Storm Forecast
Valid: Tue 05 May 2020 06:00 to Wed 06 May 2020 06:00 UTC
Issued: Mon 04 May 2020 23:05
Forecaster: DAFIS
A level 2 was issued for France and W Switzerland for large hail, severe wind gusts and tornadoes.
A level 2 was issued for Turkey mainly for large hail and severe wind gusts.
A level 1 was issued for parts of Russia, Belarus and Ukraine mainly for excessive precipitation (rainfall and hail).
A level 1 was issued for Turkey, Cyprus and Georgia mainly for large hail and severe wind gusts.
SYNOPSIS
A strong ridge has formed in the Western Mediterranean and the subtropical jet is anticyclonically curved over France resulting in impressive kinematics over a large part of the continent. A trough from Scandinavia traveling south is about to interact with the jet stream and will increase baroclinicity over Central Europe. Another long-wave trough is found in Eastern Europe which will destabilize the air masses in the Middle East on Tue 05/05. At the surface, a cold front is crossing France and provides lift to unstable air masses resulting in severe weather events. Two more cold fronts will be active during the period of this outlook, one associated with the trough over Central EU and which will bring polar maritime air masses suppressing convection, and the second one over Southern Ukraine and SW Russia is less pronounced but will result in widespread DMC events.
DISCUSSION
.... France and Switzerland ....
In the morning of Tue 05/05 we expect the surface cold front to decelerate as it crosses France. Storms are expected along its leading edge but severe weather threat should remain limited given the low values of SBCAPE. During the afternoon, the diurnal solar heating and the upper-level PVA, along with numerous LL convergence zones associated with the dissolving cold front will result in CI in Eastern France and Switzerland. An overlap of strong DLS and MLCAPE increases the threat of organized storms to produce severe weather events. Helicity values in the lowest troposphere will remain low, not favoring supercell formation but 1-2 short-lived supercells may form able to produce large hail and severe wind gusts. Especially in the northern exit of Rhone valley models forecast 5-10 m/s LLS and nearly 100 m2/s2 SREH0-1km. Along with LCLs below 600 m, these ingredients suggest a favorable environment for tornadoes. Storms will become elevated in the late afternoon and will stop during the night.
.... Turkey, Cyprus, and Georgia ....
As a long-wave trough is crossing Turkey, synoptic lift becomes important during the morning and afternoon of Tue 05/05 with strong upper-level divergence evident in the forecast maps. In addition, diurnal solar heating will provide lift to warm and moist, thus unstable air masses that have been advected from the Mediterranean. Steep lapse rates will result in up to 1000 J/kg MLCAPE overlapping with 15-25 m/s DLS. Storms will be able to organize and a few supercells are expected able to produce large hail and severe wind gusts.
A few waterspouts are expected near the coasts of S Turkey and Cyprus, especially in the early morning.
.... Russia, Belarus, and Ukraine ....
Situated in the warm sector of a cyclone with a center over N Ukraine, warm and moist air masses have been advected from the Black Sea. Also, evapotranspiration is strong given the continuous storms of the past few days and 20-25oC max temps. Diurnal solar heating will be the main lifting mechanism, so we expect widespread CI in the late morning with a peak of activity in the afternoon. Short storm motion vectors suggest that storms will be moving slowly or they will be stationary. Excessive precipitation events with flash floods are well possible given the vertical nearly-saturated profiles in the NWP models, with PWAT exceeding 20-25 mm. Freezing level heights below 3 km altitude and locally dry mid-levels also increase the threat for large accumulations of small hail. Most of the storms will stop during the late afternoon and only a few elevated storms will continue during the night but will remain non-severe.
