Model Output Discussions 12z 01/06/2017

[Captain Shortwave]

Right, this stops now okay. If you want to take issue with another forum member then please keep it via a private conversation instead of putting it in here.

Please keep to the models. 

Thank you

[ANYWEATHER]

Evening All! A rather complicated outlook  Certainly looking different from previous years with the synoptic outlook,  Both ecm and gfs ops paint a changeable to unsettled period of weather a we greet the first month of Autumn. It looks like temperatures are going to be dramatically up and down , the rainfall is impossible to predict ,but there will be some heavy totals in places , but it looks like plenty of warm fine weather in the offing , just like the last few weeks

[Sky Full]

There's one thing for sure - our weather is certainly fascinating and our wonderful models are constantly doing their best to keep our interest up, aren't they?  Take these charts, for example, all showing +120hrs, from GFS, ECM, UKMO and GEM, in that order:

   

   

All remarkably similar, i feel.  Perhaps that's not too surprising given that this is only five days away.  But now look at the charts for +216hrs - that's less than 100 hrs later.....

   

(sorry, can't post UKMO at +216! )             

These could hardly be more different, could they?  It makes me wonder how they could all come up with the same thing after 120 hours but completely diverge over the next 100 hours - there's not one feature in the same place between them.   Which one will get it right?  None of them, hopefully, as it's all pretty c##p, really.    

Edited August 22, 2017 by Sky Full
Misspelling

[Frosty.]

The models look changeable for the foreseeable with potentially some decent fine and warm spells, mainly across southern uk and especially southern / south-east england with northern / north-western uk tending to bear the brunt of the unsettled cooler weather, particularly next week..The upcoming BH weekend could be a good one across the s / se.

[Sky Full]

These charts from GFS and ECM are promising for the 1st September:

   

Both of these could evolve into a warm spell at the beginning of September if they verify, so worth watching.   I know, I know - it's nearly 10 days away etc etc, but you've got to keep your hopes up, eh?  

[Frosty.]

wow its quiet in here, could almost here a pin drop! The models don't look too bad this morning, especially the Gem 00z and the Ecm 00z ends on a high note..so to speak

In a nutshell, its looking generally changeable with something of a north-south split with southern uk having at least some fine and pleasantly warm weather at times, more unsettled and cooler the further n / nw one is.

Edited August 23, 2017 by Frosty.

[karyo]

The most interesting aspect of the models for the next few days is what happens with the remnants of Harvey as he moves over the warm waters of the Gulf of Mexico and reforms before making landfall somewhere in Texas. Despite model disagreement on the intensity of the storm they all pretty much agree on huge rainfall totals. 

[Man With Beard]

We're nearly ready to look at the detail for the Bank Holiday weekend ... or are we?

As usual, it's not a simple picture. The charts for Saturday and Sunday show fronts are nearby, but not necessarily interfering with all locations. First Saturday:

        

Fair (though not perfect agreement) on the three charts. For the SE, the charts for Saturday confirm my thoughts that although it looks closest to the continental heat, it may well end up plagued by a front dividing the warmer air and less warm air - probably just a cloudy affair but might be a disappointment in sunshine values. It's a really close call - front further south and sunny/cooler - front further north and sunny/hot - front where it is and cloudy/humid. Indeed, just a few miles might make a world of difference as the GFS chart shows (note on ARGEPE, grey/white shows clouds, but on the GFS white shows the lack of clouds). The temperature charts seem quite optimistic, but I'd be a little sceptical until cloud amounts are nailed down.

Further north, Saturday may not actually be too bad, but only if the charts verify as they are this morning. Sandwiched between two fronts, there could be a lot of sunshine, and in lightish winds, still feeling warm. Always the risk that western coasts may see more cloud/showers, but not a washout at all - as things stand!

Now onto Sunday:

    

Although any heat has been pushed away, a potentially fine day for most with variable cloud and just a few showers in localised areas further north. Again a reasonable amount of agreement between the charts, with ARGEPE perhaps the most positive. Timing is of the essence though - we're still at the stage where the Atlantic fronts could be modelled too slowly - if so, much cloudier/damper in NW areas.

Edit: The ECM is a bit more showery further north for Sunday:

Finally Monday. This I'm sure is subject to change. The Fax and ARGEPE charts don't go out this far, so looking at the GFS:

  

and it's all gone downhill for northern areas, with fronts and rain pushing well in. The south, however, could get away with a reasonable day with variable amounts of cloud and potentially very warm at first.

With so many little weather features all around us, though, it will be a difficult weekend to pin down until just before the time.

Edited August 23, 2017 by Man With Beard

[Frosty.]

Good post above, I agree the devil will be in the detail regarding the BH weekend. :-)

[Man With Beard]

This sums up the problem in forecasting the weekend! 

ECM ensembles are pretty much together at T72, but look at how the divergence grows by T96!! All down to that shortwave to the NW.

[Frosty.]

Not a bad Gfs 6z at all, at least across southern uk with most of the unsettled weather brushing across northern britain and then later in low res, a nice big anticyclone builds in to bring a more sustained settled spell nationwide!

Edited August 23, 2017 by Frosty.

[Frosty.]

I think much of the coming BH weekend will be quite pleasant away from the far n / nw with sunny spells and plenty of dry weather with just a few showers dotted around, some heavy and thundery ones possible across the SE for a time and some rain across the far n / nw...just my usual completely unbiased view of course.

Edited August 23, 2017 by Frosty.

[bluearmy]

As is evident from MWB's post above, BH monday is far from sorted re upper trough - the ecm spread as opposed to the clusters posted reveals 

[Frosty.]

