Storm Forecast
Valid: Sat 09 Jun 2018 06:00 to Sun 10 Jun 2018 06:00 UTC
Issued: Fri 08 Jun 2018 20:59
Forecaster: TASZAREK

A level 2 was issued for SW France mainly for the large hail, severe wind gusts and excessive precipitation.

A level 2 was issued for parts of Croatia, Serbia and Hungary mainly for excessive precipitation, large hail and severe wind gusts.

A level 1 was issued across parts of W, CNTRL and SE Europe mainly for the large hail, severe wind gusts and excessive precipitation.

SYNOPSIS

Broad ridge with warm, moist and unstable tropical air mass dominates over parts of W, CNTRL and SE Europe. Almost stationary cut-off is placed over NW part of Iberian Peninsula. A shallow short-wave passes British Isles while a long-wave is moving further east through Russia. Weak flow regime dominates over Europe with exceptions over E Spain (jet streak on the eastern flank of the cut-off) and jet stream over W Russia (associated with a long-wave). Enhanced lapse rates are placed over SE Europe and NE parts of Spain. Mixing ratios exceeding 10 g/kg overspreads W, CNTRL and SE Europe.

DISCUSSION

...parts of W, CNTRL and SE Europe...

Majority of thunderstorm activity in the parts of W, CNTRL and SE Europe will develop in the moderate thermodynamic instability and weak shear. Main triggering factor will be a strong diurnal heating supporting and also local convergence zones and orographic lifting within orographical boundaries. A day will start with a thunderstorm activity and MCS over W Balkan Peninsula remaining from the nighttime. Thanks to very moist boundary layer first surface-based thunderstorms will start to develop around 09-12 UTC over S Germany, Czech Republic, SW Poland, Austria and Hungary. Later, ML CAPE in the most of the places will exceed 1500-2000 J/kg and activity will also cover N and E France, Carpathians and Ukraine. In the afternoon hours a slowly moving multicell clusters over Balkans (Serbia and surrounding areas) may cause excessive precipitation and local flash flooding events. Thanks to > 7 K/km lapse rates these areas will be covered with the highest thermodynamic instability reaching in the corridor from Croatia to W Romania even 3000-3500 J/kg ML CAPE. Thus, these storms will have an enhanced potential of producing large hail, and even very large hail event cannot be ruled out. MCS in the evening hours is also possible according to few mesoscale model scenarios. Decent delta theta-e will also promote a downburst-type severe wind gusts throughout level 1. threat area. Most of the thunderstorm activity should fade in the nighttime hours, but some areas including NW Germany, SW Poland, N Austria, Bulgaria, Romania and Adriatic Sea may have lightning activity until morning hours.

...Iberian Peninsula and SW France...

This area will be divided for weakly organized thunderstorm activity within cut-off (small instability) and warm sector's activity over E Spain and SW France (small to moderate instability and high shear). Storms should start to initiate in the late afternoon hours along with diurnal heating and upper-level divergence. Veering wind profile and enhanced wind shear over E Spain and especially SW France (moderate thermodynamic instability) should promote supercells. These can be capable of producing large hail, severe wind gusts and heavy rain. The highest chances for severe weather phenomena cover SW France where a moisture convergence will set up in the afternoon hours. A good overlap of 15 m/s 0-3 km shear and 1500-2000 J/kg ML CAPE cannot rule out a linear system capable of producing damaging wind gusts. However, a chances for such scenario are rather limited as evidenced by mesoscale NWP models and main threat should be associated with supercells and multicell clusters. It is likely that MCS with increasing lightning activity will develop in the evening hours over NE Spain and SW/W France.