South West & Central Southern England Regional Weather Discussion 28/08/13 00z ------------------>

[A.J]

yep, hi-res modelling keeps a lot of us relatively dry this weekend albiet much cooler than of late, with most of the heavier pulses of rain confined to the north midlands and north wales....could be a lot worse although it's a messy synoptic pattern so wouldn't be suprised some variation on where rain does actually fall

[AWD]

Latest accumulative precip totals from now until 06:00 Saturday morning from the NAE;

Don't take too literally as it hasn't been the best model lately but it does go to show the general theme of us being in the "eye" of the low and getting away with very little rainfall tomorrow.

Looking decidedly fresh though;

Edited September 5, 2013 by AWD

[MP-R]

I was looking forward to a slack low around early next week with the slow moving thundery downpours while still warm scenario but the models seems to have backed away from that a little.

[Guest William Grimsley]

There is lots of altocumulus around, at the moment.

yep, hi-res modelling keeps a lot of us relatively dry this weekend albiet much cooler than of late, with most of the heavier pulses of rain confined to the north midlands and north wales....could be a lot worse although it's a messy synoptic pattern so wouldn't be suprised some variation on where rain does actually fall

Not really sure you're correct there. It looks like we shall see quite a lot of downpours this weekend.

I was looking forward to a slack low around early next week with the slow moving thundery downpours while still warm scenario but the models seems to have backed away from that a little.

More likely this weekend I think.

GFS is on that thought too:

 

Yeah rain for here.

I thought the emphasis might shift slightly further North, i expect the warnings will be tinkered with today. It's one of those that if you are under the yellow warning, you may see 5mm of rainfall whereas others under it will see 25 or 35mm.  

 

Currently  and already 18.6C. Gonna be another cracker!

Annoying.

[Guest William Grimsley]

It looks like most of the activity will be on Friday Night with only a little bit on Saturday and Sunday before the whole area of thundery weather moves back into France, next week.

[A.J]

Not really sure you're correct there. It looks like we shall see quite a lot of downpours this weekend.

 

re-read my post again William and then tell me I'm not correct....I stated in my post that hi-res modelling shows that little rain is forecast for my region which is backed up by the 06z hi-res model suite....I did not, at any point state that I didn't think there would be little rainfall, I was simply commenting what the model output shows

[Andy Bown]

25.5c so above 25c for the 4th out of 5 days in September so far! Mostly blue sky and unbroken sunshine with a few patches of Altocumulus, most notably a thin line of it running SW-NE to the West of here which shows very well on satellite images.

[egret]

There is lots of altocumulus around, at the moment.

 

the edge of the altocumulus currently runs in a N-S line over us, just East of Dorchester and slowly moving NE

interesting  to watch this one as we have a Meto weather alert covering all of Dorset (shaded yellow) for tomorrow and Saturday but their 5 day local forecast gives no rain on Saturday so Mapantz earlier post looks likely to be correct ( Meto to change area covered by yellow shading)

[Guest William Grimsley]

re-read my post again William and then tell me I'm not correct....I stated in my post that hi-res modelling shows that little rain is forecast for my region which is backed up by the 06z hi-res model suite....I did not, at any point state that I didn't think there would be little rainfall, I was simply commenting what the model output shows

Ok...

[Snowkissed]

This made me smile:) My garden thermometer reads 32c! I have tried explaining to it that it is now Autumn and this temp could not be achieved, but it is ignoring me, as they do. I will have to go and move it as it is obviously in the wrong place in the garden AGAIN

[Guest William Grimsley]

Met Office warning of rain:

 

Friday: Heavy rain, persistent in places, will affect many areas during Friday. The public should be aware of the risk of disruption due to localised flooding.

 

Saturday: Periods of heavy and persistent rain will continue to affect parts of the United Kingdom on Saturday.  The public should be aware that there is a risk of localised disruption due to flooding.

[Guest William Grimsley]

Now, there are lovely lines of altocumulus castellanus clouds moving from SW to NE to WSW and W of here.

Edited September 5, 2013 by William Grimsley

[Mapantz]

Alerts issued by Netweather but nothing for the South West or Southern counties, interesting ..

 

Currently 26C here. 

[ARTDEMOLE]

Sunny here. Some cloud. 22.9c. Rain expected O4:00 In the morning....Because I just watered the plants....

[Guest William Grimsley]

Alerts issued by Netweather but nothing for the South West or Southern counties, interesting ..

 

Currently 26C here. 

Yeah it is interesting, I suppose they are issued for the rain on Friday rather than the showers on Friday Afternoon, Saturday and Sunday, in SW England. I hope they do issue a weather alert for SW England, like the Met Office have.

[A.J]

no alerts from NetWeather for our region due to continued hi-res modelling progging little rainfall to make any impact in our region..........unless model output changes significantly over the next 12-24 hours then I wouldn't expect any change in the forecast.....

[egret]

Alerts issued by Netweather but nothing for the South West or Southern counties, interesting ..

 

Currently 26C here. 

Yes I think this will prove correct in general (ie nothing extraordinary such as would justify a warning for sw)

Presumably  Meto don't feel the fluctuation has finished yet and that it is too early to withdraw their longer term and fairly general 'alert', even though the models currently put the heavy rain further North

 

It does seem odd when two outputs from the same organisation (Meto) give a contradictory forecast.

