[Storms and Convective discussion - 20th March 2023 onwards]

To be fair to the met office there risk map does tie in more or less with Dan's moderate risk area and other forecasts I have read whether it kybosh s the whole thing remains to be seen 

[Storms and Convective discussion - 20th March 2023 onwards]

And From Nick

Forecast Details

Upper troughing over the North Atlantic extends across the UK & Ireland on Friday, this combined with a trough of surface low pressure moving north will bring a deeply a cyclonic southwesterly flow. Surface heating of moist flow in sunny spells developing across England and Wales beneath cold mid-levels will create steep lapse rates which is modelled to generate 600-1000 j/kg CAPE early afternoon from E Wales across much of England, instability weaker across Ireland and from northern half of N England northward. This instability will support the development of heavy showers and thunderstorms from later morning and through the afternoon into early evening.

Weak vertical shear and no discernible focus for forcing will mean convection will generally be pulse-type and generally lacking longevity to organise. However, there are suggestions of a few localised areas of breeze convergence, such as around the Bristol Channel inland through the lower Severn Valley towards the SW Midlands driven by topography and perhaps also towards the east coast of England with an onshore component to the wind against the synoptic SWly flow. This potential convergence may focus convection and lead to a risk of localised flooding. Otherwise, heavier showers and thunderstorms may produce hail to 1-2cm, strong wind gusts and C-G lightning. Storms should die out after dark, as surface heating fades.

Overnight, a shortwave trough and shallow surface low will approach from the southwest over the Atlantic and arrive across SW England in the early hours of Saturday, bringing outbreaks of locally heavy rain, some mid-level instability from lift of Tm air wrapping into low may support embedded convection that could produce lightning and some localised flooding.

Issued by: Nick Finnis

Issued by the Netweather forecast team whenever there is a risk of storms or severe convective weather, these discussion based and in depth forecasts will highlight the areas at risk and give an in depth description of the risk and the factors surrounding it.

 

 

[Storms and Convective discussion - 20th March 2023 onwards]

More Details

 

Day 1 Convective Outlook

VALID 06:00 UTC Fri 05 May 2023 - 05:59 UTC Sat 06 May 2023

ISSUED 07:05 UTC Fri 05 May 2023

ISSUED BY: Dan

An upper ridge will transit slowly across Scandinavia, while a longwave upper trough extends from the Atlantic across the British Isles. Fairly extensive cloud and showery outbreaks of rain, most persistent in E/SE Scotland, should gradually clear to the north and/or break up through the day with increasing insolation leading to heating of a moist low-level airmass (T 15-17C / Td 10-13C), especially from late morning onwards. This, in conjunction with a mid-level cold pool drifting northeastwards, will yield 500-1,000 J/kg MLCAPE across portions of England and east Wales. Numerous heavy showers and thunderstorms are likely to develop, particularly aided by areas of low-level convergence such as from southwest England across the south Midlands to East Anglia. Forecast soundings suggest ELTs around -50C, with cloud tops potentially around 30,000ft.

For the most part, limited mid/upper flow will result in weak wind shear, with pulse-type mode most favoured. That said, some backing of the low-level winds over East Anglia and eastern Lincolnshire could bolster 0-6km DLS to >20kts, perhaps aiding somewhat with storm longevity in these areas. Cells will mature as they drift gradually northeastwards, therefore the greatest lightning risk will tend to be favoured more towards eastern England, not least because some areas may have several thunderstorms pass in the vicinity through the afternoon. It is worth noting that the mid-level cold pool will begin to move out to the North Sea from 12z, and so gradual warming aloft from the southwest through the afternoon may result in shower/thunderstorm activity reducing across southwestern areas a little earlier than the typical diurnal cycle would dictate. The strongest cells may produce wind gusts up to 40mph and hail perhaps a little over 1cm in diameter, but the lack of any substantial shear will preclude the risk of any severe convective weather (aside from any localised flooding).

 

Scattered heavy showers are also likely across central and northern portions of Ireland/Northern Ireland in response to diurnal heating and low-level convergence, although here shallower convection will tend to limit the coverage of lightning (especially compared with England). It is possible there may not be much in the way of lightning activity here.

 

Overnight, most lightning activity will cease as showers slowly decay, but there may be a small risk of a few isolated lightning strikes in the vicinity of the surface low that approaches SW England towards the end of the night.

