Uk Convective General Discussion & Forecasts - May 2012 Part 3

[viking_smb]

there's plenty of the wet stuff all around us. as we are a Island.

[tara303]

Sunset at stonehenge.....

so, I have monday and wednesday off to enjoy storms...? only sighted a few distant flashes and rumbles so far this year - wonder how this week will go!

[viking_smb]

lovely pic tara. beautifully captured

I don't want storms next weekend, as we have our regatta in Cardiff Yacht Club yay

[Robbie Garrett]

Many a report of bolts,bangs and rumbles over on the Heath(Hamstead),not always weather related though.

That will be the C2C line again then? hahah!!

Sunset at stonehenge.....

so, I have monday and wednesday off to enjoy storms...? only sighted a few distant flashes and rumbles so far this year - wonder how this week will go!

That is amazing..... did you see the Moon last night by any chance?? look orange and massive at about midnight.

So, how severe would you expect these thunderstorms to be (apologies I'm a bit of an amateur with this sort of thing!)

Looking at the synoptic charts, am I right in thinking that occlusion in the middle of the week, meeting the hot air from the east, looks perfect for severe thunderstorm potential? On the same sort of scale as last June during Wimbledon?

Well looking at tomorrow, London and Harlow etc..., will get wiped off the face of the earth by tomorrow if this is correct.

Might be good for a home grown MCS, but nothing on the import potential with a convergence wind through Southern England.

Wednesday may be pretty good for a Bay of Biscay disturbance and by the looks of things the wind direction is perfect for a BOB/France Import. Someone with more knowledge on these things may be able to help but I remember a few years back, the Bay can be a nice piece of work for starting things off. With some fairly decent cape up till 2100/2200 (700-1200k/j)

Not sure if things can get organised but there will be some pretty hefty storms, probably supercelluar characteristics with some cells getting up to FL400 (40,000ft+)

[Nick L]

Why don't we have that radar system in this country? Is it too expensive?

It's not really necessary. In the US it's extensive because it's literally a life-and-death situation. Here it's just the odd deep puddle and minor damage to next door's shed!

[Costa Del Fal]

NAE 18z has initiation nicely over the West Midlands into the SE tomorrow.

[Nick L]

NMM showing the trough very nicely:

http://nwstatic.co.uk/viewimage.pbx?type=nwm;date=20120527;time=12;ext=32;file=nmmukprate;sess=425bcff0a34313f7f1d0a5a76220216f;

[Will Padz]

That will be the C2C line again then? hahah!!

That is amazing..... did you see the Moon last night by any chance?? look orange and massive at about midnight.

Well looking at tomorrow, London and Harlow etc..., will get wiped off the face of the earth by tomorrow if this is correct.

Might be good for a home grown MCS, but nothing on the import potential with a convergence wind through Southern England.

Wednesday may be pretty good for a Bay of Biscay disturbance and by the looks of things the wind direction is perfect for a BOB/France Import. Someone with more knowledge on these things may be able to help but I remember a few years back, the Bay can be a nice piece of work for starting things off. With some fairly decent cape up till 2100/2200 (700-1200k/j)

Not sure if things can get organised but there will be some pretty hefty storms, probably supercelluar characteristics with some cells getting up to FL400 (40,000ft+)

Imin Paris going to Roland Garros

That Lookslike we could get something juicy later on....blooming hot here at mo, was 28c earlier but very humid with temp still at 23c.....air on on full.....

[Aaron]

NMM showing the trough very nicely:

http://nwstatic.co.u...d0a5a76220216f;

Smack bang over Leeds.. definitely not going to pan out like that

[davehsug]

They were being shown further west this morning. I suppose I'll be gazing at anvils to the east & swearing again!

[Robbie Garrett]

Hmmmmmmmm.........just thinking, homegrown MCS tommorow afternoon/evening for Reading, London and South East?? with Essex and those counties joining in with the fun!! With that much CAPE/-LI special things can happen.

And my mate just said to me that on the forecast this evening you would be very unlucky to see a shower tomorrow, but if you did it could be torrential and could cause localised flooding.

Wednesday looks like a proper beast in the making. Going to be a fun few days..... hehe!!

[tara303]

Oh dont want to get the hopes up - but this is looking good, can't believe i'm off work so can radarwatch and windowatch whoooppeee fingers x'd...

