Storm Forecast
Valid: Mon 05 May 2014 06:00 to Tue 06 May 2014 06:00 UTC
Issued: Sun 04 May 2014 20:49
Forecaster: TUSCHY

A level 1 was issued for Greece and S-Bulgaria mainly for isolated large hail and excessive rain.

A level 1 was issued for NW Turkey mainly for an isolated large hail event.

A level 1 was issued for the CNTRL / E Ukraine mainly for an isolated large hail event.

...SYNOPSIS and DICUSSION...

A longwave trough is centered over Finland and Belarus with a weaker extension all the way to the Aegean Sea. Strongest synoptic forcing limits itself to Belarus/parts of W-Russia (W of Moscow) and the Aegean Sea/W-Turkey. The last-mentioned taps into residual moisture over the Aegean Sea. A plume of steep mid-layer lapse rates is displaced east over CNTRL Turkey, so not much CAPE to work with. Weak surface low over the N-Aegean Sea supports onshore flow of better moisture beneath 500 hPa temperatures of less than -20 °C. The same for the advection of moist air from the Ionian Sea to the SE. 400-800 J/kg weakly capped MLCAPE evolves over most of Greece to S-Bulgaria. Weak shear precludes organized convection, but slow moving and clustering storms likely pose an heavy/excessive rainfall threat, next to isolated large hail. An isolated waterspout event along the coasts is possible.
W-Turkey struggles with meager BL moisture and weak mid-layer lapse rates. DLS exceeds 30 m/s, so any deeper updraft could gain rotation with an isolated large hail threat. The setup does not justify a level 1 due to ongoing uncertainties regarding CAPE. Only NW Turkey was upgraded due to higher confidence in a temporal CAPE/shear overlap mainly before noon.

As time proceeds and night is falling, onshore storms start to weaken with loss of diurnal heating/CAPE. In addition, a second surge of cooler/drier air associated with a southbound moving cold front shuts convection down from N to S. Offshore storms however continue with an isolated waterspout risk.

The CNTRL/E Ukraine will see a cold front passage from W to E and the front is forecast to leave our forecast area during the late afternoon hours. Scattered deep convection is forecast along/ahead of the eastbound moving front. DLS remains in the 10-15 m/s range, so a few organized multicells with isolated large hail and strong wind gusts are forecast.

A ridge moves in from the west and covers most of the Iberian Peninsula to Germany. Weak short-waves along its western fringe could interact with better LL moisture over parts of NW Spain, but only sporadic initiation is forecast.
A strong low pressure area approaches Ireland/UK and Scotland, but limited CAPE precludes any organized convection. A sporadic lightning strike can't be ruled out with shallow marine convection, but no lightning area was added for now.