 

[Storms and Convective discussion - 1st August 2022 onwards]

Day 1 Convective Outlook

VALID 06:00 UTC Fri 09 Sep 2022 - 05:59 UTC Sat 10 Sep 2022

ISSUED 07:20 UTC Fri 09 Sep 2022

ISSUED BY: Dan

Upper low exits eastern Britain to the North Sea on Friday, providing another day of scattered showers courtesy of a cold pool aloft atop a humid low-level airmass. Diurnal heating and SSTs will yield 500-1,000 J/kg CAPE, and numerous showers will develop in the unstable environment. Forecast profiles reveal tall, skinny CAPE with weak shear - suggesting pulse-type mode primarily with the biggest concern local surface water flooding from slow-moving downpours that may train over similar areas. Some sporadic lightning is likely, perhaps most likely in eastern England aided by convergence zones here through the afternoon hours. Ridging and warming aloft will tend to limit the convective depth (and therefore lightning potential) over Ireland. Showers/storms will generally fade through the evening hours as nocturnal cooling of the boundary layer occurs, but a few will likely persist overnight along some North Sea coastal counties. A few funnel clouds / spouts will be possible given the unstable environment and areas of enhanced low-level convergence.

 

[Storms and Convective discussion - 1st August 2022 onwards]

for those who don't want to click the link

Day 1 Convective Outlook

VALID 06:00 UTC Wed 07 Sep 2022 - 05:59 UTC Thu 08 Sep 2022

ISSUED 08:35 UTC Wed 07 Sep 2022

ISSUED BY: Dan

The upper low to the southwest of Ireland will finally begin to migrate eastwards across the British Isles on Wednesday. Once again, cool air aloft atop a fairly humid low-level airmass will create widely unstable profiles, driving another day with widespread scattered showers and some thunderstorms. Tall, skinny CAPE will probably limit the lightning potential in some areas, but certainly scope for locally high rainfall accumulations and the associated risk of surface water flooding. A broad SLGT has been issued, but there will very likely be large areas that remain void of lightning. Showers may merge into longer spells of showery rain in places, resulting in rather saturated profiles and reducing the lightning potential. Some more organised clusters/lines of heavy showers/thunderstorms could evolve over the English Channel during the late afternoon and through the evening and night hours, as PVA rounding the base of the increasingly negatively-tilted upper trough engages with the residual >14C 850hPa Theta-W plume over France. This activity may also affect the eastern side East Anglia late evening and after midnight, although by this stage some concern exists about upscale growth into broader areas of heavy, showery rain that may reduce the lightning potential. Further thunderstorms may also affect eastern Scotland later in the

 

[Storms and Convective discussion - 1st August 2022 onwards]

Day 1 Convective Outlook

VALID 06:00 UTC Tue 06 Sep 2022 - 05:59 UTC Wed 07 Sep 2022

ISSUED 07:27 UTC Tue 06 Sep 2022

ISSUED BY: Dan

Upper low remains anchored to the west of Ireland, creating a widely unstable environment across the British Isles. A plume of steep mid-level lapse rates will cover N + NE England into S + SE Scotland, and so it is these regions that could yield some fairly active thunderstorms (potentially) with perhaps marginally-severe hail. Tentatively introduced a marginal MDT risk area where some CAM guidance suggests an active cluster may evolve through the afternoon and early evening, but it should be stressed confidence is much lower than compared with the MDT issued on Monday for example.

Elsewhere in the post-frontal environment with lower Theta-W than previous days, tall and skinny CAPE profiles, unstable also to SSTs, should aid numerous showers to develop, some heavy with sporadic lightning, but struggling to identify anything particularly well-organised given the lack of any strong forcing. Disparity between model guidance also lends to low confidence about the local detail during this forecast period, but given the widely unstable environment have reluctantly opted for a very broad-brush SLGT. There are hints a more organised cluster/area of showery rain may spread northeastwards during the afternoon and evening hours across central and southern Britain, but rather messy in appearance. A jet streak moving across northern France during the afternoon and evening will increase deep layer shear over central and southern Britain, and here 30-40kts could allow for cell organisation with the potential for a supercell if convection can remain fairly discrete.

 

Showers, and associated risk of lightning, will persist well into the night - especially in southern and western areas, but also potentially eastern Scotland and East Anglia / SE England.

