06z model discussions - wet and windy soon?!

[Troubleatmill]

Hi everyone , could someone tell me what the 528dam line is ? is it really a technical term for the polar front? or is it nothing to do with that ? , sorry if this is a dumb question , ive just heard it bounced around alot , i know it means the onset of colder air but never known quite what it is ?

Edited February 5, 2007 by arron123

[pureasthedriven]

actually they arnt that good...

But the evolution from those charts could be excellent though.

[grab my graupel]

tbh i think they are just saying that to cover themselves in the (remote) event of a major dumping... or even a minor one (lol...london!) ... should occur.

actually they arnt that good, those charts far from convince me that there will be much snow about, except for the highland areas.

Hi Mushy.

I'm often reminded of how quickly this cold spell and the last one appeared on the

models in the first place, and IMO there is still plenty of time for manouvre,

whatever direction the models decide to take.

You must be quite nervous at the moment Mushy

[Rustynailer]

Well the beast is looming and I might let him out of the cage around mid month onwards.

It would make the Evening News and most of the Internet population of Western Europe will go into meltdown if you did

Although there has been little or no chance of even sleet from all this for me, i find this thread compelling at the mo'

My take on the confusion is model un-familiararity with anything quite like a propper winter spell, i also bare in mind that this spell could miss us by 100s miles, then again it could be just nothing but the West blasting straight through... All part of the fun IMO

Russ

[Darren Bown]

Hi everyone , could someone tell me what the 528dam line is ? is it really a technical term for the polar front? or is it nothing to do with that ? , sorry if this is a dumb question , ive just heard it bounced around alot , i know it means the onset of colder air but never known quite what it is ?

I think its to do with snow. If the 528 dam line is south of the UK, then there is an increased chance of snow, combined with negative dew points, cold surface temps oh, and of course, moisture that is.

Daz

Edited February 5, 2007 by Dazmaster75

[mushymanrob]

Hi Mushy.

I'm often reminded of how quickly this cold spell and the last one appeared on the

models in the first place, and IMO there is still plenty of time for manouvre,

whatever direction the models decide to take.

You must be quite nervous at the moment Mushy

lol.. i take onboard the points made re the evolution.. true, im not out of the woods yet! and i am nervous because i want to go metal detecting on saturday, i can do that if its snowy!

the anticyclones to the north do worry me, a large scandi high wouldnt be welcome with me and it is a possible outcome later on...

[grab my graupel]

Hi everyone , could someone tell me what the 528dam line is ? is it really a technical term for the polar front? or is it nothing to do with that ? , sorry if this is a dumb question , ive just heard it bounced around alot , i know it means the onset of colder air but never known quite what it is ?

http://www.netweather.tv/forum/index.php?showtopic=2237

Try this arron

[nick sussex]

It just goes to show how much uncertainty there is when Peter Gibbs on radio 4 weather says that theres a chance of snow but they're very unsure, it could miss us and go into france or alternatively get as far north as Manchester! a nightmare to forecast only 48hrs out, this just about sums up the current models! F1 looks like now even less than 48hrs, incredible!

[Troubleatmill]

http://www.netweather.tv/forum/index.php?showtopic=2237

Try this arron

Cheers Brian ! Oh & Dazmaster !

PS I think its time to get in the fields & see if the cows are lying down going off the various models

Edited February 5, 2007 by arron123

[pureasthedriven]

Hi everyone , could someone tell me what the 528dam line is ? is it really a technical term for the polar front? or is it nothing to do with that ? , sorry if this is a dumb question , ive just heard it bounced around alot , i know it means the onset of colder air but never known quite what it is ?

If you want the techie explanation, ask someone else but I can tell you this - the number relates to the thickness of the air and the lower the number the greater the chance of snow when precipitation is about. The 528 line is a spurious figure though - many other factors come into play for 'guaranteeing' snow. It's the minimum requirement. Check the archive charts for Jan 87 and look at the thicknesses there - now THAT'S what you're after!

