why why not etc just to help me kinda understand cheers 

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Would this sort of chart produce any snow and can you explain why why not etc just to help me kinda understand cheers 

 

I think for my learning process I'd like to second this question please if I may.

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GFS p. Once again shows cold air digging in behind the system. With cold uppers the back edge of the system still showing the possibility of snow even down to the south.

post-15543-0-46321600-1419286875_thumb.j post-15543-0-87238400-1419286890_thumb.j

post-15543-0-66222800-1419286897_thumb.j post-15543-0-77340000-1419286929_thumb.j

Uppers

post-15543-0-56797800-1419286966_thumb.j post-15543-0-28366600-1419286982_thumb.j

post-15543-0-69535700-1419286996_thumb.j post-15543-0-38780800-1419287013_thumb.j

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With 6 hours newer data both GFS's the shortwave to the sw separates and heads ne, normally one would think as this occurs at T90hrs that we could be confident this first hurdle has been overcome!

 

If after 4 days of uncertainty and teases the models don't deliver at least some cold and snow I'm going to have a serious strop in the morning!

 

Anyway so far both GFS's don't back the Euro's but at least deliver some cold and a little snow, hopefully we get agreement in the morning for at least upto the weekend.

I think if ukmo ecm doesn't back gfs we will all go mad it's like the model roller-coaster up and downs let's be positive and tomorrow it will be the ups or -8 cold uppers lol!!

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Just like the models struggle with the track and intensity of ex tropical storm development in the Autumn, so too they are with the projected low pressure due to hit our shores in 96 hours. Often it is only within the 24 hour timeframe they begin to show confidence in the position of such storms - I expect it will take until Christmas Day for confidence to hit - still 3 days away.

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GFS Op. Shows some Backedge snow too not as widespread as on P.

Cold uppers filtering in behind the system.

post-15543-0-17179600-1419287233_thumb.j post-15543-0-85692400-1419287240_thumb.j

post-15543-0-38553600-1419287261_thumb.j post-15543-0-02638500-1419287268_thumb.j

So this evening the outputs once again look mixed bag there is scope for possible snow this weekend.

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Would this sort of chart produce any snow and can you explain why why not etc just to help me kinda understand cheers 

 

Maybe a little, but nothing of consequence for most. See below link

 

http://www.meteociel.fr/modeles/gfse_cartes.php?ech=132&code=0&mode=2

 

Also, note this chart below

 

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=132&mode=3

 

The darker shaded areas the 528 line can sometimes be used as a guide. Albeit because the airmass is maritime sourced it possibly wouldn't be cold enough on low ground despite what the first chart shows.

 

Its only one run though, and this isn't nailed down by a long stretch. Its the sort of scenario from experience where you best expect nothing in terms of snow and maybe we will get lucky. The meto 144 chart looks less dramatic, but is much more wintery and much colder than the charts above. Northerlies look good on the charts but in reality are often much less dramatic in terms of weather on the ground. Always check the upper air profile first (referred to as 850s). See below

 

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=132&mode=1

 

With the air mass being maritime based we really need the -8C line, whereas if it was off the continent -6C probably be adequate.

 

Hope this makes sense, but anticipating snowfall is complex and this post doesn't even consider dew points etc.

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Far better hights ridgging North on the op on this run starting at a relatively early time , from the initial northerly behind the low on 27th , more amplification . I feel we are about to start seeing developments moving into next wk with a poss easterly ?

post-9095-0-89528300-1419287809_thumb.jp

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The (possible) LP for Saturday is now in fax chart range and would bring some nasty weather with it,with rain and wind being the main features at this stage.

 

120 hrs..

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Yes, this would bring snow to some areas in the north and east.

 

 

and midlands and south........

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and midlands and south........

 

With uppers of -2C in the associated warm sector? Perhaps not....

Too far away to even discuss in detail anyway!

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With uppers of -2C in the associated warm sector? Perhaps not....

Too far away to even discuss in detail anyway!

 

-2 is cold enough for snowfall in frontal situations such as this one

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18z GFS not showing any deep cold 5 days

 

gfs-1-108.png?18

 

 

In the longer term an easterly is the only route to proper winter weather, so anything from the north is not going to cut it for anyone south of Yorkshire.

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However the GFS [P] shows sub 528dam air for all of the UK. http://www.meteociel.fr/modeles/gfse_cartes.php?ech=132&code=0&mode=3&runpara=1

 

and uppers 850hpa of -7c http://www.meteociel.fr/modeles/gfs-para/royaume-uni/850-hpa/3h.htm ]

 

Similar setups in the past has delivered heavy overnight snow of several inches on a NNW flow in the past. [snow Streamers]

 

Of course the colder the better and I am sure other people will point to similar setups which haven't delivered. Time of day is important, the best snow streamers event are generally at night time, or even best early morning,

 

However this is academic and things will change, as every run has done in recent days.

WHy are the best snow streamers at night?

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-2 is cold enough for snowfall in frontal situations such as this one

 

 

Not impossible, but usually this would occur where the front moves into an established cold pool which isn't what is happening here. This is because the temperature profile lower down in the atmosphere will be more beneficial. In this scenario you could have -6C and still get rain or sleet because it takes time to mix the warmer air out from nearer the ground. As soon as you get an easterly undercut though this can change as a continental air mass tends to be colder lower down, so you can get -2C at 850C but 0c at ground level. In this set up +3 - +5 would probably be closer. The METO 144 delivers the undercut but GFS doesn't. So really just a few flakes but nothing major I'd have thought.

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WHy are the best snow streamers at night?

 

It is colder overnight and showers are more likely to be of snow at say 6am in the morning than 4pm in the afternoon.

 

Luck plays a big part in terms of weather the same synoptics, can bring much different weather whatever time of day [or night]

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Given the volatile nature of the output and the difficulty pinning down a pattern I may as well elaborate on a "possible" scenario that isn't being modelled.

 

Here is the ridge at 90h pointing toward Greenland.

 

gfsnh-0-90.png?18

 

And here it is 4 days later pointing toward Scandinavia.

 

gfsnh-0-186.png?18

 

I don't recall ever seeing a ridge simply being moved along without being either overrun and flattened or undercut but taking it at face value it does show there is little energy in the Atlantic behind the ridge.

That could prove to be a big positive because GFS has a weakness splitting energy as explained many times by Steve M and it especially has problems detecting undercut.

 

I have no idea which way all this will go but if I were looking for upgrades (and I am) I would look for the pattern to be backed West and a little more amplification of course but also for some signs of undercut from around day 5.

It is likely that ECM would pick it up before GFS if it develops or perhaps it may appear in among the ensembles - if at all.

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Interesting FI on GFSP, split in vortex looking good, crazy strat prob helping and good be good heading into mid Jan.

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