Winter Model Discussion - 11/01/13 00z Onwards

[80sWeather]

Cant post charts on phone, but is Mondays snow event like last Febuarys?

Cold to the East and fronts approaching from NW.

[dbaloo]

Hi.Could any1 tell me what set of charts we are waiting to come out next and what time?many thanks

[Summer Sun]

Hi.Could any1 tell me what set of charts we are waiting to come out next and what time?many thanks

All chart update times can be found here -

Thanks

[Yarmy]

Looking at the verification stats for the main players:

http://www.emc.ncep....l/aczhist6.html

(BTW, is this the most up-to-date place to find them?)

Does anyone have the dates of previous SSWs (or even minor warnings) to plot against that? Might give us an idea of how the models do in those circumstances.

What stands out for me is that they seem to usually do better in the NH winter then summer (more solar energy = more volatility, I suppose). Also, they seem more consistent in the SH.

Edit: Should also note how much they have improved over the decades. Remarkable.

Edited January 11, 2013 by Yarmy

[BLAST FROM THE PAST]

not looking good for Ireland and the S.W thus far . gfs ens scatter is promising though .

Indeed any inroads/erosion is met by Ireland and SW. However, sometimes they fayre best too.

Cheers Nick S for imput and and updates

BFTP

[from russia with love]

80s weather- the snowfall for monday into tuesday is like last february however there won't be as much snow this time. I feel areas from London to the Wash will do very well out of monday's event. Places like Hertford, Cambridge and Peterborough could see 5-10cm out of the event. Charts just need firming up on how west the band is.

[bluearmy]

pointless guessing on precip amounts re mondays frontal system. the FAX has no circulation but the raw output at T96 has one. changes such as this will dictate what happens and indeed could change the track of the triple point. i would suggest tomorrow evenings FAXES (12z issue) will be the first worthwhile guidance re precip qtys and pinned down track of the system.

[exodus]

Can I ask, Is there potential of convection from the Easterly on Sunday for the East of the country as the Low passes into Europe?

[80sWeather]

80s weather- the snowfall for monday into tuesday is like last february however there won't be as much snow this time. I feel areas from London to the Wash will do very well out of monday's event. Places like Hertford, Cambridge and Peterborough could see 5-10cm out of the event. Charts just need firming up on how west the band is.

Cheers mate.

[Weathizard]

Anyone else seen the CFS at 144? It always was a very reliable model. #sensethesarcasm!

Can I just apologise in advance I won't be able to post charts for a while as I have no access to computer at the moment so if I'm referring to things rather than posting charts that is why.

[Liam J]

Anyone else seen the CFS at 144? It always was a very reliable model. #sensethesarcasm!

Can I just apologise in advance I won't be able to post charts for a while as I have no access to computer at the moment so if I'm referring to things rather than posting charts that is why.

I expect this is how many of us would like the charts to look next week! CFS keeping the dream alive

Edited January 11, 2013 by Liam J

[The Eagle]

GME 12z going the right way by the looks of things

[Orpingtoniceagedec10]

That low currently off to the nw of Ireland doesn't seem to be making any progress at all eastwards , just going due south !

[Methuselah]

GFS backdown appears to have missed quite a few on the thread today...... diluted by 35% from 00Z charts.... upgrade possible but not likely I fear

Could be more to do the the GFS's current penchant for unexpected about-faces. Could there be another one about to happen?

Eyes down! Toys at the ready!

[derrylynne]

There really is no way of prediction amounts of snow or where it will fall. Many times have I seen the south east for instance forecast a good dumping. To wake up when I lived there to nothing on the ground and new reports of standed travellers in the south west. Even if it is know where snow will fall, forecasting amounts is a very hard thing to do. Just be happy that the UK or at least most parts of it will be cold enough for snow, then keep you fingers crossed it does.

[Lynxus]

Could be more to do the the GFS's current penchant for unexpected about-faces. Could there be another one about to happen?

Eyes down! Toys at the ready!

Toys at the ready? Why? To Put back in the pram?

I truly hope the GFS gives some wonderful outputs, the last one ( Not having all the data ) wasnt too bad IMO... This one Im hoping will be an upgrade. I bet ya!

Not long to go!!!

