Gordon Webb

Update from PJB 10:00 Update Changes to Risk Boxes - None Detail The 05Z Nottingham ascent demonstrates the changes taking place in the lower and upper atmosphere quite nicely as GPH is eroded as a more cyclonic upper air pattern begins to move in from the west. The Ascent shows slowly warming at the 850mb level and slight cooling aloft. It also shows the slowly increasing and more favourable upper level kinematic environment. At 850mbs a zone of higher Theta-W is moving north across Central Southern England and this will find its way across Northern England during the afternoon. This higher Theta-W Plume will manifest itself as 850mb Theta-W >16C as we go through the afternoon and translate to fuel surface based storms which are likely to fire across Northern England. At the surface a prefrontal trough is moving across Wales, SSW winds behind the trough and SSE or SE winds ahead of the trough moving NNW across the Midlands and into Northern England . Temperatures are already approaching 20-21C across these areas and HRV imagery indicates only cold Ice cloud spreading north across the Midlands, though some thicker Alto-status or Alto-cumulus across CS England. Airmass imagery depicts a zone of increased vorticity moving NNE and this is indicated in the various model output which shows an area of increased 700mb, 500mb and 300mb Vorticity moving NE associated with a shortwave moving NE ahead of the main cyclonic vorticity centre. At 500mbs and 300mbs there is an increase in Jet Energy over Southern England, so some additional shear vorticity is likely to spread across Northern England from this Jet and at the same time we will see a strengthening SSE Jet moving NE across Ireland and Northern England finds itself under a positive area of enhanced divergence aloft as the two Jet's come together. Storms are likely to erupt across NE Wales, NW Midlands, and the Greater Manchester area and towards Derbyshire during the afternoon and move NE wards. SSW Trajectories, though if they climb high enough more likely to be steered eastwards across the Pennines and towards the Sheffield area. Modifying the Ascent at Nottingham to a temp of 24C and DP 15/16C yields significant CAPE available at over 1300 j/kg MUCAPE . Storms routed to the surface where the highest Theta- W will be located ,however the storms also will tap into the increased energy at 850mb as the zone of higher Theta-W moves and advects NE across N England. The most energy available therefore across the PURPLE BOX area on the risk map. Storms have the possibility to give very heavy or torrential rain. Given the areas likely to be affected there is scope for significant further flooding to already damaged areas and areas under recent flood warning and flood watches. Fig 1- Storm Risk Map Fig 2- Hirlam Streamlines showing the confluence and convergence across N England during the afternoon . Fig 3 - Arpege 850mb Theta- W Showing the zone of highest Theta-W during the afternoon , Storms likely to tap into this additional favourable environment and use it as additional fuel for storms. Fig 4 - Jet Energy increasing through the afternoon. Deep Layer Shear increasing and the overall kinematic environment increasingly favourable . Fig 5 - Nottingham modified ascent. Edit - Images Are very small and don't enlarge when clicked upon go here http://www.ukweatherworld.co.uk/forum/index.php?/topic/122052-convective-outlook-sunday-4th-august-2019/ to see them in enlarged size when clicked upon

Sure does look like it unfortunately places Like Derby And Yorkshire who really don't need it also look in the firing line let's hope those areas miss the worst of it

yeah maybe but their warning is of thunderstorms and outbreaks of heavy rain so they haven't put all their eggs in one basket so they covered themselves , convective weather also suggested saturated profiles which will tend to limit lightning potential with an exception of N/NW England and scotland , specific line below hence conditions will be favourable for a greater coverage of lightning activity over N / NW England, adjacent Irish Sea and perhaps SW Scotland, especially enhanced by both orographic forcing and low-level convergence during the afternoon and evening hours

