Model output discussion - hot spell beckons but then what?

[knocker]

The first warm front brought low stratus.  mist and some patchy drizzle, to these patrs today but the main frontal system is a different matter as it tracks north east this evening with the wrap around occlusion poking it's nose in as well by morning when the low center will be WSW of Ireland.  Thus belts of heavy rain moving up the country this evening and overnight reaching as far as central Scotland by morning with showers in the wake of the cold front  Becoming breezy by morning but the movement of the low is dragging up warmer air so very humid and mild in the south

Edit

Moderate rain has arrived

Edited August 8, 2019 by knocker

[Mike Poole]

Not the output I'd want to be commenting on at this point in summer, but the weather will do what it will!

Some probabilistic insight into the incoming low from the ARPEGE 6z ensembles, first cumulative rain up to T48, here's probability exceeding 20mm and 50mm:

and re max wind gusts over a longer time to T90, here's probability exceeding 80 km/h and 90 km/h:

[Singularity]

 

 

I realise it takes a big application of faith, but we do now have signs in the EPS of the tropically-foreshadowed transition to UK-Euro height rises that has been discussed on occasion this past week.

The end of the trade wind surge, and subsequent swing at least a little bit the other way as the C Pacific warmth aids rising motion and eastward propagation of equatorial tropical waves, has now entered the semi-reliable range (yellow shading taking over around the dateline i.e. 180 on the x-axis).

 

In light of that, I see reasonable grounds to anticipate that significant westward shifts to the main Atlantic trough position, such as we see here between the 06z and 12z FV3 runs, will continue to occur during the coming days. It may not be a smooth ride, but I'll be very disappointed if the actual outcome doesn't have the trough at least failing to fully move across the UK.

Some considerable changes to the polar patterns are also likely -  right good shakeup of the hemispheric setup.

Due to modelling inadequacies when handling tropical processes, this is one of those times when whole ensemble suites have to be challenged as much as is reasonable based on technical knowledge. For example, the representation of settled outcomes in the EPS for a fortnight's time really ought to be larger in my opinion.

Usual caveats apply, of course. Fingers crossed, for those who like it summery in August, that the teleconnections do us proud.

[SMU]

^^^ I would say the polar opposite will happen

Week 2 Trough anchors to the East... Summer ( August ) is in a poor position...

The overwhelming phase of the NAO being sustained negative has forced that jet through the UK only occasionally allowing for enough amplitude to get the heat out of the south...

Edited August 8, 2019 by Steve Murr

[knocker]

The gfs still developing a negatively tilted upper trough next week as the troughs merge and a surface low swings though on Wednesday

And moving on to an overview of the 5-10 period with the mean anomaly

Much the same as has recently been discussed with the hey features regarding the UK being the Block around the Labrador Straits and the TPV to the north of the UK. These features ensure that the twin upper flows, one across the Atlantic and the other around the TPV continue to effect the UK and thus a continuation of unsettled weather with temps a tad below average

Edited August 8, 2019 by knocker

[Frosty.]

Again there are hints of something more summery towards the end of the GEFS 12z  but that's 24th August range, it looks largely unsettled / very unsettled until late August at least, especially further n / nw, possibly becoming more of a north / south split  but there's a sniff of something much better during the final week of the meteorological summer..maybe a plume or a decent anticyclone!

Edited August 8, 2019 by Jon Snow

[knocker]

EUMETSAT 1745 UTC

[Methuselah]

It's hope karl, but not as we know it...nothing of note is showing on the ensembles?

   

   

                                   

[ANYWEATHER]

Good evening! An insane run from gfs tonight with some deep lows looks more like Autumn / Winter  than late summer. Some notable cooler spells too as the deep lows moving away spill cold from an increasingly cold Greenland and Artic and would not be surprised to see some frosts in Scotland and snow on the highest mountains...and even further south some chilly if not cold nights...Its been a long time since we've had a strong jet stream  fuelled by an very early freeze in the Artic and a strong sub tropical Azores .....A roller coaster run unfortunately it's still Summer!......

[Methuselah]

And, in the words of Francis Bacon, 'The root of all superstition is that men observe when a thing hits, but not when it misses'...

[Singularity]

2 hours ago, Steve Murr said:

^^^ I would say the polar opposite will happen

Week 2 Trough anchors to the East... Summer ( August ) is in a poor position...

The overwhelming phase of the NAO being sustained negative has forced that jet through the UK only occasionally allowing for enough amplitude to get the heat out of the south...

Am I misinterpreting this, or are you saying that the NAO will be negative because the NAO has been negative? 

I find this a strange manner of logic. Sure, persistence has its value, but that's when major driving forces are changing very little, which isn't expected to be the case for the 2nd half of this month.

Granted, if the tropical cycle was to stall unexpectedly, then we'd be waiting for any descent of (currently strongly above normal) zonal winds from the upper stratosphere to bring about a break from the -NAO regime, which would probably take some time.

To be honest, I'd feel happier about the winter prospects if there were some +NAO phases in Sep/Oct. Having -NAO phases pre-Nov is putting a lot of surplus heat content into the N. Atlantic, which is an unstable situation to be in.

[mb018538]

1 minute ago, Singularity said:

Am I misinterpreting this, or are you saying that the NAO will be negative because the NAO has been negative? 

I find this a strange manner of logic. Sure, persistence has its value, but that's when major driving forces are changing very little, which isn't expected to be the case for the 2nd half of this month.

Granted, if the tropical cycle was to stall unexpectedly, then we'd be waiting for any descent of (currently strongly above normal) zonal winds from the upper stratosphere to bring about a break from the -NAO regime, which would probably take some time.

