Winter Model Discussion 18Z 5/2/13 onwards.

[Mucka]

The mighty NOGAPS getting "amped"

[Cloud 10]

The usual caveat's apply when viewing the AO forecast,but still might raise an eyebrow

or two.

[Weather-history]

Looks like a recipe for some potentially very heavy snowfall to me. Uppers of -2 or lower should suffice in this situation with advection of lower dew points due to LP tilt plus heavy precipitation. Marginal but right side of marginal on this run.

Another factor that never gets mention in these scenarios is the wet bulb freezing level.

[johnholmes]

Below is the link to the NOAA 500mb anomaly charts. Not unlike trying to understand the Stratosphere outputs one has to be careful not to read too much into what they show. It takes time, whatever meteorological knowledge one has, to really understand what they show and what they cannot show.

Used sensibly they can be extremely useful. Note I say used carefully.

http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php

I will have more time tomorrow so will use the above and the morning output from ECMWF-GFS and the NAEFS output to try and explain what they show and also what they have been showing over the last few days. One set is no more use than one run from any other model.

Just briefly the link above is showing a changing pattern again from the last 2-3 days and helps explain why UK Met are, along with all the other data they have, not going for any mild weather and are, to some perhaps, sitting on the fence a bit in the 6-15 day time interval. More tomorrow.

[Tim Bland]

Have to say the 12z GFS was actually better for snow than the 18z and synopticaly they are very different so take both with a bucketload of salt

[bluearmy]

The usual caveat's apply when viewing the AO forecast,but still might raise an eyebrow

or two.

it was referenced by noaa cpc. apparently gem and ecm ens not so keen.

[Panayiotis]

Below is the link to the NOAA 500mb anomaly charts. Not unlike trying to understand the Stratosphere outputs one has to be careful not to read too much into what they show. It takes time, whatever meteorological knowledge one has, to really understand what they show and what they cannot show.

Used sensibly they can be extremely useful. Note I say used carefully.

http://www.cpc.ncep....14day/500mb.php

I will have more time tomorrow so will use the above and the morning output from ECMWF-GFS and the NAEFS output to try and explain what they show and also what they have been showing over the last few days. One set is no more use than one run from any other model.

Just briefly the link above is showing a changing pattern again from the last 2-3 days and helps explain why UK Met are, along with all the other data they have, not going for any mild weather and are, to some perhaps, sitting on the fence a bit in the 6-15 day time interval. More tomorrow.

To anyone who are new, it has shows a mid Atlantic ridge, ridging into Greenland with low pressure low heights just to the south of Britain, feeding in a NE wind.

Edited February 6, 2013 by Panayiotis

[Mucka]

To anyone who are new, it has shows a mid Atlantic ridge, ridging into Greenland with low pressure just to the south of Britain, feeding in a NE wind.

Well that is where you need to be "careful" because they are not a snapshot in time but show forecast anomalies over regions for the period.

Edited February 6, 2013 by Mucka

[johnholmes]

To anyone who are new, it has shows a mid Atlantic ridge, ridging into Greenland with low pressure just to the south of Britain, feeding in a NE wind.

not low pressure, low heights, its at 500mb not the surface, that is the -/+ areas you are referring to and that is exactly what one must be very wary of making snap decisions about them. Over a period, I use 3 days, and IF ALL the ouputs from the different centres show similar then one can begin to draw conclusions about the UPPER air not necessarily the surface although with experience and practice it is possible to make general assumptions as to air sources and overall weather types, nothing more detailed than that-so beware but more tomorrow which I hope will help.

[Panayiotis]

not low pressure, low heights, its at 500mb not the surface, that is the -/+ areas you are referring to and that is exactly what one must be very wary of making snap decisions about them. Over a period, I use 3 days, and IF ALL the ouputs from the different centres show similar then one can begin to draw conclusions about the UPPER air not necessarily the surface although with experience and practice it is possible to make general assumptions as to air sources and overall weather types, nothing more detailed than that-so beware but more tomorrow which I hope will help.

Thank you, I guess im still learning too, edited original post so no confusion is caused. Edited February 6, 2013 by Panayiotis

[Timmytour]

I like the GFS run but....taking next week as a point in time....

I then look at the ECM for the same point in ttime....

....and then I remember that the GFS is rubbish! I don't know why we're even bothering to look at it tonight!!

Edited February 6, 2013 by Timmytour

[weatherguy]

The GFS had to get a mate to call him a taxi home after that pub run!

[Ryan Dutch Weatherman]

My idea , you see the Snowbomb for my country as wel as UK.

Than the second in the morning my thoughts , .

Some people say it is impossible, well you see now just at a reliable 192 hours.

Wen this is locked , ist over, the battle wil win.

Looking afterwards will mean only cold weather with snow.

Btw i see a second snowbomb at GFS 18z at the 14e februari.

But loook at this .

[Panayiotis]

I like the GFS run but....taking next week as a point in time....

Bu then I look at the ECM for the same point in ttime....

....and then I remember that the GFS is rubbish! I don't know why we're even bothering to look at it tonight!!

If you cut the 2 images in half, the rights sides look v.similar but on the left is where the divergence occurs, you can see a small seperate low on the GFS which is southerly tracking and because of this, it is driving the Azores north, forcing the shortwave (NE of the Azores) to move SE, whereas on the ECM the low on the western side of the Azores, is part of bigger low stretching up and around the Azores, this causes the low to 'ride' on the Azores and by doing this it flattens the Azores/pattern. Edited February 6, 2013 by Panayiotis

[johnholmes]

a request please?

Does anyone know of a link that show what the average height over the north Atlantic is for February, say the past 25 maybe 50 years?

