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Gordon Webb

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    Storms and Convective discussion- 15th August onwards

    in Storms & Severe Weather

    Posted · Edited by Gordon Webb

    11 minutes ago, Alderc said:

    Another poor outlook for the south coast, convective sewage from France. Would be better if it didn’t bother at all, at least then we’d have some sun. 

    Seems like the changing air-masses of climate change are making it more difficult to generate sharp cold front boundaries on exiting plumes etc in general (I know that not the case for tomorrow) to create additional forcing in an eastwards motion. Same in winter really, convective actively down in all seasons here not just summer. 

    Yep East And West Looks good for tomorrow , as for you on the S coast to say your have been shafted this week is a bit of an understatement now for tomorrow it's SW/W and SE/E and not so bad in the middle

    Storms and Convective discussion- 15th August onwards

    in Storms & Severe Weather

    Posted · Edited by Gordon Webb

    Convective Outlook / Forecast - Sunday 16th August 2020
    Valid 06:00 BST to 23:00 BST Sunday

    Risk Zone 1 - Southern Counties of England & Channel Islands
    Risk Zone 2 - Central and Southern Parts of England (Away from the South Coast, Eastern England, London, Lincs, Midlands, Central, Southern & Eastern Wales.

    Headline

    Upper level low with surface inflexion will drift NE towards to the UK to lie over the English Channel by Late Sunday. Associated Trough will move North during tomorrow morning with risk of Elevated convection and some Heavy Showers. As trough moves inland it will decay and insolation will take over. Surface based storms will develop during the afternoon in response to heating with a low risk of organisation and severe storms developing over Eastern England.

    Detail

    Large upper level low is very well placed on Airmass imagery , with a PVA max located in the Central Bay of Biscay. This PVA Max has engaged some higher 850mb air over parts of Biscay and has allowed for Elevated Thunderstorms to to erupt as the airmass was lifted north from Iberia. This trough development will move NE towards the English Channel tonight and then move close to the South coast during Sunday Morning. Rain / Showers/ Thunderstorms are likely to push towards the Channel Islands early on Sunday and then slowly move north, but likely to decay as they move north across the Channel during the diurnal minima. However saying that I have allowed for a risk of Showers / Thunderstorms from this trough to move into Southern Counties of England during Sunday.

    The trough is finally however likely to push north the rather complex airmass that has sat over Southern England for the past few days with only limited insolation but high PWAT Content. This higher theta-W air and high Moisture is likely to be pushed North during tomorrow to replaced by somewhat more buoyant air arriving from the South.

    During the afternoon, Sunshine will develop more widely over England and parts of Wales, and there will be an increase in low level thermal advection from 850mb to the surface as a tongue of warmer air from the continent moves into the SE and East Anglia. At the same time as this the upper level low will move north and this will lower 300-500mb temperatures across much of England & Wales,. The Net effect is to steepen Lapse rates significantly during the afternoon and forecast ascents are much more unstable compared with those of today with several hundred j/kg of CAPE perhaps up to 1,500 k/kg of CAPE over parts of England especially Eastern England.

    In addition to this improved thermodynamic environment we will also see an increase in Deep Layer Shear aloft as the upper trough approaches with an increase in winds especially at 300-500mbs over Eastern England and East Anglia. Therefore Any Thunderstorms which develop here have the potential for some modest organisation and have the potential to produce moderate gusts and perhaps hail. Given the PV aloft and the increased dry air at the 400-700mb level I see a much improved prospect of Lightning vs Sunday across these parts. High PWAT content likely to remain esp across parts of Eastern England and here again totals from rain / thunderstorms will be quite large. (though cells not expected to be as slow moving as recently)

    During the afternoon several convergence zones and trough axis are likely to develop. One close to the coasts of Eastern England, One over SW England, One over SE Wales and parts of Western England. These will be the focus for the development of Heavy Showers and Thunderstorms given the expected increase in Temperatures and Sunshine. Storms once developed will move NW on the SE steering flow.

    Storms have the potential for Organisation and perhaps to become marginally intense over Eastern England during the late afternoon & evening.

