Jump to content

Archived

This topic is now archived and is closed to further replies.

Coast

Winter Model Discussion - Cold Hunting -12Z 03/01/13

Recommended Posts

Just a brief reminder to please stick to the topic title and consider your posts are about the model output and how you feel it translates into any subsequent weather or conditions.

I'll just add Ian Fergusson's last post from the old thread to set off this model run discussion:

Just an addition re current viewpoint from Exeter - I can't offer all the detail regarding their modelling on this I'm afraid, but can paraphrase current thoughts just given to me as follows, to simplify for those of you who might be new to an understanding of where we might be heading in these circumstances:

"At the moment it (SSW) is starting to have an effect at the top of the modelled atmosphere but not yet propagating down to the surface. It’s being monitored with interest and we’ll see what happens there...." (then on the issue of impact upon current model ouput / reliability): ".....Logic suggests it could make things less predictable in mesoscale terms through NWP output, simply because if a blocking high does develop, the position of it could have anything between a huge and a negligible effect on e.g. the UK’s weather...."

The old thread can be found here:

http://forum.netweat...ing-12z-301212/

Share this post


Link to post
Share on other sites

PS new UKMO-GM just arriving and less progressive on this run

As others said, what does that mean exactly please?

Share this post


Link to post
Share on other sites

As others said, what does that mean exactly please?

I would hazard a guess he means less of a west to east flow or more blocked..... but that would only be my guess

Share this post


Link to post
Share on other sites

As others said, what does that mean exactly please?

I think it depends in what context IF meant , you could be talking about the development of a Artic High being less progessive or the influence of the atlantic.

He may pop back to claify

Share this post


Link to post
Share on other sites

gfs is there something brewing over the pole a t120hrs and greece well blimey eastern europe is in the freeeeeezerhelp.gif

Share this post


Link to post
Share on other sites

I believe progressive in this sense means a tendency for low pressure systems to continue advancing (usually quickly) in a generally west to east direction across the Atlantic, with a fairly flat (non-meridional) shape to the jet stream. Less progressive means this motion is less pronounced, possibly because of buckling of the jet stream due to blocking highs (possibly HLB or high latitude blocks), allowing for greater potential for us to source colder air masses from the N, E or NE.

The sometime used phrase 'overly progressive' can also refer to a synoptic evolution playing out more rapidly than is considered likely, due to a number of reasons.

Aside from the obvious chaotic influences we're potentially expecting from the SSW (s!), typical signs to look for to get out of these flat, progressive patterns would be, for instance, large amounts of energy being deflected up the west coast of Greenland from low pressure systems on the eastern seaboard of the US. Such changes 'upstream' are key to the buckles in the jet stream being set up and allow for the building of the blocking HP features we need if we are looking for a sustained cold outbreak as opposed to a 'toppler' (transient cold outbreak usually part of a cold segment in a low pressure system passing through west to east, quickly overthrown by change back to a milder air mass). The placement of the HP areas are therefore fundamental to what we as a group of smallish islands on the wrong side of a large relatively warm body of water then receive, since we need them to be in just the right place to avoid being the recipients of all the heat energy and moisture that 3,000 miles of ocean can unleash on us. Get it slightly wrong and we get mild dross, get it right (chances are usually not favourable, hence the number of addicts on this site) and we can be locked into 2 weeks + of biting cold.

Share this post


Link to post
Share on other sites

As others said, what does that mean exactly please?

Its a better sign, as 'progressive' means that any heights that is built is quickly knocked down by a low pressure system, so I guess what he is saying is that the UKMO is the opposite to this. Well thats what I understand by the word as it has been used quite a lot over the years.

Share this post


Link to post
Share on other sites

npsh500.png

When looking at the big picture, it's startling actually that the PV is already split more or less, with plenty of high latitude blocking...Just a shame right now that we've not ended up in the right area for cold; looking good for the balkans though!

Will be interesting to see what the models start to show in FI after another week or so as the effects of the SSW event start to influence the models more firmly. We'll know then what may be in store for the 2nd half of Jan.

Share this post


Link to post
Share on other sites

UKMO takes full trough underneath GL at 144hrs. Poor really if that was the outcome.

UW144-21.GIF?03-17

Share this post


Link to post
Share on other sites

http://modeles.meteociel.fr/modeles/gfs/runs/2013010312/gfsnh-0-174.png?12

A very nice position, but the train will be stopping short-

the UK will need more movement of the jet across the UK in a direction SOUTH of east to encourage the cold uppers over our shores..

UKMO 144 isnt at the races yet...

S

Share this post


Link to post
Share on other sites

In what sense?

I would guess that it's not what the Meto bods are expecting to happen but this is what their computer model has projected so that is what they have to show?

Maybe the fax charts which are modified by hand will be different?

Share this post


Link to post
Share on other sites

In what sense?

in that the model output will not (even remotely) accurately reflect how the SSW will affect the outcome as yet

even though the SSW is beginning, there is no effect as yet on the troposphere, therefore the input data will not be affected by it yet. which would mean that the models will, for the time being, keep chugging along as if there were no SSW

Share this post


Link to post
Share on other sites

It's unconvincing. Frankly.