 

[Storms and Convective discussion - 1st August 2022 onwards]

Day 1 Convective Outlook

VALID 06:00 UTC Mon 05 Sep 2022 - 05:59 UTC Tue 06 Sep 2022

ISSUED 07:07 UTC Mon 05 Sep 2022

ISSUED BY: Dan

Upper low will remain anchored to the west of Munster on Monday, with several shortwaves rotating around the main parent upper low. The first shortwave will drive an area of occasionally heavy rain across Scotland during the morning hours, but this should weaken and slowly clear northwards. The associated waving cold front will have largely cleared to the North Sea, but bends back westwards as a rather diffuse warm front lifting north across East Anglia and the Midlands at 12z, reaching Scotland by the evening. Surface heating of a moist low-level airmass (15-18C dewpoints) may yield several hundred J/kg CAPE by the afternoon hours across portions of England and Wales. In the absence of any large-scale forcing, most CAM guidance is rather unenthusiastic in developing many showers/thunderstorms; however coarser-resolution parameterised global model guidance continues to suggest the potential for a few scattered showers/thunderstorms developing in response to diurnal heating (and perhaps also aided by sea breeze convergence). Examination of forecast profiles suggests some hints of capping, with CAPE also fairly tall and skinny. Therefore it is hard to ascertain if many showers/thunderstorms will develop during the afternoon, but given unstable profiles and modest speed shear it is possible isolated/well-scattered activity could occur generally south of Merseyside-Humber initially, but expanding north of this line during the evening.

During the late afternoon/early evening, the next shortwave will arrive from the south and may be accompanied by a small surface low approaching from northern France. This seems tied to a quasi-warm front as advection of 16-18 850hPa Theta-W plume occurs into southern England. Surface heating coupled with cooling aloft as the shortwave approaches may yield CAPE in excess of 1,000 J/kg CAPE across parts of SW / Cen S England, Wales and the SW Midlands. CAM guidance varies, but there is a signal for multiple lines and/or clusters of very active thunderstorms to develop over these areas during the second half of the afternoon and through the evening hours as low-level convergence increases. Given increasing wind shear during the evening (30-40kts with low-level winds becoming more backed) some of these cells could become very lively and organised, with a supercell possible if cells can remain semi-discrete. This brings the threat of large hail, locally greater than 2.0cm in diameter, gusty winds and perhaps an isolated tornado - a SVR has been included to highlight these threats (main focus Dorset, Somerset, Wiltshire, Gloucestershire and SE Wales) alongside local surface water flooding, and also across portions of Ireland for gusty winds and an isolated tornado, primarily the afternoon and early evening hours here.

 

Thunderstorms will continue to migrate northeastwards across the Midlands and southern England through the evening and night hours, perhaps joined by additional cells approaching from the English Channel and NE France, and perhaps also expanding into more of N/NW England for a time. Later in the night there may be an uptick in elevated convection spreading into E/SE Scotland from the North Sea.

 

[Storms and Convective discussion - 1st August 2022 onwards]

 

 

THUNDERSTORM WATCH - MON 5TH SEPT 2022

Issued 2022-09-05 08:50:19
Valid: 05/09/2022 0600 = 06/09/2022 0600

Forecast Details

Upper and collocated surface low will be slow-moving to the west of Ireland, a set of fronts wrap around a fairly deep surface low to the west of Ireland, with a slow-moving waving cold front lying NW-SE across Scotland and N-S across along of just off coast of E England at 06z. A new wave along the cold front will buckle the front back W and NW across Britain, with warm front pushing N across England through the day, with warm, moist and unstable air pushing N across England and Wales to the south of this front.

Although there will be no discernable upper forcing to support any organised areas of convection during much of daytime, warm moist airmass (dew points of 14-17C towards S England and S Wales) will advect north across England and Wales through the day and will be increasingly unstable to surface heating – with 800-1200 j/kg CAPE simulated by some models. With this in mind, some models do break out scattered heavy showers and thunderstorms across S England, Wales, Midlands and E Anglia this afternoon, some elevated as warm moist plume is destabilised by cooling / subtle forcing aloft, but also some surface based showers/storms, as the cap is eroded by stronger pockets of surface heating. Surface breeze convergence, particularly towards the west, will also create lift to support heavy showers and storms. With deep layer shear of 30-40 knots and low level backing of winds across S. Ireland, Wales and SW England – there is potential for any surface-based storms to organise here to produce an isolated risk of large hail, strong wind gusts and maybe even an isolated tornado, but will refrain from delineating a severe risk, as the risk looks rather low.

