06z model discussions - wet and windy soon?!

[CLOUD NINE]

It may well be puzzling you Nick, its well beyond me!

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.

[grab my graupel]

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

That just reminds me.

Where's January Snowstorm today

[Frosty.]

I think that mild air will have arrived in all except northern scotland by saturday. The Scandinavian High will probably hold firm. A brief snowy headline grabbing event followed by a rapid messy thaw is odds on favourite between wednesday and friday. The other possibility is for a brief snowy event followed by colder but drier air feeding in from the north east with the fronts pulling back west or sw.

Edited February 5, 2007 by Frosty039

[johnholmes]

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!

If you look at Nick's Fax chart you can find the 'guarenteed' snow line right west over the middle of the Atlantic, and nowhere near us at all. Which, in my opinion, means marginal. Having said that frontal snow is possible with higher dam values.

nothing wrong with your points mate.

As for a definitive link. This is to an ex colleague and gives a very good in depth explanation.

http://homepage.ntlworld.com/booty.weather/tthkfaq.htm

John

in fact I would go so far as to say ANY question about meteorology if you are not happy after reading our Guides then this is your first and probably only stop needed!

j

[VillagePlank]

nothing wrong with your points mate.

As for a definitive link. This is to an ex colleague and gives a very good in depth explanation.

http://homepage.ntlworld.com/booty.weather/tthkfaq.htm

John

in fact I would go so far as to say ANY question about meteorology if you are not happy after reading our Guides then this is your first and probably only stop needed!

j

Yes, it's an excellent site, pointed out by Evo, I think on another thread. A superb quote that many people should consider from that page, though:

In the course of this work, Boyden confirmed what others have already pointed out, that the 500-1000 hPa thickness parameter is the poorest discriminator for rain/snow. The best was height of freezing level and surface temperature, both difficult to forecast in 'critical' situations, and the next best/least worst was the 850-1000 hPa value, though Boyden devised the correction 'factor' that we all now use to take account of mean sea level pressure and local height.

Edited February 5, 2007 by VillagePlank

[andy_leics22]

Absolutely awful run!! Just as I thought the battle was being upgraded with each run, this 06z just wrecks the potential altogether. Dear oh dear oh dear

[Troubleatmill]

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

Thanks for that John , really appreciated ! i never knew snow was so complicated ! no wonder we never get any !

But its great that someone like yourself will take the time out to answer my question

Edited February 5, 2007 by arron123

[MKN]

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.

If that low to the east of scotland became any stronger surely that could bring a reasonable amount of snow in itself. I feel the details of thursday wont be ensured until tuesday evenings 18z. The timing of the rain/snow band could also make a big difference, atm around 0600 is the time and surely that would give us the best possible chance of snowfall further south if only for 2 or 3 hours.

[PersianPaladin]

Is that the beast looming at ECM T144?

[john mac]

Would it be better for us if the low on wednesday stayed south. would this give a more prolonged cold snap

[Paul]

Will be closing this one shortly ready for the 12z models.

[PersianPaladin]

Edited as off topic - please post into the appropriate thread.

[jimbo36]

Hey Everyone......I don't normally post on here, but i'd plead to everyone getting so upset over the GFS 06z run. It is just one run of many. Look at how all of the other models have behaved over the last 48 hours. They're all over the place and because this set up is so unlike anything we've had for a number of years, they don't know how to handle it past 24hrs.

I feel most of you won't be dissapointed by what happens later this week, bearing in mind whay NOAA have been showing.

Remember this is the beauty of British weather. You never really know what is round the corner until you're nearly there.

If you want snow that much, then try a holiday in Lapland or Canada. Once you've been there a week or two, you'll soon rave for the warmth and light of summer!!!

Sorry to write something that doesn't entirely flow with the model output discussion, but i feel too many people on here are basing their future hapiness on just a few computerised models.

Remember, what will be will be...........these models will change again and i know most of you will be happy with the results!!

Be lucky, be happy.......Jimbo

[grab my graupel]

Is that the beast looming at ECM T144?

It appears you have been doing the same as I have, and that is

looking into F.I. and the ensembles for signs of encourgement.

John Holmes will be giving us a telling off.

[Upgrade]

Would it be better for us if the low on wednesday stayed south. would this give a more prolonged cold snap

the "cold snap" seems mroe likely to be now be 3 or 4 days of slightly below average for the time of year day time temps or 3 or 4 degrees C for most of the country.

the latest models don't show any ice days or any snow for most people and the forecasters on the TV are seriously hedging their bets as the scenario looks very difficult to forecast, though the weekend's charts led to a tantalising forecast like we used to get in the good old days , on countryfile, today the charts have made the prospect of frontal snow which doesn't turn back to rain, seem remote.

We await the 12z with baited breath for a more hopeful view! lets see what happens to the snow Factor, the positioning of this low is crucial but i think that the warm SST's and the jet may conspire to spoil the party.

has to be said though that the progression back to the full zonality looks not that convincing to my amatur eye.

[MKN]

Hey Everyone......I don't normally post on here, but i'd plead to everyone getting so upset over the GFS 06z run. It is just one run of many. Look at how all of the other models have behaved over the last 48 hours. They're all over the place and because this set up is so unlike anything we've had for a number of years, they don't know how to handle it past 24hrs.

I feel most of you won't be dissapointed by what happens later this week, bearing in mind whay NOAA have been showing.

Remember this is the beauty of British weather. You never really know what is round the corner until you're nearly there.

If you want snow that much, then try a holiday in Lapland or Canada. Once you've been there a week or two, you'll soon rave for the warmth and light of summer!!!

Sorry to write something that doesn't entirely flow with the model output discussion, but i feel too many people on here are basing their future hapiness on just a few computerised models.

Remember, what will be will be...........these models will change again and i know most of you will be happy with the results!!

Be lucky, be happy.......Jimbo

It seems to me the gfs over played the high pressure over scandanavia to begin with, and has now undercooked it, hopefully we get some sort of middle ground as this would probably lead to the best result for most of us

[wellington boot]

Wow, ive only just got to look at the 6z. What a bizzare set of models today. The gfs which has led the push for cold snoy weathr with a strong scandi high and a southerlky tracking jet, just reverses completely and decides to go with the ecm after all. Meanwhile the ecm does the same and decides the gfs was right all along. Ukmo standing firm though. Good potential with those fax charts. I suspect theres going to be a pleasant surprise with the 12z gfs though.

[The Eagle]

Im looking forward to the 12z but another poor run would really be a nail in the coffin at this late stage but we will see.

[PersianPaladin]

Casts PP jinx-spell on 12z.

[grab my graupel]

Im looking forward to the 12z but another poor run would really be a nail in the coffin at this late stage but we will see.

Yep I can feel the tension building already, it is an important run this one,

but which way will it go?

Actually I think it will be very similar to the 06z.

[Paul]

Locking this one now - new thread is open for the 12z's:

http://www.netweather.tv/forum/index.php?showtopic=36194