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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

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26 minutes ago, Astral Goat Juice said:

Gavin, it's an Easterly flow - which is usually quite dry for a lot of areas, the models DO NOT pick up on convection as the winds cross over the warmer sea creating instability which will = heavy snow showers, predominantly in the East. 

As a learner can you help me here,  I know and have seen with my own eyes that models are poor at picking up snow and that it can pop up from nowhere, 'get the cold in then worry about snow etc.'  if that is the case, why where there so many posts in the last few days about how much snow the models where showing?  

Can you see how that confuses a learner?    Comment on the models when they show snow, thats fine, but when they dont, ignore them, they cant pick up snow????

Is it not the case that some of the model runs have shown set ups that are very likely to deliver lots of snow to large areas, and other runs have shown set ups that may see snow popping up but less likely and to a smaller area?   If that is the case, is it not legitimate to comment on that? 

 

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10 minutes ago, chris78 said:

As a learner can you help me here,  I know and have seen with my own eyes that models are poor at picking up snow and that it can pop up from nowhere, 'get the cold in then worry about snow etc.'  if that is the case, why where there so many post the last few days about how much snow the models where showing?  

Can you see how that confuses a learner?    Comment on the models when they show snow, thats fine, but when they dont, ignore them, they cant pick up snow????

Is it not the case that some of the model runs have shown set ups that are very likely to deliver lots of snow to large areas, and other runs have shown set ups that may see snow popping up but less likely and to a smaller area?   If that is the case, is in not legitimate to comment on that? 

 

Only advice I can really offer is:

1. Get the cold in, the snow will follow
2. Ignore PPN charts unless in UKV NAM etc range
3. Stick to reading the more knowledgeable posters - Steve Murr, Chiono, Nick F etc, with my personal preference who always offers a fantastic insight with details and zero bias - John Holmes. 
4. Use the ignore function for the rest :rofl:

It's well known that Easterly flows are sometimes dry - but the depth of cold, and the instability that will be caused as it crosses the North Sea will cause heavy snow showers penetrating well inland. 

To be honest, I've been here since day one of NW, and I have never seen such an influx of new member WUM accounts so I can fully understand for new members how confusing this is and for the MODS to get a hold of who's genuine and who isn't. 

Anyways, don't worry about it, it's freezing here today with frost, so the cold is already here.

Edited by Astral Goat Juice
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6 minutes ago, chris78 said:

As a learner can you help me here,  I know and have seen with my own eyes that models are poor at picking up snow and that it can pop up from nowhere, 'get the cold in then worry about snow etc.'  if that is the case, why where there so many post the last few days about how much snow the models where showing?  

Can you see how that confuses a learner?    Comment on the models when they show snow, thats fine, but when they dont, ignore them, they cant pick up snow????

Is it not the case that some of the model runs have shown set ups that are very likely to deliver lots of snow to large areas, and other runs have shown set ups that may see snow popping up but less likely and to a smaller area?   If that is the case, is in not legitimate to comment on that? 

 

It's hype they don't really know mate I would suggest that you wait until at least the week of the event. Not even the models have a handl on it until much nearer the time. Ask John Holmes!

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1 minute ago, Team Jo said:

^^^ I think the last few posts highlight my earlier point.... lots of learners in here at the moment. Writing off prognosis on one run is just bonkers. (IMHO)

Thanks Jo and the others who responded!

Am I right in thinking then that posters getting really exited about snow the last few days are being just as foolish as posters panicking about lack of snow today?

 

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Some strange comments in here this morning,some folk might think we are heading for mild sw winds, all looks good to me if its cold and snow you are after, anything after 120 is always subject to change and often much sooner, dont get too hung up on individual runs, it will drive you crackers.

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A bitterly cold Easterly airstream below -10hpa as is shown on the models hitting the U.K. by about sun into Monday ,crossing the relatively warm North will more than likely produce snow showers on the East and SE coasts from Monday and spreading further inland as it’s looking fairly windy too.The stronger the wind the further inland the snow showers will penetrate inland.

The high res models will be picking up on this soon,so,it’s best to follow them in a couple of days time.

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The signals from all the models are superb for the prospects and no one is being foolish for getting excited about this cold

spwll as it looks remarkable. But snowfall is notoriously hard to predict and often can materialise very quickly. The upper air temps will start to drop from today in my view and continue to do so over the weekend. Welcome to the discussion 

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Can’t post charts at the minute but all models look very good for cold and snow England and Wales look to be in the firing line the future north and west you go less cold and brighter but could change on next set of runs. :cold:

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28 minutes ago, chris78 said:

As a learner can you help me here,  I know and have seen with my own eyes that models are poor at picking up snow and that it can pop up from nowhere, 'get the cold in then worry about snow etc.'  if that is the case, why where there so many posts in the last few days about how much snow the models where showing?  

Can you see how that confuses a learner?    Comment on the models when they show snow, thats fine, but when they dont, ignore them, they cant pick up snow????

Is it not the case that some of the model runs have shown set ups that are very likely to deliver lots of snow to large areas, and other runs have shown set ups that may see snow popping up but less likely and to a smaller area?   If that is the case, is it not legitimate to comment on that? 

