Valid: Thu 30 Jun 2016 12:00 to Thu 30 Jun 2016 16:00 UTC
Issued: Thu 30 Jun 2016 12:10
Latest observations indicate that the cold front and a prefrontal convergence line over central Europe are located about 200 km further east than the forecast models suggested. Latest 11z observations suggest a position of the cold front near a line Salzburg - Prague - Poznan and that of the convergence line along Vienna - Svitavy - Wroclaw. This shift places especially the convergence line into the "best" airmass at the optimum time of day and increases the risk of severe storms compared to earlier, NWP-based expectations.
Converging winds and "moisture piling" have driven 2m dewpoints along the convergence line to values up to 18°C in SW Poland and the central Czech Republic and even beyond in N Austria. It is likely that CAPE magnitude rises from about 500 J/kg to the north to 1500 J/kg to the south across the highlighted area, possibly up to 2000 J/kg near Vienna where the best moisture is concentrated (e.g. T/Td values of 31/20°C in Tulln at 11z).
A couple of storms have recently initiated, and coverage will increase in the next few hours. With 0-3 km shear around 10 m/s (or locally up to 15 m/s), an organization into multicells is likely, and one or two supercells are not ruled out. Momentarily, as long as storms are still inflow-dominated, large hail is the main risk and even a tornado might occur - two funnel clouds were already photographed under the storms in northernmost Austria. If storms manage to grow into larger clusters later on, severe downbursts and flash floods become possible as well.
Conditions for storm formation are best right along the mentioned convergence line. In its wake, decreasing temperatures and dewpoints limit the potential, though embedded thunderstorms may still occur along the cold front. Ahead of the convergence line, low-level moisture has been mixed out more efficiently by strong southerly winds, and 2m dewpoints have mostly dropped to 10-15°C. Initiation and sustenance of storms is less likely in this environment due to high clouds bases and strong entrainment.