model discussion Model output discussion 11th July onwards

[MP-R]

20 minutes ago, sheikhy said:

Very dry runs again this evening from the main three models!!cant believe how long this dry spell is going on for!!got a few showers on thursday but apart from that any rain that is forecasted is going to be light and hardly gona do anything to the very dry ground we have currently!!

Hmmm...

[stodge]

Evening all

What I take from tonight's modelling is a progressive change to a more "traditional" and seasonal pattern as we move into and beyond the middle of the month.

The extended period of LP over the Continent looks to be easing as, at long last, the Azores HP builds NE through France instead of being forced to the north of the British Isles.

This may be due to more energy over Greenland (perhaps the result of ex-Hurricane Larry) which finally fires up the long-dormant jet forcing heights back just to the south as a more typical autumnal SW'ly sets up later in the month. 

[sheikhy]

First run of real unsettled weather from ecm this morning!!!these cut off lows seem to be causing all sorts of issues with the modelling at the moment!!gfs and ukmo  still pretty dry throughout!!

[Frosty.]

Now this from the Gfs 0z op would blow the cobwebs away ? .. shame about the timeframe, I think a change from benign once the heat is gone would be welcomed?… looking at benign charts ad infinitum would surely become boring?..well I think so anyway!!!!……! ? ?  

ps..I have nothing against spiders! ? ? 

 

 

Edited September 8, 2021 by jon snow

[mb018538]

A lot of forecasting headaches through the weekend and beyond with this low pressure spinning down around Iberia.

UKMO looks ok with a weak high over the UK for Monday



GEM makes a bit more of an upper feature which gives rain in the North/West:



GFS slides this upper feature through the UK, though Monday isn't too wet:



ECM has the upper low as a shallow feature, though it ends up a bit more a of a rain maker, especially into Tuesday/Wednesday where the Iberian low swings through the UK giving a period of heavy rain. Some places on the ECM run (Cheltenham area) receive 60mm of rain in 24 hours, so potential there for flooding!




Nothing set in stone with these pesky little upper lows and features though. 

[sheikhy]

3 minutes ago, mb018538 said:

A lot of forecasting headaches through the weekend and beyond with this low pressure spinning down around Iberia.

UKMO looks ok with a weak high over the UK for Monday



GEM makes a bit more of an upper feature which gives rain in the North/West:



GFS slides this upper feature through the UK, though Monday isn't too wet:



ECM has the upper low as a shallow feature, though it ends up a bit more a of a rain maker, especially into Tuesday/Wednesday where the Iberian low swings through the UK giving a period of heavy rain. Some places on the ECM run (Cheltenham area) receive 60mm of rain in 24 hours, so potential there for flooding!




Nothing set in stone with these pesky little upper lows and features though. 

To be fair i reckon it will be gone on the next ecm run!!

[Methuselah]

I must confess that after two days out in the sun, I'll welcome the rather more 'temperate' weather suggested by this morning's GFS 00Z:

    

    

    

Though, my guess is that things will stay somewhat warmer than what the operational run suggests:

    

One thing I'd like to see (given how last January's nor'easter gave us nowt but umpteen days' rain/sleet showers) is a rapid diminution of heat around the Med?

 

 

[BrickFielder]

CDC GFS blocking forecast keeps shifting and I guess this down to Hurricane Larry. GFS Jetstream forecast looks extremely implausible to me at the moment. 

At this point I usually take a step back and think about what the key air flows are that are affecting the outlook and what the likely consequences on weather are.

Hurricane Larry as been a bit of an odd ball, through having a lot of eyewall replacement cycles, at times a very large eye and speeds which should give upwelling to kill it. These factors have confused the models. What we have is not a particularly strong hurricane but with a significant warm core which is likely to cause significant expansion as it goes extra tropical and give a deep low pressure system. The hurricane although moving north slowly is forecast in the near future to accelerate North such that it has barely turned ex tropical before it slams into Greenland  and onwards into the artic. This will cause warm air to be spread into the artic and alter artic wind patterns. Mountain torque from the wave breaking caused by the storm crashing over Greenland is likely to create an upward propagating wave. This type of wave during winter can cause the polar vortex to shift or split in the stratosphere giving a blocked winter pattern. During autumn the most it can do is shift stormy weather towards Russia or Canada. A blocking low in Northern Russia might  be a reasonable response in my view. That gives Scandinavian or continental high and still a blocked pattern for the UK. It all depends on the timing and course of ex hurricane Larry which has already had some oddball characteristics so all bets are off.

[Frosty.]

As with the 0z, the Gfs 6z op says the benign weather will be terminated into the last third of September with a much more active autumnal pattern with spells of rain and strong winds interspersed with sunshine and showers…as I’ve said, I don’t want the largely benign pattern ..   going on..and on..and on!..would be sooo boring but the 6z op has made me happy!  ? ?  