Through this evening and overnight, there looks to be a more organise push for clusters of thunderstorms to break out, as upper support increase with a shortwave trough, currently to the NW of Iberia to the west of the Bay of Biscay, ejects NE towards SW Britain this evening, before lifting N and NE across England and Wales tonight. So clusters of storms look to develop towards the S and SW and push northeast across parts of England and Wales this evening and overnight. Some storms could be quite electrically active and produce some high rainfall totals in a short space of time leading to flash-flooding, along with gusty winds and perhaps hail locally.

Issued by: Nick Finnis

 

[Storms and Convective discussion - 1st August 2022 onwards]

apparently had 3 rumbles last night as it went through according to what I heard this morning , personally couldn't tell from my vantage point of under the quilt

[Storms and Convective discussion - 1st August 2022 onwards]

 

Day 1 Convective Outlook

VALID 06:00 UTC Wed 17 Aug 2022 - 05:59 UTC Thu 18 Aug 2022

ISSUED 07:26 UTC Wed 17 Aug 2022

ISSUED BY: Dan

Cut-off upper low lingers over the Bay of Biscay through Wednesday, slowly filling in-situ. At the surface, a warm, humid airmass (dewpoints 15-18C) will be slowly scoured away southeastwards by a cold front, this marking the boundary to somewhat fresher conditions for the remainder of the week.

A rather messy evolution is once again anticipated, with extensive cloud and areas of showery rain, perhaps with embedded thunderstorms, across parts of central and southern Britain first thing on Wednesday morning. With time much of the general precipitation should weaken and decay, with cloud breaks allowing better surface heating across southern England and East Anglia, and potentially yielding 1,000-1,500 J/kg CAPE in places. Scattered heavy showers and a few thunderstorms may develop in response to sea breeze convergence and some upslope flow over the Downs, Dartmoor etc. Broadly east of the Isle of Wight the steering winds will attempt to push showers to the W or NW (ie parellel to the coast or even further inland), while west of the IoW showers/storms should drift offshore. Therefore, although shear is still relatively weak it is arguably stronger across SE England to enable some level of cell organisation, and (like Tuesday afternoon in Norfolk) an isolated supercell may just be possible. Any organised storms would be capable of producing hail perhaps to 2cm in diameter, and to a lesser extent strong gusts of wind. Perhaps of greater concern more widely in southern England and East Anglia is the risk of local flash flooding given slow-moving torrential downpours and potential for back-building, which is the primary reason for issuing a SVR.

 

 

[Storms and Convective discussion - 1st August 2022 onwards]

19 minutes ago, Mapantz said:

FAX chart is a bit meh for tomorrow.. it's slipping things further south and east.

typical after the met office Extend risk N & W

[Storms and Convective discussion - 1st August 2022 onwards]

10 minutes ago, minus10 said:

Well i expect to see rain at 7pm this evening...because the BBC have said so!

probably got a margin of 12 hours or so

[Storms and Convective discussion - 1st August 2022 onwards]

opinions on this

UK storm warning: Britain faces 10-DAY lightning blitz - new maps show 'absolute deluge' | Weather | News | Express.co.uk

WWW.EXPRESS.CO.UK

---

BRITAIN faces a 10-day thunderstorm blitz as swathes of the country brace for an ‘absolute deluge'.

o

[Storms and Convective discussion - 1st August 2022 onwards]

3 minutes ago, Alderc said:

All the crappy showers in the channel really going to hamper surface heating today. Not sure I'd be feeling very confident if I'd written a convective outlook forecasting widespread surface based storms.

to be fair Dan's forecast is more conservative than is be been made it out to be , just have to read first paragraph of 6 lines to get that impression

[Storms and Convective discussion - 1st August 2022 onwards]

8 minutes ago, The Tall Weatherman said:

Dan’s Convective weather forecast is looking quite optimistic today. Sadly I have to go to north wales today so I will probably miss out.

all down to how people see it as always , seems to be near the M4 corridor seems to be where CZ will hover give or take a few miles of course has the greatest chance , going near Birmingham seems to get more uncertain and then further N than that well seems little point if you read Nick's and Dan's forecast

[Storms and Convective discussion - 1st August 2022 onwards]

8 hours ago, BrickFielder said:

I see a few discussions about supercells in the last day and thought a simple explanation might help. If winds change direction as you go up in the atmosphere then clouds will have a tendency to twist as air rises. If winds at a low level are light and winds increase with height then louds will tilt along with the higher winds aloft. Tilting will separate updraft and downdraft regions  and the twisting will rotate the cloud giving a supercell. If winds at the surface are very light and higher at the cloud base level  then winds will tend to have a rolling barrel effect below the cloud. This rolling or horizontal vorticity can be picked up by a twisting updraft region to form a tornado. This is very rare in the UK but not so rare in Europe hence why Estofex alerts tend to happen more in Europe.

