Mesoscale Discussion
Valid: Sun 20 Jul 2025 11:00 to Sun 20 Jul 2025 14:00 UTC
Issued: Sun 20 Jul 2025 10:33
Forecaster: TUSCHY

A Mesoscale Discussion was issued to highlight an increasing severe risk into the afternoon/evening hours.

A strong upper low is placed over NW Europe. Numerous waves circle that feature with one prominent wave lifting from CNTRL France N/NE towards SE England until the evening. This causes a progressive cold front over CNTRL France to shift E and the front should cross the MD area during the evening into the overnight hours.

Latest remote sensing data reveals enough prefrontal diabatic heating for a growing unstable warm sector. BL dewpoints in the mid to upper tens assist in 500-1000 J/kg MUCAPE admit a slight mid-level cool-down from the W.

Shear improves steadily along/ahead of the approaching frontal boundary with point source soundings within the MD area showing DLS around 20 m/s and 0-3 km shear approaching 15-20 m/s from the SW near the sloped frontal zone.

Increasing Cu fields along the orography in the southern part of the MD area point to a growing risk for a few prefrontal semi-discrete to discrete cells during the following 2 to 3 hours, which graze extreme NW Switzerland before entering SW Germany. These cells mature in a WAA dominant regime with enhanced 0-3 km helicity, pointing to a mix of probably dominant right movers with some splitting cells. Large hail, strong to severe gusts and heavy rain will be the main hazard thanks to a mixed BL airmass.

Another concern arises around the already onging and gradually intensifying DMC activity over CNTRL France, which now enters the plume of unstable and sheared prefrontal airmass. NWP guidance still diverges, where to initiate dominant DMC activity with latest RUC placing too much focus on the more stratiform part of the ongoing activity. However most models agree in CI along the SE fringe of the ongoing convection with additional CI ahead in the warm sector. Improving shear should support a mix of bowing line segments with semi-discrete cells. Swaths of strong to severe gusts, some hail and heavy rain will be the main threat, which spread into the CNTRL and N part of the MD area. An issue will be left splitting cells over SW Germany, which could induce some BL stabilization ahead of the French convection and a strengthening cap during the evening hours. This trend needs to be monitored in nowcast.