Storm Forecast
Valid: Fri 31 May 2019 06:00 to Sat 01 Jun 2019 06:00 UTC
Issued: Thu 30 May 2019 09:40
Forecaster: TUSCHY
A level 2 was issued across S-Bulgaria mainly for large/very large hail and excessive rain.
A level 1 surrounds the level 2 for similar hazards with lower probabilities but also for isolated severe wind gusts and tornadoes.
A level 2 was issued across S-/CNTRL-Romania mainly for excessive rain.
A level 2 surrounds the level 2 for similar hazards with lower probabilities but also for isolated severe wind gusts and tornadoes.
A level 1 was issued for N-CNTRL Turkey mainly for isolated large hail and severe wind gusts.
A level 1 was issued for parts of the CNTRL-Ukraine and SW-Russia mainly for large hail and heavy rain.
SYNOPSIS
A quasi-stationary deep vortex perches over the CNTRL-Mediterranean with persistent downstream and upstream ridging. A progressive flow pattern continues over N-Europe.
A wavy frontal boundary runs from Bulgaria to the CNTRL Ukraine into Russia. Abundant low-tropospheric moisture cumulates along that front.
DISCUSSION
... Bulgaria, S/E-Romania and Greece/Albania ...
Placed along the southern tip of the front, rich BL moisture is analyzed over Bulgaria and S/E-Romania with lower values towards Greece/Albania. Partial convective overturning from the previous day and a displaced EML keep mid-level lapse rates on the low-end side, but compensating LL moisture pushes MLCAPE in the 1000-2000 J/kg range over S-CNTRL Bulgaria and S/E Romania with slightly lower values towards Greece.
Cap remains weak, so early CI is anticipated. The main synoptic-scale impulse arrives in Greece around noon and in Bulgaria during the evening hours. However numerical guidance indicates at least one lead short-wave ahead of the main impulse lifting N over our area of interest.
A 20 m/s mid-level speed max is about to lift NE but changing geometry of the main synoptic-scale vortex causes a delay of the jet or rather a weakening of the overall wind field. Hence DLS in the 15-20 m/s range remains confined to Greece and Bulgaria with lower values (aorund 10 m/s) further north (Romania).
Scattered to widespread CI is forecast over parts of Bulgaria already around noon. Initiating convection poses a large to very large hail threat over S/E-Bulgaria with elongated/straight hodographs (indicating enhanced probs for a few splitting supercells). A few severe downburst or cold pool driven severe wind gust events are also possible. Despite weak LL shear, slightly curved LL hodographs, potential deviating storm motions and outflow boundaries laid out from the previous day/night all serve as foci for isolated tornado activity (also enhanced by up to 150 J/kg LLCAPE).
An insignificantly stronger cap over E-Bulgaria could delay CI a bit into the afternoon hours but similar hazards are also forecast. Overall activity grows upscale beneath divergent upper flow regime with excessive rain the dominant risk (next to an ongoing isolated large hail threat). Hence the level 1 was expanded far inland to highlight the rainfall risk despite drier low-tropopsheric air over N-Bulgaria.
Early CI/ongoing activity from the previous night affects S-Romania already before noon. A constant moisture input from the E ensures CI all day long despite weaker synoptic-scale forcing. Slow moving and clustering thunderstorms pose a large hail and excessive rainfall threat. The main risk for back-bulding convection exists over S-/CNTRL-Romania mainly during the evening into the night as a subtle LL wave passes to the W. Enhanced 1-2 km AGL flow (20-30 kn) will be enough for temporal training. LL flow remains too weak for a tornado risk although an isolated mesoscale-driven event can't be excluded with adequate LL CAPE.
Over E-Romania, better curved hodographs indicate a risk for temporarily rotating updrafts with isolated large hail. However capping could be too strong for anything more than isolated CI.
Over Albania and parts of Greece, lower CAPE/shear values preclude organized DMC activity, although isolated hail and strong wind gusts are possible. Slow moving convection may also bring locally heavy rain.
... Moldova, CNTRL-Ukraine to Russia ...
A broad/weak ridge atop keeps CI on the more isolated scale. Mesoscale-driven events along outflow boundaries from the previous night could serve as foci for isolated CI. Model discrepancies regarding CI remain significant and hence this part of the outlook is uncertain. A confined level 1 was issued due to slow moving convection with isolated large hail/heavy rain (500-1000 J/kg and around 10 m/s DLS).
... N-CNTRL Turkey ...
Daytime-driven pulsating convection poses an isolated large hail and severe downburst risk with substantial elevated CAPE and a deeply mixed sub-cloud layer. Despite passing subtle mid-level waves, strong cap may keep CI on the very isolated scale. Hence we issue a mix of low lightning probabilities with a level 1.