Edited January 11, 2013 by Lynxus

[Methuselah]

Quick reminder, peeps...If your post has disappeared, you'll probably find it here:

[raul_sbd]

I know its been said many times but what time exactly starts the GFS? And what time will be the key time T96? Thank you and sorry for my ignorance

[Wilxy]

Well here we go again, so how is everyone preparing themselfs, toys at the ready or a nice warm cupa.

I think the model to really watch tonight is the UKMO be intresting to see where we end up near the end of next week.

[Interitus]

This has been mentioned before, but just a quick clarification of the term 'polar vortex'. For those that aren't aware, the troposphere and stratosphere vortices are related, but they are NOT the same.

Here we can see the average Northern hemisphere January 1000mb pressure pattern with high pressure over the land (especially eastern Siberia/Mongolia) and parts of the frozen Arctic ocean - these are areas caused by intense surface cooling aided by snow cover, long winter darkness and distance from the tempering effects of the sea.

Meanwhile there is low pressure over the Northern Atlantic and Pacific oceans - areas where there is strongest contrast between the cold and the warmer sea. This is the average surface pattern as typically seen represented by isobars on weather maps, there is no polar vortex here.

The surface cooling extends through approximately 5km of atmosphere or to around the 500mb pressure level and here and above is where we see the troposphere polar vortex, extending across the North Pole with lobes over Eastern Siberia and the Canadian Arctic - this is typically seen in the darker blue and purple colours shown on the model pressure charts, or in the Northern hemisphere 500mb anomaly height charts with their pattern of ridges and troughs used by JH.

This is not a surface feature, and it is perfectly normal that this vortex can lie above surface high pressure areas shown in the 1000mb chart as the surface cooling helps to create the low pressure above. So when an area of low 500mb heights is shown to move over the Northern continents it doesn't mean that high pressure can't form there as is sometimes suggested.

While the troposphere vortex exists all year round, smaller in summer, the statosphere polar vortex is formed by radiative cooling from the Autumn onwards which gives it the alternative name of polar night vortex. This is shown below over the North Pole at the 100mb level

Here is a view of the stratosphere potential vorticity (pv) north of 70°N showing the formation of the vortex from September high in the strat and this grows downwards throughout the winter and may eventually reach the base of the stratosphere by February - as shown by the green band which is the upper trop/lower strat pv anomaly - before disappearing in spring.

Below is the SSW of January 2009, with a sudden drop in vorticity which never fully recovered before the normal end of season (source for graphs http://www.staff.sci...ResponseSSW.pdf)

With an SSW this vortex becomes disrupted, can be moved, split or even largely dissipate which affects the location and shape of the tropospheric vortex below, and there is thought to be perhaps -5m/s effect on tropospheric west to east flow. Counteracting this are the normal meteorological processes of the troposphere below which makes up 70-85% of the total atmosphere by mass. The stratospheric vortex once disrupted can remain so for a couple of months, or might not properly reform during the rest of the winter, but the troposphere vortex will continually reform and shift to varying extents.

If the models struggle with SSWs must be purely down to modelling the up/downwelling and interaction between the trop and the strat because they certainly are not a new concept as this random article from 1961 describes - http://journals.amet...ROTDCO>2.0.CO;2

[Great Plum]

I know its been said many times but what time exactly starts the GFS? And what time will be the key time T96? Thank you and sorry for my ignorance

3.30 and about 4pm!

[Snowy Liverpool]

I know its been said many times but what time exactly starts the GFS? And what time will be the key time T96? Thank you and sorry for my ignorance

3.30pm, key time will be 72-120 imo which will be around 3.50-4.10pm, to see if the shortwave moves southeast and to see if we get an undercut.

Edited January 11, 2013 by Snowy Liverpool

[raul_sbd]

Many thanks both of you greatings from the North West

[dbaloo]

I know its been said many times but what time exactly starts the GFS? And what time will be the key time T96? Thank you and sorry for my ignorance

All chart update times can be found here - http://forum.netweat...t-update-times/

[Liam J]

GME 12z going the right way by the looks of things

With much better heights +20mb towards Svalbard than the 6z GFS for the same time frame on the 14th, and a much better placed shortwave about to sink over the UK. Even the the heights around Greenland look better orientated to deflect everything south. Wishful thinking perhaps! But definitely a better looking set up.

Edited January 11, 2013 by Liam J