Storm Forecast
Valid: Fri 08 Apr 2016 06:00 to Sat 09 Apr 2016 06:00 UTC
Issued: Thu 07 Apr 2016 19:52
Forecaster: TUSCHY

A level 1 was issued for E-Hungary, W-Ukraine, far SE Poland and S-Belarus mainly for large hail and isolated severe wind gusts. An isolated tornado event is also possible.

A level 1 was issued for N-Algeria mainly for large hail and an isolated severe wind gust event.

SYNOPSIS

A longwave trough, centered over W-Europe, moves leisurely to the SE. Various smaller scale mid-tropospheric waves circle around that feature and affect most areas of the W/CNTRL Mediterranean. A gradual weakening trend is anticipated as another potent impulse approaches NW Europe from the NW
during the day. For Spain, a weak ridge moves in from the Bay of Biscay, whereas a more intense ridge still affects most of SE/E-Europe.

Low-tropospheric pressure configuration supports ongoing advection of dry/stable air far south over France towards the Iberian Peninsula. Further east, a complex LL depression exists from Italy to W-Romania. Models give a variety of LL pressure minima, but in general one NW-SE elongated vortex is placed over the Adriatic Sea with another one moving from E-Hungary to the NE while weakening. Due to intense LL WAA regime along/ south of a quasi-stationary warm front, a channel of low pressure finally develops from Croatia to the W-Ukraine, which serves as primary focus for organized DMC.

... E-Hungary to W-Ukraine to S-Belarus ...

Deep moisture convergence along a quasi-stationary warm front results in a deepening BL layer with rather rich LL moisture. Yesterday's soundings south of that front already showed steep lapse rates at mid-levels and overlap with best BL moisture should offer a SW-NE aligned tongue with weakly capped 500-1000 J/kg MLCAPE. With a prolonged period of enhanced LL lift along that front, numerous waves, circling the ridge axis and later-on QG forcing of an approaching major wave from the SW should all cause adequate lift for long-lasting thunderstorm development in the highlighted area. 0-3/6 km shear remains modest with 15 m/s, but this already supports a mixture of isolated supercells and organized multicells. Large hail will be the main risk with broadening CAPE profiles in the hail growth layer but rapidly increasing LCL heights south of the front with a deepening dry subcloud layer should also add an isolated severe downburst risk.

Thunderstorms, which move along/just north of the warm front,
could see a temporal risk of an isolated tornado event, but limited time for discrete storm mode and weak/modest SRH forecasts keep confidence quite low.

The activity diminishes after sunset with isolated nocturnal storms spreading into N-Belarus and far E-Poland. Nothing severe is forecast with this activity.

... Balkan States to NW-Italy ...

Broad LL vortex supports an ongoing south/southeasterly flow which advects a BL air mass with mixed-layer mixing ratios of 7-9 g/kg towards the S-Alps. This moisture spreads beneath mid-level temperature of -18 °C or less, which is enough for widespread low/moderate CAPE build-up. Most robust CAPE signals exist over the Ionian and the S-Adriatic Sea with MLCAPE of 800 J/kg. Further north and especially onshore, CAPE rapidly diminishes to 500 J/kg or less. Shear depends on final geometry of that vortex, so uncertainties remain. However, mean shear oscillates between 10-15 m/s for the 0-6 km layer. This kind of CAPE/shear overlap supports isolated better organized multicells with large hail the main hazard.
Convection along the French/Italian border will be slow moving
with storm motions of 10 kt or less, so despite only modest
PWATs, local flash flood problems could occur. Clustering storms over the Baltic States probably cause another focus for local flash flooding, but no serious excessive rainfall risk can be detected right now.
A risk of waterspouts/funnels exists along the E-coast of the
Adriatic and NE Ionian Sea, where LLCAPE of 150 J/kg and more exists. 850 hPa winds temporarily increase to 20 kt, but
stay in general between 10-15 kt. Combined with convergent
flow along the coast, a few spout reports are possible.
Thought about upgrading 50% lightning areas to level 1 areas, but messy picture in model data with various solutions precluded any upgrading. Local severe reports are possible however.

... N-Algeria ...

A cold front and an intense vorticity lobe affect N-Algeria during the forecast and insert an augmented risk for widespread CI. Overlap of 15-20 m/s DLS and 500 J/kg MLCAPE point to organized multicells/isolated supercells with large hail the main hazard. During the night, the main activity moves south and out of our forecast area.