Edit: sorry, just seen the raft of responses!

Edited February 5, 2007 by pureasthedriven

[Matty M]

There is a crumb of comfort from this mornings runs and that is that the UKM has backed up the 0z with its 6z output to 48hrs..

This at least shows that it has a totally different feel on things as the GFS

certainly a 50:50 throw up at this point

[multi cellular thunderstorm]

Hi everyone , could someone tell me what the 528dam line is ? is it really a technical term for the polar front? or is it nothing to do with that ? , sorry if this is a dumb question , ive just heard it bounced around alot , i know it means the onset of colder air but never known quite what it is ?

I think its to do with the air mass.

Heres a chart for today showing the 528 DAM line heading south over the UK.

Once the 528 DAM line has passed over I think there is a greater risk of snow.

I'm sure someone else can explain better. They already have

Edited February 5, 2007 by multi cellular thunderstorm

[Darren Bown]

http://www.netweather.tv/forum/index.php?showtopic=2237

Try this arron

Cheers Brian ! Oh & Dazmaster !

I was kinda right

Daz

[Slinky]

lol.. i take onboard the points made re the evolution.. true, im not out of the woods yet! and i am nervous because i want to go metal detecting on saturday, i can do that if its snowy!

the anticyclones to the north do worry me, a large scandi high wouldnt be welcome with me and it is a possible outcome later on...

Mushy, I hope you work with the Portable Antiquities Scheme

The models to me are fascinating at the moment, its going to go right down to the wire this one! Will certainly be interesting to see which models handle these synoptics more accurately!

[mushymanrob]

Mushy, I hope you work with the Portable Antiquities Scheme

The models to me are fascinating at the moment, its going to go right down to the wire this one! Will certainly be interesting to see which models handle these synoptics more accurately!

indeed...my flo records everything...

[Troubleatmill]

I often wonder whether i would take as much notice of the GFS if other models went out to T384 & had runs four times a day ? i wonder if this is why myself & others allways look at the GFS as the main one to look out for as it feeds us more free data & more often per day ?

Edited February 5, 2007 by arron123

[Harsh Climate]

Hmm Im starting to think that the 06z (GFS) might have been a duff run!?

Each run from the the 06z is very similar and theres not 1 run that strays far away from the mean...(if you look at the esemble panel.)

Anyone know if there was a lack of data/sources put into this run?

[Snowyowl9]

It just goes to show how much uncertainty there is when Peter Gibbs on radio 4 weather says that theres a chance of snow but they're very unsure, it could miss us and go into france or alternatively get as far north as Manchester! a nightmare to forecast only 48hrs out, this just about sums up the current models! F1 looks like now even less than 48hrs, incredible!

Too see such uncertainty in such a short timescale before,we`ve got to go back to the 70s/80s for this.

Take one day at a time this week I think.

Tomorrow Scotland looks like seeing some snow anyway

http://85.214.49.20/pics/brack0a.gif

[grab my graupel]

Too see such uncertainty in such a short timescale before,we`ve got to go back to the 70s/80s for this.

Take one day at a time this week I think.

Tomorrow Scotland looks like seeing some snow anyway

http://85.214.49.20/pics/brack0a.gif

Yes exactly it is nail biting stuff at the moment,

The 12z should be interesting tonight, it's going to be a long agonizing wait.

And yes Scotland looks like the place to be tommorow, Unless your Mushy

of course.

[CLOUD NINE]

Hi Nick, just a quick question, do you think this will be one of the times you quote in future? I.E I remember in Feb 2007 when the models still looked like FI 48 hours out?

It just goes to show how much uncertainty there is when Peter Gibbs on radio 4 weather says that theres a chance of snow but they're very unsure, it could miss us and go into france or alternatively get as far north as Manchester! a nightmare to forecast only 48hrs out, this just about sums up the current models! F1 looks like now even less than 48hrs, incredible!