[Robbie Garrett]

[ZONE 51]

Last year it was the North East that got most of the storms but looks like this year is back to normal. The SE is traditionally supposed to the area in the country that gets most storms. I agree though that so far this year it has been a bit unfairly distributed, but mother nature is not known for her fairness.......

Interesting you should say that!(bold)

And with the increased SE storms and continental imported storms this year that i am predicting, then these then take the route North. I think generally a thundery summer with alot of action, this all fitting in with the large scale pattern change and movement of weather systems that affect thundery distribution.

[ZONE 51]

South East? Ha! I should be so lucky...no decent storm here for four years now! Gone are the days where we'd have a sultry, hot afternoon followed by distant rumblings heralding the arrival of a vicious French import

I know that is something that really i miss and many others of course!! the slow build up and frequent flashes from the s and se horizon, and these storms would turn up here around 1-2am and last many hours, it is something that has not been what used to be normal, would there be a summer without at least one night of storms or an MCS? not here, the night storms always occured at least once and usually always from the continent.

[ZONE 51]

Today for some places there is the risk of thunderstorms and some of these are likely to become severe with hail and flash flooding a risk, also slow moving storms lasting for many hours and possibly into the late night. An interesting day! another warm or hot day, and feeling humid.

I have done a storm risk map.

Today is the type that we cannot be sure of the exact locations of thunderstorms, radar watching and sky watching these build up, it could be that if you don't get a storm you may just see them looking great in the distance! or if they last until dark-which i expect some late eve/night ones to continue-then some distance displays in there to! but if you get a direct hit then you would know about it!!

This week is a thunderstorm expedition!!

[Stuart]

Good Morning just seen daybreake weather maybe it time for my 1 st storm of the year

MDT: London, Home Counties

SLGT: W + SW Scotland, NW Eng, Midlands, C + E Wales, W Country, Home Counties, London, SE Eng

Synopsis:

Slack conditions become present across the British Isles between a large area of high pressure south of Iceland, and a complex low west of Biscay.

Discussion:

Under slack circumstances, seabreeze convergence often form, but only once a sufficient temperature gradient has become established at the surface between land and sea. Thus, storm initiation will rely on seabreeze effects, and, further north with a much drier airmass, topographical forcing. As a result, such storms will be late developing (mid afternoon into the evening hours).

As LSTs rise, steepening lapse rates will allow locally in excess of >800J/kg CAPE to develop, generating a few distinct lines of showers/thunderstorms. Main focus is given to the Pennines SSEwards towards London/Home Counties, but other small-scale lines are likely over the Scottish Highlands, Welsh mountains and parts of Northern Ireland. Greatest instability, however, will be along the low-level convergence between the Pennines and South Coast, with a few pulse-type thunderstorms developing capable of producing a significant amount of lightning, and due to slow storm-motion some locally high rainfall totals, increasing the risk of flash flooding.

Speed and directional shear are both relatively non-existent, thus such storms are unlikely to be severe due to their inability to separate updrafts and downdrafts to sustain storm development, and therefore resulting in their pulse-type nature. Main primary threats are locally torrential rainfall, frequent lightning and hail. The general model consensus indicate a surface low is likely to form over London and surrounding environs, where there is the greatest potential for storm development.

Showers/storms are likely to persist into the evening but will gradually decay near and after sunset.

http://www.ukasf.co.uk/storm-forecasts/176

[Norfolk Sheep]

Dammit, looks like I'm too far east yet again. Hey ho, roll on August, might get something as it's usually our best month. Soon be Christmas

[Supacell]

Can anyone post the ukasf map please. For some reason if I go into the ukasf site I can just see a blank box.

Met office rainfall prediction tool has the storms well east, almost the SE coast with even places as east as London missing out, being too far west .

[Chris.R]

Could somebody tell me, is the wind likely to be from the NW or W today and wednesday, because if so, you can forget about storms around here yet again!

[Coast]

Can anyone post the ukasf map please. For some reason if I go into the ukasf site I can just see a blank box.

Of course!! Morning storm nutters!!