Convective Weather Forecast Day 2 Convective Outlook VALID 06:00 UTC Tue 30 Jul 2019 - 05:59 UTC Wed 31 Jul 2019 ISSUED 20:38 UTC Mon 29 Jul 2019 ISSUED BY: null A near-vertically-stacked low (slightly tilted to the NW with height) will drift slowly northeastwards from Devon to Yorkshire through Tuesday and Tuesday night. The associated upper cold pool will overspread warm SSTs and diurnally-heated land to bring a day of widespread deep convection. Showers and perhaps a few weakly-electrified thunderstorms will already be affecting parts of SW England / S Wales early on Tuesday morning, and are expected to expand in coverage across much of Britain through the day - organising into distinct circular bands rotating around the main surface low centre. Instability will increase through the day in response to diurnal heating, with 300-700 J/kg CAPE likely fairly widely, and up to 1,000 J/kg CAPE in parts of northern England and SW Scotland. Almost any shower could produce a few sporadic lightning strikes, although fairly saturated profiles / excessive cloud cover and fairly weak shear will tend to limit the lightning potential. That said, a zone of steep mid-level lapse rates will exist on the northern flank of the upper low, in an environment with some reasonable shear and good forcing aloft, after a morning of relatively cloud-free skies - hence conditions will be favourable for a greater coverage of lightning activity over N / NW England, adjacent Irish Sea and perhaps SW Scotland, especially enhanced by both orographic forcing and low-level convergence during the afternoon and evening hours. As such, a MDT has been issued for the risk of lightning - and here hail up to 2.0cm in diameter will be possible from the strongest cells. An isolated supercell cannot be ruled out if organised convection can develop relatively early before shear reduces through the afternoon. The main threats will be flash flooding from both slow storm-motion (so prolonged downpours), but also shower training over similar areas - especially given already saturated ground from recent heavy rain over the NW Midlands / NW England etc. There could also be quite a few funnel clouds / weak tornadoes (or waterspout) close to the low centre (so primarily in a zone from the West Country to the W Midlands, and later NW England). http://www.convectiveweather.co.uk/forecast.php?date=2019-07-30

the get out clause of that forecast and tomorrow's forecast is outbreaks of heavy rain , if people are reading into that forecast that everywhere will get thunderstorms I think a few will be disappointed with just heavy rain and the closest they'll get to a lightning strike will be watching replays from last week

yeah I tried to do them as well but mucked up the order so that post that was quoted is now hidden to hide the outcome and I had hoped nobody had been quick enough to quote it , oh well can't have everything

He is probably referring to his location of Glasgow where I suspect chances of heat like we had recently will be lower than Lincolnshire

looks like they'll go over the same areas like a conveyor belt good if you like that sort of thing well not so good if you don't

Convective Weather Updated Again UPDATE 18:47 UTC Right-moving supercell over NE England continues to lift NE into the SE Borders. A new line of storms is heading due north towards Edinburgh along the line of our original HIGH risk area! http://www.convectiveweather.co.uk/forecast.php?date=2019-07-25

looked nice enough last time I passed through

that's a rather philanthropic attitude you have

must be terrible in Scotland If you love heat but hates storms

that's the important bit for those further south

it's not exactly racing across it either

Doesn't everything from france hate the english channel

most of them actually today are pretty similar It just comes down to interpretation of the model data and there points of view of course

for those who may have been surprised at the activity here's a snippet from convective weather for daytime CS + SW ENGLAND / WALES / MIDLANDS / NW ENGLAND THURSDAY DAYTIME ... Elsewhere, gradual moistening at the top of the EML (in the 600-700mb region) may lead to a few scattered elevated showers or thunderstorms developing over CS / SW England around noon, these then drifting northwards across Wales / Midlands / Irish Sea / NW England through the afternoon. The depth of convection will likely be quite shallow, so lightning may be somewhat sporadic and very hit-and-miss. Given the very deep hot, dry airmass beneath the cloud base (also approx 8,000 ft, but note this is from elevated convection rather than the surface-based convection mentioned earlier) any rain would likely evaporate before reaching the ground. for the entire forecast http://www.convectiveweather.co.uk/forecast.php?date=2019-07-25

all forecasts now saying the same thing N midlands Northwards seems to be the place to be and this activity wasn't really unexpected and the Convective Weather forecast basically said as much as I'm not certain about the wisdom of chasing considering the speed of their movement 40mph , good luck trying that on the british road network

well if it goes to forecasts and it seems to be at moment you should be in a decent spot later on

That's the general opinion I think yes

perhaps he coloured the zones in the wrong colours

Well convective weather suggested it and Nick F forecast is of similar lines , I think these are one forecasted to when they move in to more northern areas are expected to go barmy (not a technical term i know)

mentioned on convective weather in their forecast relevant portion below .. CS + SW ENGLAND / WALES / MIDLANDS / NW ENGLAND THURSDAY DAYTIME ... Elsewhere, gradual moistening at the top of the EML (in the 600-700mb region) may lead to a few scattered elevated showers or thunderstorms developing over CS / SW England around noon, these then drifting northwards across Wales / Midlands / Irish Sea / NW England through the afternoon. The depth of convection will likely be quite shallow, so lightning may be somewhat sporadic and very hit-and-miss. Given the very deep hot, dry airmass beneath the cloud base (also approx 8,000 ft, but note this is from elevated convection rather than the surface-based convection mentioned earlier) any rain would likely evaporate before reaching the ground.

true but the description has it for N Wales N England and Southern Scotland , matt hugo tweeted that N Midlands N England and convective weather has shropshire only in the slight zone so I wouldn't be too worried leaving it behind and enjoy your holiday

only in the slight zone for me and looking quite unremarkable compared with Tuesday but go north and east and there's a lot for storm lovers to like