Mesoscale Discussion
Valid: Tue 12 May 2015 15:00 to Tue 12 May 2015 21:00 UTC
Issued: Tue 12 May 2015 15:16
Forecaster: TASZAREK
... Thunderstorms expected within denoted areas with increasing threat of large hail, severe wind gusts and in lesser extent for tornado...
DISCUSSION
Satellite images indicate that convection is currently developing along the wind convergence line in the sector of warm and moist airmass of tropical origin. Surface observations in central Germany indicate temperature of around 25-27C and dew point up to 16C (Braunchsweig), that is consistent with previous NWP forecasts. Soundings from 12 UTC in Bergen (region of CI) indicate DLS: 28m/s, 0-3km shear: 20 m/s and LLS: 11 m/s. Given temperature and dew point correction for surface measurements from 14 UTC, SB CAPE exceeds 1000 J/kg, so similar as predicted by NWP models. However, due to dry layer above, ML CAPE that seems to be more reliable estimate of real thermodynamic instability amounts around 400-500 J/kg. Basing on soundings from Meiningen, Bergen, Greifswald and Lindenberg 0-3km SRH amounts from around 100 m2/s2 to 300 m2/s2.
In such environment it is predicted that in the northern area of MD convection will cluster into well organized line (especially due to overlap of strong 0-3km shear and forcing) and move eastward. Possibility of squall line and strong low level flow create threat for widespread severe wind gusts that can exceed 25 m/s. Good overlap of moist boundary-layer moisture and DLS over 25 m/s create also threat for large hail up to 3-4cm.
In the southern part of MD convection may be more isolated and organize into supercellular thunderstorms capable of producing large hail up to 5cm and severe wind gusts exceeding 25 m/s. Isolated convection, low LCL and favorable vertical wind profile create also risk for tornado occurrence.
It is expected that thunderstorms will be considerably active until 2100 UTC and spread E and NE-wards with time. It is not rulled out that they may even affect areas outside MD towards the nightime hours.
