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AnvilCrawlers

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    Storms and Convective discussion- 7th August onwards

    in Storms & Severe Weather

    Posted

    6 minutes ago, Alderc said:

    I’m going to be well stroppy here - I hope it does! I hope it leaves a great big cloud shield over central England. I’m not going to put up with warm rain only for the same areas further north to get battered for a fourth day in succession in some places....

    No point putting a shield here as I already got one,endless heat and humidity this week and no storm

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    Storms and Convective discussion- 7th August onwards

    in Storms & Severe Weather

    Posted

    14:00 Discussion Update

    Latest Surface observations have shown temperatures have reached the low 30s across parts of SE England and Southern England have reached 28-31C. The 11Z Herstmonceux Ascent has a surface parcel lifted given the surface and DP's and over 2,500 j/Kg of CAPE. There is little environmental forcing or ascent however to trigger any convection. The Ascent is a little dry, but not overly so. This implies that the atmosphere over England & Wales is storing
    large amounts of CAPE.

    The Herstmonceux ascent indicates that T-Storms when they do develop have the potential to become intense, with tops to over 40,000 ft or to around -60C or 180mbs or slightly above.

    In order to release this we will need some low level local ascent or convergence or we will need some larger scale atmospheric lift or ascent.

    The local ascent may occur over parts of Southern and Central England later this afternoon. Mesoscale models suggest some low level confluence will extend to around 925mbs and come together over parts of the Thames Valley, West and NW of London during the late afternoon and evening as the current ESE flow backs more NE over the Midlands, and veers South to SE over parts of Southern England. This suggests that focused ascent will occur and large intense thunderstorms can develop and move slowly WNW in the flow at 850mbs. 850mb Theta-W is also 20-22C across Southern England, much of Wales and into the Midlands too. These storms will be intense but quite scattered.

    To the South - Airmass imagery indicates more substantial synoptic scale ascent and vorticity is moving north assoc with a well marked shortwave trough moving north. T-Storms have died back this morning during the Diurnal minima over France, but this area is likely to see further intense storms develop through the afternoon and evening and as the trough moves north it will further augment the ascent over Southern England and further intense T-Storms will likely develop at times through the evening and night over Southern PArts.

    Models are all over the place with regards to where storms break out and individual detail should not be taken too literally. The models are really struggling to resolve the complex thermodynamic structure given their vertical resolution and the rather constant changes and ongoing modification which T-Storms themselves develop.

    The steering flow is rather poor from the South , so imports from France seem rather unlikely - however as the upper trough moves north it will overrun the theta-W plume and provide some larger scale ascent and spin. Again further intense storms are likely to develop and break out over Southern England during the night, either routed to the surface or from the 850mb level . Many places will miss the storms but where they occur they are likely to release very large amounts of CAPE, Dangerous C/G Lightning, Hail, Torrential rain which may easily give 50-100mm of rain in a very short period of time.

    Whilst this outlook expires at 06:00 further heavy and intense thunderstorms are likely to develop across Southern England during Thursday which may be more located in Southern Counties of England during the afternoon as a confluence/ convergence zone develops over Southern England.

    PJB UKWW

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