 

As John Hammond (ex-BBC) stated on his online video yesterday, models are notoriously poor at picking up convective precipitation (showers). He explained that they tend to vastly underplay the amount of precipitation that will fall further inland in this type of scenario.

The bottom line is this - we will never really be confident of the exact amount and location of snowfall until we are within 24/48hrs of the event. Even then the models can be wrong and very much becomes a case of nowcasting and radar watching. 

With regards to the cold spell next week - the excellent model runs over the last few days have excited many of us due to all the right ingredients being in place for a convective easterly, as opposed to a dry, cold easterly. What are those ingredients? Very low 850 temps (sub -10), low thicknesses, high lapse rates, relatively warm sst’s over the North Sea, late February sun being stronger than midwinter (which can fuel shower activity inland) etc etc. 

Ofcourse, if high pressure builds over us and we lose that feed of very cold 850 temps and pressure increases, then shower activity will be cut off or reduced. 

So don’t pay too much attention to precipitation charts beyond a few days, or even less. Many of the best convective snow events have popped up at short notice. If I remember correctly, the Feb 2009 Thames streamer was picked up within 24/36 hrs.

Edited by danm
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Icon similar to its previous run   High perhaps more north. cold uppers entering the UK   early Monday Morning,  For me at the moment thats all we should be concentrating on.  

Edited by weirpig
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3 minutes ago, ZK099 said:

Early doors but the 6z looks even further south... We'll see anyway. May be a premature judgement. 

That said the Canadian vortex looks better orientated to allow better height rises to the North. Should be an interesting run. 

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16 minutes ago, chris78 said:

As a learner can you help me here,  I know and have seen with my own eyes that models are poor at picking up snow and that it can pop up from nowhere, 'get the cold in then worry about snow etc.'  if that is the case, why where there so many posts in the last few days about how much snow the models where showing?  

Can you see how that confuses a learner?    Comment on the models when they show snow, thats fine, but when they dont, ignore them, they cant pick up snow????

Is it not the case that some of the model runs have shown set ups that are very likely to deliver lots of snow to large areas, and other runs have shown set ups that may see snow popping up but less likely and to a smaller area?   If that is the case, is it not legitimate to comment on that? 

 

Those who are looking at "snow potential" are dabbling a little bit in the "crystal ball" artistic dalliance to be fair, however it's not entirely that baseless.

When we talk about "good potential for snow" and "|dry as a bone" we are actually really focusing on a few key factors that make up the level of instability in the charts, the higher level of instability in the charts the better the potential for snow. What you're looking for is:

  1. Colder uppers - to raise the difference between North Sea surface temperatures and North Sea upper temperatures (in a Westerly this would be Irish/Atlantic Sea). It's the difference between these two temperatures that creates convection (an oversimplification I know); the more convection that is being created the higher the chance there is off it snowing, naturally. This is why there was discussion before about -8 uppers instead of -10 or -12 uppers being worrying. Whilst it is definitely snow at that level of cold uppers, for areas that are on the wrong side of the country (in the case an easterly, but the same rule can be reversed for westerlies) then the chance of snow being present is lower, due to the lower rate of convection. The reason we're looking for real cold uppers in the west coast is so there's a chance of inland convection which increases snow risk. 
  2. Strong winds/low pressure systems - If a low pressure system is showing on a run with tighter isobars we are looking at the likelihood of snow for areas that are under those tighter isobars showing lower dam numbers. This is a more definite signal than the above, and usual when you start hearing the word "blizzard being thrown about". On the other hand if the isobars are stretched wide and showing higher numbers then we are looking at potentially freezing weather with very little snow. One of the main risks with this set up for fans of snow is that we become part of "the block" which would mean being sat under the high pressure system and ending up in this situation. The cold air then diverts round the bottom of us and heads to France and the Channel Islands.

 

There's other factors that might come into play nearer the time, but this is the best gauge of snow potential we have at the moment. The reason you're told not to look to much into it is sheer volatility, from run to run these parameters will massively change as we have seen the past few days. 

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4 minutes ago, danm said:

As John Hammond (ex-BBC) stated on his online video yesterday, models are notoriously poor at picking up convective precipitation (showers). He explained that they tend to vastly underplay the amount of precipitation that will fall further inland in this type of scenario.

The bottom line is this - we will never really be confident of the exact amount and location of snowfall until we are within 24/48hrs of the event. Even then the models can be wrong and very much becomes a case of nowcasting and radar watching. 

With regards to the cold spell next week - the excellent model runs over the last few days have excited many of us due to all the right ingredients being in place for a convective easterly, as opposed to a dry, cold easterly. What are those ingredients? Very low 850 temps (sub -10), low thicknesses, high lapse rates, relatively warm sst’s over the North Sea, late February sun being stronger than midwinter (which can fuel shower activity inland) etc etc. 

Ofcourse, if high pressure builds over us and we lose that feed of very cold 850 temps and pressure builds, then shower activity will be cut off or reduced. 

So don’t pay too much attention to precipitation charts beyond a few days, or even less. Many of the best convective snow events have popped up at short notice. If I remember correctly, the Feb 2009 Thames streamer was picked up within 24/36 hrs.

Thanks for the explanation Dan. To help us complete novices out, can you briefly explain please in layman's terms what you mean by thicknesses and high lapse rates.  

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