Mesoscale Discussion
Valid: Sat 27 Apr 2024 08:00 to Sat 27 Apr 2024 11:00 UTC
Issued: Sat 27 Apr 2024 07:24
Forecaster: TUSCHY
A Mesoscale Discussion was issued for SW France into far NE Spain for organized convection with an augmented severe risk. A few significant events are possible.
Time-frame for organized convection: 11Z-20Z
Latest WV loop shows a pronounced dry slot rotating NE into the MD area, providing better clearing during the following hours. This clearing takes place atop a structuring and N-ward pushing warm sector, which gets framed by a rapidly N-ward lifting warm front and a slowly E-ward progressing cold front. Plenty of forcing is forecast as the upper trough approaches from the W in tandem with the mentioned cold front. In addition, the orography and diurnal heating also assist in CI during that time-frame.
Moderate MLCAPE in the 400-800 J/kg range faces impressive kinematics beneath the mid/upper jet with DLS in excess of 30 m/s and 0-3 km shear aoa 20 m/s. Forecast hodographs are very long with strong SR winds feeding any deviant storms. Some 800-600 hPa CAA over NE Spain assists in lots of crosswise vorticity and hence a potential caveat for rapid storm organization. Multicells and a few supercells are still possible with large hail and severe wind gusts. Strong cross-barrier flow along the Pyrenees with abundant upper ventilation assist in temporal training of convection which increases heavy rainfall risk on a local scale.
Further N over SW France, deep WAA regime provides favorable shear conditions for supercells with large to very large hail, damaging wind gusts and heavy rain. LCLs are on the higher-end side with readings in the 800m range, but 20 m/s SR inflow into deviating storms with better streamwiseness could also support a tornado or two, especially NW/N of Toulouse, where orographically funneled SE-erly BL winds enhance backing of LL wind field. Upscale growth into bowing line segments is forecast betimes with damaging winds, heavy rain and large hail. During the evening into the overnight hours, the eastward moving cold front pushes thunderstorms out E of the MD area.