 

As for today the altostratus is edging back westwards so we again appear to be on the edge of it. At lunch time it was interesting looking at con trails which started and stopped very abruptly and cleanly on each edge of the bands of altostratus cloud. This shows nicely the undulation in the boundary between the moist and dry (or cold and warm) layers of air. The con trails evaporated very quickly in the clear air. It would be really nice to see that mapped in cross section to visualise just how the boundary is behaving.

Edited September 5, 2013 by egret

[Mapantz]

no alerts from NetWeather for our region due to continued hi-res modelling progging little rainfall to make any impact in our region..........unless model output changes significantly over the next 12-24 hours then I wouldn't expect any change in the forecast.....

 

I would usually agree with that 100% but there's been times this year where the high-res models have progged the rainfall so badly, it almost made me angry lol - A couple of times the NMM was easily 70 miles out when modelling a similar slow moving weather front in the North.

The continuing yellow warnings from the MO are leaving me with an open mind, could the South West be in for some intense slow moving showers?

 

I think i'll just radar watch tomorrow rather than rely on anything for now.  Interesting to say the least though.

[Andy Bown]

no alerts from NetWeather for our region due to continued hi-res modelling progging little rainfall to make any impact in our region..........unless model output changes significantly over the next 12-24 hours then I wouldn't expect any change in the forecast.....

Yes AJ, I had done extra work today due to the likely very wet day tomorrow, however having seen the lunchtime forecasts I may be in bonus territory by midday tomorrow! Heavy rain moving through Hampshire/East Wiltshire, heavy showers developing West Somerset and the rest of the SW, meanwhile a large area in between with only a few showers!

 

I really wonder if having had so little rain in the summer months if tomorrow can do likewise and if we miss the showers over the weekend and pressure rebuilds next week the real dry theme will continue!

 

However I am fully aware that if the front invigorates 50 miles West than currently predicted it will be very wet in the morning!

[Guest William Grimsley]

The continuing yellow warnings from the MO are leaving me with an open mind, could the South West be in for some intense slow moving showers?

 

I think i'll just radar watch tomorrow rather than rely on anything for now.  Interesting to say the least though.

Yeah, I think we have a very good chance of seeing some slow moving downpours on Friday.

Same here best to keep things simple in complicated weather situations like this.

no alerts from NetWeather for our region due to continued hi-res modelling progging little rainfall to make any impact in our region..........unless model output changes significantly over the next 12-24 hours then I wouldn't expect any change in the forecast.....

I think we could be positively surprised, tomorrow.

[A.J]

Yeah, I think we have a very good chance of seeing some slow moving downpours on Friday.

Same here best to keep things simple in complicated weather situations like this.

I think we could be positively surprised, tomorrow.

ha! you will, i won't......you may like the idea of steady rain, but being an outdoors worker I certainly don't......thunderstorms are different kettle of fish entirely, but I'd be surprised if they're any about tomorrow...I'm struggling to see where the necessary instability is coming from.....there's a little bit of surface energy and lift in the lower levels over the south west peninsular tomorrow afternoon/evening but that's just about it....lapse rates are quite high to to an upper cold pool, probably some showers (maybe the odd heavy one dotted around)

[SunnySouthCoast]

Very hot & sunny today, hit 29C earlier! Think tomorrow is going to be a shock to the system

[Guest William Grimsley]

ha! you will, i won't......you may like the idea of steady rain, but being an outdoors worker I certainly don't......thunderstorms are different kettle of fish entirely, but I'd be surprised if they're any about tomorrow...I'm struggling to see where the necessary instability is coming from.....there's a little bit of surface energy and lift in the lower levels over the south west peninsular tomorrow afternoon/evening but that's just about it....lapse rates are quite high to to an upper cold pool, probably some showers (maybe the odd heavy one dotted around)

All the instability is coming from the altocumlus and altocumulus castellanus clouds that have been around here all day.

Very hot & sunny today, hit 29C earlier! Think tomorrow is going to be a shock to the system

Exactly!

[A.J]

All the instability is coming from the altocumlus and altocumulus castellanus clouds that have been around here all day.

Exactly!

no William, that is incorrect.....there's is a little mid level instability (about 100j/kg) over our region caused by a currently decaying cold front, hence the altocumulus, but the altocumulus is not causing the instability rather it's a symptom.....calling it AcCas is stretching it a bit, as the Ac is struggling to turret, more akin to standard altocumulus...

 

The cold front is expected to reinvigorate as it encounters more mid level instability (and WAA) over more eastern parts of the UK hence the chance of heavy thundery downpours overnight and into tomorrow in those areas......It's possible that this rain may also affect eastern parts of our region, with more general bog standard showers from attendant low pressure over devon & cornwall tomorrow

Edited September 5, 2013 by ajpoolshark

[Guest William Grimsley]

no William, that is incorrect.....there's is a little mid level instability (about 100j/kg) over our region caused by a currently decaying cold front, hence the altocumulus, but the altocumulus is not causing the instability rather it's a symptom.....calling it AcCas is stretching it a bit, as the Ac is struggling to turret, more akin to standard altocumulus...

 

The cold front is expected to reinvigorate as it encounters more mid level instability (and WAA) over more eastern parts of the UK hence the chance of heavy thundery downpours overnight and into tomorrow in those areas......It's possible that this rain may also affect eastern parts of our region, with more general bog standard showers from attendant low pressure over devon & cornwall tomorrow

Yes, but these showers over Devon and Cornwall are likely to turn out heavy and thundery on Friday Afternoon. I saw some turrets earlier today...