I cannot find any link that gives long term averages.

I will drop an e mail to UK Met to see if they can help as well.

thanks to anyone in advance if they can help.

John

[Tamara]

The mighty NOGAPS getting "amped"

The future lies herein and further assists previous thoughts about the outlook Assuming of course that 'amped' is an abbreviation for amplified jet stream?

[TEITS]

I don't wish to be rude to anyone as we are all entitled to our opinion but I really disagree with some of the earlier comments about the Atlantic moving in.

Before I focus on week 2 (17th -22nd Feb) its looking very likely Sun/Mon could bring a snow event especially away from the far SW. At first this could begin as rain for some parts but its pretty clear this will turn to snow. After this a 48hr period of snow showers into E areas and contrary to some posts the models do suggest a convective period.

The period I disagree with some members is from Wed - Saturday 16th. I kept on reading "The Atlantic is moving in" but sorry I don't see it this way. During Wed-Sat its likely to be mainly dry, very cold with frosts as night.

Look at the ECM mean and the ensembles.

http://www.meteociel...M1-240.GIF?06-0

http://www.knmi.nl/e...agse/index.html

First of all the extended mean has dropped compared to recent days but have you noticed how the mean at 0C continues to be extended. Think back to these ensembles 5 days ago and you will see what I mean.

We then have the JMA/GFS. The Atlantic certainly isn't moving in on these charts.

http://www.meteociel...192-21.GIF?06-0

http://modeles.meteo...fs-0-240.png?18

Now onto the 17th -22nd Feb.

I said a few days ago that ideally we need to see an arctic surge move S on the right flank of the HP to our NE and at the same time this block moving W. This in my opinion is now looking possible and it wouldn't surprise me if this period turns out to be the coldest week of the winter. Forget about the time of year because it won't make any difference when you have upper temps of -15C or below across the UK!

I disagreed last night with the Ian F/Met O suggesting the SW is most at risk of snow as I expected a shift E and that has occured today. Now today I disagree with the return of the Atlantic and SW,lys. Lets hope the excellent trend continues for this period because im becoming very excited at the potential.

Edited February 6, 2013 by THE EYE IN THE SKY

[Cal]

My idea , you see the Snowbomb for my country as wel as UK.

Than the second in the morning my thoughts , .

Some people say it is impossible, well you see now just at a reliable 192 hours.

Wen this is locked , ist over, the battle wil win.

Looking afterwards will mean only cold weather with snow.

Btw i see a second snowbomb at GFS 18z at the 14e februari.

But loook at this .

Why regard the GFS at such a range when we know it is woefull modelling a particular set up as this? Having watched the GFS over the last week or so it really has been Dog SH*T at handling troughing over the UK with High pressure to the East, only slowly but surely (run by run) has it come on board with the Euro models, yes the GEFS Means have been far better n as far as i can gather this is what we should be looking at in the meduim term, but as always most seem to be caught up in every intermodel run... why i dont know!

[Mucka]

The future lies herein and further assists previous thoughts about the outlook Assuming of course that 'amped' is an abbreviation for amplified jet stream?

Indeed it is - or amplified pattern, all synonymous. Unfortunately shortwave spoiler prevents a tatsy 144 chart but nice to see a better pattern out west being modelled again.

ECM London ensembles.

[beefy201]

I remember the good old days when loging on to the weather news group when they were well informed views and banter out to t96 accuracy was say 60/40 back then. I do have a giggle to myself reading the views on here beyond that! Even the metoffice confidence during the winter drops to 50/50 beyond t120 in 2013 :-) :-)

[Mucka]

GFS 18z short ensembles (Southeast)

http://modeles.meteociel.fr/modeles/gens/graphe_ens3.php?x=295&ext=1&y=127&run=18&runpara=0

[Timmytour]

If you cut the 2 images in half, the rights sides look v.similar but on the left is where the divergence occurs, you can see a small seperate low on the GFS which is southerly tracking and because of this, it is driving the Azores north, forcing the shortwave (NE of the Azores) to move SE, whereas on the ECM the low on the western side of the Azores, is part of bigger low stretching up and around the Azores, this causes the low to 'ride' on the Azores and by doing this it flattens the Azores/pattern.

But does that happen because the left hand sides are different? ie the Azores ridge is weakened to some extent by what the ECM has on the eastern seaboard of the States and thus the low is able to ride over the top of it rather than go round?

Edited February 6, 2013 by Timmytour

[Tamara]

Indeed it is - or amplified pattern, all synonymous. Unfortunately shortwave spoiler prevents a tatsy 144 chart but nice to see a better pattern out west being modelled again.

ECM London ensembles.

Its a case of rather watching and waiting once again to see if the pattern builds on the basis of such sustained amplification hopes (and cautious expectations) However we are always subject to shortwave development at short notice well within 5/6 days

[Mucka]

Its a case of rather watching and waiting once again to see if the pattern builds on the basis of such sustained amplification hopes (and cautious expectations) However we are always subject to shortwave development at short notice well within 5/6 days

The thing is with the GFS popping out runs 4 times a day and each run having its own bias it is hard to know if we are seeing the start of a trend or natural variance between these runs. That said the 18z ensembles predominantly have an East based flow at day 10. Not masses of eye candy (out to day 10) but I would think that is a very strong signal that there won't be any Atlantic domination or even serious incursions any time soon. (according to this specific set, trend or natural variance? We will know more tomorrow morning)

Edited February 6, 2013 by Mucka

[TEITS]

Last post from me tonight.

18Z GEFS mean at +240.

Atlantic moving in? No chance based on the above.

Keep an eye out tomorrow for an incredibly cold airmass to surge S out of the Arctic in the model output in FI.