Model output discussion - 20th Feb onwards

[Summer Sun]

Its looking a bit windy for the boat race on Sunday!

[Singularity]

The 12z ARPEGE is very different to the 06z and the core of the low actually seems to become disassociated with the cold front which has detached and raced off ahead. It seems to try and develop independently which just leads to a battle between competing centers, neither one managing to attain the strength that a single core can achieve. 

That 06z ARPEGE, with 92 mph gusts for the Isle of Portland, was pretty wild, though. GFS is consistently in the 70-80 mph range for coastal parts.

 

WRF 12z just rolling out:

 

The orientation of the trough axis does look more SW-NE than earlier runs.

[Cloud 10]

ECM going for a distinctly chilly start to April.

 

[bluearmy]

Gfs op and para have been keen on the height rise to our north/northeast in week 2 for quite a while. For one run at least, ECM op comes on board. 

[phil nw.]

Yes Blue the Scandi. heights  starting to show from around days 8/9 on both this evening and supported by the GFS mean.

                                                                                                                  
 

It looks like after the Easter low fest the Atlantic stalls out west as pressure rises towards the end of the week.Maybe a few days of drier easterlies with some sunshine but again the N.Sea cloud could be a problem depending on the exact surface wind direction.

 

Edited March 25, 2016 by phil nw.

[Scorcher]

1 hour ago, Cloud 10 said:

ECM going for a distinctly chilly start to April.

 

It could well be short-lived in that setup though, ECM also shows quite a dramatic shift to warm conditions by the Sunday.

[Singularity]

The past three GFS runs for Friday 25th, in chronological order:

  

The theme of height rises near Scandinavia was already picked up on a couple of days ago, but with the undercut of the jet taken too far. This has since been refined, with the idea of that high retrogressing being put back in time. In terms of the airmass, we have tended to be near or on the boundary between unseasonably warm air to the south, and rather cold air to the north.

Now the same treatment with the ECM output:

  

The upgrade a few weeks back doesn't seem to have helped the model out in this situation - assuming the Scandi height rises do turn out to be the way forward. The disruption of the troughs as the jet heads down into Europe has taken until today to be captured. 

It's an interesting setup, and all the more so when there is no attempt to flatten the high in the 9-10 day range such as GFS goes for. In this respect the 12z GFS seems to be a bit of a rouge run, with previous runs keeping the high at higher latitudes and maintaining the potential for both warm incursions from the S/SE and cold incursions from the N/NE. Notable is the lack of westerly components to those possibilities. 

[Man With Beard]

ECM mean at D10 also killing the Atlantic trough slowly, and beefing up the Scandi High

This turns the mid-period into a slight lottery. The trough could park over us (cool rain), drop a little south (brisk easterly, probably cool), or fall just short of the UK (perhaps an ever-warmer SE).

Have to say, maybe some of those wacky GEFS runs from a few days ago showing warm SElys were not so wacky! 

[knocker]

This amplification over the eastern Atlantic/Scandinavia has been on the cards a wee while now and the current difference between the GEFs and ecm/EC32 is the position of the upper trough.

Obviously this will influence the orientation of the HP and LP but going with the ecm/EC32 we are looking at the trough settling south of the UK leading to a general area of low pressure over NW Europe with a SE flow, certainly in the southern half of Britain. Although the GEFS tends to align the trough a little further west and thus veering the winds to a more southerly as the Scandinavian HP declines

[knocker]

And within the same time frame

 

[Singularity]

The 18z ARPEGE seems to have ground to a halt at +60 hours but it's clear that this run has the storm holding together and bringing stronger winds than the 12z - but not to quite the extent of the 06z.

So the uncertainty continues. The model is also suggesting around 30 mm of rain from the system, most of that falling during the night. This follows 10-15 mm from Sunday's showery affair.

