Mesoscale Discussion

Mesoscale Discussion
Valid: Mon 10 Jun 2019 14:00 to Mon 10 Jun 2019 16:00 UTC
Issued: Mon 10 Jun 2019 14:02
Forecaster: PISTOTNIK

This Mesoscale Discussion (MD) is issued to describe current developments of the pre-convective environment across central Europe according to latest observational data and its implications for the possible imminent severe weather outbreak.

Mid-level clouds and bands of elevated convection continue to move NE-ward in the strong warm air advection regime across NW Italy, Switzerland (with an attendant risk of heavy rain and flash floods in the Alps) and increasingly SW Germany and W Austria. 2m temperatures/dewpoints only around 19/14C yield little to no CAPE in SW Germany (see 12z Stuttgart sounding), hence these storms will initially stay elevated and non-severe. However, they will encounter increasingly warmer and moister air along their further track towards E and NE Germany, where the airmass has recovered pretty well from mid-level clouds and showers in the morning under some hours of insolation and steady warm air advection from the southeast. The 12z Lindenberg sounding already showed 1000 J/kg CAPE under 15 m/s 0-3 km shear. It appears likely that the leading storms from SW Germany will root down to the surface and turn supercellular in the next few hours. Additional initiation is not ruled out elsewhere from central into NE Germany. Depending on the degree these storms propagate to the warmer and moister air, the most severe storms are expected to aim at Saxonia or even NW Bohemia, though uncertainty about their tracks is still considerable. Large to locally very large hail must be expected as soon as these storms turn supercellular. Severe downbursts and excessive rain become additional risks, especially in case upscale growth begins.

The convergence zone from Prague to Salzburg described in the previous MD, laid out by elevated morning convection and thermally direct circulations across the frontal zone, has vanished again by 13 UTC and has given way to uniform NE-erly winds with 5 m/s as the Alpine heat started to ingest moist air from the Alpine foreland. As a result, the dryline along the North Alpine rim has sharpened. Another perpendicular (north-south) oriented convergence zone will likely emerge over Bavaria soon as the westerly outflow from the elevated storms starts to push eastward, re-establishing the familiar L-shaped convergence zone that should be monitored for possible convective initiation. CAPE rises strongly from west to east on the moist side of the dryline - from a few hundred J/kg in western Bavaria to probably up to 4000 J/kg in Lower Austria, when modifying the already impressive 12z Vienna sounding with latest station measurements from e.g. Lunz am See (2m temperature/dewpoint of 27/17C at 600m height) or Lilienfeld (27/19C at 700 height).
Capping remains strong, hence it is still unclear to which degree, and if at all, convective initiation will happen in this extraordinary thermodynamic environment. So far there were only a few struggling and short-lived thunderstorms near the dryline, but no persistent development yet. However, any storm that forms can soon turn severe with a high risk of large hail and severe downbursts!

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