Storm Forecast
Valid: Mon 02 Dec 2013 06:00 to Tue 03 Dec 2013 06:00 UTC
Issued: Sun 01 Dec 2013 20:56
Forecaster: TUSCHY

A level 1 was issued for parts of Corsica, Sardinia and N-C Algeria mainly for excessive rain.

A level 1 was issued for parts of Italy mainly for excessive rain. An isolated large hail, tornado risk exists over S-Italy.

A level 1 was issued for the SE Aegean Sea and parts of the E-Mediterranean mainly for excessive rain, large hail, severe wind gusts and an isolated tornado event.

SYNOPSIS

There are no major changes in the synoptic pattern compared to 24 hours ago. An high-over-low pattern continues over W-Europe while an intense upper trough over E-Europe amplifies during its eastward motion. This pattern supports ongoing advection of cold and dry air for most of Europe. Moisture quality over the C/E Mediterranean is a tad better.

Cold air advection downstream of the progressive E-Europe trough results in rapid postfrontal pressure rise and hence an eastward shift of the 1030 hPa (plus) high pressure area from W/C Europe to SE-Europe. A fierce extratropical cycone affects most of Scandinavia but slim BL moisture content keeps marine convection shallow and without serious electrification.

DISCUSSION

... Mediterranean ...

Scattered to widespread showers and thunderstorms continue mainly over the C-Mediterranean. A surface depression SW of Sardinia continues to weaken but holds up a brisk easterly flow regime over most of the C-Mediterranean. Meager BL moisture, sub-500 J/kg MLCAPE with warm ELs point to a low-end risk of electrified convection. Still, a level 1 was issued for eastward facing slopes of Sardinia and Corsica, where convectively enhanced precipitation could bring more than 100 mm/24h in the mountains. The same for parts of N-C Algeria.

A similar set-up exists for Italy, although moisture access will be better. Inflow features 500-800 J/kg MLCAPE, so repeatedly onshore moving showers/isolated storms could again bring rain in excess of 100 mm/24h for eastward facing slopes over C Italy. Training storms are possible over S-Italy with excessive rain the main risk. Shear parameters remain unimpressive with DLS < 15 m/s, but moderate steepeness of mid-level lapse rates with 10-15 m/s DLS could support isolated large hail with stronger storms next to an isolated tornado risk. Thunderstorm activity increases further south over the Ionian Sea ... especially during the night, as a cold-core upper low approaches from the SW. Heavy to excessive rain is forecast with clustering and slow moving storms, but the main hazard remains offshore over the Ionian Sea. For this overnight convection however, the level 1 was expanded far west to Sicily, where slow moving storms could once again result in heavy rainfall amounts.

... SE-Aegean Sea ...

Placed beneath the left exit of a potent subtropical jet and squeezed between an eastbound moving and dissolving cold front from the Ionian Sea and a southbound moving cold front from Bulgaria, isolated to scattered showers and thunderstorms are anticipated during the forecast. Rich BL moisture in excess of 11 g/kg mixed-layer mixing ratio with steep mid-level lapse rates atop result in 500-1000 J/kg MLCAPE. DLS tops out at 15-25 m/s with 10-20 m/s in the lowest 3 km so organized thunderstorms with large hail, excessive rain and strong to severe wind gusts are forecast. Also, an isolated tornado event can't be ruled out. Coverage will be isolated to scattered due to weak forcing and rather warm temperatures at 850-700 hPa (capping) . The thunderstorms leave the area to the east during the night.