Tomorrow looks relatively tame with 5-10 mm being suggested in association with a front that now looks to take until the evening to reach eastern reaches of the UK such as London. The adjustment to a slower progression has been notable over the past few days, and allows for tomorrow to be another day of decent temperatures for the time of year, though with a fair bit of cloud and some showers to contend with.

[knocker]

Midnight Monday the ecm has Kate 973mb north Cornwall coast and by 12z the North Sea adjacent to the Lincolnshire coast.

[Singularity]

1 hour ago, knocker said:

Midnight Monday the ecm has Kate 973mb north Cornwall coast and by 12z the North Sea adjacent to the Lincolnshire coast.

That is very concerning. Based on other model guidance (generally not quite as deep), that could mean near 90 mph gusts in the Channel in the early hours, then a swathe of 70-80 mph crossing parts CS England on the S flank of the trough as it moves NE.

Then there's the sting jet potential. With those 850 hPa winds such a thing would be devastating. Hopefully it will be avoided - what do people think?

I'd look in more detail but all I have to hand today is my phone.

[SMU]

If we look at this set up & then compare October 1987 there are a lot of similarities-

I havent looked on the METO page but there should already be amber warnings out & sunday overnight into monday may eventually be upgraded to red...

S

[knocker]

59 minutes ago, Singularity said:

That is very concerning. Based on other model guidance (generally not quite as deep), that could mean near 90 mph gusts in the Channel in the early hours, then a swathe of 70-80 mph crossing parts CS England on the S flank of the trough as it moves NE.

Then there's the sting jet potential. With those 850 hPa winds such a thing would be devastating. Hopefully it will be avoided - what do people think?

I'd look in more detail but all I have to hand today is my phone.

Going strictly by the ecm it has gusts 55-60kts in the channel and briefly 60-65 Kent and Sussex around 06-12 Monday. Still of course very dependent on how much it actually deepens and the precise track.

[Summer Sun]

With BST arriving tomorrow the models will be updating 1 hour later from the 00Z's

Approx times are;

GFS

00Z - 04:30-05:45

12Z - 16:30-17:45

ECM

00Z 07:00-08:00

12Z 19:00-20:00

UKMO

00Z 06:00-07:00

12Z 18:00-19:00

[knocker]

42 minutes ago, Steve Murr said:

If we look at this set up & then compare October 1987 there are a lot of similarities-

I havent looked on the METO page but there should already be amber warnings out & sunday overnight into monday may eventually be upgraded to red...

S

Well at the moment one hopes not too similar. The 1987 depression dropped to 953mb as it approached the western Channel from Biscay.

Edited March 26, 2016 by knocker

[johnholmes]

1 hour ago, Steve Murr said:

If we look at this set up & then compare October 1987 there are a lot of similarities-

I havent looked on the METO page but there should already be amber warnings out & sunday overnight into monday may eventually be upgraded to red...

S

from memory Steve I think the low in Oct 87 came from a more southerly point with the explosive deepening occurring a bit further south I am pretty sure the upper air pattern, once we had collated data after the event, was not that similar really to what is being predicted for Easter Monday. For a really accurate comparison the check the Met O site as they have a pretty good account somewhere in there.

this link leads in to all kinds of information on it-not had time to llok at any of them

http://www.metoffice.gov.uk/news/in-depth/1987-great-storm/fact-file

Edited March 26, 2016 by johnholmes
adding info and correcting spelling

[Nouska]

5 hours ago, johnholmes said:

from memory Steve I think the low in Oct 87 came from a more southerly point with the explosive deepening occurring a bit further south I am pretty sure the upper air pattern, once we had collated data after the event, was not that similar really to what is being predicted for Easter Monday. For a really accurate comparison the check the Met O site as they have a pretty good account somewhere in there.

this link leads in to all kinds of information on it-not had time to llok at any of them

http://www.metoffice.gov.uk/news/in-depth/1987-great-storm/fact-file

The ECMWF ERA reanalysis has recently been made available on Meteociel. I've set it to the time of the Oct.87 storm.

http://www.meteociel.fr/modeles/archives/archives.php?day=14&month=10&hour=0&year=1987&map=0&region=&mode=2&type=era

It did come from further south, this snapshot is very similar to what is being currently modelled over the Brest area. Airmass temp is different, still polar winter rather than early autumn.