[johnholmes]

Hi everyone , could someone tell me what the 528dam line is ? is it really a technical term for the polar front? or is it nothing to do with that ? , sorry if this is a dumb question , ive just heard it bounced around alot , i know it means the onset of colder air but never known quite what it is ?

hi Arron

I'll try.

The 528dam line is actually a measure of the depth of air between the surface, often taken as 1000mb and 500mb, roughly 18000ft. The lower the value you see on the msl/500mb chart then the colder is the air in this depth(1000-500mb). The colours are NOT values at the surface. 528Dm(decametres) is the number often quoted as below which inland areas have a fair chance of snow. However, you must look at various other factors as well. What is the temperature at 850mb(5000ft), it needs to be -7C or below. What is the dry bulb and dewpoint temperature at the surface. Roughly a dry bulb temperature not above 3C and a dewpoint that is below 0C in frontal conditions are needed. It is a very complex matter.

hope that helps a little.

Do have alook at the Net Wx Guides, and learning areas. Most of it is covered in there.

regards

John

see my answer to you Arron and hope it helps, probably lost in all the posts but if you go to your original I have answered it for you.

John

[nick sussex]

Hi Nick, just a quick question, do you think this will be one of the times you quote in future? I.E I remember in Feb 2007 when the models still looked like FI 48 hours out?

Well only if its a happy and snowy ending and not loads of drama about a damp squib! You see just when it couldnt get any more complicated this shallow low over the north sea causes even more model drama, this stops a ridge from scandi backing west further south, this feature was originally progged to dissipate and allow the ridge further sw, on top of everything else causing problems this feature is another pain to contend with!

http://85.214.49.20/wz/pics/brack0a.gif

If the ukmo cant call where if any snow is going to be under 48hrs away then that really shows just how much uncertainty there is.

[VillagePlank]

According to here:

• Rain and snow are equally likely when the 500-1000 hPa thickness is about 5225 gpm (or 522 dam)
  
• Rain is rare when the 500-1000 hPa thickness is less than 5190 gpm
  
• Snow is extremely rare when the 500-1000 hPa thickness is greater than 5395 gpm; it is rather uncommon when the value is greater than 5305 gpm.
  

522 is deemed to be the snowline (ie that which falls behind this line and has a lower thickness increases the probability of snow. As John said, it's a measure of how much distance there is between 1000hPa (notionally sea-level) and 500hPa (some 5kms upwards)

But you really do need to heed John's advice. Although it is helpful, (because of the correllation between the thickness and temperature )the value indicates a mean air temperature over some 18,000ft which, in certain circumstances, can lead you right up the garden alley!

[edited]

If you look at Nick's Fax chart you can find the 'guarenteed' snow line right west over the middle of the Atlantic and right up North in Scandinavia. An interesting coincidence that the occluded front looking to push down over Britain is going to be on, or very near the 522 line (not pictured) but it looks to me that is that the more that occlusion travels south the more you are going to need altitude the closer to the 528 line.

I'm not sure but if you lived at 100m (like me) and you're under the 528 line (like me) , then this effectively makes the thickness 518 (since 528 is actually 5280 metres) and your altitude clearly reduces the thickness. A clarification from an expert, perhaps?

Edited February 5, 2007 by VillagePlank

[Cumulonimbus Tower]

I am not criticising people for enjoying the rollercoaster - I enjoy it, it is hard not too.

But there is a difference between watching and sharing the ups and downs and mixed fortunes of each ouput and taking them consequentially at face value afterwards. A big difference.

It is not criticism at any level - just humble well meant advice.

Hopefully that finally clears this up.

I think it is only really an issue if people start getting grumpy as a result of synoptics changing

[john mac]

Correct me if im wrong but on the beeb pressure charts later in the week it appears that london is just to the north of the channel feature this can only be good news cant it?