43 minutes ago, bluearmy said:

As is evident from MWB's post above, BH monday is far from sorted re upper trough - the ecm spread as opposed to the clusters posted reveals 

I think BH Monday will be the main dodgy day of the coming weekend with a band of rain and strong winds gradually crossing the uk from west to east but the south-east could escape with a dry, bright and warm day ahead of the rain. Through the rest of next week it looks like a generally north-west / south-east split with the lions share of the cooler unsettled weather affecting the NW whereas further s / se should see decent largely fine and warm surface conditions at times with a risk of some thundery showers across the southeast. 

Edited August 23, 2017 by Frosty.

[Frosty.]

Looking at the GEFS 6z mean, Fri / Sat / Sun could be largely fair and warm across at least central and southern uk but I will add there is a risk of some heavy thundery showers affecting the southeast early in the weekend but Monday could also be fine and warm across the SE corner. Next week shows pressure falling across the uk with a band of rain pushing from west to east during BH Monday but the main unsettled zone next week looks to be further NW closest to the low with southern uk seeing slightly higher pressure with some pleasant weather at times. Further ahead indicates a potentially more settled spell gradually developing through early september with the azores high / ridge becoming more influential, at least across southern uk during the course of week 2.

Edited August 23, 2017 by Frosty.

[Sky Full]

1 hour ago, Frosty. said:

Looking at the GEFS 6z mean, Fri / Sat / Sun could be largely fair and warm across at least central and southern uk but I will add there is a risk of some heavy thundery showers affecting the southeast early in the weekend but Monday could also be fine and warm across the SE corner. Next week shows pressure falling across the uk with a band of rain pushing from west to east during BH Monday but the main unsettled zone next week looks to be further NW closest to the low with southern uk seeing slightly higher pressure with some pleasant weather at times. Further ahead indicates a potentially more settled spell gradually developing through early september with the azores high / ridge becoming more influential, at least across southern uk during the course of week 2.

 

I am very much liking the promise of settled weather for early September as suggested by the charts you posted above, Frosty, but can't help feeling they are still a loooong way off....   Is the GEFS guilty of being generally more optimistic than the other models or will they catch up in the next few days? 

[Frosty.]

7 minutes ago, Sky Full said:

 Is the GEFS guilty of being generally more optimistic than the other models or will they catch up in the next few days? 

I think the latest GEFS reflects what the met office are currently thinking which is that there may be a longer spell of settled weather during early September..Fingers crossed!

Edited August 23, 2017 by Frosty.

[Frosty.]

Some gorgeous charts later on the Gfs 12z with high pressure building in strongly and warm too..this would tie in with the met office saying early september may bring a longer spell of settled weather..just staying positive.

Speaking of warmth, the SE becomes very warm for a time early next week with temperatures into the high 20's celsius and the bank holiday weekend itself looks respectable across the south / southeast especially.

Edited August 23, 2017 by Frosty.

[Frosty.]

The unsettled and cooler shot from the NW next week is more of a glancing blow on this evening's Ecm 12z with the south barely involved and thereafter pressure rises strongly across the uk with an increasingly fine and warmer spell developing later in the run.

Edited August 23, 2017 by Frosty.

[Frosty.]

Good recovery on tonight's Ecm 12z ensemble mean following a glancing blow with a low next week, just like the operational our weather becomes more settled later in the run..potentially a fine and warm early september to look forward to..with the usual caution of course!

Edited August 23, 2017 by Frosty.

[Man With Beard]

So quite a lot of warm, even hot weather on the 12Zs!! The GFS had the southeast close to 80F on 5 consecutive days starting this Friday.

[Frosty.]

4 minutes ago, Man With Beard said:

So quite a lot of warm, even hot weather on the 12Zs!! The GFS had the southeast close to 80F on 5 consecutive days starting this Friday.

Yes there are encouraging signs from the models today, shame its so quiet in here but nice to see there are a few of us keeping the discussion alive!

[Singularity]

So much upstream complexity at the moment as the La Niña-like signal from those strong C Pac traded propagates across to the subtropical Atlantic but then gets distorted majorly by numerous tropical or subtropical systems, so changing what we find ourselves dealing with here in the U.K.

There does tend to be a net effect in September of sending warm air aloft over NW Europe which help build ridges of HP there. Trouble for us is this is achieved via enhanced zonal flow so a strong jet running west-east with a distinct dividing line over the UK that can easily lie anywhere between Southampton and Edinburgh and occasionally as far as the northernmost reaches of the UK.

Sometimee though, the divine tendency to the jet that the La Niña-like signal encourages can form a sort of treaty with the NW Euro ridge signal such that lows keep dropping down a little way SW of the UK. Unfortunately those lows rarely get stuck there with such an active jet unless they can be totally cut off such as UKMO and GEM spent a few days toying with the idea of recently. So they typically drift across the UK after a day or two with scope for some large rainfall totals.

So I suspect there will tend to be an often quite warm but muggy state of affairs at least here down south for the next week or two, with a few heavy doses of rain to contend with but a reasonable are amount of dry and usable weather in between.

I wish I could say the same for those at the other end of the UK. You're not without a change but it's a pretty slim one.

[Flash bang flash bang etc]

I hope this signals some vaguely unusual and interesting weather - and not just more  18->22° days with variable cloud - which is basically what we've had since mid July

[mb018538]

Well, it looks like me may have our next straw to clutch onto going into September. The next week doesn't actually look too terrible, with low pressure tracking to the north of the UK - usual caveats apply (NW wetter and windier, SE drier and warmer etc.)

High pressure is signalled to build in through the middle and latter half of next week:




The UKMO 144 chart has a similar theme to ECM and GFS:



All will hinge once more if we get more low pressure development/low pressure tracking south again to hinder the pressure build around day 7.