 

 

Edited September 8, 2021 by jon snow

[MP-R]

37 minutes ago, jon snow said:

As with the 0z, the Gfs 6z op says the benign weather will be terminated into the last third of September with a much more active autumnal pattern with spells of rain and strong winds interspersed with sunshine and showers…as I’ve said, I don’t want the largely benign pattern ..   going on..and on..and on!..would be sooo boring but the 6z op has made me happy!  ? ?  

 

 

All very standard for this month. I can remember many more unsettled second half to Septembers than settled. Had we not had help from tropical storm activity, we'd probably be in a much more unsettled pattern than August already.

It does look like a largely benign week next though in the main. Much cooler but still pleasant enough and much better air quality.

[Frosty.]

Although the Gfs ops so far today have trended unsettled longer term, the mean doesn’t really suggest that, so the largely benign / blocked bore fest could continue even towards the end of September?…there are some members that support the ops but they are relatively few in number…honestly, I’m looking forward to the pattern changing if we are now at the end of the heat / plumes?!! 

Edited September 8, 2021 by jon snow

[Cambrian]

The ECM 0z shows only two proper (albeit relatively shallow) circulatory lows gracing our shores over the next 10 days.

The first, for today and tomorrow, but still lurking around until Saturday as it fills, is modelled to bring most of its rain, hit and miss thunder and showers in reality, to the northern half of Ireland and parts of western Britain, with highest 24h totals mostly between 20-40mm over land.

 

The second, in 7 days time, looks at this stage to have a rain band that is a bit more notable in organisation and longevity, delivering in excess of 60mm to a good many parts of England and Scotland. 

 

 

The accumulated total precipitation for the next 10 days gives most parts in the range of 30-90mm, so probably no more than close to average rainfall for a 10 day period in September for most, but one or two places getting well above normal where they happen to land the bangers. 

 

 

[Methuselah]

It looks as the GFS operational run is in the process of flipping again. And, what's worse, I just noticed I was whistling Hark The Herald Angels Sing!

    

Edit: MetO Ten-Day Forecast:

 

Edited September 8, 2021 by Ed Stone

[summer blizzard]

A messy period of weather upcoming with the UK near the boundary between tropical/polar maritime air sources. While pressure over the next ten days is generally cyclonic in nature, warm air is not properly cleared in its totality during the period until day 10 when the Euro, GEM and GFS (possibly as default) attempt to move a more powerful cold front through. 

Similar to early June perhaps with a relatively warm but mainly at night pattern.  

[Frosty.]

I would call this from the Gfs 12z operational BLOCKED…I would call it something else but I don’t want to test the swear filter!   

Edited September 8, 2021 by jon snow

[I remember Atlantic 252]

21 minutes ago, jon snow said:

I would call this from the Gfs 12z operational BLOCKED…I would call it something else but I don’t want to test the swear filter!   

North sea fret for me, cold and windy, no thanks

[LetItSnow!]

As we progress further into September and October, any easterlies will quickly become quite cloudy, raw feeling and drizzly

[Alexis]

Nah, not until second half of October usually. 

[Cheshire Freeze]

On 08/09/2021 at 18:49, LetItSnow! said:

As we progress further into September and October, any easterlies will quickly become quite cloudy, raw feeling and drizzly

As a general rule of thumb, it's usually from late September onwards. Mostly because overnight cooling of the land mass becomes dominant past the equinox (more hours of cooling than heating= net cooling effect). 

As with spring where you need an increasingly 'perfect' flow from the NE to get deep cold, you need a pretty perfect S'ly flow to get warmth late Sept into Oct.

Edited September 8, 2021 by CreweCold

[Frosty.]

The Gem 12z shows an Atlantic breakthrough of sorts longer term…get in!!!  

[Mike Poole]

Well the ECM has a big high moving in at T240, but i don’t buy the evolution at T168-T192, it just looks wrong to me.

[Frosty.]

The duality of early autumn in a nutshell on the ECM 12z op! ?     

Edited September 8, 2021 by jon snow

[Scorcher]

2 hours ago, LetItSnow! said:

As we progress further into September and October, any easterlies will quickly become quite cloudy, raw feeling and drizzly

A bit early for that. Morning fog can become more of an issue late in the month but easterlies can still be warm.

[damianslaw]

Lots of uncertainty as we move into the middle of the month. Models playing around with height rises but the atlantic looks menacing to the NW, with quite a sharp temp gradient setting up fuelling the jet. Much depends on its stength and ability to nose out the high pressure. Could be one of those set ups where it splits and energy is passed both underneath the high and far to the NW, it then depends on where most energy is exerted. Throw in any ex hurricane activity and it becomes a forecasters headache. 

In the short term, gone is the summer heat, replaced by something nearer average but still relatively warm in southern parts at least, and for many there first bout of proper precipitation for nearing on 3 weeks.

[Mike Poole]

ECM clusters in the T192-T240 resolutely sticking to a scandi blocking regime:

I’m not buying any return to Atlantic driven weather until they shift at this timescale.  One question is, how close is the high - might be an issue with cluster 2?