To be honest, I'd feel happier about the winter prospects if there were some +NAO phases in Sep/Oct. Having -NAO phases pre-Nov is putting a lot of surplus heat content into the N. Atlantic, which is an unstable situation to be in.

It doesn’t seem to matter what state the NAO is in during autumn, it’ll still lead to a mild winter, probably. I think I’m right in saying there’s no real correlation between the two?

[knocker]

This evening's EPS mean 5-10 mean anomaly has a large slack area of low pressure to the north of the UK with associated troughs into Alaska and, more to the point, south west into the NW Atlantic whilst retaining some ridging over northern Canada.The Atlantic subtropical high is pushing north to some extent so although still a strong westerly upper flow exiting the eastern seaboard under the trough and continuing unsettled with temps a tad below average, perhaps tending towards a N/S split. NOAA more or less on the same page

The only significant changes that are readily apparent in the ext period are positive anomalies over the Arctic and a loss of the NW Atlantic trough resulting in a more general upper westerly across the Atlantic. Ergo still unsettled qwith temps below average. The usual caveats vis the detail and airmass mixing in the westerly flow/

Edited August 8, 2019 by knocker

[tinybill]

morning  all just looked at   gfs wish i had  not  i think augest we can write  it off its  going to be very wet  in places  with flooding a huge problem

http://www.meteociel.fr/modeles/gfse_cartes.php?mode=2&ech=6

http://www.meteociel.fr/modeles/gfse_cartes.php?mode=2&ech=204

[knocker]

The North Atlantic 500mb and surface analysis for midnight and the 0300 WV image

The band(s) of heavy rain, associated with the main frontal system of the low to the south west, currently moving north up the country, will continue to do so through the day and just about clearing northern Scotland by 1800. Behind this over England and Wales, bands of showers will run around the in the circulation and coalescing at times courtesy of troughs/fronts embedded in the flow. Despite being breezy quite a warm day in the east/south east.

Tonight the low will continue to track NE and showers will continue to sweep across the country, merging at times to give longer periods of rain, and the wind will pick up with coastal gales in the south by morning

By midday Saturday the low is centred near Edinburgh but has become distorted as the subtropical high zones amplify either side and the upper trough swings around the lobe near Iceland. Ergo still a day of frequent heavy showers with thunderstorms breaking out near the center of the low. Remaining very windy in the southern half of the country

Over Saturday night and through Sunday the low continues to track NE into southern Scandinavia so winds will abate but the country is still under the influence of low pressure with the odd trough/front around so still some showers with sunny intervals on by now a rather cool day.

Monday and Tuesday the upper trough continues to swing around the Iceland lobe so essentially another couple of cool days of sunshine and showers perhaps with some thunder in the mix, But to the west a trough has broken from the main trough over NE Canada (previously discussed) and has tracked east and by Tuesday evening rain from the associated fronts is approaching Cornwall.

 

 

 

Edited August 9, 2019 by knocker

[knocker]

The gfs then tracks the system across the south of the country through Tues/Weds

Taking an overview of the 5-10 period and still the key features remain the high cell northern Canada and the TPV near Iceland with associated negatively tilted trough resulting in the westerly upper being augmented by another around western Greenland. Ergo continuing unsettled with temps a tad below average with the usual caveats vis regional variations and the phasing of the airmasses.

[knocker]

A snapshot of the ecm illustrating unsettled and airmass phasing

[knocker]

The cold front would appear to be clearly defined on the 0600 sat image

[Methuselah]

Maybe, just maybe, the GEFS 00Z is onto something...a subtle realignment from around Day 10?

   

 

Though it could be, I suppose, down to the fact that the operational is very-much on the warm side of the pack?

   

   

So, possibly one to watch, but there'll be a lot of water to flow under the bridge, before then...?

[Paul_1978]

21 hours ago, chrisbell-nottheweatherman said:

Makes me wonder why some members here seem to quote the CFS outputs as though they're going to be accurate.

People will do well to remember this in Winter when posting charts at T+1000 - a completely futile exercise.

[feb1991blizzard]

2 minutes ago, Paul_1978 said:

People will do well to remember this in Winter when posting charts at T+1000 - a completely futile exercise.

Come on, no one posts charts with 1 specific target date at 1000 hours because they think they will happen, they are posted because they are extreme charts in the main.

[Alex]

Small steps but I definitely can see a trend for the jet stream to slowly relax north - unfortunately not enough next week to prevent influence but over time into week 2 this could allow a ridge across the far south /SE.

[mb018538]

2 hours ago, Alex said:

Small steps but I definitely can see a trend for the jet stream to slowly relax north - unfortunately not enough next week to prevent influence but over time into week 2 this could allow a ridge across the far south /SE.

GFS has shown heights finally starting to lower to the NW at the very end of the run in the last day or two:



Slight trend for an increase in SLP at the end too:



A straw to clutch at anyway. Until then, then next 10 days at least staying unsettled.

[mushymanrob]

well theres no ambiguity here, these charts are clear as crystal... they dont expect anything other then a pretty stiff mean upper westerly flow. theres no hint of any lasting pressure rise here, on the plus side any atlantic systems will be barrelled through quite rapidly. but according to these, its unsettled all the way for the next 2 weeks.

[Methuselah]

Very tentative signs that HP to out south will gain in influence, with time?

   

   

 

And the ensembles:

   

   

It is of course one run from one model. But it does tie-in with the thoughts of 'others'?

Edited August 9, 2019 by Ed Stone