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snowfall09

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    Storms and Convective discussion- 15th August onwards

    in Storms & Severe Weather

    Posted · Edited by snowfall09

    ESTOFEX Issued a level 1 for the SW & Wales today (24th Aug)

     

    A level 1 was issued for parts of Great Britain and Ireland mainly for severe wind gusts and to a lesser extent for tornadoes.

    ...Great Britain and Ireland...

    At the end of the forecast period, the cold front enters the LVL1 area. It is emphasized by a maximum in the LL moisture convergence field which indicates a small moisture tongue. Along that tongue forecast soundings indicate the possibility that a bit (MU)-CAPE can develop which enhances the possibility for DMC.

    However, the development of CAPE and thus the possibility of thunderstorms along the cold front is the main factor of uncertainty.

    If storms indeed develop, they can benefit from high DLS and strong mid level winds. In combination with the entering dry intrusion with descending dry air from above, the threat of severe to extremely severe wind gusts is enhanced.

    In addition, also LLS is high and LCLs are low. Therefore the development of a short tornado event can not be ruled out.
     

    2020082506_202008232303_1_stormforecast.xml.png

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    • Thanks 3

    South East and East Anglia Weather Discussion Sept 2019 onwards

    in Regional

    Posted · Edited by snowfall09

    Looking promising.

    Screenshot 2019-10-14 at 15.13.22.png

    DISCUSSION

    Along a line from Jersey to Bordeaux, a line of storms has formed, featuring embedded waves/supercell structures has formed in an environment characterized my modest instability (400 - 1000 J/kg MLCAPE) but strong wind shear. With an 850 hPa wind speed of around 25 m/s near the line, and the wavy appearance on radar, a distinct threat of severe wind gusts exists. Locally, some large (2-4 cm) hail may occur and, in addition, an isolated tornado cannot be ruled out given the strong low-level shear (10-18 m/s 0-1 km).

    The storm system is projected to travel north-northeastward. Model guidance suggests it should weaken during the evening as low-level cold air advection from the west intensifies and upper-level support is weak.

    • Like 1

    Storms and Convective Discussion - 20th April 2019 onwards

    in Storms & Severe Weather

    Posted

    2019062506_201906240302_2_stormforecast_xml.thumb.png.8f38aa28a9e01f12dec7b89a33165682.png

    Storm Forecast
    Valid: Mon 24 Jun 2019 06:00 to Tue 25 Jun 2019 06:00 UTC
    Issued: Mon 24 Jun 2019 03:02
    Forecaster: VAN DER VELDE

    A level 1 and 2 were issued across western France and southern UK mainly for severe wind gust, large hail and tornado chances, and in Ireland for spout-type tornadoes.

    A level 1 was issued across southeastern Europe mainly for large hail and extreme rainfall.


    SYNOPSIS

    The strong southerly flow east of an Atlantic low has advected a layer with steep low to mid level lapse rates out of the Sahara and Spain northward into central France, where high low level moisture converges in a thermal trough. Meanwhile, southeastern Europe continues to be under influence of an upper cold pool, with relatively weak flow but significant CAPE.

    DISCUSSION

    ...Western Europe...

    A level 1 over central France illustrates mainly the uncertainty of storm initiation, where MUCAPE over 1000 J/kg meets 500 m2/s2 0-3 km SREH and 20-25 m/s DLS. Td2m forecast to be 19-21C. Across western France and southeastern UK various models produce precipitation likely from elevated convection along the cold front, with weaker CAPE. The lifting action of shortwave troughs also reaches central France, and relatively weak CIN is calculated on the convergence line. However, models hesitate producing any storm in the otherwise severe weather supportive environment, except for an evening/night MCS developing most likely over Normandy, moving NNE-ward.

    Initially convection will start as clusters of cells including rotating ones (supercells) even if elevated base, which can produce very large hail and severe gusts. If rooted in the boundary layer of the surface convergence line, then with 0-1 km shear exceeding 10 m/s and the strong SREH also tornadoes are possible. However, such collocation is not what COSMO model suggests, which keeps nocturnal development west of the line. But if indeed clustering into an MCS over the late evening, a squall line may form with the potential of organized severe wind gusts.

    • Like 1

    Kent, Home counties and south London general weather discussion 25/02/2018 onwards

    in Regional

    Posted

    4 minutes ago, Nick F said:

    Plenty of twigs on the T+00 fax for 18z this evening

    fax18z_260218.thumb.gif.baf6b86f2a8caf3d0b45e6115acb8a77.gif

    Wind seems to be veering more from NE to ENE upstream over the S North Sea and Holland, so hopefully we may see the snow showers currently affecting coastal E Anglia, Kent and Sussex perhaps shifting a little more inland toward the W in the night.

    Does this now mean theres a higher chance of seeing a Kent clipper setting up overnight? 

    • Like 1
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