I would say the UKMO jet at 144 is to flat- there would be no ridging up towards Eastern Greenland-

GFS will be slower & hence more amplified ( i know you know this )

Lets see what the ECM brings-

What would I say tonight- A step in the right direction from the last 2 GFS runs on the trot towards a polar high & a lobe of the vortex dropping into western russia-

However the cold signal for the uk at this stage is very much muted.-

S

Share this post


Link to post
Share on other sites

GFS fi very strange looking to me, beautiful artic high but I don't really understand what causes that megalow to suddenly spawn barrel towards the southern UK then stall. I know I probably shouldn't do this but I think I'm going to bin this OP run as it doesn't look right at all to me. Will look at the ENS mind.

Share this post


Link to post
Share on other sites

I would say the UKMO jet at 144 is to flat- there would be no ridging up towards Eastern Greenland-

GFS will be slower & hence more amplified ( i know you know this )

Lets see what the ECM brings-

What would I say tonight- A step in the GFS 2 runs on the trot towards a polar high & a lobe of the vortex dropping into western russia-

However the cold signal for the uk at this stage is very much muted.-

S

Its early days Steve, and models only just showing IMO the evolution ahead. A good start though and big turnaround happening.

BFTP

GFS fi very strange looking to me, beautiful artic high but I don't really understand what causes that megalow to suddenly spawn barrel towards the southern UK then stall. I know I probably shouldn't do this but I think I'm going to bin this OP run as it doesn't look right at all to me. Will look at the ENS mind.

Oddly enough I think it isn't outlandish with the atlantic LP assault from WSW....

BFTP

Share this post


Link to post
Share on other sites

I wouldn't get too excited yet folks GFS hunts around and doesn't get there really. Only two runs with a drift towards a cooler outlook need a few more with a tendency towards cold.

Share this post


Link to post
Share on other sites

GFS fi very strange looking to me, beautiful artic high but I don't really understand what causes that megalow to suddenly spawn barrel towards the southern UK then stall. I know I probably shouldn't do this but I think I'm going to bin this OP run as it doesn't look right at all to me. Will look at the ENS mind.

DONT BIN THE RUN!! BIN LOW RES POST T192 !!

Share this post


Link to post
Share on other sites

The trop is seeing the signs from the SSW, but at the moment little cold is heading to the UK. FI ends on the 19th so realistically the last week of Jan at the earliest for potential very cold weather. And the signals for that remain average at best.

Arctic High: post-14819-0-15804100-1357231664_thumb.p

Jet ploughs on: post-14819-0-07355200-1357231696_thumb.p

PV piece still stopping ridging in west Atlantic and keeps the quasi-zonal flow over the UK, with highs to our east meaning stalling cyclonic westerlies over the UK: post-14819-0-74910000-1357231732_thumb.p

Better than a few weeks ago, as the trough is slightly further south. This pattern has been very strong in GFS FI now, so maybe the second warming is needed for the UK to get something more substantive than transitional cold/snow.

Share this post


Link to post
Share on other sites

I don't see a lot to change forecast much, quite a bit of uncertainty going into mid-Jan but no I see no strong cold signal yet, although definitely some hints of something stiring in the model output lately. We'll see.

Weather forecast based on latest model output (3 Jan):

Mild/very mild TM air is now established over the British Isles and high pressure to our S will keep things mild and settled for the rest of this week. It will remain cloudy and dull for most with the best of any brighter weather to the SE. Occasional pieces of drizzle and light rain are possible at times chiefly in the N and W also will hill fog over higher ground. Winds light in the SE, breezy at times in the NW. Mild/very mild with double figure temperatures widely.

As we head into next week the new week will bring new weather, with high pressure to our S weakening allowing Atlantic weather fronts to move in from the W with rain at times, especially in the N and W with the SE corner perhaps staying largely dry. Turning cooler and fresher for all. Winds staying light in the SE, perhaps breezy in the N and W. As we move through the week there is a continuing risk of rain at times, again chiefly in the N and W with drier weather perhaps returning later in the week and a continuing cooling trend likely.

Going into the middle of January considerable uncertainty as usual at this range however things look to turn more seasonal with either a cooler increasingly unsettled Polar Maritime influence with snow possible in the North and over higher ground (and wetter in most other places) or a change to a more cold and drier outlook looking the most likely outcomes. We will have a better idea of which of these is most likely over the coming few days.

Share this post


Link to post
Share on other sites

DONT BIN THE RUN!! BIN LOW RES POST T192 !!

I always do, BA!good.gif

Share this post


Link to post
Share on other sites

DONT BIN THE RUN!! BIN LOW RES POST T192 !!

maybe even earlier BA. i would advise anyone hanging on the GFS later stages to stop doing so and start reading Ian Ferguson's posts!

Share this post


Link to post
Share on other sites
Guest
This topic is now closed to further replies.

  • Recently Browsing   0 members

    No registered users viewing this page.

×