ESTOFEX don't have a forecast for today so straight into that UKASF one by Dan (Staplehurst):

Forecaster: Dan

Last Updated: 2012-05-28 08:25:00

Valid: 2012-05-28 00:00:00 - 2012-05-28 23:59:00

Areas Affected:

MDT: London, Home Counties

SLGT: W + SW Scotland, NW Eng, Midlands, C + E Wales, W Country, Home Counties, London, SE Eng

Synopsis:

Slack conditions become present across the British Isles between a large area of high pressure south of Iceland, and a complex low west of Biscay.

Discussion:

Under slack circumstances, seabreeze convergence often form, but only once a sufficient temperature gradient has become established at the surface between land and sea. Thus, storm initiation will rely on seabreeze effects, and, further north with a much drier airmass, topographical forcing. As a result, such storms will be late developing (mid afternoon into the evening hours).

As LSTs rise, steepening lapse rates will allow locally in excess of >800J/kg CAPE to develop, generating a few distinct lines of showers/thunderstorms. Main focus is given to the Pennines SSEwards towards London/Home Counties, but other small-scale lines are likely over the Scottish Highlands, Welsh mountains and parts of Northern Ireland. Greatest instability, however, will be along the low-level convergence between the Pennines and South Coast, with a few pulse-type thunderstorms developing capable of producing a significant amount of lightning, and due to slow storm-motion some locally high rainfall totals, increasing the risk of flash flooding.

Speed and directional shear are both relatively non-existent, thus such storms are unlikely to be severe due to their inability to separate updrafts and downdrafts to sustain storm development, and therefore resulting in their pulse-type nature. Main primary threats are locally torrential rainfall, frequent lightning and hail. The general model consensus indicate a surface low is likely to form over London and surrounding environs, where there is the greatest potential for storm development.

Showers/storms are likely to persist into the evening but will gradually decay near and after sunset.

SkyWarn and TORRO not posting any forecast so far so here are some of the usual indicators to consider for your area:

Lovely big area of red centrally over London and the Home Counties later this afternoon:

The HiRLAM charts don't give massive amounts of CAPE at all:

GFS much more bullish!

Central over London and surrounding area then all the way up to the Pennines:

RAIN!!!!! (maybe hail?)

Also some spout potential:

To sum up from GFS:

[Carl46Wrexham]

Could somebody tell me, is the wind likely to be from the NW or W today and wednesday, because if so, you can forget about storms around here yet again!

In truth it would not surprise me in the least if the favoured spots get everything again, not just today but through to Wednesday, with the rest of us scratching our heads going "storms? what storms?"

There has definately been a pronounced shift eastwards with regards to where thundery weather occurs. I have not yet

heard or read a satisfactory explanation as to why things have so markedly changed in recent years. Why it is now that in Western Britain that thunderstorms are now an extremely rare phenomenon. I know and accept they occur more in the east naturally, but this does not explain the complete lack of storms in large parts of the West in the past few years.

[Coast]

Tuesday still on down here in the South maybe, but Wednesday looking active!

[GreyCrag]

Dare I say it but anyone missing out on a storm the next 3 days to come will be extremely unfortunate given the majority of England is progged to see something from the CF remnants, now situated in a line north-south from Cheshire to Essex. for us northerners GFS has a area of storms moving out from the Mersey and transitioning just south of West crossing over the Peak District by 9pm. From here the line slowly dissipates once more into the early morning hours.

Wednesday is simple home-grown showers transitioning into a MCS, aided by moisture injection coming in from behind the CF which by then is in the North Sea and probobally not even noticeable in stature.

[Robbie Garrett]

Looking good for central London it may seem, London CIty TAF going for 40% prob heavy thunderstorm in hail, rain showers. With everywhere else PROB30

In truth it would not surprise me in the least if the favoured spots get everything again, not just today but through to Wednesday, with the rest of us scratching our heads going "storms? what storms?"

There has definately been a pronounced shift eastwards with regards to where thundery weather occurs. I have not yet

heard or read a satisfactory explanation as to why things have so markedly changed in recent years. Why it is now that in Western Britain that thunderstorms are now an extremely rare phenomenon. I know and accept they occur more in the east naturally, but this does not explain the complete lack of storms in large parts of the West in the past few years.

I was thinking could it be due to the fact the difference in temperatures/contrast between the different airmasses, being pretty much the same.... compared to a few years ago when say a cold front coming through was a proper strong cold airmass.