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camturbo

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    Storms and Convective discussion - September 2023

    in Storms & Severe Weather

    Posted

    9 minutes ago, Liam Burge said:

    For those thinking they're gonna miss out in the SW, I believe most in somerset will see a massive thunderstorm roll through sometime between 2am and 3am. We can already see the start of it forming in the channel, and it's expected to merge together into a massive storm.

    image.thumb.png.d980cba7813b17ea9f29510142213289.png

     

     

    Let's hope your right fella,appears to be a bit more action just off of brest so fingers crossed

    Storms and Convective discussion - August 2023

    in Storms & Severe Weather

    Posted

    35 minutes ago, Eagle Eye said:

    Convective Outlook ⚡

    On Friday. Initially, a line of showers and storms may form in the morning across the western coasts of the UK. It weakens as it moves east but may pick up in the SE. Then overnight, strong storms with frequent lightning could ride the east coast area, along a sliding Theta-E airmass.

     

    The morning showers and storms in the west coast will form rapidly but quite quickly lose energy as they move northeast. The line appears to be tilted SE with a few in the channel and moving into the south coast. They have a severe status potential for wind gusts and rain right along the west coast. With the wind gusts coming from the downwards energy from the storms. Whilst not particularly large, may be enough to force strong wind gusts. Along with strong moisture, for surface flooding from torrential rainfall. The wind gusts restricted to the coast due to this being the area of best forcing for downwards momentum transfer between laminar and viscous flow which is more forced by the coast rather than inland.

     

    This occurs mid to late morning along an area of PBL Theta-W airmass that can hold elevated thunderstorms if need be. So earlier in the morning than usual, is initiation time it appears. Steepening low-level parcel temperatures in recent forecasts have increased 3CAPE to post severe levels (50+ J/KG) and lowered the LCL. That increases ECAPE hence the uptrend in strength recently.

     

    Mid-level hydrolapse rates are now more akin to storm activity than thundery rain with high mid-level hydrolapse rates. The rapid loss of dewpoint and decreasing moisture advection with height is helpful for lightning activity. Eventually, the showers and storms forced into a line will weaken but will pickup again along the south coast with re invigorated forcing. Then there may be some random popup storms, especially in the SE during the day. This is before the evening and overnight. This is where a Theta-E mass advection occurs with a developing strong PV lobe. Mainly in the south, SE and up to the mid eastern coast where some tropical like Theta-E airmass temperatures can advect. A surface inversion holds off most of the surface energy and surface buoyancy at bay, however, the energy beyond the surface m inversion is strong and can tap into a strong Theta-W airmass.

     

    This has strong saturation but very tall EL's with 35,000+ feet storm heights and DLS supporting it. So with the direction of shearing, along the PV lobe, a squall line or an MCS will likely form. Moving NNE with frequent lightning likely given the amount of energy and the height that its stretched over. These might form over the channel or the south coast and move NNE. Slowly, initiation should change further east with a couple rounds of initiation
    with such a pool of energy and high PBL Theta-W air in the channel and the south and east.

     

    With such strong forcing for the DCAPE, severe squally wind gusts are possible along with frequent lightning and surface flooding. Some small hail may occur given the potential for pre-MCS Supercells ,which would make the most of the sub-zero CAPE available and the hodo is favourable. Buoyancy isn't particularly favourable at the surface but at cloud height is particularly unstable. So some 0.75 inch hail may be possible. However, a Supercell pre-MCS would only happen if the MCS meets the tropopause and sends out gravity waves and strengthens any cumulus fields pre-MCS which could then break through the capping.

     

    A tornado may be possible given the larger inflow layer in recent forecasts allowing for high SVC intake at layers. However, the lifted LCL will likely mean that the tornadic potential is limited and most energy will be transferred in outflow winds despite the low-level vorticity fields available, the mid-level vorticity will naturally be different due to the change to laminar flow less favourable for the atmospheric instability pattern needed for tornadic formation. Viscous flow appears much more favourable for small-scale rotation. There is significant LLS available so if something can latch onto a surface feature along the warm front then a tornado may still form. However, warm fronts tend to have high surface capping and be more renound for their hail and wind gusts capabilities In Ireland, there's a local increase in CAPE to 400+ J/KG during the overnight hours which may form some storms. These have the potential for during wind gusts and surface flooding in the night hours.

    20230817_211529.thumb.jpg.023aac2c84c788f6b2be589d37046078.jpg

    Think that's me out,well informative though

    • Thanks 2
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