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Nick F

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    Storms and Convective discussion - July 2023

    in Storms & Severe Weather

    Posted · Edited by Nick F

    Pretty active area of storms organising across east Wales, west Cheshire and now nudging into Wirral + Merseyside.

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    I highlighted the Welsh Borders being an area in the afternoon for possible severe storm development in the Netweather Severe Thunderstorm Watch issued yesterday evening. A look at model wind profiles and in the upper levels there appears to be a shortwave trough and left exit of a strong jet streak arriving behind it moving up from the south, creating strong divergence aloft across Wales.

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    Worth keeping an eye on this area which looks like growing upscale into an MCS, NW England could have some issues with this storm complex next few hours!

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    Storms and Convective discussion - July 2023

    in Storms & Severe Weather

    Posted · Edited by Nick F

    Something brewing over the Channel with IoW's name on it.

    Screenshot_20230708-074909_SamsungInternet.thumb.jpg.1be16444e47f84062107d8bf2b590420.jpg

    Also can see the arc of Ac cas bringing spotty showers and storms across N and E England lifting N on the nose of higher theta-w plume streaming N

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    00z models bit over the place still, not really modelling storms mid E Channel too well, ahead of cold front rain, UKV probably closest and has a line move NE tbis morning, maybe a bit slow, EC perhaps similar but faster. 

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    NW England looks sweet spot this afternoon for surface based storms to develop

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    Storms and Convective discussion - July 2023

    in Storms & Severe Weather

    Posted

    Evening, I'm back my my two pennies worth.

    Early elevated storms breaking out Saturday morning northwards from English Channel across CS England and forming a line on into Midlands and perhaps N England, the line moving swiftly NE to N and E England through morning. This won't be the cold front, rather likely a lobe of vorticity streaming NNE interacting with 16-18C theta-w plume advecting north.

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    But more of intetest from a severe perspective is post cold from area of storms models develop across western England / Welsh Borders which then look to organise, perhaps into an MCS by evening, as left exit of strong jet streak arrives from SW. Given 1000-1500 j/kg CAPE forecast and 30-40 deep layer shear, these storms could be severe with large hail IMO.

    viewimagenc-21.thumb.png.251221ef8d3f39a8329e7497dfce968e.pngviewimagenc-20.thumb.png.146e76e15c16b76aa1355161dfbba2a2.pngpreciprate_20230707_12_029.thumb.jpg.db1fa4578571bac54dc680092de0c68a.jpggfs_stp_eur27.thumb.png.baa61cd318748c1eb394b41033cff953.pnggfs_srh_eur27.thumb.png.d370aa0e72d903a0a1f6cd3bf8c600cd.png

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    SEVERE THUNDERSTORM WATCH - SAT 08 JULY 2023

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    Issued 2023-07-07 21:11:01
    Valid: 07/07/2023 2100 - 09/07/2023 0600

    Forecast Details

    An upper level low and collocated surface low will be slow-moving centred just the west of Ireland on Saturday. A plume of warm and humid air continues to advect north across the British Isles ahead of the low to the west heading into Saturday. The plume will become increasingly unstable from the south on Saturday, as areas of vorticity moving northeast across Britain, surface convergence and later a shortwave trough and left exit of a jet streak moving NE create lift of warm / moist plume – supporting heavy showers and thunderstorms to develop and spread NNE across the British Isles.

    In more detail: plume characterised by theta-w values of 18C is forecast to arrive tonight across S England from France and will be inherently unstable with steep mid-level lapse rates. Although there is still some uncertainty, as is often the case with destabilising plumes over the UK, models loosely agree on developing showers and elevated storms over English Channel and pushing into central S England in the early hours of Saturday within axis of higher theta-w plume moving north, likely in response to a lobe of vorticity moving north and wind convergence. A line of elevated storms then looks to extend quickly north along lobe of vorticity streaming north through plume from CS England to N England during Saturday morning before the line then moves NE towards the east coast of England and into E Scotland through the morning and into the afternoon. Some localised flooding and locally frequent C-G lightning is possible with this activity. It’s also possible that a separate area of rain and linear convection with isolated lightning will develop along the cold front following this activity, the front reaching N and E England during the afternoon.

    Post-cold front environment across England will still be warm and moist, with dew points of 15-17C forecast, surface heating of moist air beneath increasingly cold air in the mid-levels advecting NE is forecast to yield 1000-1500 j/kg SBCAPE from CS/SW England across Welsh Borders, Midlands to NW England by afternoon. This strong instability combined with N-S breeze convergence in the same areas and an upper shortwave trough ahead of left exit of strong jet streak both moving northeast causing larger scale ascent, are forecast to support the development of surface-based thunderstorms, perhaps initially developing from SW England up through Welsh Borders to NW England, before storms organise into clusters or perhaps upscale into an MCS, given 30-40 knots of deep layer shear, which tracks NNE across N England and on over Scotland through the evening. Given storms are likely to organise given strong CAPE, favourable shear and increasing divergence aloft, perhaps one or two supercells can’t be ruled out during initial storm development, there is a risk of localised large hail (2-4cm), strong wind gusts, intense rainfall leading to flash-flooding and frequent cloud-to-ground lightning. A severe storm risk area has been highlighted for N and W England – where these severe risks look possible.

    Storms will tend to clear away north across far N of England during the evening and Scotland overnight – where they will tend to wane.

    Issued by: Nick Finnis

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    Storms and Convective discussion - June 2023

    in Storms & Severe Weather

    Posted

    06z GFS still indicating severe thunderstorms possible on Sunday Midlands northwards - as a sharp upper trough and preceding surface cold front move eastwards and engage high theta-w airmass . Lightning Wizard, which uses GFS, shows significant tornado parameter and supercell composite areas over Midlands to NE England. E Mids to Lincs and up through S, E and N Yorks looks prime area for severe weather looking at CAPE and the severe parameters mentioned.

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    Storms and Convective discussion - June 2023

    in Storms & Severe Weather

    Posted

    Had a close CG earlier - my water butts are full up now too.

     

     

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    chance of severe storms, perhaps a few supercells, over parts of E England today, more in my Severe Thunderstorm Watch here: 

     

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    here's a few charts of parameters that suggest a severe risk. High theta-w / high CAPE, some DL and LL shear (note significant tornado parameter) Lincs could be prime position 

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