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phil nw.

Model Output Discussion 1st January 2014-06z onwards.

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Hello 

 

As a newbie I have a question regarding air circulation around high and low pressure areas and how to interpret them on the various models.  I'm not sure if this is the right place to post but the site is fairly daunting with the sheer volume of message boards so apologies if I'm in the wrong place (please feel free to point me in the right direction).

 

Anyway the question is when looking at airflows hitting a low pressure area on one of the models output pages: how can you infer whether the Coriolis effect will dominate or the pressure gradient force?  Also I'm struggling with how to interpret the impact of friction on the Coriolis effect and whether I really need to consider it if the airflow is a westerly, given it's coming of the ocean?

 

I'm sure these questions betray my own ignorance but an answer would help me in interpreting model output even if it's "You are missing the big issue and focusing on a small/irrlevant one muppet!"

 

Hey,

 

Generally, friction becomes more dominant at the surface whereas the pressure gradient force and coriolis effect tend to balance each other out aloft. Now of course you get rising and falling air etc etc, so air will always converge towards the low centre and diverge from the high centre, but crossing of isobars is more pronounced at the surface.

 

Make sense?

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Not currently something of concern for the weekend. Further down the line things get more complex, obviously given messy NWP solutions, and all the more so given emerging signals high aloft. But eventual outcome has great uncertainty given wide raft of model flux even just beyond the weekend, let alone even further ahead.

thanks for the update mate!!

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Ahh, so suddenly the GFS seems to be everyones best mate this evening... I wonder why lol.What a difference a day makes!

I for one still despise te model but it's good to have less uncertainty looking further ahead

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Ahh, so suddenly the GFS seems to be everyones best mate this evening... I wonder why lol.What a difference a day makes!

 

I'm not sure Steve should even be allowed to enjoy a single GEFS perturbation, given his rhetoric?

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I for one still despise te model but it's good to have less uncertainty looking further ahead

Hopefully, the april update to the model will vastly improve It's later output score.
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Cold ens emerging from Eastern Europe and Scandinavia, with some very cold runs in the mix.

 

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Hey,

 

Generally, friction becomes more dominant at the surface whereas the pressure gradient force and coriolis effect tend to balance each other out aloft. Now of course you get rising and falling air etc etc, so air will always converge towards the low centre and diverge from the high centre, but crossing of isobars is more pronounced at the surface.

 

Make sense?

Yes thanks - I understand friction is lower closer to the surface, but I've read that the effect is  10 - 15 degrees deviation in direction between boundary airflows and those at surface level coming in off the ocean, and around 40 - 50 degrees from the land.  I'm lacking a relative scale, I understand it puts the centre of the low further forward but am not sure to spot this from the model output.  Is the best method simply looking at model output at different levels of the troposphere?  I guess I'm looking for output that would show wind spiralling towards the low pressure centre, or out from a high pressure centre, at the surface layer, compared to a bigger swing right at higher boundary levels if the Coriolis effect dominated the pressure gradient at this height?

 

The impact would appear significant to me but I lack the experience or confidence in how all the variables interact to work out whether I should be obsessing about this.  It just seems a big deviation, and as a economics lecturer and financial modeller it stood out.  As said I'm very new to this but I am enjoying watching mathematics versus mother nature.  Almost as interesting is the range of posts on this board and the topic of behavioural finance.  Some might call it human nature but then I'd be out of a job. Best call it cognitive dissonance and confuse people with terminology!

 

On a side note I think I'm an fan of extremes hot, cold, windy or whatever.  Watching the models of these brutal lows steaming in off the atlantic and then seeing the effect has been a buzz.  Hey I got stuck on a steam train visiting Santa with a four year old and one less than two, due to a fallen tree.  When you've survived three hours of that and the blitz spirit being rekindled by railway enthusiasts singing Rudolph the red nosed reindeer you know its been an amazing period of weather. I've learnt a lot seeing the pressure gradients and temperature differentials between Canada/US and the warmth of temperate air from the South fuelling the Atlantic to unbelievable levels.  Not cold for the UK but amazing to watch and a rare event. 

Edited by Trom
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It's on folks and much earlier than may have been previously thought. 00z GFS is very good potential.

 

 

This is what we want to see at 120 hrs

 

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Edited by The Eagle
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Posted Image

post-11361-0-86599000-1389157347_thumb.g

(if you don't know your want to be looking at Scandinavia on this chart not the US freeze for our real cold air, not saying it won't affect in some way it would but the north and east is where we keep watch for the real cold for here)

Posted Image  sorry are have some more sensible posts next time..

 

Well it is the first real cold of winter!! (possibly)

Edited by ElectricSnowStorm
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GEM 00z

http://www.meteociel.fr/modeles/geme_cartes.php?ech=6&code=0&carte=0&mode=0&archive=0

UKMO - 144

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Both excellent for different reasons.

That GEM run is fantastic! Almost reverse zonality with a band of high pressure to the north and lows to our south driving easterlies out into the atlantic... and this is within the next 10 days, very interesting.

Dan

Edited by SNOWPLOUGH
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GEM is superb.

This has developed so quickly, just goes to show that you can never write a particular weather type off.

Now let's hope no shortwaves spoil the party!

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That GEM run is fantastic! Almost reverse zonality with a band of high pressure to the north and lows to our south driving easterlies out into the atlantic... and this is within the next 10 days, very interesting.Dan

 

 

 

 

UKMO is very good evolution too. Possibly better. It's actually time wise similar to the GEM. The next chart on the UKMO (168) would almost certainly be east or north easterly with generous low heights in the continent.

 

Also look at the cold source on UKMO east of Scandinavia. It gets no better than that any time of year.

Edited by The Eagle
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UKMO is very good evolution too. Possibly better. It's actually time wise similar to the GEM. The next chart on the UKMO (168) would almost certainly be east or north easterly with generous low heights in the continent.Also look at the cold source on UKMO east of Scandinavia. It gets no better than that any time of year.

Yes thats very true- straight source from siberia, the perfect source considering the mild continent at present too. I also like the lack of depth to that low to our south on the +144 UKMO chart, perfect for sliding under the block.This has developed at a pace I dont think ive seen before, hopefully we can continue with the Upgrades and keep all the models on board.Edit : There is also a lovely Northern Italian low on that UKMO chart!Dan Edited by SNOWPLOUGH
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Edit : There is also a lovely Northern Italian low on that UKMO chart!Dan

 

The jet stream is perfect.

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Mean 850hpa temps now hit -5c next week.

post-12721-0-91883600-1389160950_thumb.j

Control run must be good viewing.

Edited by AWD

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ECM good start at 72 hrs

 

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The crucial ridge forced ahead of the secondary low to the south west. Slightly higher pressure to the north east. Could be interesting.

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Well what a fantastic set of overnighters to start a new day with (ECM still yet to come).

Crucially a continuation from yesterday's output and no climb down thus far overnight. Will be watching the ECM roll out with everything crossed.

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The UKMO, GEM, GFS looks very good this morning all now showing a colder trend next week, crucial timeframe is between 72h-144h :) very happy with the output.

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