    Fig 1 - COnvective Outlook Sunday 16th August
    Fig 2 - Airmass Imagery 15th Evening Interpretation

    Issued Paul Blight
    20:38 15th August.

     

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    Storms and Convective discussion- 15th August onwards

    in Storms & Severe Weather

    Posted · Edited by Gordon Webb

    5 minutes ago, Jamiee said:

    AROME                                                        WRF-NMM 0.05°                                                 ARPEGE

    image.thumb.png.cd2ddb3049990424242b48c8c7f657db.png     image.thumb.png.333e4a3ecdd1d0c03cf7ab8425775a35.png            image.thumb.png.ddc806d2947fa73af5b9efe28589d700.png   

     

    ICON

     image.thumb.png.14b65ee2bc572439c51eb90e434ee3f7.png

     

    AROME has imports earlier than the rest with main consensus of imports being in the late afternoon.

    WRF-NMM has SB-based storms in the early morning before imports arrive in late afternoon.

    ARPEGE is SB-based storm galore with imports arriving around the same time as AROME.

    SB-based storms are looking good to develop but imports is another tricky issue.

     

    sb based storms were also looking not too bad for last 2 days for certain places which really didn't pan out , this is far from clear and I see you didn't mention the ICON but I understand why the only water you get from that is the tears of those in the SE looking at it

    Storms and Convective discussion- 15th August onwards

    in Storms & Severe Weather

    Posted · Edited by Gordon Webb

    14 minutes ago, Flash bang flash bang etc said:

    This has more chance of happening than anything else. Usual areas, usual storms.

    not exactly the usual places much more focus on East Anglia / East Midlands for heaviest rainfall taking that run at face value also ties in with where met office expect the heaviest rainfall to be again taking their warning at face value but I've see these before then on the day the reality doesn't match up , for those wanting storms best to approach tomorrow with expect nothing and hope for something , as for me I hope for nothing and expect something

    Storms and Convective discussion- 15th August onwards

    in Storms & Severe Weather

    Posted · Edited by Gordon Webb

    met office have updated there warnings removing parts of the midlands for today and having storms and showers moving north tomorrow with higher chance of severe storms more especially Eastern England and later East Midlands into afternoon and evening for tomorrow and this contradictory warning for Monday

    which reads thus

    Thunderstorms are expected to develop in many areas of England and Wales during Monday. Some slow moving thunderstorms may form during the afternoon before these largely die out through the evening. Many locations within the warning area will miss the thunderstorms altogether, but where they do occur 30-40 mm may fall in an hour with 50-70 mm possible in 3 hours. Thunderstorms may be accompanied by large hail, frequent lightning and gusty winds

    this is tomorrows

    Areas of heavy showers and thunderstorms are likely to move north across England and Wales during Sunday. Some locations within the warning area may miss the thunderstorms altogether, but where they do occur 30-40 mm of rain may fall in an hour with the potential for 60-90 mm in a few hours. The most likely areas to see the larger totals are in the East of England and then the East Midlands during the afternoon and evening. The thunderstorms may be accompanied by large hail, frequent lightning and gusty winds.

    the only possibility for higher rainfall totals maybe slightly warmer temps are expected further East tomorrow but I suggest they really don't know

    but given uncertainty even at short range can these warnings really be taken at face value considering their warnings from yesterday and today not really panning out and most probably tomorrow and Monday been the same as well

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    Storms and Convective discussion- 7th August onwards

    in Storms & Severe Weather

    Posted · Edited by Gordon Webb

    7 minutes ago, Thunderbuddy92 said:

    OK I'm terrified of storms so follow this thread as I trust your guys judgements and forecasts/now casts however, what I would give for that after storm freshness right now down in Worthing, I canny cope with this heat anymore. 

    same here , yesterday was the last of the scorching days and today the last of the just about 30c days after this it's more mid 20's at best , also hoping that stuff near Luton doesn't make it here

    • Like 1

    Storms and Convective discussion- 7th August onwards

    in Storms & Severe Weather

    Posted · Edited by Gordon Webb

    5 minutes ago, Ndc Ozzie said:

    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

    almighty cheers ring out across the south of the M4 for tomorrow and the met office is forecasting thundery rain for the south tomorrow too

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