As for today then the models would suggest storms for the west , east and north but not central areas.

Upper level cooling is not really there like yesterday  for Northern parts so maybe not as high a risk of severe storms although I notice some model anomalies.

 

Looking at Satellite images then I see a frontal system moving eastward across parts of the west with embedded storms. That front seems to be moving faster than forecast so I am not totally convinced by modelling of where and when storms will occur. 

 

 

Tomorrow is a different scenario with a frontal system turning  thundery across Wales and central areas through the afternoon. Upper level cooling is better but the atmosphere profile has a tendency to be moist all the way up to the troposphere so there is a risk of very messy convection.

Think radar watching might be a better option at this point.

 

like reading your posts always informative and as for tomorrow are we looking like more larger areas of thundery rain in the afternoon rather than shall i say more discrete showers\storms because of front or is that a simplistic way of looking at it

oh and anybody feel free to answer

[Model Output Discussion - Autumn arrives]

8 minutes ago, mb018538 said:

ECM 00z shows the first heavy/active frontal system to cross the entire UK in what is literally months next Sunday - giving all areas a really good & much needed soaking.

certainly hope so , as even this breakdown looks a little more benign than expected

[Model Output Discussion - Autumn arrives]

1 hour ago, cyclonic happiness said:

not yet, that's just a smaller cold(ish) front, the main thing will come through in the early hours  

 

Greetings from Park Road Bedworth, btw  

oh ok my mistake

[Model Output Discussion - Autumn arrives]

20 minutes ago, Cambrian said:

The 12z GFS operational run shows the heat slowly seeping away overnight, though minima still remaining just above 20 degrees in some parts of central and eastern parts of England, a much easier night for many.
7pm  / midnight / 5am

  

Northern Germany experiencing something similar to Southern Britain last night. 

thank god , cold front seems to be going through my location now ,

[Model Output Discussion - Autumn arrives]

11 minutes ago, JayAlmeida said:

The GFS seems to have amplified the heat potential of the plume and extended its influence into Monday. The rest of the run is pretty bad but not to be taken as reliable at this point IMO.

well surely you mustn't take the run as a whole as reliable not just the less appealing parts of it ?

[Model Output Discussion - Autumn arrives]

6 minutes ago, BenFreeman_91 said:

That is true, I'll enjoy the next two days and see where we are! 

Well I for one expect to be in the same location

[Model Output Discussion - Autumn arrives]

48 minutes ago, mushymanrob said:

These charts have gradually progressed shallow troughing to become dominant over the UK for the last third of the Month..
Pretty average id have thought with some much needed rain for many.
I cant see any quick route back to heat, other than an odd day here and there with the Southeast being favoured.

in a nutshell normal after Tuesday , Works for me

[Model Output Discussion - Autumn arrives]

33 minutes ago, Paul33 said:

Am I not correct in thinking that these official warnings only started in 2021 ?

Yes that's right and a year later the first red warning

5 minutes ago, MattStoke said:

UKV 3z. 40’C Monday. 42’C Tuesday  

yep especially in Lincolnshire up to Yorkshire for Tuesday , down to a mere 37'C for me at that time LOL

[Model Output Discussion - Autumn arrives]

51 minutes ago, Backtrack said:

Can I please ask a question here.

 

I have been a member here for years, and so so so many people discuss ‘poor in the north west, fine in the south, wet in the north west’. 
 

Where is the north west that people are referring to when discussing? I live in north west England, are you referring to here? Or the north west as in Scotland?!

depends on who you ask , for some it's North West Of Dover

[Model Output Discussion - Autumn arrives]

8 minutes ago, Weather26 said:

You'll see soon enough when the mid-month heatwave doesn't materialize. 

if your referring to mid months GFS temps , I'd be surprised if that occurs exactly like that but lets not knock nails into the good weather coffin before it has even arrived , dodging showers loses its appeal after a while and of course its traditional that the weather goes to hell when schools break up in England so enjoy the weather before then