Midnight Oct 16th 1987    

          forecast 42 hours

Some of you will remember the French models had the correct track but of course we never got to see such things back then.

I'm not suggesting something severe this time, just looking at synoptic similarity in the positioning of the low.

Edit to thank @johnholmes for an interesting insight into the post event analysis.

Edited March 26, 2016 by Nouska

[knocker]

Or

https://www.netweather.tv/forum/topic/74723-25th-anniversary-of-the-october-1987-storm/

[Man With Beard]

Going by GFS, probably 80-85mph max gusts on the south coast Sunday into Monday. In 2014, the GFS was among the most accurate inside 48 hours. So severe indeed, though (hopefully) not a storm of historic proportions such as 1987. Thankfully, the worst seems to be overnight.

[johnholmes]

2 hours ago, Nouska said:

The ECMWF ERA reanalysis has recently been made available on Meteociel. I've set it to the time of the Oct.87 storm.

http://www.meteociel.fr/modeles/archives/archives.php?day=14&month=10&hour=0&year=1987&map=0&region=&mode=2&type=era

It did come from further south, this snapshot is very similar to what is being currently modelled over the Brest area. Airmass temp is different, still polar winter rather than early autumn.

Midnight Oct 16th 1987    

          forecast 42 hours

Some of you will remember the French models had the correct track but of course we never got to see such things back then.

I'm not suggesting something severe this time, just looking at synoptic similarity in the positioning of the low.

I agree there are similarities but it is important to look at what the upper air pattern was prior to the 24 hours leading up to the 1987 storm, and assuming the models predictions for the Monday storm turn out to be correct. In my view the development was fairly if not quite different. Yes the French model at T+12 was much better than the Met O model at that time. In the previous 3-4 days it had been, it turned out when we went back and spent several days analysing the situation, uncannily accurate in many aspects. Hindsight is a wonderful thing, but at the time, the assessment at Bracknell was that the French model in the run up to the last 12 hours was not correct.

Much of the error in the Bracknell model was the fact that the late arrival of important upper air data was not available for the computer, nor for that matter to the French model. We never really did discover why the French model gave the most accurate T+12 prediction for 00z of that night.

Edited March 26, 2016 by johnholmes

[tinybill]

5 hours ago, Steve Murr said:

If we look at this set up & then compare October 1987 there are a lot of similarities-

I havent looked on the METO page but there should already be amber warnings out & sunday overnight into monday may eventually be upgraded to red...

S

steve  i hope  your wong!!! us in the se  know what happened   no power  for 2weeks after the great storm

[Man With Beard]

On the GFS 12Z the strongest winds stay away from the coast.

The latest Argepe, however, is another story - it tries to develop what I imagine would be a sting jet late Monday Morning, with gusts over 90mph in off the Bristol Channel. 

Edited March 26, 2016 by Man With Beard

[damianslaw]

Short term - all models show a developing deepening low tracking through just to the north of the channel, meaning gales in southern parts possibly severe gale and some localised disruption bank holiday Monday - not good anyone wanting to visit the south coast. Heavy rain will spread across much of England and Wales and into eastern/se Scotland, so a wet miserable scene. Tomorrow looks like a very showery day with some sporadic thundery downpours and hail most likely. Not expecting much sunshine. Feeling cool.

As we end the month, the models show low pressure being squeezed out by a temporary ridge building in from the SW, before low pressure topples in again as we start April but perhaps becoming erratic in its movement eastwards. Overall cool and showery, something drier come Thursday-Friday but cool still, turning unsettled again as we start April with temps near average. All quite average affair.